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 Post subject: Re: No head gasket?
PostPosted: Mon Sep 11, 2017 5:37 pm 

Joined: Thu Jun 09, 2011 6:39 pm
Posts: 735
Location: Narooma NSW Aus
H2RTuner wrote:
Not many of us here have worked oin liquid cooled Yamaha two stroke road race engine top ends, but, they do not use a head gasket, per se. Those setups do have O ring grooves in the cylinder deck, three of them. One is for the O ring that seals the liquid cooling chamber from the outside of the barrel, the other two, same, but to keep coolant out of the cylinders. The actual sealing is handled by the machined flat surfaces of the cylinder and head.

I have a large number of these Yamaha top ends for those engines, and have never had a compression leakage issue, nor coolant leak, even when a "helper" omitted the two compression groove O rings in one engine run in an AMA National road race that my rider won. Never have had to resurface either a cylinder, nor head, either.

Only things you have to do to run no head gaskets are, sealing surfaces must be flat and true, and, to get the squish clearances right, you have to know what you are doing in measuring, machining and tuning. I used to have stacks of factory road race H engine series head gaskets, round for H1R and H2R special stuff, and stock pattern for street barrels converted, in various different thicknesses to set the squish clearances, never used them.

thanks for your knowledge on all things Tuner , I really enjoy reading your input and your racing history lessons :thumbup: :thumbup: , urs Al in Aus


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 Post subject: Re: No head gasket?
PostPosted: Mon Sep 11, 2017 6:05 pm 

Joined: Thu Jun 09, 2011 11:25 am
Posts: 3137
The original idea on the stock groove was to create a relief to have a narrow band in the head gasket be captured as the rest of the soft copper gasket crushed as the head was being torqued down.

In a performance situation where a dead soft copper gasket is used, a different design groove is cut, to hold, usually, a stainless steel round wire. This actually compresses the copper gasket where the stainless ring is, for a better gasket crushed, and sealing.

We used to do that a lot to the 4 striker's when I ran the engine shop at RC Engineering. And, as noted with the rubber O rings on the Yamaha two stroke racers, to ensure no liquid leaks into cylinders.


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