Engine gurus please

[maicoman18]

Gentlemen, assistance please. Bike is a ’74 250 mag engine.
When I bought the bike, it was low on compression when kick starting. It still started and ran fine, just not very fast. Took the head off and found a thin gasket between cylinder and head. I know that huskys do not have a gasket here. Positioned piston ring just below exhaust port and measure end gap and I believe that the ring is still ok by the owner's manual. Please bear in mind that we are talking about an electrician using feeler gauges. Considering that a gasket was used, I am guessing that there is a problem with the mating surfaces of the cylinder to head.
Question 1
If I put some fine wet and dry emery paper on a flat surface and move the cylinder around in a figure “8” pattern will this fix that surface?
Question 2
How can I prove the head mating surface is true?
Question 3
Any other theories on the low compression?

Thanks in advance guys

Ed

[Tomas]

The gasket can be responsible for low compression. Get rid of the gasket.  Check head/cylinder surfaces for damage. Use sand paper to flaten damaged surfaces. You can use valve grinding paste to mach cylinder and head surfaces. Put the cylinder and head back on and check compression.

[sleepy]

Does the head fit down over the sleeve or are both surfaces just flat?
If it is the first option you can use lapping paste between head and cylinder and with studs or bolts removed rotate the head back and forth till both are flat.
Is the ring a stepped (dykes) ring? If so the they use combustion pressure to help seal so on kick over leak a bit but be ok when running.
As far as being slow it could be anything on a 40 year old bike. Do you know the history of the motor? Is it all completely original or has it been stuffed with.

[maicoman18]

Should have mentioned that I got rid of the gasket straight away. No visible sign of damage but that doesn't mean that the surfaces are true to each other. Will try the emery paper and valve paste.
Head fits down over cylinder. Ring is a Dykes. Do not know history of engine but the cylinder does not have any obvious signs of being fiddled with.
After I removed the gasket and used the bike a couple of times, I removed the head and there was a lot of moisture (unburnt fuel I guess) on the mating surfaces again making me think that the surfaces were not true.
Thanks for your input gents. Will try to clean up the surfaces and see what happens

Ed

[80-85 husky]

check out the café husky website, the tech bulletins and the parts/ owners manuals and tips on owning old husky's are there in the left kickers section including a bulletin on lapping the heads down.

also a neat "how to prep a bike for the ISDE" by Burleson and co