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

ttr steve · Super Guru

350cc Big Bore Kit for the TTR250 - updates and gossip!

devon_rich · Senior Member

350 KIT

leigh · Senior Member

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

tom112 · Member

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?

devon_rich · Senior Member

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...

petenz · Super Guru

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...

...

TTRfan · Super Guru

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 biggrin biggrin

Brian

petenz · Super Guru

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...

..

TTRfan · Super Guru

What do reckon to rough cost of that Pete?

Stroking the 350 would be interesting wink

petenz · Super Guru

TTRfan wrote:
What do reckon to rough cost of that Pete?
Stroking the 350 would be interesting

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...

mossproof · Super Guru

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.

petenz · Super Guru

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

mossproof · Super Guru

It aint gonna happen before Christmas biggrin

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 TEST smile 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 virtue smile

Glad there's some interest out there,

Ride safe,

Simon.

ttboof · Super Guru

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

mossproof · Super Guru

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.

BM Steve · Guru

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.

..

mossproof · Super Guru

350cc Big Bore Kit for the TTR250 - updates and gossip!

Kaos · Senior Member

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??

mossproof · Super Guru

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.

mossproof · Super Guru

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.

mossproof · Super Guru

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...

mossproof · Super Guru

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.

Padowan · Senior Member

Exciting progress Simon. Watching this with interest.

FBRConcepts · Veteran Member

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

mossproof · Super Guru

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.

FBRConcepts · Veteran Member

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 mid and high RPM ranges without sacrificing much low end at all. A stroker 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

mossproof · Super Guru

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.

Juvecu · Member

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.

pedrosan · Senior Member

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

mossproof · Super Guru

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.

ttr steve · Super Guru

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

mossproof · Super Guru

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.

devon_rich · Senior Member

Any guesses on the likely cost of these. Just a ballpark is at all possible.

mossproof · Super Guru

Sorry for not answering yet Rich - v difficult to tell until my machinist has actually done one - it's the last unknown (what D Rumsfeld would call a known unknown!)
It will be more than a 325 kit, but hopefully not too much considering the only machining you need to do is the crankcase opening, as barrel and sleeve will come already done.
Once again, I can only apologize for the time this is taking. More news soon, promise...
Simon

mossproof · Super Guru

Yeehaw, we're finally getting somewhere. Got 2 shiny 350 barrels back from the machinist today. 2 prototypes on the way to production. I have ordered a pair of pistons from Wossner (the only people who would do small quantities for reasonable money). Unfortunately, another 6-8 weeks of nailbiting anticipation, but I've got to put my crankcases back together first anyhow.

Here are some pictures of the machining:

2017-12-09 10.49.28.jpg

2017-12-11 10.23.37.jpg

2017-12-18 09.22.49.jpg

-- Edited by mossproof on Friday 22nd of December 2017 08:29:58 PM

katana · Senior Member

What are the cons of Nicasil instead of a steel liner?

mossproof · Super Guru

Mmm, shiny!

If you look closely you can see the machining of the crank case side. This is the biggest sleeve that will fit in these cases. If you want to go bigger than 350 boys, one of you is going to have to develop a stroker. It ain't me babe. (At least not this year!!!)

As far as costs go, the most horrendous bit was the casting pattern. Not putting too fine a point on it, it cost just under a couple of K to get it foundry ready. Casting plus sleeve, custom made piston, and machining costs were all quite evenly priced. With this in mind, and recognizing that we are not going to be selling hundreds of these kits (would be nice, but let's be realistic) I suspect that a final figure is likely to be around, or just below, the £800 area. This is obviously more than the Thumper 325, but all you need to do to the engine is get the crankcases machined out. FYI, I had mine done for £30 by my machinist. Nametab Engineering in Redditch.

When it's all together and run-in there will be several dyno sessions with various exhaust setups, starting with totally standard.

Fingers crossed for the new year...

Ride safe and dream of bigger wheelies,

Simon.

mossproof · Super Guru

RE Nicasil

Cost, for one, especially small batch. Plus you're stuck with that and no oversize pistons later on. These off the shelf liners are not expensive. It was the cost of castings that bumped this up so much. Alternative was 3D scanning an original barrel and modifying the scan where necessary then machining out of a lump of billet LM25TF alloy, which I'm reliably (maybe) informed would probably cost even more for the low volumes.

pug · Guru

Barrel looks good and if my math is good then a 86mm piston on the 59.6 MM stroke will give you 346cc same size as a XT350 any chance the xt piston has the same G pin size and piston height from the pin I would near put money on it being a match but might need work on the valve pockets on the piston crown for the TTr valves to clear. And my hat is off to you for the time and money put into this I could have made a one off with the gear I have at home and work but it would have been at the limit on the casting we don't have that bigger Furnace/pot on are set up at the school it would not hold enough alloy to poor the thing.

Pug

mossproof · Super Guru

Way ahead of you there Martyn. Different gudgeon pin, compression height, valve reliefs, compression ratio... Price for custom pistons from Wossner is not prohibitive. We went through all this in minute detail before deciding to go ahead.
346 - Your maths is correct

TTRfan · Super Guru

Hello from a very sunny Spain! smile

I think the cost of the kit is probably less than a couple of Katoom farkles so is excellent value if it delivers the torque we are expecting smile

Brian

ttr steve · Super Guru

Very nice job smile the big difference against the 325 and this, is that there will be able to give one more re-bore on the sleeve, giving a vast amount of longevity against the thumper kit, that does not allow this. Also the the extra cc will be more than the thumper kit.

It may be a little more £, but much better value smile smile smile smile

Now I need to get my Crankcases sorted!

TerryK · Super Guru

Just out of interest any idea on the power increase ?

I know the difference in power between the TTR & WRR & is it worth the money & effort required, does not stop with the bore as the carby would need a fair bit of work to provide the air / fuel ratio of the greater CC.
Years ago I used to modify my cars & bikes & would spend hours & hours to try & get it perfect, not having a go, just asking the question

Terry

mossproof · Super Guru

"Always with the negative waves Moriarty?" (Kelly's Heroes) smile

Well I managed 27hp and 27Nm of torque from my 325 with practically no tuning (see the dyno in "325 kits what's involved" thread) Motad exhaust, minor airbox mods and smaller jets.

Until it's actually built I can't answer you!

I would like to see 30hp, but like I say, I'll start with standard exhaust, airbox and carb and play on the dyno. I expect it to run too rich to start with (the 325 does on standard jets) Mods I will try: freer flowing end can, maybe shorty header, different jetting, minor airbox mods. Eventually probably some porting work on the head. I think it'll need more air rather than more fuel (that's just my gut feeling) but the threads on alternative carbs make interesting reading for further experimentation.

Is it worth it? A chap's gotta have a hobby. I don't drink much, got no wife or kids, I like engineering projects. Yes, it's worth it smile

TerryK · Super Guru

Hey no wife & kids, plenty of time for projects. 30HP would be good & I guess being a big bore the power increase would be low down. As for $$$$ bikes are not a good investment except for the mind. Then it's all worth it.

Any one remember the TT350, always wanted one back in the day, how does that engine relate to the TTR 350 big bore & it's a pity the 350 didn't continue, much like the XR400R I had, great power & wish I still had it.

Cheers Terry

mossproof · Super Guru

TT/XT350 and XR400 both excellent bikes (Yams let down by prehistoric suspension I believe) but both missing that electric leg. That's really what I'm trying to get to.
(I also have an XR400 with estart conversion that I'm playing with, but my 325 TTR handles better and is less complicated electrically.)

TerryK · Super Guru

I think the TTR handles better than the XR400R I had but unsure what it would be like with more power, BTW the WRR handles better again, I looked at fitting an electric start to the XR but the cost was huge

Terry

honda15i · Senior Member

I own TTR 250 and Suzuki DR 350. I had a chance to compare the cylinders. see the pictures. Seems like DR is smaller.

DR can be bored to 441cc or even to 480

http://dr350.wikia.com/wiki/Big_bore

It is probably cheaper and easier to buy second bike like DR 250/350 and bore it!

TTRfan · Super Guru

honda15i wrote:
It is probably cheaper and easier to buy second bike like DR 250/350 and bore it!

Quite likely but it still won't be a TTR wink

mossproof · Super Guru

honda15i wrote:
I own TTR 250 and Suzuki DR 350. I had a chance to compare the cylinders. see the pictures. Seems like DR is smaller.
DR can be bored to 441cc or even to 480
http://dr350.wikia.com/wiki/Big_bore

It is probably cheaper and easier to buy second bike like DR 250/350 and bore it!

Nobody's stopping you smile

I think the DR350 is a bit of an old slug, but that engine in the better TTR frame would make an interesting project.

For comparison Bore & stroke 79.0 x 72.1, 349cc, 30hp (claimed), CR 9.5:1

-- Edited by mossproof on Friday 5th of January 2018 05:11:03 PM