Ty 250s Mono Pinging

[woody]

I'm no technicaL expert but ask yourself this before removing metal from anything - did every TY250 mono sold back in the 80s and 90s detonate?

I can't remember it ever being an issue. None of mine did, none of my mate's bikes did, none of our club/centre rider's bikes did. It just didn't happen. If they did and a design fault with the squish band was the cause, every biike would have had to have been modified in the way described to cure it. Recalls to dealers/importers etc. None of this ever happened. And would Yamaha have let a problem like that continue for the 10 year production run of the bike?

If everything is set correctly on your engine, timing/carb etc. and there are no air leaks etc. a probable cause is a choked exhaust - you don't say what condition the exhaust/silencer is in - I'd start there if it was me and I'd definitely ask Nigel Birkett about the squish band issue before having anything modified. He has just rebuilt an engine for a mate of mine, 270cc and ported - no modifications to squish band on that motor and there is no detonation - there wasn't before either.

I'm perfectly happy to be proved wrong, just can't see it myself, if it was designed wrong they'd all detonate and they don't.

[jse]

I'm no technicaL expert but ask yourself this before removing metal from anything - did every TY250 mono sold back in the 80s and 90s detonate?

I can't remember it ever being an issue. None of mine did, none of my mate's bikes did, none of our club/centre rider's bikes did. It just didn't happen. If they did and a design fault with the squish band was the cause, every biike would have had to have been modified in the way described to cure it. Recalls to dealers/importers etc. None of this ever happened. And would Yamaha have let a problem like that continue for the 10 year production run of the bike?

If everything is set correctly on your engine, timing/carb etc. and there are no air leaks etc. a probable cause is a choked exhaust - you don't say what condition the exhaust/silencer is in - I'd start there if it was me and I'd definitely ask Nigel Birkett about the squish band issue before having anything modified. He has just rebuilt an engine for a mate of mine, 270cc and ported - no modifications to squish band on that motor and there is no detonation - there wasn't before either.

I'm perfectly happy to be proved wrong, just can't see it myself, if it was designed wrong they'd all detonate and they don't.

I agree with you. Unlike the 350's we got over here (whose squish bands measured from .078" to .091" on average and rattling was the norm) the 250's seemed to run fine, not detonate, and I think the performance, overall, was better. The reason I thought he should first check the squish on his personal engine were the two statements: "engine is fresh" and "pinging it's head off", which makes me suspicious of what should be verified first as I've seen some very "creative" ways to choose and assemble parts. When that variable is dispensed with, then he needs to look at a leak-down test (or a least a soapy solution on suspect areas, especially the manifold) and exhaust system examination to begin with.

I'm with you, he shouldn't need to remove any material and from my experience, the 250 (well set up and maintained) is not prone to pinging.

Jon

[jse]

Chris Johnson is an engineer in the US with quite a lot of experience of the TY Yam mono, and while the TY350 is not quite the same as the 250 model the info regarding the squish is relevant to both bikes, as are most of the other mods.

http://myweb.cableone.net/bcanderson/Mods.htm

Chris and I are close friends and we had a good time working together with Bruce for his TY portion of that website. When Chris and I get together we usually drive others to drink with our needlehead ramblings about engines, suspension and such....

Jon

[jon v8]

CJ info seems just about spot on, but worth bearing in mind that if you do need to do much machining to reduce excessive squish clearance, that compression ratio is also going to increase, and too much compression can cause detonation in the same way as excessive squish clearance.

All of which is easily sorted - but what has not been sorted is the proof,(via photos) that you own a bike at all............

We are still waiting.

[pedronicman]

All of which is easily sorted - but what has not been sorted is the proof,(via photos) that you own a bike at all............

We are still waiting.

Couldn't agree more - as they say -the proof is in the pudding!

[jse]

Hi Guys,

I was wondering if anyone has any answers for stopping the pinging or minimising it on my TY250. The motor is fresh and unmodified but it pings it head off.

I beleive the original pistons had dishes in the crown ( I could be wrong) but my piston is flat.

I'm using 95 octane fuel mixed at 50:1. I have tried raising the needle which improved it a little but its still doing it.

I know some peoples answer will be to run it on Avgas but this is really not an option I want to do, as it is road registered and I fill it up at the servo sometimes.

I have heard that removing the head gasket to reduce the amount of squish greatly reduces the pinging has anyone who has done this, able to back this theory up?

Or any other ideas would be greatly appreciated

Thanks

Back to your problem. If the squish measures out within reason (and the correct piston was installed), the next place I would look (provided your jetting is o.k.) is the manifold/reedcage area. Sometimes the older bikes develop cracks on the manifold and any air being sucked in there will lean out your jetting. Another problem I see there, is that the manifold will be tightened down too much and that will "bow" the sealing area between the screws and allow air to be sucked in there.

By the way, what is your jetting? I'm sure that the TY250 guys on the forum can tell you if there's a problem there.

Cheers.

Jon

[woody]

Have some posts been deleted from this thread...!!?? So it's finally been mentioned that reducing the squish will also increase compression - another cause of detonation - but a day after recommending it should be done so it is a bit late.

The recommendation to remove metal from the base of the barrell (post deleted?) doesn't mention that this will also alter the port timing. Machining say 1mm off will mean that the piston at BDC no longer fully clears the transfer port and this can cause lumpy running off idle - I know this from experience. That is in addition to the increase in compression. Another reason not to go indiscrimately hacking off metal.

[trickymicky]

Have some posts been deleted from this thread...!!?? So it's finally been mentioned that reducing the squish will also increase compression - another cause of detonation - but a day after recommending it should be done so it is a bit late.

The recommendation to remove metal from the base of the barrell (post deleted?) doesn't mention that this will also alter the port timing. Machining say 1mm off will mean that the piston at BDC no longer fully clears the transfer port and this can cause lumpy running off idle - I know this from experience. That is in addition to the increase in compression. Another reason not to go indiscrimately hacking off metal.

Several posts have been deleted,presumably to negate the responses from others,which is a shame.-spoils the thread.

[tt5th]

Well I'm not going to bother removing anything, its a good point that they wouldn't have sold a bike that pings as standard so something must be amiss.

I can't remember the numbers but mine has had a slightly richer main jet and stock idle with a piston replacement at some point.

I'm concerned about the possible difference in pistons so I'll get Mr. Birkett to supply an appropriate replacement when I'm ready.

First I'll check and de-coke the front pipe, I've checked for leaks on the carb side and I assume the crank seals are good as I don't lose any oil.

I cleaned and repacked the silencer recently so that should be ok.

I'll check the exhaust gasket when I take the pipe off, could a knackered gasket here cause this kind of pinging/pinking?

Has anyone got any tips on de-coking an exhaust? You may consider me a cowboy but the only way I know how is to pour petrol in and set it alight!

Edited April 20, 2008 by tt5th

[jse]

Well I'm not going to bother removing anything, its a good point that they wouldn't have sold a bike that pings as standard so something must be amiss.

I can't remember the numbers but mine has had a slightly richer main jet and stock idle with a piston replacement at some point.

I'm concerned about the possible difference in pistons so I'll get Mr. Birkett to supply an appropriate replacement when I'm ready.

First I'll check and de-coke the front pipe, I've checked for leaks on the carb side and I assume the crank seals are good as I don't lose any oil.

I cleaned and repacked the silencer recently so that should be ok.

I'll check the exhaust gasket when I take the pipe off, could a knackered gasket here cause this kind of pinging/pinking?

Has anyone got any tips on de-coking an exhaust? You may consider me a cowboy but the only way I know how is to pour petrol in and set it alight!

[/quote

It might be a good idea to clean and adjust the carb just to make sure what your jetting is to start with. I'd also check behind the flywheel to see if the alternator side seal is weeping and it would not cause loss of tranny fluid or excessive exhaust smoke.

Everybody seems to have a pet way of cleaning out head pipes and you'll probably get several suggestions. One way is to use oven cleaner ("Easy Off" is one we have over here) to soften the carbon and then flush it out. Then use a speedometer cable with a frayed end, chucked in a drill and pulled back and forth inside the pipe, the frayed end will scrub the walls . The Ty pipe is kinda convoluted and the speedo cable will be able to get way back inside the pipe.

Jon

[tt5th]

Thanks for the advice Jon, I'll give it a try.

[rory]

Hi petrol heads ! This is kinda a question. I have read here & else where that removing d head gasket help d squish & Reduce pinging ? Surly it would be better to just skim the head the thickness of the gasket. wouldn't that have the same results ?? Anybody know where to get jets for these Teikei carb ?

[worldtrialchamp]

Guys,

I have a TY250R (1991). The exhaust was blocked from front to rear. I burnt it out with an oxy-acetylene (spelling?) torch. It took a lot of work as the centre area was well and truly clogged. If you do this best to be somewhere away from your neighbours as the process will resemble a house on fire.

The result was significant. A lot more power and the motor could now rev freely, but it still stuttered. I also found that the crank seals (both) were well worn to the point that the springs had lost their ability to tension the seal, and the lip of the seal of was gone. This also made a big difference to the hot running.

Finally I bought an OKO 3030B flatslide carb and this made the biggest difference. Got rid of the pinging (and tendency to surge) and the bike is very smooth and responsive. The carb bolted straight on and I haven't needed to touch it other than the tickover and mixture settings.

I would recommend these three mods to anyone with a TY250 monoshock. The total cost was inexpensive and transformed the bike.

I am thinking now to cut off the flywheel weight to get a bit more immediate response. Although if you use yours to ride on the road best leave it on I would think.

Worldtrialchamp

[wherry]

OK. I've got a mate who has been trying to get his Yam 250 mono to run right for about the last couple of years. He has rebuilt the engine, with new seals and bearings etc, and rebored with new piston and rings. He's cut the back out of the middle exhaust box and cleaned all the crud out and repacked it all nicely. He's got a nice new WES tail pipe and a new irridium plug. He's replaced the ignition coils I think and just now bought a 26mm OKO for it as we thought the only thing left was that the Teikei carb on it was worn out. Whatever we try it just rattles it's guts out on the over-run.

So questions - Can anybody give us an idea of what jets might work as a starting point for the new OKO just in case the one's we've got are widely different for some reason?

And just what in the name of all that is holy causes these engines to knock so badly now when they patently didn't when they were current? Is it down to the petrol these days or some other thing that has changed? I really can't bring myself to accept that it's any sort of inherrent design deficiency. It's been discussed before but anymore thoughts anyone?

[sherpa325]

Hi , I just thought I would throw my thoughts in on this topic. I have been riding competitions for 37 years and at last count have had 30 trials bikes, I still have four in the shed. That said I am very fussy about the tuning of my bikes and without a doubt the mono yamaha is the most difficult bike to get to run correctly, even back in the days when they wre new. The easiest way to stop the problems with the detonation is to run two headgaskets[reduces compression ratio and runs cooler]. The 350 is more prone to it than the 250 [i have owned both] The correct way to do it is to make a .5 mm headgasket [std is 1mm]and machine or sand the combustion chamber to achieve the same volume- this will give you the correct squish and correct combustion ratio. The bikes are prone to overheating so the compression ratio and fuel quality are critical ,the 350 is worse due to less fins to dissapate the heat, less compression means less heat! I became so frustrated with mine I really started to look deeper into these motors and found some strange facts,- first of all the motors run a 68mm stroke, much longer than any other trials engine 60mm is the norm, this is going to make the motor rough at lower revs, secondly the port timing is like no other trials engine. I did mine back in 85 and compared the timing against a 348 cota , a 325 sherpa and a 325 italjet [all the european bike were nearly identical whereas the yam was completely different] If I remember correctly John Shirt made some radical engines for these bikes where he changed the bore and stroke presumably to mirror the europen style bore/stroke and porting .I cant recall anyone ever doing this to any other trials motor.You would have to ask yourself why bother going to this much trouble if there wasn't an inherent problem. I dont know if this will help but these are my thoughts from the 80's.