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Post Info TOPIC: 350cc Big Bore Kit for the TTR250 - updates and gossip!


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350cc Big Bore Kit for the TTR250 - updates and gossip!
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Some of you may have realised by now, there is talk of a 350 kit becoming available.

There has been some really hard work done by a fellow TTR nut, to see if it could work. Measurements have been taken, suppliers and manufactures have been approached and it would seem it is a feasible project.

The seed for this project was planted a long time ago ( you may guess by who)  and it is only the recent efforts of some forum members that is bringing this tantalising project to fruition.

This is not going to be like the 325 Thumper kit.

It will be made with a new barrel, that is going to be cast thicker than the original to compensate for the bigger piston and sleeve.

We would appreciate what other forum members think?

Please give some feedback.

Steve



-- Edited by ttr steve on Wednesday 9th of November 2016 09:04:40 AM



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Coooool !!

I may be keeping the TTR after all !!

I just need a good excuse.

biggrin



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Sounds quality to me. Would love to see the dyno figures on the 350 kit

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Would love to see the figures and what the life of it is in regards to wear. Any plans for reboreability?
Any need for mods to head, carb upgrade etc

Good call though. Like the idea.

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sounds good is this from china i ask this because i have a honda c90 workhorse to go to work on weather permitted i have just fitted a barrell and piston to it not bad quality done over 3000 miles on it no smoke or does not burn any oil quality of parts from china are getting better they used to be rubbish johnboy

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This is not from China, it is all being made in the UK with top trades people. I do agree some of the Chinese stuff is quite good, but it is a bit pot luck. Rich, good question, will ask.



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This sounds pretty bloody good. I'd be interested for sure.

I often think my next bike will be a WR250R (when the ttr dies in 1000years) but then I think maybe I should get another ttr, and do up the engine to a 325 and then swap the engines over. Would be much cheaper than getting a WR and I still think I like TTRs more anyway.

Bolt on kit?

Leigh

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Ideal. The TTR defiantly needs more power to lift the front wheel more easily. What are the rough cost figures? Or to early to say?

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ttr steve wrote:

This is not from China, it is all being made in the UK with top trades people. I do agree some of the Chinese stuff is quite good, but it is a bit pot luck. Rich, good question, will ask.


 It was my problem with going from standard to 263

 Bit risky in a few years when you need to bore again. Would be sensible to allow at least one...



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How about a stroker crank to go with the 325 kit to give 350...
haven't done the numbers but for 25cc prob only moving the crank pin
a couple millimeters out...





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petenz wrote:

How about a stroker crank to go with the 325 kit to give 350...
haven't done the numbers but for 25cc prob only moving the crank pin a couple millimetres out...


Hi Pete

Presumably you would need to cast a new crank plus a shorter conrod to stop the piston hitting the head? 

One of the issues with fitting the 325 sleeve for the Thumper kit is that it leaves the aluminium barrel side walls quite thin and requires very accurate machining to get them right.

If thicker bodied barrels are cast then they would also be usable for the Thumper sleeve and piston big bore kit but that's where the thought "Why not go to 350cc?" kicked in biggrinbiggrin

Brian



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So how meany componts make up a ttR crank...5?..
left & right ends / 2 crank wheels / crank pin..
is it a compont crank...
If this is the case you would only need the 2 crank wheels
with the crank pin hole moved out.... can be machined out of
soild bar...

shorter rod.... or barrel spacer plate...
cam chain may need to be a link or two longer...




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What do reckon to rough cost of that Pete?

Stroking the 350 would be interesting wink



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TTRfan wrote:

What do reckon to rough cost of that Pete?

Stroking the 350 would be interesting wink


 cost wise.. no real idea...

i have not seen a TTR 

once a cnc progamme has been made its easy to spin up the crank wheels..

they would  most lightly have the centre holes splined and would need oil holes then balanced..

a spacer plate can be laser cut..... cam chain guide length could also become a issue...

a lot of numbers to be crunched...

cost wise it shouldn't be any more than casting a barrel block then boreing and decking it

making a sleeve and fitting it...

 

there is another way .. make a eccentric crank pin... but the extra stroke is dependant

on the TTRs diffrents between the jernal size and the dia of the ends that press into the

crank wheels....

IE.... if the diffrent was 6mm you could geat around  4mm longer stroke...

the real issue with this way is the crank pin can turn so it needs to be locked

in place.... welded or pined/keyed to be safe... why it is not a common practice...

 

 



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I think the crank is 3-piece? 2 ends (crank wheel and main bearing shaft are 1 piece) and the pin.

I think for an eccentric crank pin you'd require a new shorter conrod forged, with a smaller big end bearing. How do you fit that over the ends of the crank shaft pin? You would definitely need new crank wheels and a straight big end pin. (Much simpler on a car 2-piece conrod)
Smaller bearing = lower load capacity. Definitely a shorter conrod, the more I ponder it - the compression height on a ttr piston is pretty marginal as it is so you couldn't shave the crown down. Presumably the piston drops further down the barrel too - don't know how close the piston skirt gets to the crank wheels at bdc...
Extra length cam chain opens up another can of worms...

Good points though Pete, there's more than one way to skin a cat!

Ride safe,

Simon.

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Guru

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thats the limiting factor with a offset crank pin...
the offset can be no more than the dia big end jernal...

if the main shafts and crank wheels are one peice it becomes a lot harder..

 

they do make stroker cranks for the yamaha XT660 motor
up to +12mm...

.



-- Edited by petenz on Thursday 10th of November 2016 10:09:07 PM

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Bump, any more info yet ??

 



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It aint gonna happen before Christmasbiggrin

A significant amount of research has gone into the feasibility of this idea and a lot of time taken finding suppliers/manufacturers. With a green light from those involved, a patternmaker has now been lined up. The barrel casting has been the most important bit to get right. We are at the stage of commissioning the pattern. There's a couple of months at least before casting of prototypes can begin. The steps are 1: Pattern, 2: Cast barrel, 3: Machine barrel (quite complex), fit sleeve and bore/hone/machine to requirements, 4: Custom pistons to specify and order (also up to 2 months lead time), 5: Machine a crankcase, fit together and TESTsmile Of course, some of these steps can be concurrent to reduce lead times to first prototype testing.

We're getting there and are optimistic.

Once we're running a couple of prototypes, we'll be off to the rolling road for jetting tweeks and performance figures...

Patience is a virtuesmile

Glad there's some interest out there,

Ride safe,

Simon.

 



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Im keen but wont touch my engine till it needs pulling down last one did over 70.000ks with no issues so will have to watch from the side lines 

I fitted a wisco 310 kit in an xt a long time ago went well got a bit hot on days over 35deg wisco suggested extending the fins on the side of the barel to compensate 



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I've had no problems with my 325 in high temperatures, and Robin Webb's adventures in Utah on his didn't result in any seizures as far as I'm aware, but I think a decent oil cooler would be a wise precaution in hot climes, as much to increase oil capacity as to improve cooling. I don't know how much the fins would need to be extended to make any realistic difference?

Going back to Devon Rich's question, rebores should be feasible. If the kit becomes financially viable it will be done with this sort of long term useability in mind.

S.

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Exciting times - I am going to be like a child waiting for Christmas wink



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that's only a bit over 3 weeks away !

I have spent over $3300 over the last few months on stuff for my DRZ

It's like a birthday present every few days biggrin

Except I have to pay for it  wink

at least I never know what is arriving till I open it !

 



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I'm hooked on the extra power now of the DRZ

but still like the TTR a lot, the 6th gear, lower weight, air cooled, I think a nicer build than the Suzuki, suzuki did some weird things.

How about making a Sticky with updates and info about the new 350 kit.

be much better than having to search the posts all the time

Call it "All things TTR350" or something like that.

 

..

 



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350cc Big Bore Kit for the TTR250 - updates and gossip!
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Well the patternmaker has finally got the barrel casting pattern at the top of his list of things to do! He did tell me "starting it at end of Jan", so we're not far off! I will speak to him soon to sort out some details, but the ball is now rolling


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YES!

Well done Simon, can't wait to hear moresmile

Steve



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X 2 ☺!!

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I was surprised to see the old TT350's ran the same stroke as our TTR250's. Just a much bigger piston.

86mm x 59.6 for the TT350 compared to the TTR250 is 73 x 59.6.

Is that what you guys are aiming at, something similar to that?

Those old TT's were reknown for their reliability.

Have you used a tt350 barrell as a reference. I know they don't bolt up.

Do the two motors share a similar bottom end??

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xt/tt350 piston unfortunately has a 1mm larger gudgeon pin, but that was the initial hope - to use a 350 piston. It all started with slight dissatisfaction over the way some of the barrels machined out for the 325 kit (closer to 315cc actually) split and weeped oil (the origin of which we have never really ascertained!) Solution - cast a bigger barrel. Then the thought arose - why not make it a proper 350? Why not?
The 350 conrod is longer and slightly larger at both ends, but with a number of 325s about, it seems the 250 bottom end is up to it. Only one way to find out...
Watch this space. I hope to have a couple of running prototypes by (northern hemisphere) summer. (Everything seems to have a 6-8 week lead time, from the patternmaker to the foundry to the piston maker!)
I'll keep you all updated as progress occurs.
Ride safe, in anticipation of more cubes,
Simon.

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I have a bike waiting for a new transplantwinkwink



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Spoke to the patternmaker today. He's hopeful that the majority of the pattern will be done by the end of the week/beginning of next week. I will ring the foundry soon and prime them.
Have to admit I was getting a bit despondent. Rang up expecting no progress and p/maker expressed suprise that I hadn't been pestering him more (although it would have made no difference)!
Ride safe,
Simon.

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Exciting stuff.

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Any updates on this exciting project?

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Bump. If this comes out i can keep my old OE instead of buying another bike so any info regarding?

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Weeeell, first proof casting was done a couple of weeks ago and I've been running around between the foundry and machine shop discussing it. The fettler also damaged one of the fins so I am rejecting this casting, but I'm also not totally happy with the quality of workmanship from the moldmaker. Unfortunately, they're on shutdown this week, and I'm away riding the week after, but we are making some progress. Pics to follow...



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3 fiddy 020.JPG

This is the pattern for the barrel casting. Fill each section with casting sand, wait for it to set, take it out and fit all the lumps together on the black platform like a 3D jigsaw then fill it with molten aluminium and you get this:

NYorks 008.JPG

It will look much prettier when it's machined and properly dressed, and even better with that shiny new 86mm sleeve fitted!

Once machining is underway I will spec the piston and get one ordered.

 



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Exciting progress Simon. Watching this with interest.

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Oh lordy, I can barely contain myself!!!! Continue the great effort Simon!!

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Really cool thread and project! Have you given any though to the cylinder head? with the larger bore (gaining 100cc is significant) you are opening up the bore enough to house significantly larger valves but my guess is the cylinder head would require a redesign for the valve spacing accomodation. this will also allow larger intake and exhaust runner ports to handle the new airflow potential the larger bore offers. without increasing the airflow in the head, the restriction the stock or even a stock ported head will present will nullify much of the gain from the mid to high rpm range. also a larger inlet boot/flange design and larger carb with hefty airbox mods along with a better flowing (larger diameter) header pipe ad muffler.

I bring up those points because going from 250cc to 350cc is a 28.5% increase in displacement, but, more importantly you are getting there by increasing only the bore diameter and not the stroke. This will yield a bore stroke ratio more inclined to shift power and torque output into the mid to upper rpm range and flow from the peripheral intake and exhaust will certainly be needed to see the most benefit of such an increase. i think the bigger power would really be noticed in the changes to the cylinder head and increasing valve size to maximize the curtain area of each valve for flow.

An additional 13mm of bore diameter gives you a healthy bit of room in the bore for valves.. but it also will mean determining what size you can fit and what cam profile you will want to use and THEN designing up a custom piston with valve reliefs for the larger diameter valves that will certainly drop lower in the bore and become a critical measurement for piston to valve clearance while the piston is chasing the exhaust valve at the end of the exhaust stroke. but man oh man if all of those items are done there will be an obnoxious amount of gained power from the mid to high rev range, it will be a screamer for sure!

Chris



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We've been approaching this from a slightly different angle, having been running Thumper 325s for some time, so the actual bore increase from that to the 350 is not that great. I will not be doing any major head work other than minor porting (but this will be after initial testing so that we can see what effect the 350 conversion has on a standard bike) My intention has been solely to see if a 350 is physically possible. Low to mid range is more my priority as a trail rider but I think it should rev nicely retaining the standard con rod length and stroke.
Of course, when the kit makes it to totallyttrs shop, buyers will be more than welcome to continue development with camlift/profiles, freeflow exhausts, shorty headers, larger bore flat slide carbs etc etc. I would naturally expect the dyno results to be shared with us here
I'm glad there's plenty of interest in the project. So many people have said "why not just buy a bigger bike?" but going orange is not my thing! Keep watching - we're making progress - I'm waiting for a second casting so my machinist has one spare if the first flies out of the milling machine:-0
Ride safe,
Simon.

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It will certainly make more power and torque simply due to the increase in cubes. I'm just thinking that the benefits of the large bore would significantly increase output in the mood and high RPM ranges without sacrificing much low end at all. A stoker would do well with the small ports and valves as they are stock and make silly low RPM stump pulling torque, but the short stroke big bore is a different animal altogether. The piston speed is much slower and won't become as efficient until higher RPM at which point the intake and exhaust ports will become a restriction. A 28% increase in volume per engine cycle is a huge increase over stock and the design for the port configuration was not designed to handle that increase in airflow.

I would investigate the feasibility of a new head casting while you have access to the pattern maker. May be able to cut it out of a solid chunk of billet if the production run is going to be small. If anyone has a spare scrap head laying around they would like to send me I'd be happy to model it up in solid works and see if I could cut it on my machining center..

Keep up the great work! Exciting project!!

Chris

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It's a long time since my i/c engines course at college, but I agree with you. The XT350 did indeed have twin carbs and twin headers making breathing easier, but I've not yet found valve dimensions to compare the innards. (I believe the twin carb setup was actually a pain in the butt)
The expense of the patternmaking nearly knocked the project on the head at the start. The complexity of a head would probably push it beyond my financial limitations - It would be more cost efficient to convert a TT/XT350 engine to electric start I think! (Or, god forbid, fit a DR350 engine in the frame)
Frankenbike here we come?
Simon.

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I think it was sensible to not try to change everything at once. Capacity is a good pick, start with that and then you can faff around with the other stuff if you really must or call it a "failed" experiment and smile at the stuff you learnt and the fun you had doing it.

Messing with the rest of the stuff is like trying to redesign half the engine. Valves, ports, cams, crank and next you'll want different gear ratios and before you know it you've built an engine that's already on the market in some guise, but for a lot more money. Stick too much power in it and you'll want to change the suspension too, while you're at it the brakes, and then you end up with a something where only the TTR frame and wheels are still stock. Might as well have bought a different bike and saved your self a lot of trouble and money (unless you do it only for the fun of doing all the work, hehe.)

I'd love to see some pictures, or even a video, of the machining part if that's possible.

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I had to get rid of my TTR 250, was looking at a CRF450 in the style of a (commuter) CRF 250L, but have now seen this thread and think I'll hang fire until you put this out for testing. It could be just what I'm after

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'94 Yamaha TTR 250 Raid (with Open Enduro headlight, grrr...)

'54 plate Suzuki GSF 650S (Bandit)

Previously Yamaha YBR125, Yamaha TY125, Yamaha TY250



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any update to this it would be nice as a christmas present

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A couple of barrels will be at the machine shop at the end of this week. The foundry has been really slow - first they damaged a barrel with clumsy fettling (fettling is a real term in the foundry business, basically meaning to knock the rough edges off), then took ages to cast another, then took ages again to get the heat treatment done (makes the material easier to machine), then every bank holiday week they shut down... noone more frustrated than me by this, believe me! I'm going to order pistons as soon as the machine shop tells me the barrels look feasible as there's a 6-8 week lead time for custom pistons too!
I would love to have some kits ready to sell by Christmas, but realistically I suspect we will only have a couple of prototypes under testing by then - I want to put a couple of thousand km on one run-in, tuned and dyno'd, before retail.
Patience is a virtue
Cheers,
Simon.

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Patiently waiting in the states, thanks for the update Simon!



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Aww Oh well any news is good news i guess as long as it isnt canceled i will eagerly await it patience is not my strong suit haha thanks for the update though

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Check the gasket out, just shows you how much bigger the pistons will besmilesmilesmile

gasket.jpg



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Glad to see there's still some material around the metal ring! I want to speak to the loctite rep about suitable sealants to "help" the base gasket, which I think is going to be quite skinny. Looking forward to hearing from my machinist with some news soon. He's been trying to "clear the decks" so that he can concentrate on the barrels, and I have faith that he will do the best job or find someone even better than he is if he's not sure, but it is EXTREMELY frustrating playing the waiting game, and I'm sorry that Pete (bluettr) couldn't wait any longer and is going for a bigger bike
Have faith brothers, we will see the myth become reality!
Simon.

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Exciting stuff - thanks for the update guys biggrinbiggrin

Brian



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