leakdown test

well I was pleasantly surprised today. All the parts in my motor measured so close to new that I decided to just give a fresh cross-hatch and re use the rings. For a while I thought that I had made a big mistake because I had blowby from the breather.

So after putting a few hundred miles on the bike I broke out my leakdown tester (called differential compression tester on aircraft). All the cylinders are at about 9% or below, with no audible hissing coming from intake, exhaust or breather. On aircraft we allow a maximum of 25% on an individual cylinder. Usually when they are that low the cylinder is noticeably colder than the others too.

I have my crankcase breather routed into my #2 pod filter but I have a clear tube and I havent seen anymore blowby either. Good thing because blowby sure makes the oil dark in a hurry.

J,As you will, no to 3% leakdown is standard for me. G

on air cooled motor cycle engines anything up to 10% percent leakage is fine especally on these air cooled engines in a perfect world you want zero leakage but i don't know if anybody has noticed it's far from perfect. also on some of my race motors depending on where in the season i am i've had twenty percent or better just emptied out my puke tank more often and changed my oil lots.