Gasket tickness

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Guy53
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Gasket tickness

Postby Guy53 » Sun Sep 18, 2011 4:27 am

I every one

I am '' overalling '' a TY 250 ( 434 ) for a project and I have 2 cylinder base gasket, one is .012 in and the other is .005 in, does anyone have an OEM gasket and could you give me it's tichness ?

Also I bought a Mikuni vm 8074 26mm carb that I should receve this week, now some people tell me that the slide should be 2.00 and other 3.00 anybody actualy tested a vm8074 on a 434 250 ?

Thank you in advance

Guy

PS We had a comp at the end of august and the special guest was Mick Andrews, I would meed 3 pages of comment to describe the weeckend. Everyone want the organisation to invite im again next year.



TriCub
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Re: Gasket tickness

Postby TriCub » Mon Sep 19, 2011 3:53 pm

I don't have a TY250 base gasket but all of the Yamaha's from that period had a .5mm gasket which is around .020".
This is why someone fitted 2 gaskets to get close to the original.
It is quite difficult to get hold of .5mm paper but it is available if you look hard.



Stanm
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Re: Gasket tickness

Postby Stanm » Wed Sep 21, 2011 7:29 pm

Hi
I don't have an original gasket but have compared the thickness and made my own gaskets I chose 0.5mm gasket material.
I believe this correct. The bike runs OK. But I also would be interested in the OEM unused thickness.

Cheers

Stan



FM350
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Re: Gasket tickness

Postby FM350 » Thu Sep 22, 2011 8:15 am

A fair few TY Yams have such wide squish clearance, that running is improved quite a bit by not using any gaskets at all at base or head, which closes up the clearance a little. The later TY250 Mono was even worse in this respect, and sometimes needed the cylinder base machined to reduce the clearance (wide clearance causes pinging/pre ignition).



Guy53
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Re: Gasket tickness

Postby Guy53 » Thu Sep 22, 2011 9:58 am

Hey guy's, I won't enter the debate about performance: more compression equal more low end torque, Ty have no low end power etc, everyone idea on that is ok.But!! Can I thighten the head with NO gasket and it won't leak??
Guy



David Lahey
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Re: Gasket tickness

Postby David Lahey » Thu Sep 22, 2011 10:03 am

If you lap the surfaces you might get away with it. Why not just fit a thin head gasket? Another alternative is to machine the gasket surface on the head away by the amount you want and use the standard gasket.


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FM350
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Re: Gasket tickness

Postby FM350 » Thu Sep 22, 2011 4:41 pm

No real need to lap the surfaces together, you simply need to assemble using silicone sealer. First of all though you need to accurately measure the squish clearance, and see how much you have currently (can sometimes be as much as 1.5mm!).



Guy53
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Re: Gasket tickness

Postby Guy53 » Thu Sep 22, 2011 7:37 pm

Hi David ,

Shaving the head ( and reshaping the '' pot '' ) is the final goal, but I would like to test different compression before. The problem is head gasket material is hard to fine .



David Lahey
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Re: Gasket tickness

Postby David Lahey » Thu Sep 22, 2011 9:15 pm

Guy there is a suplier who will sell and post small pieces of copper sheet of different thicknesses. I bought a few different thicknesses when I was experimenting with compression ratios on my big-bore TY175. The other thing you can use for a head gasket is aluminium sheet which is probably also available in shim thicknesses. The copper supplier was a hobby metal supplier from Western Australia and they advertised on eBay.


relax, nothing is under control

FM350
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Re: Gasket tickness

Postby FM350 » Fri Sep 23, 2011 3:14 am

Squish clearance in most cases tends to make more difference than compression ratio on low revving 2T trials motors. Increasing compression much more than std can mean problems on older motors, all of which were designed using far better fuel than the stuff we have available today.

On any of the TY motors properly adjusted squish clearance, in conjunction with a large volume air box fitted with a modern filter element, flat slide carb, and improved exhaust system, will mean a big improvement over the stock set up.

Unfortunately other than the carb, its a matter of making parts like air-box and exhaust, and simple (and not that effective) alterations like increasing capacity being much more popular.




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