Ty 250s Mono Pinging

[badbowie]

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

[mattylad]

Try removing the head gasket as this often works well.

[pedronicman]

One of the reasons the TY often detonates badly is due to excessive squish clearance, and this problem is made worse by poor fuel qualtity. If your bike is a 250 and you have the wrong (flat top) piston fitted, this will increase clearance even more and worsen the problem.

The way to sort this out properly is firstly to fit the correct piston, accurately measure the squish clearance, then machine the base of the cylinder to bring the clearance down to the proper amount. Finally if you have been running 50:1 fuel mix for any length of time, your exhaust system is likely to be choked with carbon/oil/crap, and will need stripping and repacking properly, and remember to avoid this problem not to use oil/fuel ratios of 50:1 unless you are wanting to run a very cheap unbranded 2T lawnmower oil of some sort..................80:1 using quality fully synthetic oil, is fine for any air cooled trials machine.

Modern fully synthetic 2 stroke is designed for modern watercooled trials/mx bikes with a chrome liner, it can be used on some steel lined barrel twinshocks/air cooled mono's to good effect but should NEVER be run on these weaker than 50:1 mix and DEFINATELY NOT 80:1 -unless you want to blow your engine to bits!

Modern fully synthetic oil is too good in an older bike- i know that sounds strange - but the oil does not get fully burnt away as the older type engines don't rev as high as a

modern 2 stroke.

I would recommend -fully synthetic at 50:1 OR a good branded semi synthetic at 40:1 and run old type four star or super unleaded.

Don't run weaker than 50:1 unless you want serious engine trouble.

i'm not the only one who will tell you that!!!!.

[jon v8]

The well worn Ty250R that I had from 88-90 ran like a chaff cutter when I first got it,but I managed to sort it to a smooth runner just with very careful adjustments to the carb,I remember that the main jet size was critical to avoid dieseling/knocking when hot.I guess the difference now is that most if not all of them will have been rebuilt,(often badly)more than once.The Ty80 I have just rebuilt for my son runs like a sewing machine - but much time and money was spent in doing it,very glad that I coughed up

[jon v8]

When I get that trick "steel" liner fitted to my old Majesty I now know I am going to need to start using 40:1 oil/fuel mix, rather than the 80:1 mix I have been using trouble free for the last 15 years............

So can we see a piccy of it ?

[andy m]

Not wanting to rise to the bait put down by the Majestyman340 I will just remind all that a TY250 has a steel liner. And he is now deleting posts in other threads if people do not bite. Last time I get involved with the idiots waffle.

[tt5th]

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

Hi, have this same problem with mine and am still looking to solve it fully.

I've improved it by moving to a 'Super' unleaded, Tesco 99 ron works well, and adding a bit of Castrol Lead Replacement/Octane boost stuff.

The point about modern synthetic oils being 'too good' for an old bike is an interesting one. A friend of mine recently persuaded me to swap to the Silkolene Semi Synthetic from the fully synthetic I was using and it definately seems to have reduced smoke and plug fouling.

Still mixing at 50:1 for now but still fouling plugs every few laps (It was once a lap before!). Something I'll find the answer to soon I'm sure!

I might try removing the top gasket but does anyone have any recommendations on what to seal it with instead?

Thanks.

John.

Edited April 16, 2008 by tt5th

[trickymicky]

Not wanting to rise to the bait put down by the Majestyman340 I will just remind all that a TY250 has a steel liner. And he is now deleting posts in other threads if people do not bite. Last time I get involved with the idiots waffle.

I too , along with others, it would seem, have decided not to respond directly to his posts. Most are not worthy of a response anyway, although posting inaccurate technical information,if deliberate,is a matter for others. In this same thread he is advocating mixes of both 80:1 and 40:1.-Unhelpful at best. Granted the latter figure appears to be because he has picked up that a steel liner was refered to,as most do rather than cast iron, but chooses not to say that.

[pedronicman]

I too , along with others, it would seem, have decided not to respond directly to his posts. Most are not worthy of a response anyway, although posting inaccurate technical information,if deliberate,is a matter for others. In this same thread he is advocating mixes of both 80:1 and 40:1.-Unhelpful at best. Granted the latter figure appears to be because he has picked up that a steel liner was refered to,as most do rather than cast iron, but chooses not to say that.

Well said!!!

[woody]

Instead of guessing and/or relying on information from people who may or may not be qualified to give a definitive answer on forums, why don't you phone Nigel Birkett and ask his opinion on why the bike may be detonating. There is nothing he doesn't know about Yams.

I know nothing about squish bands but find it hard to believe Yamaha produced a bike for nearly 10 years with a wrong squish band. I owned 3 monos, an '86 'S' I bought new, and '87 'R' and and '88 'R' both bought used from a local rider so the history was known. NONE of these bikes detonated at all, not even once. In fact, the S model was quite firey and I had at least 2 head gaskets fitted to soften it off, maybe 3, can't remember now. That presumably increases the squish but there was no detonation. I ran them on 50:1 as I do everything else with no problems.

We have a rider in our club who owns a mono Yam and it is the foulest sounding and smelling bike I have ever heard. It is loud, smokes and pinks like crazy. The reason it does this is because the exhaust system is choked. The rear silencer needs repacking and the middle box may be coked or have broken baffles. With those fixed it would be a different bike. Check the condition of your exhaust so that when Birks asks you the question, you at least know the answer to give him. It's a common cause of poor running and detonation.

[woody]

Finally if you have been running 50:1 fuel mix for any length of time, your exhaust system is likely to be choked with carbon/oil/crap, and will need stripping and repacking properly, and remember to avoid this problem not to use oil/fuel ratios of 50:1 unless you are wanting to run a very cheap unbranded 2T lawnmower oil of some sort..................80:1 using quality fully synthetic oil, is fine for any air cooled trials machine.

ANY air cooled machine..?? - I think you'd be pushing your luck using 80:1 on a Villiers/Ossa/Bultaco etc. and isn't the sort of advice to give to someone who may do it and suffer a seized engine.

Castrol TTS at 50:1 works fine in the following bikes - Yam TYZ, KTM 300EXC, Ossa, Bultaco and has never gummed up rings or silencer or anything else. The TYZ could easily run on 80:1 but I prefer 50:1 - it doesn't smoke, runs perfectly clean, pick-up is clean as a whistle and it doesn't have a coked up exhaust. I have no technical knowledge of oils to back this up, just the experience of what I have used with no problem.

There is no way I would ever run an Ossa or Bultaco (air cooled machines...) on 80:1

[tony283]

There is so much talk of barrels, liners etc that I'm amazed that some so called "experts" ever have time to ride anything! Traditionally most 2 stroke engines were designed to run on 20:1 back in the 70's. Autolube on the early Yams effectively delivered 25:1 but we were using leaded fuels. Currently most 2 stroke trials engines that are liquid cooled run on 80:1 FOLLOW THE MANUFACTURERS SPECS

An older 1970's aircooled motor currently runs well, and without problems, on 40:1

The 1980's air cooled engines seem to run best on 50:1

Liquid cooled engines normally run at 80:1

Other current problems come from some of the fuel itself with all its "enviromental additives" and some do not even MIX well with oil. They also can go off quickly resulting in very poor power delivery that you would think was poor jetting/ignition. If in doubt drain it and start with fresh every time.

Tony

[andy m]

I agree with TRICKYMICKY. People refer to liners as being steel, put one in the rain for a week or two and see what happens to it, it will rust. Plus of course they can be rebored.Majestyman you are a knob and you have been told in other threads, so you do not need to get all technical as others know what I was talking about.

[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

Hi,

I've got an 85' TY350 I've had since new and have encountered a little of what you speak of. I'm not sure if all my observations will be spot-on as mine is a 350 and yours is a 250, but you can consider that. I'll try to speak from direct experience, rather than theory or belief, and that will probably help me stay out of trouble (does not always work for me, however...).

From what you describe, you probably want to find out what the measurement and configuration of your squishband is to start with. You can do that by taking the plug out and form two short strands (maybe 5" or so) of soft solder into curves and using a wrench on the flywheel nut (don't use the kickstart) turn the engine over so that the piston is close to the top (TDC) and insert the solder, one to the front and one towards the back and then turn the piston past TDC and remove the solder. The reason to use two pieces of solder is that compensates for "piston rock" and give a more accurate result.

By measuring the thickness of the squished ends of the solder with calipers, you will know what the clearance is between the piston and head at TDC. Another thing it can tell you is if there is a problem with the configuration, meaning that the squishband and piston crown are not "paralel" or have the same clearance over the area where they meet.

Generally, a clearance of about 1mm (.039") is close to optimal in a 250/350 Trials engine and my 350 measured out at .087", which needed to be dealt with by some machine work which has eliminated the knock ("ping") altogether. I'm not sure what the configuration of the 250 combustion chamber is but the 350 had the trapeziodal type (rather than the later, and better "hemi" type) and that type lended itself to pinging problems when the squish was off. Not all the TY's rattled, but it was fairly common in the 350s imported to the U.S.

95 octane and 50:1 should work fine from my experience and I use Castrol TTS at 50:1 in my TY with no problems. Since you ride on the street you may need to re-evaluate your jetting, possibly, as you want to avoid detonation at all costs. Detonation is caused by the unburned air/fuel mix around the outer edges of the squish area reacting to heat and pressure by auto-igniting, essentially creating another flame front moving to the center of the chamber where it meets the "other" flame front caused by spark ignition. When those two fronts collide, the pressure in the combustion chamber spikes, usually before TDC, and the resultant loud "knock" is what you hear and it's the functional equilivant of smashing the piston crown with a sledgehammer. It's easy to tell when an engine has experienced detonation as the outer piston crown and outer edge of the squishband in the head will look like it's been sandblasted with large grit.

Why don't you measure your clearance and let us know what you find?

Cheers.

Jon

[badbowie]

Hi guys,

Thanks for the replies it appears that the squish is where I need to start. I will have a go at measuring squish over the weekend and get back to you guys.