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TTR250 - fitting a 325cc big-bore kit
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Steve H (a member of this new forum who lives a few miles away from me in sunny Exmouth, Devon) and I each bought a 325cc big bore kit from Thumper Racing for our TTRs in 2010. 

I read about the 325cc kits years ago and my own view is that a 350cc 4-stroke e/start would be a pretty much ideal trail bike but you gotta start with what you got and what you know.
I had a spare TTR engine that needed a rebore so took the plunge. I mentioned it to my mate Steve H who also fancied his TTR having a bit more grunt to lift the front wheel over obstacles etc so between us we got a good deal from Thumper Racing for a pair of kits.
My thoughts were that its amazing what little 50cc engines can do in bikes and scooters so an extra 75cc for the TTR was not to be sneezed at.

This is what came with the kit. No air filter was provided and the jets were later found to be an incorrect fitting:
325kit 001.jpg
The work needed to fit them was to (i) press out the liners from the barrels, (ii) bore the ally barrels to take the bigger diameter liners, (iii) bore the crankcases to take the bigger sleeves and (iv) bore the barrels for the new pistons.
The crankcases were stripped down and the barrels cleaned and it was at this stage that we found that there wasn't any engineeers locally that could do both the ally work and the rebore.
So, Exe Engineering in Alphington Rd, Exeter, were used for boring the barrels and the crank cases and Autoservices on Haven Banks were to do the rebores for the new pistons. 
Sadly the guy doing the work at Exe Engineering had a heart attack and it was 3 months before the work was completed. Even then the liners had not been sweated into the barrels.
I took both sets to Autoservices to finish off the job. This was done in just over a week and it was time to start rebuilding the motors.
Another twist in the tail, which shows the advantage of getting all the work done in one place, was that the liners sat proud of the barrels by a small amount but enough to prevent the headgaskets seating properly. This was caused by what we thought at the time was an insufficient rebate having been made for the liner lip when boring the barrels. I got an expert bike engineering buddy to look at them and he confirmed that they needed machining flush. So, the barrels went back down to Autoservices (Scratch) for the work to be done.
Whilst waiting for the barrels (again) we got on with cleaning out the swarf in the crankcases and start to put back the zillions of bearings, washers and gear bits in the crankcases - trying hard to remember where all the bits go disbelief


Original crankcase opening
Original crankcase opening.JPG


Bored out to fit the oversize sleeve
Bored out crankcase opening.jpg

Quite a lot to strip out under the clutch cover!
Under the clutch cover.JPG

After stripping off the innards of the generator and clutch covers, split the crankcases and this is what their insides look like
Inside the crankcases.JPG

If you decide to strip out all the bearings before getting the crankcases opened up then these are the ones in the RH engine case. Not easy to get out without a bit of heat:
Bearings in RH crankcase cover.jpg

Starting to put the engine back together:
Rebuild in progress.jpg

Comparison of old and new pistons:
Old and new pistons.jpg




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The crankcases and re-sleeved and bored barrels were back from the engineering firms so we started to build the engines.
First off the crankcase bearings had to be fitted which involved putting the crankcases in the oven (with Mrs TTR's permission) to expand the bearing housings - and the bearings went in the freezer to shrink 'em as much as possible. Worked well but I don't think I cleaned the WD40 off Steve's cases as well as I should have as the kitchen had a distinctive pong which made me a bit unpopular. I decided to try a cooking a pizza in the oven for lunch and it was fine! The slight after taste introduced by my earlier "cooking" meant I had it all to myself biggrin

The first problem was that Steve's crankshaft had come out with the interference main bearing (clutch side) still attached when we did the original disassembly many months ago. No way was that going back in despite the freezing/heating process so it was necessary to drive off the bearing which means it's then unusable - hey ho. I now have an All Balls bearing kit with just one new bearing in. cry

All the bearings were now fited in both sets of crankcases and I needed to make up some sort of puller device to pull the crankshaft squarely into its main bearing. Yamaha's own device pictured below but MotoWard quoted about £120 for the special tools confuse
I don't have any pipe big enough diameter to fit over the end of the crank so put my thinking cap on. The crank is only an interference fit on one side thank goodness!
Crankshaft installer.jpg
After a bit of lateral thinking I used the starter ring, 1/2" drive socket and the flywheel bolt to pull the bearing on - worked a treat - see pic below:
Pulling_in_crank.jpg
to be continued.............


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We then made some good progress on Steve's engine and the bottom half rebuild was complete - until we spotted a left-over washer which kinda looked like it should have been somewhere INSIDE the crankcases.

We studied the workshop manual and had a look at another stripped engine and were able to spot where it should have gone - underneath the shift lever assembly cry 

We packed it in for the night at that point but will have to take off the clutch cover and strip out the clutch to be able to put the washer in. Hey ho!

I also started on my engine but didn't get very far as the interference fit main bearing wasn't! The crankshaft just popped through it which is a bit odd. I have an All Balls main bearing kit to hand so will fit a new bearing on that side just in case.

The crankcases were stripped last year prior to boring out to accept the new liners to avoid them getting contaminated with swarf etc in the machining process. With the benefit of hindsight, if I was to build another 325 engine I think I would try and cover the bearings in the crankcases rather than remove them all. It must be possible using perhaps hard plastic and silicone sealer that sets?



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Well, six months after starting the project we got both 325s running biggrin

After Steve's washer incident, I kept double checking boxes and maragarine tubs used to store all the bits to make sure nothing was left behind. In fact, it was quite the opposite in that the "Borrowers" had been busy in the workshop and lots of important little bits and pieces were missing! Good job I have one or two TTR spares lying around to keep the rebuild on course smile

Anyways up, I managed to get it all back together and running and SteveH appeared on his own TTR325 just in time to witness the inaugural run down the lane and back. So far so good and now need to start the running in process. Can't go too far until I have up jetted. The jets supplied by Thumper Racing with the 325 kit didn't fit confuse

Updatea plug check indicates its running OK with the standard jetting - a bit rich if anything.

A knowledgeable friend responded to my question about up jetting as follows:

"Why bigger jets? Higher gas speed over a fixed orifice will automatically draw disproportionally more mixture through. So it may run too rich as is - unless you know otherwise!"

And I was assuming I would need a bigger main jet...



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PROBLEM cry

200 miles done & the head gasket on Steve's 325 blew.

Stripped it down the liner has very slightly settled into the block making it a fraction lower than the face which meant the head gasket couldn't seal properly.

I stripped my engine down and the same had happened so we took both barels back to the engineering shop to be skimmed to bring the barrels back level with the liners. This will increase the already quite high compression so we will need to sort that.

On a brighter note it looks like the mixture was pretty good, judging by the condition of the valves etc. although a tad rich as we had guessed.

There was then a delay waiting for special head gaskets from ThumperRacing in the States before we could get the engines back together again.

This problem was not a fault of the kit or its design but the engineer who didn't press the sleeves fully into the barrel.

Although it saved us money in the first instance, I am convinced that if I built another 325 I would find a workshop that could do all the work in one place such as our friends in Bridgewater. 

As I mentioned we were slightly worried about raising the compression ratio even more than the 13:1 we think it is at the moment. Also, the piston will be getting a tad closer to the cylinder head than I would like hence we will probably need to put in an extra base gasket to compensate.

It's all a learning experience and not life or death - thank goodness biggrin



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Has anybody any information on the 280cc kit?

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Hi Lin

The so-called "280 kit" is the biggest oversize (+2.0mm) piston but, in reality, gives 263cc rather than 280. 

I am putting this in my project TTR  - scroll toward the bottom of http://ttr250.activeboard.com/t43731716/modernising-a-1993-yamaha-ttr250-open-enduro/

Brian




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Barrels weeping oil
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The next challenge was that some hairline cracks appeared on the barrels between the fins where there was very little metal left after boring out for the bigger sleeve allowing some oil seepage. See pic below.

Leaking barrel.jpg

Not a big problem but unsightly.

Rather than put both engines back together with the newly machined heads on the barrels, we decided to put mine back together and test it first to check there were no other problems. This we did and I started to rack up the mileage with no problems and really enjoying the extra punch of the bigger engine biggrin

Meanwhile, an opportunity arose to have Steve's barrel aluminium metal sprayed which sounded like a permananent repair to the leak problem. This process was unknown to us but involves blasting the barrel clean and then "spraying" a couple of mm of aluminium on with the help of oxy-acetylene and compressed air!

This is what the treated barrel looked like.

Aluminium sprayed barrel 002.jpg

By this time, the barrel on my running 325 was getting messy with leaking oil so I am hoping that we have found a solution. We decided to take a belt and braces approach and covered the problem areas between the fins with a coating of Chemical Metal - just in case.

We put the engine together and put it back in Steve's bike last night. Steve was tight for time so only gave it a short run and we will have to wait for a while to see if the leaks have been cured.

To be honest, I am enjoying my 325 as it is and am not desperate to strip it down to treat the barrel. I may put up with the slight oil weep for a bit longer to give Steve plenty of time to test his barrel repair out first wink

There is a TRF event on Sunday which will be the first time both Steve and I will have managaed to get out together on our 325s. Should be fun!



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RE: TTR250 - fitting a 325cc big-bore kit
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I rode only around 10 miles this evening but it's all going well biggrin

It seems to be noisier now though, possibly due to the new short header pipe though I need to check all the joints, i'm not convinced the new domed bolts are tightening enough.

I may try the original end can to see what thats like, if it's better i'll sell the aftermarket one.

By the way, talking 325's, this is me on Brians recently

2.jpg

Sorry mate, I got it a bit dirty biggrin



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I am pleased to say that both TTR325s put very big smiles on their owners' faces today at our Haccadown event with many laps under their belts and no problems at all - except with the riders who had to make a few adjustments to cope with the added zip and stronger engine braking biggrinbiggrinbiggrinbiggrin



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DSC00072.JPG

Two 325's at the same venue smile

As Brian said, they both performed brilliantly, everything I hoped the bike would be after all that work biggrin



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Yipee - it was obviously worth waiting for then.

That must explain the ear to ear grins of you two proud riders. biggrin

Even your badger looks smug, Steve! wink

Martyn



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I took my 325 over to S Ireland for a week's trail riding up and over the mountains and it performed better than I expected.

With a big knobbly on the back it got me through some difficult bogs and up some very steep mountain trails with ease biggrin 



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I discovered last week that the cause of our cracked and leaking barrels was wrong size liners sent to us by Thumper Racing no

However, I have now had some excellent customer service from Travis at TR . I am sending over a couple of barrels and he has agreed that TR will machine them and fit the new sleeves. They have offered me new pistons at cost so I am taking them up on that offer and they will bore the sleeves to take them.

The amount of oil leaking is very small but it will be nice to fit the new kit and have a clean engine (and boots) again biggrin

I will report back on how it all goes.

Brian



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Success at last!

Pity they didn't tell you about the problem before you told them - they must've known about it. hmm

Still - you've got a replacement piston at cost so the motor should be good for a few decades now. blankstare

You will have to go to Ireland again to run it in now. confuse

Martyn



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Hi Brian,

Thanks for the link to this site, I have copied the text from the other site so everyone else can fully the thread.

I bought my big bore kit about 2 1/2 years ago from Thumper Racing, I have no idea if the liner is oversize as mentioned above. It could be as the oil leak apprears to be similar.

Just to clarify, I didn't fit an O ring at the base of the liner as there wasn't an O ring supplered with the kit and the crankcases were not machined to compress the O ring correctly. I didn't check the crankcases before getting them machined for the bigger cylinder liner but am guessing there needs to be a chamfered edge on the crankcase for the O ring.

It sounds like Thumper Racing have fronted up to the problem pretty well, it's get to get some good service especially when so many companies in the industry have such crap service and a take it or leave it attitude, top marks to them.


Bruce



Hi there, I am new to the forum, I have the same experience with the big bore kit I installed in my TTR, not long after installing the kit an oil leak developed in the front of the cylinder between a couple of cooling fins.



I must admit to struggling to understand where the oil was coming from as there shouldnt be any oil in that area of the cylinder to leak out. After much head scratching the only conclusion that made any sense was the oil was finding its way up between the over-sized cast iron sleeve and the aluminum cylinder casting. This didnt make a whole lot of sense as the liner is a press fit into the cylinder but what I did notice was there as an O ring fitted between the crankcase and the cylinder liner on the standard engine and there was not a similar O ring supplied as part of the big bore kit.



The oil leak wasnt really a big deal but is was bugging me so it was time to get the leak sorted out.



The engine was stripped down and I couldnt be 100% confident the oil was actually leaking out from where it looked to be leaking, I have found over the years that leaks dont always originate from the obvious location. I bought a Dye penetrant test kit, they are specifically designed to find cracks and holes in castings or welds. The results of the test was pretty conclusive, the oil was leaking out from between the cooling fines.



I reasoned that the oil could only be getting by being forced up between the liner and cylinder when the engine was hot and working hard, the oil is thinner when its hot and there may be slightly more crankcase pressure as a result of the bigger piston displacing more air in t he crankcase.



Adding an O ring to the oversize cylinder liner meant a complete strip down of the engine to facilitate machining a chamfered edge on the crankcases and I wasnt keen on that much work just in case my reasoning was wrong and the oil wasnt getting in where I thought it was. I decided to reassemble the engine with a silicone based gasket sealant applied to the join between the cylinder liner and cylinder casting, I used Three Bond 1211 and smeared a very thin coating on the join prior to reassembling the engine. The silicone gasket should seal the liner and cylinder casting as well as the O ring.



The engine re-assembly was completed and the engine re installed in the bike, so far the engine is oil tight once again and the problem seems to be resolved.



I liked your approach of metal spraying the cylinder as that should seal the cylinder casting permanently, have you repainted you cylinder or does it look OK as it is?



Overall I am very very pleased with the performance of the engine with the big bore kit, with the way it delivers the power has transformed the bike. I have no idea if it makes any more peak power, I think it must, but the real gains and in the midrange and the big increase in torque that have exceeded my expectations.


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Dunnycans wrote:

Brian

Have you had any problems with the electric starter?
Are you still running the original or upgraded?

Greg


No problems at all with the starter.

If you consider that the e-starter on a WR450F is of the same design (and actually looks smaller!) then I am of the opinion that, as long as you start off with one with a perfect pinion, there shouldn't be any issues.

I bought a decrompressor kit thinking that I would need it to help get the engine spinning but haven't bothered to fit it. It's not necessary.

Brian



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i mentioned my weeping barrel to Travis at TR by email and he didnt reply

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Sleeves should be pressed in using green Loctite to seal the joint between barrel and sleeve. Common practice on race car engines.

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Brian

I just fitted a big bore kit to my TTR250.

I had the same problem with the leak but instead of pulling the engine down again I stood it up on the back tire and put some Loctite 290 on the area where the oil was comming from.
I left it overnight and took it for a run the next day. So far it has stopped the leak.

What settings did you end up with on you carby?
When I got my bike it had a staintune muffler on it and had been tuned with the following
Pilot jet 50
Main jet 147
Needle set in the centre.

So far I have adjusted the needle right up.( clip on the bottom closest to the point)
And it seems to have more pull.

Greg

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Hi Greg

Sorry to hear you have the oil "weep" but hope your Loctite trickery cures it!

Can you remind me, did you have the sleeve fitted locally or by Thumper Racing?

I have a kit on my bench where Thumper fitted the sleeve and am hoping that it will be OK.

The weep on my current 325 (sleeve fitted locally but Thumper admit it was too wide and one of a "bad" batch that escaped their quality control) is minimal and I am quite happy to put up with a bit of mess. You don't see it anyways when the engine is covered in gloop wink

I am using the totally standard "blue" model carb settings and jets with a Motad silencer and it seems absolutely fine.

Brian



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Brian

 

I had the sleeve fitted locally by Dr Mac in Maitland, NSW.

If my loctite trick doesnt work they are happy to remove the sleeve and apply loctite to the sleeve and bore before assembly.smile

Greg



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Dunnycans wrote:

Brian

 

I had the sleeve fitted locally by Dr Mac in Maitland, NSW.

If my loctite trick doesnt work they are happy to remove the sleeve and apply loctite to the sleeve and bore before assembly.smile

Greg


 It might be worth checking the o/s diameter of the sleeve with Thumper Racing to make sure they haven't given you one of the "bad" batch.



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what should the outside diameter be Brian?

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The correct o/s diameter is 86mm - or at least that is what the latest sleeve from Thumper Racing measures. Once bored that leaves a wall thickness of 2.5mm.

Brian



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Well after getting my 325 kit from Brian last November I finally put time aside to fit the engine this weekend and joy oh joy it works perfectly and have ridden it all of 6 miles. Pulls like train. I used a donor bike/ engine bought from Brian last year. No idea on mileage of bike but upon stripping was encouraged by the overall condition. Everything was removed with exception of bearings in crankcases. Crankcases were taken up to Hamlins in Bridgwater and were machined out for £70 and in about 5 days. Excellent service. Cases taken back and washed out for about an hour in a parts washer. Assembly in reverse order with the aid of a very comprehensive Yamaha manual just took about 6 months due to other commitments. Actual build time was probably about 6 hrs ish.Only glitch which Brian saved me from was the realisation that there are 2 timing marks on the flywheel and I had misunderstood what a Japanese "T" looked like. Will update when I have actually ridden the new machine in anger

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Excellent news Simon and thanks for the update!

I still have another 325 kit in stock for when I feel like doing another engine rebuild.

Learning from your experience:

a) I will certainly use Hamlins for boring the cases next time as we had real hassle and were delayed by months by our local engineering firm.

b) I won't go to the hassle of removing all the bearings from the cases before boring them!

What gearing are you running on your 325? I am still running 13/48 and 70mph is easy to reach but I chicken out of seeing what the top speed is because I am not too sure of how the knobbly tyres will cope - plus of course it would be illegal wink

I might put a 14 tooth on when the existing sprocket starts to hook.

It is interesting that we have at least four 325 owners on the forum now - welcome to what seems to be a very exclusive club!

Brian



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Morning Brian When do you sleep?!? Bike is 14/52 combination but does feel to low geared on initial ride. Still going out on the bike for a proper ride this evening so will report back after that. Thank you for the welcome. Let's hope it's a long membership of this exclusive club Cheers Simon

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Morning Simon!

Can't afford to sleep wink

14/48 might be good bearing in mind standard for the 250 was 14/44 but see how it goes.

Have a good ride biggrin

Brian



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Well I took it out tonight for a couple of hours and it runs really well. Just a little more vibration when accelerating from low rpm but I guess a larger piston plays a part in that. Much more engine braking but the real surprise is the ability to pull one gear higher on known tracks-marvellous. Hasn't leaked or burnt any oil yet. Yep a good move for a lardy bike with a lardy rider! Thanks again Brian for the recommendation and advice Cheers Simon

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Brian

 

Loctite trick did the job. Havent pulled it back down to check sleeve diameter yet though.

I'm running 13/49 at the moment. Was having trouble getting up a few hills in the Barrington tops before I fitted the 325 kit. Was running 47 rear which I might change back to now I've had a few runs with the 325 kit installed. Certainly pulls well.smile

I'm finding now though that the front end is starting to wash out a fare bit. Feels like I've got a flat tyre. Running about 12-14psi in the tyres. Where I ride there's a bit of clay and loose stuff.

Have you any ideas of how to improve the front end?confuse I have been told to increase the oil level in the front forks. Not sure how that will go. Have also heard of people fitting yz or wr front shocks.

Greg    



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Thanks for the update Greg - good to hear you are pleased with the extra grunt!

Before going to the hassle of changing the forks, make sure that the existing ones are working as Mr Yamaha intended.

  1. They need clean oil at the correct level - I can't think that increasing the oil level will affect the action of the forks, 
  2. check there is no play in fork bushing - get TTR on stand, grab both fork legs firmly and see if there is any back and forth movement,
  3. check the fork seals are not leaking,
  4. if all good so far, perhaps try adjusting the clickers at the bottom of the fork legs to see if you get an improvement - details in the owners handbook
  5. you could also try putting a bit of air pressure in the forks to see if that helps
  6. also try different tyre pressures in the front tyre

Worn swing arm or linkage bearings or a dodgy rear shock will also affect how the TTR steers.

Its all a good excuse to do more riding wink

Hope that helps a bit

Brian



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The 325 started to smoke on start up but, once running, doesn't burn oil. My assumption was that the valve stem oil seals needed replacing so I did that today.

When I took the exhaust header pipe and the cylinder head off it was obvious that the engine had been running very rich. The bore looked absolutely clean and the soot wasn't oily.

So, whilst the carb was loose, I took the float chamber off and checked the main jet. It was a 147. I have a couple of spare 137 jets so have fitted one of those.

Once put back together, the TTR started fine so I have taken it for a short test run - short because its pouring down with rain again cry

The engine seems much more responsive and I am hoping to improve my fuel economy. Before the change, the 325 was drinking more petrol than my mates CCM650 and WR450F disbelief

Got a trail ride booked for tomorrow but am not sure whether to chance taking the 325 after only such a short test drive confuse

Brian



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Brian

Havent had my head off to check the sleeve size or if it is running rich or not, however the loctite trick seems to have done the trick. 400km in the Barrington tops near Gloucester NSW and justr a small weep. Once the muds on her you wouldnt know.

The extra grunt loves the mountain climbs and is going well against the 400 and 450's the old girl is running against. I love the fact you can throw the ttr at anything and she doesnt give up. I noticed I now have more back pressure to which is great for the downhill runs.

The only thing I have noticed is if you lay her over she starts ok but runs rough at 1/3 idle and you need to clear her throat. Once you do that she runs well. Maybe if I keep here upright more often I'll be right doh

Changing from the 147 back to a 137 would be a big step confuse  Can you get one in between to trial first?

Thanks for keeping us updated.

Greg

 



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Hi Greg - good to hear you are enjoying the 325!

I did a 70 mile trail ride today on the 325 and it is pulling really well with no pinking or misfiring under load. The engine blubbers if I pull the choke on so I am pretty sure that I am not far off with the 137 jet and its not giving too lean a mixture.

There is some slight hesitation when the revs build up with a wide open throttle and I will see if raising the needle a couple of notches improves things.

On its first run out on the new jet and in very wet and muddy conditions, with lots of low gear work, I got over 50mpg and I am pretty sure that I can improve on that.

Brian



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I pulled the plug today and it looks like I am going to have to go for a bigger main jet after all. I will try a 142 which is midway between the 137 and 147.

Plug with 137 jet.jpg

Just spoke to Fowlers and they don't keep stock but will order me in a 142 jet (part # 288-14329-71-00) so fingers crossed it arrives before I need to use the 325 again!

Brian



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Hello Brian

Sitting here bored in peak district and looked at your updates. Just over 50mpg seem very high. I am sure I am still getting 65 to 70mpg although I am probably a lot slower than you.

Also the plug looks nice and black around the edge and white/clean in the middle which is where you would expect it after so few miles wouldn't you???

I think I said that since my conversion without a jet change it hardly needs any choke and is instantly rideable which would indicate too rich despite the engine displacing more air. The plug however looks spot on.

 



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CHANCEY wrote:

Hello Brian

Sitting here bored in peak district and looked at your updates. Just over 50mpg seem very high. I am sure I am still getting 65 to 70mpg although I am probably a lot slower than you.

Also the plug looks nice and black around the edge and white/clean in the middle which is where you would expect it after so few miles wouldn't you???

I think I said that since my conversion without a jet change it hardly needs any choke and is instantly rideable which would indicate too rich despite the engine displacing more air. The plug however looks spot on.

 


 Hi Simon and good to hear from you! Is the weather bad up there?

Thanks for the reassurance on the plug. I confess that when I pulled it I saw it as white but, upon closer inspection it probably is OK. I might raise the needle a notch or two to see if it improves things though.

My guess is that you are running the later carb with a 147 jet so maybe you would like to try the 142 I just ordered and probably now don't need wink

Brian



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Hi Brian

unfortunately weather is ok so I can't avoid the peak trekking. Even the dog is complaining about some of the gradients!

Anyway will have a look at what I have got fitted upon my return and let you know. With the 325 kit you gave me a jet and a new air filter neither of which I have fitted so don't know if the kit filter makes some sort of difference in flowing more air thus the difference in running . As for fuel use are you sure about 50 mpg?.

Speak when I get back

Cheers

Simon



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I had wound the air screw out over 4 turns as advised by another 325 owner but, having read the carb info on this link, that probably made the mixture a bit lean at lower revs. I therefore wound it back to about two turns out and it has made a definite improvement in pick up.

I will do it a bit more scientifically when I have time wink

Brian



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Hi Brian

Checked my main jet and its a 145. The jet supplied with the 325 kit is also a 145 so thats probably why it runs fine so must be thereabouts. What sort of trick plug is that? If its a platinum tipped plug I believe and in my 2CV experience they only work properly when thrashing the engine. Have you tried a standard plug?

Cheers

 

Simon



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hey Brian, that's a nice informative animated carb diagram in the kdx200 based article, buts it's a bit misleading about the low speed circuit, if applied to a ttr250..

The kdx200 is a typical two-stroke and has an AIR screw located on the intake (air filter) side of the carb.

But the ttr250 is different.
It has a FUEL-MIXTURE screw, located on the engine side of the carb, not the air intake side of the carb.

And with such a fuel mixture screw, you are adjusting a small flow of air mixed with fuel from the pilot jet, so when you screw it in (clockwise), the relative amount of fuel getting to the engine is less - ie screwing it out to say 4 turns, rather than the standard 1.5 turns or whatever, would actually make it run richer, not leaner, than standard, at near idle speeds.

For what it's worth, my own bike doesn't seem particularly sensitive to this setting (given an appropriate corresponding idle speed re-adjustment).

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A bit of a negative update I am afraid cry

My 325 began smoking on start up and this gradually got worse until recently I was almost too embarrassed to start it at home disbelief

It would start smoking a few seconds after starting up and would stop after a minute or so. It was using hardly any oil so I wrongly assumed valve stem oil seals. I fitted new ones but they made no difference.

The engine still goes really well and, despite my 17+ stone weight, is happy to get the front wheel pawing the air under power in 2nd gear if I pull away fairly enthusiastically. 

Anyways up, I decided to swap out the engine to give me time to strip it for investigation without being in a hurry to get the TTR back on the road.  

Those of you that have followed the this thread will know that I built my 325 alongside another owned by my mate Steve. He then bought a WR250R and decided to sell his TTR with a standard engine in so we did a swap and I have had his 325 engine in stock since then. It has only done 350 miles since the build and it is now happily sitting in my TTR. It starts and runs well with no smoking so my trail TTR is back and ready to go.

I am very disappointed to have these problems after less than 2,000 miles but will report back on my findings.

What sort of mileage do other 325 owners get without problems?

Brian



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Update

Thumper Racing don't keep oversize pistons in stock but Travis has offered to get one made for me - $360 USD (dealer cost) plus $60 shipping to the UK blankstare

The alternative is a new liner at $109 but this depends on the original piston being in good shape and needing just a set of new rings. However the cost of fitting the new sleeve and rebore need to be taken into account. This would still be my preferred option as Thumper originally supplied the wrong size liner. It was too big and the barrel developed small cracks where it was thin and seeped oil and got a bit messy. A new liner in another barrel would solve this.

The 325 is a great motor but needs to be able to do more than 2,000 miles without needing a rebuild!

Next move is the strip down but I am waiting for my engine stand to come back from the powder coaters wink

A friend with an XT600 that has done only 3,000 miles had the same smoky symptoms. He stripped his motor yesterday and found the oil control ring to be very "tired" and I am wondering if this might be the case with mine. It would be good if it was that simple!

Brian



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It's a real shame to hear about your problems with the conversion Brian, even if you sort out the burning oil there is still the oil seepage from the barrel. You would expect to get far more than 2,000 miles from new rings / piston and barrel. If there was a better success rate with this conversion I am sure a lot more people would go for it. Thumper racing should be taking the feedback onboard and doing something about the problems.

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To be fair to Thumper Racing, they did take on board the fact they supplied us with wrong-sized sleeves and Travis gave me a reasonable deal on a couple of new kits. This time I sent a pair of barrels over to Thumper and got them to fit and bore the sleeve.

To try and recoup some money, I have sold one of the kits but still have the other on my bench which I could fit tomorrow. However, I am not one to take the easy way out and would really like to sort out the engine I have. I am really hoping it is something simple as it was really running great and was a joy to ride. 

My mate wasn't so lucky with his XT600 that he thought might just be a slack oil control ring. He took his barrel to a local engineering firm who found it was very oval so he has had to have a rebore and new piston at 3,000 miles no

Brian



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Brian

I removed the barrel on mine and put a small chamfer on the crankcase then fitted an oring on reassemble.

This has so far stopped the oil leak.smile  I now know why there is an oring groove on the standard barrel.

If you are going to machine another barrel you could even put the oring groove in the barrel itself.

As for my engine, It would only have done about 1000kms. So "so far, so good". No smoke.

Thanks again for the update.

Greg



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The chamfer is a good idea. Yet to decide what I am doing with my smoky engine.

I am waiting for my new engine stand to come back from the powder coaters before taking mine apart. Back Tuesday I hope smile

I haven't got a 325 sleever or liner out of a barrel but have got one installed in a barrel but not yet fitted so I have measured that one.

The dimensions are:

86mm o/s diameter

81.90 inside diameter after boring

Height is 101.70mm

The lip at the top is 4mm wide but I can't tell how deep it is.

The thickness of the liner is about 2.40mm - I realise this doesn't add up so there must be a flaw in how I have taken some of the measurements disbelief

If anyone has an uninstalled kit from Thumper, any chance you can measure your liner for me please?

Brian



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TTRfan wrote:

On its first run out on the new jet and in very wet and muddy conditions, with lots of low gear work, I got over 50mpg and I am pretty sure that I can improve on that.


Haven't improved on that with Steve's 325 engine fitted. I got 51mpg in similar wet and muddy conditions.

Brian



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I have been asked offline if I would recommend the 325 conversion and this was my answer:

The 325 kit transforms the TTR and I highly recommend it.

The problems I encountered were due to getting the engineering work done by two different firms and the firm that fitted the liners making a mistake in not fitting them properly. It didn’t help that Thumper sent liners that were too big in diameter and caused the barrels to weep oil.

Also, having stripped my 325 engine down to investigate why it smokes so much on start up, I now recall (mistakenly) asking for the barrels to be bored with a bit more clearance than Wiseco recommended. The piston and rings are in excellent condition but it is this extra clearnce that is causing the smoking on start up. When the piston heats up and expands a bit the smoking stops.

If you wanted to go the big bore route then I would recommend sending your barrel to Thumper for them to fit the new sleeve and bore to fit the new piston. Get the crankcases opened locally. This is what my friend Simon (Chancey on the forum) did and his 325 is proving very reliable. If you think about it, the starter is actually bigger than Yamaha use on their 450s! 

Out of the three local 325 TTRs, none have had starter problems and fire up no problem even on the coldest days. 

Brian



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