Gasket tickness

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FM350
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Re: Gasket tickness

Postby FM350 » Thu Sep 29, 2011 5:56 am

[quote="FM350"]The old TY250 twinshock motor is a little gutless, and the main reason for removing the flywheel weight is to give them a bit more get up and go, which makes the bikes easier to ride in modern type sections, which are often a lot tighter than those common in the 1970s. Better still though is to fit better intake and exhaust systems, do some alterations to the porting and squish clearance, which will greatly improve running, to the extent you can then fit a heavier flywheel weight.

Easy and cheap way to improve the exhaust, is to fit back box from something like a YZ125, which can often be found used on Ebay, and will fit many bikes after a few simple alterations. The TY front boxes are very restrictive though (as are the WES replacements!), and making something suitable seems the only way to go here.



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Re: Gasket tickness

Postby Jon V8 » Sun Oct 02, 2011 3:18 am

FM350 wrote:
FM350 wrote:The old TY250 twinshock motor is a little gutless, and the main reason for removing the flywheel weight is to give them a bit more get up and go, which makes the bikes easier to ride in modern type sections, which are often a lot tighter than those common in the 1970s. Better still though is to fit better intake and exhaust systems, do some alterations to the porting and squish clearance, which will greatly improve running, to the extent you can then fit a heavier flywheel weight.

Easy and cheap way to improve the exhaust, is to fit back box from something like a YZ125, which can often be found used on Ebay, and will fit many bikes after a few simple alterations. The TY front boxes are very restrictive though (as are the WES replacements!), and making something suitable seems the only way to go here.

We have recently had this conversation on TC about TY250's being gutless - I made the case for the other side,both of the Ty250D's I have run well and dont lack power,both have standard carbs,but my main bike has a WES exhaust on it.removing the flywheel weight makes them pick up quicker,but as said much too easy to stall.I put mine back on after I started riding my HT5 Ariel.(Which is ridden just on the throttle hoverever tight the section,the clutch is left well alone)Getting back on the Yam and trying to leave the clutch alone has resulted in me becoming a far better rider as this years results have shown.
As for the carb,there is simply nothing wrong with the standard one,keeping it clean is all it needs.
As I said on TC, most trials riders "think" they need more snappy power,but in truth for twinshock/classic events standard engines are fine - they just need to be in good condition,properly set up and maintained.Being able to trust an engine to do the same thing each time you roll the throttle open or closed is all you need.The number of riders I see fighting with immaculate bikes that are clearly running badly makes me wonder.They have obviously spent the money on all the trick bits but have no idea how to tune the motor.......



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Re: Gasket tickness

Postby Guy53 » Sun Oct 02, 2011 7:45 am

Jon V8, you are partialy right. First if the sections in trial we have to ride ( here in Canada ) were like the section were in the 70's and not setup for late 80's to mid 90's bikes it would help, and if the suspension' s( tire and shock ) would be as they were in the 70' where you would spin the rear wheel in 3rd gear on a flat rock I would totaly agree with you but it is not the case anymore. I don't say it is for the better, but it is what we have to ride, when the guy that is in front of you ride a SWM 350 and the one beind is on a M199 Sherpa you realy feel like a bit of Red Bull would help your TY 434. You are right in saying that a well tune moto is a far better companion in a section than a nice looking one.
Guy



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Re: Gasket tickness

Postby JC1 » Sun Oct 02, 2011 8:24 am

FM350 - what do you suggest would be "something suitable" for the front box?

Likewise for "some alterations to the porting" ?


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Re: Gasket tickness

Postby FM350 » Sun Oct 02, 2011 8:55 am

JC1 wrote:FM350 - what do you suggest would be "something suitable" for the front box?

Likewise for "some alterations to the porting" ?


The stock TY exhaust system is very restrictive, and the WES ones while they are lighter are almost as restrictive as the stock parts, and appear to be dimensionally similar to those made for the TY175.

Its possible to make a front box reasonably easily, but you would need to find some very fine perforated sheet steel to making the silencer core, which would take up about 75% of the internal area of the pipe, which ideally needs to around double that of the stock/WES systems.

Firstly on any TY you need to adjust the squish clearance, before even thinking about porting of any kind. Once the squish is adjusted, and if you are able to sort out the intake and induction systems properly, raising the exhaust roof, widening the inlet, and seeing if you can improve the reed block/reeds at all, will add to the improvements resulting from properly working intake and exhaust.

However before even thinking doing all this work, I would suggest having a good ride on a TY175, which with a few simple alterations to the steering, and footrest position etc, is likely to work a fair bit better than the much more dated feeling TY250.



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Re: Gasket tickness

Postby Jon V8 » Mon Oct 03, 2011 4:38 am

FM350 wrote:
JC1 wrote:FM350 - what do you suggest would be "something suitable" for the front box?

Likewise for "some alterations to the porting" ?


The stock TY exhaust system is very restrictive, and the WES ones while they are lighter are almost as restrictive as the stock parts, and appear to be dimensionally similar to those made for the TY175.

Its possible to make a front box reasonably easily, but you would need to find some very fine perforated sheet steel to making the silencer core, which would take up about 75% of the internal area of the pipe, which ideally needs to around double that of the stock/WES systems.

Firstly on any TY you need to adjust the squish clearance, before even thinking about porting of any kind. Once the squish is adjusted, and if you are able to sort out the intake and induction systems properly, raising the exhaust roof, widening the inlet, and seeing if you can improve the reed block/reeds at all, will add to the improvements resulting from properly working intake and exhaust.

However before even thinking doing all this work, I would suggest having a good ride on a TY175, which with a few simple alterations to the steering, and footrest position etc, is likely to work a fair bit better than the much more dated feeling TY250.

Or you could just get on and ride it.......
Few,if any twinshock trials need anything like a trick bike,anyone who thinks different is kidding themselves.Individual rider skill and fitness is far more important.



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Re: Gasket tickness

Postby FM350 » Mon Oct 03, 2011 7:45 am

Nothing at all to stop anyone riding a heavy underpowered TY250 in totally standard form if they are happy with that! However the UK Sammy Miller Championship round held yesterday, was won by a very trick TY250 twinshock/mono, with another very special TY fitted with an ex works 340cc motor taking second place. So while a standard bike is fine for anyone wanting to ride very easy club level events, you are not likely to see them being used by any of the riders with a serious chance of winning higher level competitions.



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Re: Gasket tickness

Postby JC1 » Tue Oct 04, 2011 9:46 am

FM - you haven't answered the question about the front box. You claim that the TY & WES ones are very restrictive, but you give no substance to your claim. Are you claiming that the outlet is too small, the volume is too small, the header is too small, or what?


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Re: Gasket tickness

Postby FM350 » Thu Oct 06, 2011 6:24 am

The volume is too small, and the internals of the WES systems appear to be more suited to the TY125, possibly in an attempt to reduce noise and or make the bikes run smoother.

Any of the TYs run an awful lot better with a properly designed and made exhaust system, and very few people realise that the exhaust system on all old TS trials bikes was made primarily with the lowest possible cost in mind, with little or no attention being paid to whether or not they worked well.

A good example of this is the dreadful "clubfoot" exhaust systems fitted to various models of Bultaco............these are very heavy, get clogged up with oil/carbon very quickly, and do a pretty good job of restricting the potential of the motor to run well.



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Re: Gasket tickness

Postby Jon V8 » Thu Oct 06, 2011 10:07 pm

FM, I guess you mean this bike;
TY250.jpg

I really fail to see how this bike is accepted in the Sammy series,its just not in the spirit of twinshock trials.Chris Koch would most likely still win on a bog standard whatever.Using bikes like that just winds up other riders who use appropriate kit.




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