Yamaha TRX850 Enthusiasts Forum

Despite missing some parts still, I started re-assembling the engine in order to measure the squish so that I can get it correct while waiting for the parts.

I got the advice to put some soldering lead (or whatever that soft material is called) from front to rear of the cylinder. Did this, but with JE pistons, there wasn' much resistance on the inlet side. so the pistons tilted... I figure positioning the soldering stuff like this works better on 4 valve engines. So I made up some arty soldering creations to cover the areas between the inlet valves. Now I have more accurate measurements, but as the inlet side had to compress more material than the exhaust side, the pistons tilted again...

How did You measure the squish?
Should I take the average value?
What's a good squish value (with JE pistons and Kent cams)

Cheers,
Hans

Generally, what you have already done would be correct - if the squish deck heights were the same. The best method is to measure from the fireface, (the top of the cylinder block where the head gasket sits) to the squish decks on the piston using a depth micrometer. Then measure to the corresponding positions in the cylinder head. Don't forget to factor in the head gasket thickness.

Thanks! But that is the problem though, isn't it, to know the thickness of the gaskets when compressed?

I learned one thing today though, as a word of advice for others trying the same thing. Just use small pieces of the soldering material, like 1-2 mm long, and put them on the piston top with a little grease as "glue". Try to position 4 bits as evenly around as possible, to minimise the tilting.

And I searched on "squish" at the old site, and found the recommendations were something like 1,2 mm, not less.

HansJ wrote:Thanks! But that is the problem though, isn't it, to know the thickness of the gaskets when compressed?

Rebuild with the old gasket and use that to measure squish

I was told 1.2 was what i should aim for