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

tiddler · Veteran Member

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

tripodtiger · Senior Member

mossproof wrote:
Thanks for the update. Good to hear things are running well (including the carb mod).
I don't think I'm a sensitive (or fast) enough rider to feel the benefit of gold valving the forks, but as I've more or less run out of other things I want to modify, I suppose I should try!
Cheers,
Simon.

I haven't read through to see if anyone replied but, emulators may be the best modification you can do to damper rod forks. No matter how fast or slow you ride. The fact that the emulators will force you to buy new springs, probably better suited to your weight, has to be part of it.

tripodtiger · Senior Member

mossproof wrote:
JOHNYBOY wrote:
why not vent it to atmospere up the frame & to the back like they did on a lot of british bikes

Well the breather sucks as well as blows - every time the piston goes up and down, so you risk drawing dust/water into the crankcases, quite apart from the oily mess that will build up (not a problem with old British bikes, which were an oily mess from the factory

Add a filter to the end. You'll see it on most road race bikes. They have a small in-line catch bottle with a filter down line of that. Of course, that depends on how deep you want to go and where you're going to put it. S'pose that's why the manufacturers stick the crankcase vent into the airbox.

Why am I looking at this thread? Well, I have just picked up a dismantled engine... the brain is working. Just reading. Probably wont happen as I've got too many other irons in separate fires. Surely enough to keep me going for a couple of years. I'd best get into one...

-- Edited by tripodtiger on Saturday 30th of July 2022 02:28:04 AM

Forgorin · Senior Member

Morning gents! I just did a compression check. I'm about 100 psi dry and about 115 wet. I am guessing its more valves than rings.

I find working on the bike in the parking area of my flat a real challenge.

Forgorin · Senior Member

Oh, the bike also makes one hell of a banging noise on start up. It sounds like the pistion is hitting something something. Once the engine catches it goes away. Any ideas?

Forgorin · Senior Member

Got the engine apart. I was really surprised with the amount of carbon build up. I'm assuming it's not normal and because the bike is running too rich?

The barrel looks good, but there is a tiny bit of wear on the top of the photo. I can just feel it with a finger. Just...

Anyways, time to figure out how to get the valves off!

Kaos · Senior Member

Well my 350 kit is finally underway. At last. Engine is out and cases off for machining.

ttr steve · Super Guru

Good news Steve and remember we all like to see photos smile

Kaos · Senior Member

ttr steve wrote:
Good news Steve and remember we all like to see photos

Will do. All good so far, everything looks good internally when pulled down, got all the new bearings gaskets etc required. And just heard the machining has been finished and looking good.!!!

Kaos · Senior Member

Getting there now!!

263cc Hi comp v the 346cc.

263 v 346 barrell piston.jpg

mossproof · Super Guru

Looking forward to seeing your results Steve, once running in and tuning is done.
Good luck!

Kaos · Senior Member

TTR350 back from the shop.jpg Well the TTR350 is built and running well. Have to find some time to run it in now. Also upgraded the clutch with new HD plates and springs. Only ridden it around the yard at this stage but so far so good. Plenty of torque, lifts the front easily in 3rd will a roll of the throttle, looking forward to a proper ride, I might wait for a cooler day though a bit hot today.

Kaos · Senior Member

So its list of mods:-

WP 48mm forks, Brembo front brakes & braided brake line. Magura fat bars and Magura levers. All off a CCM404e.
Wilbers rear shock.
WR250f footpegs
Totally TTRs 350 kit with ported head and 36mm Keihin PWK carb. Modified airbox.
Totally TTRs shorty header pipe and GYTR muffler.
Powder coated rims.
Custom higher seat.
B and B bash plate (not shown)

Anyone want to buy a WR250f (280!!) ?? :)

Forgorin · Senior Member

Just a quick update (life has been too busy), it seems that I had no valve seals.... I've got the parts to put it back together. Just waiting for hunting season to be finished in a few weeks...

Kaos · Senior Member

TT350 finished.jpg TTR350 TT350 2.jpg

As well as my TTR250 big bore 350 build, I have also just completed a full resto on a 1986 TT350, powder coated frame, full engine and suspension rebuild, with a full TTR front end. The TT350 I use for Vintage Enduro pre 1988 class.

Here's some pics.

Both need running in. So far I have only managed to put half a tank of fuel through the TT350. Its very strong down low and through the mid range. And it feels bigger and wider to ride than the TTR. The TTR250 feels slimmer, shorter, turns faster and feels like it might make a bit more power, revs quicker, and better brakes. But they feel quite similar to ride. But the E start alone makes the TTR much nicer.

TT350 TTR250 1.jpg

Kaos · Senior Member

Later this year when they have both been run in and properly tuned there I will organise a dyno shoot out. Both have similar modifications. ie -Modified airboxes, upgraded carbs and headers, mufflers and head porting. Standard cams. The TT350 is 1.5mm oversize so a 87.5mm Wiseco at 358cc.The previous motor 354cc in similar spec to this one was 29 HP. Gadgets TTR350 (which looks just like my TT350 - confusing I know) beat it by half a HP on the same dyno. Hoping the bigger carb will see 30 HP on the TTR350, it's motor was previously 25.5hp as a 2mm oversize 263cc.

-- Edited by Kaos on Tuesday 14th of March 2023 07:19:05 AM

Kaos · Senior Member

ttr big log.jpg

Got out for two days riding bush tracks on the newly built TTR350. Running really well with loads more torque. Its a good hill climber too! Well and truly fast enough through the trees for me.
Pic of a log crossing on one track wrecked by storm damage, you get so far in you don't want to turn around. It wasn't all like this!! So many trees down it was hard to find a path through. Otherwise brilliant couple of days riding.

Kaos · Senior Member

Camerons Hut.jpg

Camerons Hut in the Pyrennes Ranges Victoria.

Ttboof · Veteran Member

I've recently sold A dr250 to make the 350 susuki fitted a different crank increasing the stroke . So it's a big job to do the 250 .but the 350 could be bored .

Still have the ttr though

Kaos · Senior Member

TTboof what are you building? A DR350 bored out?

ttr steve · Super Guru

Kaos wrote:

Got out for two days riding bush tracks on the newly built TTR350. Running really well with loads more torque. Its a good hill climber too! Well and truly fast enough through the trees for me.
Pic of a log crossing on one track wrecked by storm damage, you get so far in you don't want to turn around. It wasn't all like this!! So many trees down it was hard to find a path through. Otherwise brilliant couple of days riding.

Love that picture smile biggrin

Ttboof · Veteran Member

Kaos wrote:
TTboof what are you building? A DR350 bored out?

I decided the Dr wasn't as good as the ttr

So sticking with the ttr

Kaos · Senior Member

Good move!!

mossproof · Super Guru

Some nice gentle running-in there Steve!
It's all in the torque. Max power at max revs is irrelevant in the woods

Kaos · Senior Member

mossproof wrote:
Some nice gentle running-in there Steve!
It's all in the torque. Max power at max revs is irrelevant in the woods

I'm going to call it run in. 3 days of bush riding but only about 200 km but a lot of hours. Time for an oil and filter change. I must/will put an hour meter on it! Very happy with it.

Mate on his kx450 pulled up sore from the ride, but with the TTRs plush suspension, smooth power and a soft seat I pulled up fine. I thought gee this TTR is quick now, then I rode the KX450. That was stupid fast. Repeat, stupid fast. Fun in open terrain but the TTR is fast enough for my old bones, 60 next year, and very fast through the bush.

Yes enjoying the added torque. Monos!! I'm also running taller gearing now, previously always a 13T now a 14T front sprocket, and finding it pulls it nicely. Even with the taller gearing with the 350's torque I was using second at slow speeds mostly whereas previously it would have been mostly 1st. And it's cured the 250s weakness, when the speeds are up and you come up fast on a puddle/log/hole etc just twist the throttle and lift the front over. The 250 struggled there.

Very capable bike, so thanks for engineering the 350 kit!!!

I am also contemplating removing the WP USD front end and putting the bike into "stealth mode" with conventional forks and fork boots!! I like the idea of a sleeper, fairly stock appearance but with trick suspension and motor. Even though I like the current WP front end set up and it works really well. I can't use the original TTR forks, they are doing duty in my vinduro bike, the 1986 TT350. Gadget has sold me a full DRZ400e conventional front end. Front wheel, brakes, forks, triples. I've had these forks previously, 49mm Showa cartridge forks with modern internals, fully adjustable. I'm confident I can get them as good as the current set up. If not I can always bolt the WP's back on.

Oh I still have a bigger 38mm PWK carb to try yet! I'll see which one feels best to ride then some dyno time with both carbs 36/38 later in the year.

Getting close with jetting.

TTR350 plug May 23.jpg

-- Edited by Kaos on Monday 8th of May 2023 01:26:31 AM

dlee22 · Senior Member

My 350 managed to get to 4890m up a horrible corrugated track in Argentina :) There was a loss if power obviously but still pulled fairly well especially as I'm only running 13:44 sprockets.

Last time I was at that altitude was when the engine was a 250 and the performance is much better now!

ttr steve · Super Guru

Good news and thanks for the update smile

TWR250funbike · Member

mossproof wrote:
They definitely breathe more heavily than a 250, leaving more oil in the cyclone separator. If you have a 4GY engine with the crankcase breather behind the starter motor, getting a later type cam cover, or modifying the existing one with a breather outlet, helps reduce the oil mist getting ejected, but I have not found a perfect solution yet. Using both breather tubes, and a larger cyclone would be good, but I haven't had the pipe blow off from excess pressure.

If Kaos is reading, how big is the crankcase breather on the TT350?

https://www.mikesxs.net/yamaha-xs650-reed-type-engine-breather-valve-pcv.html

-- Edited by TWR250funbike on Tuesday 18th of July 2023 07:56:19 PM

-- Edited by TWR250funbike on Tuesday 18th of July 2023 07:58:01 PM

JOHNYBOY · Super Guru

it probably wil till the engine beds in rings to bore might breath a little nothing to worry about

mossproof · Super Guru

No John, we're talking about the crankcase breathing caused by the uppy downy piston movement.

Not sure the reed type breather would separate the oil mist, but it would allow use of a catch bottle and external vent without risking dirty outside air being sucked into the crankcase. Are you the Mike of Mikesxs.net TWR250? Interesting solution anyway. The negative cc pressure would reduce strain on the base gasket too...

-- Edited by mossproof on Saturday 22nd of July 2023 04:03:44 PM

TWR250funbike · Member

mossproof wrote:

Are you the Mike of Mikesxs.net TWR250? Interesting solution anyway. The negative cc pressure would reduce strain on the base gasket too...

-- Edited by mossproof on Saturday 22nd of July 2023 04:03:44 PM

No.

Yes, a T-Dub with a 4GY engine shoehorned in there...It's a hoot.

This is a very interesting thread, I have many future questions. Sorry for being so late to the party... One of the first thoughts that came to mind once I realized what you were attempting, was sealing and crankcase breathing issues, sorry to say, but I've never had a 4GY apart far enough to know the critical issues. I have however had the SRX250, XT250&350, plus TT350 motors, far enough apart to know you're probably better off going with a low 80's mm bore than going to a full 86mm cylinder (if you wanted an electric start, mid sized, 4 valve , SRX engined based XT).

TWR250funbike · Member

mossproof wrote:
No John, we're talking about the crankcase breathing caused by the uppy downy piston movement.

Not sure the reed type breather would separate the oil mist, but it would allow use of a catch bottle and external vent without risking dirty outside air being sucked into the crankcase. Are you the Mike of Mikesxs.net TWR250? Interesting solution anyway. The negative cc pressure would reduce strain on the base gasket too...

-- Edited by mossproof on Saturday 22nd of July 2023 04:03:44 PM

https://www.heidentuning.com/xs650-shop/engine/camshafts-camchains-valves-guides/engine-breather-system-reed-valve-complete-detail.html

Those reed breathers are made by an outfit called Heiden Tuning in the Netherlands, apparently they make two versions, anyone thinking about giving one a try, may want to contact them first.

-- Edited by TWR250funbike on Sunday 23rd of July 2023 04:45:51 PM

JOHNYBOY · Super Guru

surely crankcase breathing worn piston / rings bore newly piston / rings not bedded into bore blocked breather crankcase compression or am i missing something simon educate me please you are never too old to learn johnboy

mossproof · Super Guru

smile If you imagine sitting inside the crankcase looking up, you will see the underside of the piston going up and down. This displaces an amount of air equivalent to the swept volume in the cylinder every rotation of the crankshaft. In a multicylinder engine, as one piston is going down, another will be going up, (more or less) so much of the displaced air will just swish across from one bore to the other, but in a single it has nowhere to go except out through the breather (and then back in through the breather as the piston rises again leaving a void underneath which creates a vacuum)

Because air is squishy (technical term biggrin ) it doesn't all go out and return through that tiny pipe every time, but the air that does go out will have oil vapour in it from all the mechanical thrashing around going on in there. The cyclone filter manages to remove some of this, which is what ends up in that little closed off bit of tube underneath. It also traps some of the condensation which accumulates in the cases, which is a good thing. The 350 trap pipe definitely fills with oil faster than my 250 did, I think because of the higher pressure air flow carrying more oil vapour with it.

Thumpers are known to "breathe more heavily" than twins etc, and although generally mechanics mean piston ring blow-by when they say "breathe heavily", I believe in our particular case it is crankcase pressure pulses that are the cause, not leaking combustion pressure.

Because the crank case breather in the TTR250 is not designed to cope with 350cc of swept volume, there is more pressure built up in the sump when the piston falls, which could put extra strain on base gasket and various seals (countershaft seal and gear shift shaft, and kickstarter shaft if you have one)

The breather valve that Mike has found and linked us to allows the air to escape from the cases as the piston falls, but does not allow it back in as the piston rises. This is intended to create a slight vacuum in the crankcase. For the speed merchants this is a good thing because there will be less air resistance against the moving parts so more power. It IS measurable, even if it's hard to believe confuse For big bore TTR owners the main advantage would be reduced crankcase pressure spikes. I had oil seeps from the timing chain side of the head gasket on 350 #1, and Dan had a base gasket seep on his. The base gasket on the 350 is particularly skinny. (This is why I recommend a thin smear of flange sealant in these areas to 350 builders as extra surface bonding)

Is everyone asleep yet?

TWR250funbike · Member

Mossproof, I was reading up more on the XS, dedicated bunch of modders, they are. I found a page on breathing you may find interesting...

thexscafedotcom.wordpress.com/category/m-engine/motor-breathing/

ttr steve · Super Guru

Hi All

I am finding this all very interesting, every day is a school day smile biggrin

mossproof · Super Guru

It's a very deep rabbit hole Steve. I fell down it 2 hours ago and have only just emerged!
The Heiden Tuning reed valve has been redesigned I believe, as a bolt-on rather than the hose-in, hose-out, which makes it slightly more complicated to experiment with (80 euros doesn't help!). More reading I think...

TWR250funbike · Member

Breathing Is an important subject, When the Tdubbers do the 200 to 230 case mod, they also see cylinder base leakage issues. Yamaha didn't just bore a bigger hole, the entire case is different and a different clutch cover was fitted.