ty 250 mono aftermarket parts

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Ferretflasher
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Re: ty 250 mono aftermarket parts

Postby Ferretflasher » Tue Aug 30, 2011 6:27 pm

Rode the Pinky with Fox shock at weekend ....... it works OK and handles fine. I weigh-in at some massive lardy pigged-out 95kg / 1.8m inc riding gear and found the shock a bit feeble with 150 psi inside. There is NO damping adjustment to my knowledge, it appears to be factory set ... and it is well damped both compression and rebound. Dont know yet if you could turn top relative to bottom to alter damping rates but as found it's too much damping rate for me but maybe I can just learn to cope with it. Anyway pumped it up to 170 psi and found it behaved better with a bit more ride height, I shall try another day with 190 psi inside and see how it performs with that pressure.
Anyone know the max pressure allowed??



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Re: ty 250 mono aftermarket parts

Postby Ferretflasher » Sat Oct 15, 2011 6:41 am

Getting along OK with the air-shock, found that the optimum pressure needed is about 170 psi ( I am some 15 stone with full riding gear) and with that its OK. The draw-back is that there is no damping adjustment or re-bound adjustment, its all tied in with shock pressure which relates to pre-load so no real advantage.

Run into some trouble with mi second Yam and its engine mods, shortened inlet, twinshock piston, Boyesen reeds, it always runs rough until about 2500 rpm when it takes off power wise. This I but down to the Boyesen reeds ..... as the inlet velocity increases then the flow becomes uniform and the motor breathes easier. Anyway until I get to see what the inside of the MA engine is like I shall have to live with it. I measured the squish I had and found about 68 thou, a bit too much according to the Google sites etc. The piston top gives 17 thou, the head is some 12 thou and the copper head gasket is 40 thou. I rebuilt it without the copper gasket (just used silicon sealant) and it runs OK in garage, so a guess I can take a bit more off the barrel base (45 thou looks OK for starters) which should give a tiny bit more crankcase compression and lower all the port timing. I should be able to put the barrel in a big lathe at work once I make a big enough strong-back and figure out how to centre it.
Another cause for concern is my choice of piston, is a forged item and much heavier than standard, this I think makes it slightly out of balance as it dont rev as sweetly as the MA engine in first bike. In fact it has twice started to self-detonate/run away even with throttle shut and kill switch pressed, but the revs die again below 2000 rpm but is still should NEVER do that trick, put it down to being almost out of fuel and having a the combustion chamber badly coked up. Cleaned it back to bright alloy now and shall see how it fares.
More later.



FM350
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Re: ty 250 mono aftermarket parts

Postby FM350 » Sat Oct 15, 2011 8:34 am

Interesting that Boyeson reeds result in a rough running motor......................new one on me!



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Re: ty 250 mono aftermarket parts

Postby Ferretflasher » Mon Oct 17, 2011 4:23 am

Yep me too ......... its possible they are just too efficient for the hopelessly in-efficient inlet boot or exhaust system. I need time to eliminate other possible causes before I say for certain. I have it from MA that it is quite easy to do too much to a Yam and spoil its best virtues, so the Boyesens maybe the culprit. I need to sort out the squish, the barrel height, the carb slide may be worn and leaking air, the ignition timing maybe out a tiny bit, could be one or all of the above ???
Anyway need to get another carb first and go back to steel reed petals. The #1 bike (the MA engine) has 4-fibre petals reeds and it is really smooth whereas the Boyesen you had to cut away 4 supports and fit a much large petal assembly so it has a much large free air flow area and while this may be OK for a MX version of the TY engine, it's no good for trials version ??? Dont forget that the TY engine is firstly a MX engine that was softened to make it a trials engine...!

And theres the matter of the heavy forged piston, maybe MA uses a twin shock piston at 70mm which is much lighter as its cast !!



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Re: ty 250 mono aftermarket parts

Postby FM350 » Mon Oct 17, 2011 5:03 am

The TY motor I have is fitted with CR125 reed block, and DT250 piston, which results in capacity of 270cc. Seems to run pretty well, but anything using the very poor stock air box and exhaust system isnt likely to be anywhere near as good.

TY motor has an awful lot wrong with it if you are wanting to use one for serious trials, not least the fact that the inlet tract is far too big for good gas speed at the sort of rpm a trials motor spends most time at. But they can be improved a great deal, and it would be worth speaking to Nigel Birkett, as this might mean you can avoid following advice which is often far from accurate?



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Re: ty 250 mono aftermarket parts

Postby Ferretflasher » Tue Oct 18, 2011 4:23 am

Here is what I did as per Boyesen instructions (on left) compared to standard with steel shim petals. However I did think as I was doing work that it looks too big for a trials engine. Anyway shall put 8 petal steel back in for this weekends club trial and see what transpires.
Incidentally those Boyesens petals never fully sit down closed while the steel shim ones can be made to sit tight on the rubber substrate, the Boyes are always ever-so-slightly open ???
Attachments
IMG_3291.JPG
Boyesen Left Original Right



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Re: ty 250 mono aftermarket parts

Postby FM350 » Tue Oct 18, 2011 5:34 am

If your reed petals are not fully seating, there is little or no chance of the bike ever running properly. I would think a smaller reed block, adapted to fit the TY cylinder, and reducing the volume of the reed housing, would speed up the gas flow and improve running a great deal.



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Re: ty 250 mono aftermarket parts

Postby Ferretflasher » Tue Oct 18, 2011 6:24 pm

Could a smaller reed block be achieved by plating-off half the petals with a solid piece? That way you send more charge through just 4-from-8 petals and thereby increase the opening of the remaining petals. My #2 engine has never really had a problem with high revs, it just needs to be progressive off the bottom. Both engines pink, rattle & ping when fuel is getting low especially on the road but I can find a "sweet spot" with the throttle on the road that is smoother .... but when it runs out, sounds like engine is going to throw a rod!!
Anyway back to standard reeds and no head gasket this weekend, so see what it does!



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Re: ty 250 mono aftermarket parts

Postby FM350 » Tue Oct 18, 2011 9:40 pm

No thats not a good idea. The reed housing is too big, as is the reed block itself.............this leads to low gas speed through the port at the type of rpm common on trials bikes. Knocking on the TY is generally caused by excessively wide squish clearances, which lead to high piston crown temperatures, that cause detonation/pre ignition. I have run 212cc Fantic motors with 20 thou squish clearance, and this provided a good increase in performance, and piston seemed to run cooler.



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Re: ty 250 mono aftermarket parts

Postby Ferretflasher » Tue Oct 18, 2011 11:46 pm

OK ta for the info, I shall stick to fibre reeds at the moment from Hy-Tech. The squish clearance I shall aim for about 25 thou so that will mean some 45-48 thou off the barrel base ... but I need to make a tool to hold the barrel centrally in a works lathe ... just need the boss to go & play golf for a 1/2 day !!!! =D>

Looking at latest Mono pistons, these were fitted with raised bits front & rear to reduce the squish (on the cheap) and still retain standard barrels (better for production dept suppose) but its certainly what everyone thinks is the best direction to go !




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