A forum for owners of Yamaha TTR250 trail and enduro bikes!

with that engine, you may be able to climb even a straight wall of neighbour's house

-One question: is there any risk for engine overheat if run in summer temps?

I split the bored crankcases and they needed a good clean out in the parts washer as there was some evidence of swarf from the boring. I need to be very careful with the cases as they are a gasketless fit so the mating surfaces need to be pristine.

I have new main bearings and the clutch shaft bearing in stock but need to order the other two. My supplier has the main output (sprocket) shaft bearing in stock but will have to order in the balancer shaft bearing so that will put me back a bit

I am not sure why these bearings had been taken out as they rarely cause problems and it would have been easy enough to have masked them up before boring the cases 

 

Before I can split the cases on my donor gearbox, there was the small issue of a untidily welded up gear changer shaft! It wouldn't pull through without damaging the seal and bearing.

 

A quick attack with the disc cutter and problem solved 

 

I have a good spare gear change shaft so that's not an issue.

Here are the donor gearbox cases opened.

 

Apart from the gear change shaft, everything looks good on quick inspection. Each part will be cleaned and oiled before fitting so I will make the real check then.

Brian

Hi Kimani - good to hear from you!

The project has stalled a tad as my new balancer shaft bearing is on back order 

Meanwhile is there anything in particular you or any other owners would like to see me cover in detail?

Brian

I ran mine on a dyno not long ago. The results are near the end of the thread on "325 kits from a UK perspective" in the modifications section. The rolling road is car sized rather than bike specific, and I was on Heidenau k60 tyres rather than road pattern. Don't know for sure how this might affect the results, but my main reason for the run was to check air/fuel ratios rather than power/torque, and unfortunately I didn't first test the original 250cc bike as a control. Might one day borrow a 250 to try on the same dyno if I can find a willing volunteer... I'm very happy with the result!

Ride safe,

Simon.

The balancer shaft bearing arrived this morning so the build can continue 

After fitting the new bearing, I dug out a crankshaft that I had reconditioned with a new big end and conrod. This is to give the new engine the best possible chance of longevity.

I used the large starter gear, 3/4" socket and the flywheel bolt over the LH side of the crankshaft to pull it through the main bearing as it is an interference fit. 

 

It is now a case of removing parts from the donor gearbox, cleaning and checking them and then fitting them to the 325 starting with the balancer shaft - making sure the punch marks were lined up.

Next up is to look through the manual again to make sure that I don't get caught out by being over confident 

Brian

...covering both sides with some non-hardening flange seal...

Tomorrow, please take time to fully cover this part of topic: advantages over using a regular gasket, how to and how Not to do, what can go wrong, etc... 

My advice on putting the crankcases is to take your time! I will explain later.

Firstly make absolutely sure that you have the dots on the crankshaft/balancer cogs and gearchange shafts are lined up. Also, make sure that the two locating casing dowels are in place.

I smear flange sealant (I use Loctite 574) on the crankcase mating faces.

 

Then, with the half with the gears in at the bottom, fit the cases together. A bit of wiggling may be required but no force should be needed.

If the sealant was spread correctly then there should be a bead of it squeezed out around the whole of the mating faces.

 

Turn the gearbox over and fit the crankcase bolts and torque them up to 10Nm.

 

I then use some blue workshop paper soaked in clutch/brake cleaner to wipe off the surplus sealant.

I have had some extra practice doing the job this morning as I forgot to do the final checks before putting the cases together. I got as far as torquing up the bolts before a nagging doubt made me decide to split the cases to check 

Of course, everything was as it should be but it put my mind at rest 

Hopefully that was what you wanted Sena?

Brian

Very Cool indeed Brian. And I'm soooo jealous!

So whats the plan for the engine when finished ? Do you have a TTR ready to accept it ?

Interested to know how often people have to resort to the kicker? In hot conditions on the VINCE last year my old battery failed in the morning. From cold she wouldn't go with the kickstart and I had to push her anyway!
What's your kickstart history like Brian?
Simon.

Bent the tabs on the tab washers over on the clutch nut and primary drive gear. The clutch one is always difficult because of access 

Next were a few "don't forget"s.

Replace the clutch push rod and ball bearing.

 

After fitting the clutch basket, adjust the clutch actuating arm so that the pointer lines up with the casting mark on the casing. Difficult to see when the engine is in the frame.

 

Yep - the eagle eyed may have spotted the return spring was the wrong side of the arm but that was easily rectified.

Fitted the cleaned gauze oil filter - only goes in one way so you can't get it wrong unless you force it.

 

Now ready to replace the cover.

 

The filter cover O rings looked a bit tired so I replaced them with new.

 

And it was all going so well........ until I torqued up the cover bolts and the last one wouldn't tighten 

So it was off with the cover again to fit a thread insert.

I have had quite a few of these strip out so am familiar with doing the job 

This is the culprit.

 

I use Recoil kits as they do the job nicely and are a better price than some others.

 

That's it for today!

Brian

Great progress, it reminded me to add the filter cover O rings to my next order.

Andy, CLICK THIS for the YZ link

Martyn

Oops - bad luck.

You're in good company with "retail therapy".

That phrase happens to be ever upon Mrs. Cubber's lips.

I have a torque wrench but on little nuts/bolts I much prefer a proper sized spanner, experience and and discretion.
However, it doesn't ALWAYS work but mainly it does.

Martyn

I fitted the large starter gear and flywheel and it seems that the most technical part of the rebuild is over.

 

As I am using parts from a donor engine, I checked that the small starter gear had the correct number of teeth for the new large idler gear I was fitting - and it did - 16T/14T - see here to understand why it was important!

The generator cover gasket was in good shape so usable. I fitted the cover making sure the stator wires were correctly located before tightening it up. I couldn't find a used 72T/19T idler gear so had to break out a new one.

The starter gear cover was then fitted (with some decent bolts to replace the originals which invariably round out) and that's another stage completed.

 

I must remember to add my engine stand to the "Essential Workshop Tools" thread

Both the generator and the clutch covers will need quite a bit of tidying up before I respray the whole engine prior to fitting it to the frame. But that is still a little way off.

Here is the 325 kit ready to go on next.

 

The Warranty Disclaimer for the piston kit isn't very encouraging 

Brian

I managed to do a bit more on the engine today.

Fitted the Wiseco piston first. Note that the 325 piston doesn't have an arrow pointing to the front so need to make sure the bigger inlet valve pockets are at the rear of the engine.

Is it just me that struggles getting the gudgeon pin circlips in? I just Googled "gudgeon pin" to make sure that I had the correct spelling and found the following video. Methinks his circlips weren't as strong as mine were today!

Anyways up, I fitted one circlip and the rings on the bench. After a good lubing up I then installed the piston on the little end and fitted the 2nd circlip.

 

The Wiseco instructions for the placement of the ring gaps is a tad confusing as I think it is for a multi-cyinder engine as it shows the front of the engine in line with the gudgeon pin - see below:

 

My understanding of the "rules" is that ring gaps should never be over the gudgeon pin, no gap should be above another gap and the compression ring gaps should be at the rear away from the exhaust port - as per the standard TTR manual. So this is how it should be - in my opinion!

 

Before the barrel was fitted, I put on a new base O ring. You can see from the photo below that it is much smaller than the standard O rings. I had a bevel machined in the barrel before the sleeve was fitted which Thumper don't do on their conversions. Just a bit more insurance against any oil leaks.

 

After lubing and fitting the barrel over the piston (can be tricky with only two hands!), I used the kickstart to turn the engine over to make sure the piston moved freely to check the rings were all sitting correctly in their grooves.

 

Before I packed up for the night, I put a bit of plastic sleeving on the timing chain so that I can retrieve it if it falls down into the cases later on. I also fitted the two dowels which locate the cylinder head and the front cam chain slipper. A few less things to forget later!

 

I stopped at this point as I need to decide what I am going to do about a cylinder head for it 

Brian

Amazing thread as always Brian, your attention to detail always impresses me, well done again! 

I can hardly believe it's over 4 months since I have done any work on this project 

Anyways up, I needed to clear the bench to work on Steve's engine.

I don't want to muddle up any of my parts with Steve's and, rather than just pack everything away, I have had a tidy up and reminded myself of what needs doing on the 325.

What stopped me before was a problem with pitted exhaust valves. The valve seats are fine so are they made of harder material or is it just that the valves get hotter?

To save time I have just grabbed a couple of new ones from stock so that I can carry on and assemble the head.

Hopefully the photos below will show the poor state of the original valves. The new valves are sitting behind them.

 

Now for the job I don't particularly enjoy - lapping in the valves 

After finishing Steve's engine I felt sufficiently motivated to tackle my 325 project again.

Didn't take long to fit the head and cam gear. The engine is now back together and ready for tidying up before fitting it into its rolling chassis. Just got to find a few parts like the kickstart and gear levers - they gotta be tucked safely away in a box - somewhere - if I haven't used them on another build in the meanwhile 

Photo of the engine below with rolling chassis in the background.

My step-daughter works for a "workplace" supplier Pete - very handy for gloves, etc 

Oh glad you know where the little fella came from .For a moment I thought you were going to say I found the the mystery whinening noise from Ttr Steves engine!!!! 

good luck!

Engine in!

6 weeks later and I have re-started the new build. I need to get a move on now as I don't have a TTR to use laning otherwise!

Rather than run backwards and forwards between the garage and workshop checking cable and wire routing etc I have both my old "donor" 325 and the new build side by side in the workshop and it will certainly make swapping and installing parts a whole lot easier.

Handlebars, levers, switches, headlight, speedo mount and indicators to be moved over first. The speedo head will stay with the old TTR so that it has the genuine mileage showing and I have another lined up for the new bike.