Combat compression

Cambo · Jul 14, 2019

This has me stumped. I rebuilt a ‘72 Combat engine and used a 2S camshaft. Std. base gasket and ‘flame ring’ head gasket. Using a SnapOn compression gauge I am getting 220# per side. Much too high. The head and barrel are not modified.

Thoughts?

concours · Jul 14, 2019

I have Snap-On gage (and a couple others) that is flaky. Try it on something else, see if it is above expectation as well.

swooshdave · Jul 14, 2019

If you can get it to run, heck kick over, then don’t worry.

comnoz · Jul 14, 2019

Cambo said:
This has me stumped. I rebuilt a ‘72 Combat engine and used a 2S camshaft. Std. base gasket and ‘flame ring’ head gasket. Using a SnapOn compression gauge I am getting 220# per side. Much too high. The head and barrel are not modified.

Thoughts?

Has it been run yet?
Do you have excessive oil in the cylinder?

baz · Jul 15, 2019

Are you certain the compression rings are the right way up?

ILLF8ED · Jul 15, 2019

Valve tappet clearance .008” intake .010” exhaust? Cam timing correct? My combat camshaft timing was off by 15 degrees with all the dots lined up per the manual.

Cambo · Jul 15, 2019

Further disclosure: I am using a ‘gapless’ 2 Nd ring. I did put 200 miles on the bike, started, ran and idled fine. Now a confession: I did not do a retorque. Just had not got around to it.

comnoz · Jul 15, 2019

Cambo said:
Further disclosure: I am using a ‘gapless’ 2 Nd ring. I did put 200 miles on the bike, started, ran and idled fine. Now a confession: I did not do a retorque. Just had not got around to it.

That would be a normal cranking compression with a gapless ring. No worries. The cylinder pressures will be down to normal at running speeds.
Better get that head retorqued. Jim

acotrel · Jul 15, 2019

A dry motor is different to kick over than one with a gutful of fuel.

jseng1 · Jul 16, 2019

Cambo said:
Further disclosure: I am using a ‘gapless’ 2 Nd ring. I did put 200 miles on the bike, started, ran and idled fine. Now a confession: I did not do a retorque. Just had not got around to it.

what kind of pistons?

Combat compression

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