I'm restoring a 241 Progress 2 and have bought a gasket kit from InMotion. There appeared to be 2 base gaskets in the kit (although they were very slightly different shapes) should I have used both?

I have just used one base gasket and tightened up the head bolts but now I'm worried that I should have used both for the extra squish.

Anyone know the answer?

If you’re a bit cunning you can measure the squish without taking the head off!

Get a length of solder that’s long enough to have each end close to the bore of the cylinder and have a loop in the middle that fits up the spark plug hole.

Fold the ends back to they will fit down the plug hole but still point towards the edge of the bore.

Bring the piston up to somewhere near TDC.

Carefully feed the solder down the plug hole. As the ends hit the piston they should push out to the edge of the bore.

Turn the engine past TDC. Only do this once and don’t take it too far past otherwise you will lose the solder inside the engine.

Pull the solder out of the plug hole and the ends will have been squashed you can measure this area to tell you the squish gap size. Unless it is under 0.6mm I wouldn’t worry.

This is how I check my two stroke race engines. I normally do it as I build the engine up but it is easier as the head bolts on separately. Pushing the solder down the plug hole does work on a 125cc engine, although it could be a bit more difficult on a bigger engine where the solder would need to be longer. 

Thank you.

I'm not bothered so much about measuring the squish, I just wanted to know if it's "safe" to have just one paper gasket in.

I have found a discussion elsewhere saying that people regularly used 2, 3 or even 4 gaskets on the 240 engine (same engine as the 241) "back in the day" to soften the power.

On that basis I have fitted the extra gasket so it now has two.

Sorry maggar, I got so involved in the description of how to do it I didn’t really highlight the important thing!

A squish gap of 0.6mm or above will be safe.

I normally set my race engine 0.6-07mm but have run it as low as 0.55mm and not had a clearance issue. I suspect that on a relatively low stress, low revving trials engine you could probably go down to 0.4mm without an issue.

Personally I would get the squish gap right and if I felt the engine needed to be softened find another way of achieving that.

Squish size, shape and gap have a much bigger effect on overall engine performance than most people realise. 

Thanks Smokey.

I will do as you suggest.