When doing a compression test w/throttle wide open, good batery, and watching the gauge,
How many revolutions should the motor turn over to achieve satisfactory reading.
How can I tell between the rings, or valves which could be an issue by gauge behavior.
75 XLH, bored 0.30 over.
Thanks, db.

 

Let it turn over about 5-6 revolutions or until the gauge doesn't climb any higher.

If you add a small amount of oil to the cylinder and the compression jumps significantly , your rings need attention. If it only increases very slightly, suspect valves or head gasket as the source.

 

what if i use the magic snak oil?? WIll that double my hp?? Just kidding, another way to find out where you have a problem is a leak down test. They will let you know what % od leakage you have and if it is rings, valves and which valve , intake or exhaust. Nice tool to invest in .

 

Lets say the head gaskets were new, and in good shape, If the gauge jumps pretty high on the first couple revolutions, then settles close to spec. compression, does this indicate one kind of problem,
while the next cylinder pumps up slowly, say 30 to 50 psi per stroke.
Can't buy Magic Snake oil anymore!
Thsanks
db.