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Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
I'm trying to do cylinder leakdown test on my 2006 Heritage Softail Classic EFI.
I did compression test and both cylinders show ~145psi.
When trying to do leakdown test, I cannot get piston to stay at TDC, even though I put bike in 5th gear and applied brake. As soon as I put air in the cylinder, piston moves. I tried to put 100psi right away and i also tried to slowly increase pressure, with the same result.
Is there something I'm doing wrong? I know when piston is on TDC of exhaust stroke, exhaust valve will be open - and I could hear air escaping through exhaust in that case. So I'm sure it is at TDC of compression stroke. I use a straw to check the piston position.
Use 50 lbs and adjust the leak down gage set to get what gage set says for a test. However, you need one that is matched that has been calibrated to a good similar engine.
You're only listening to determine where the issue is. With a leak down, that all you really need to know. The leak down gage sets are all a little different that have the % and color scale to indicate engine health.
The compression test is what's important and usually what's called out in service manual.
Did you have a warm engine with throttle wide open for compression test?
Book I am pretty sure for a stock 8.9-1 is 150-160psi. You are off 5 lbs (3%) with perfectly matched cylinders.
Sounds like a very healthy engine unless my figures are wrong. Do you have a running issue?
Last edited by Jackie Paper; Sep 25, 2025 at 03:42 AM.
I use a 1" wooden dowl in the rear rim on top of the swing arm with towels to protect everything to keep the engine from spinning over.. Takes a little playing sometime but it works..
Or any kind of belt wedge style locking tool in the rear pulley.. And yes 5th or 6th gear.
The only time other time leak is good than what Dan says, is when you take a fresh motor and leak it then use that info to monitor a motor. Typically, guys do this with race motors..
The only time I saw that was worthy was years ago one a brand new 1977 CB750A that I serviced. While syncing the carbs, the number 4 cylinder sleeve dropped about 0.010 inch and the motor started leaking compression.. Compression test showed the drop but the service manager at the time didn't believe me. Leak down convinced him..
Use 50 lbs and adjust the leak down gage set to get what gage set says for a test. However, you need one that is matched that has been calibrated to a good similar engine.
You're only listening to determine where the issue is. With a leak down, that all you really need to know. The leak down gage sets are all a little different that have the % and color scale to indicate engine health.
The compression test is what's important and usually what's called out in service manual.
Did you have a warm engine with throttle wide open for compression test?
Book I am pretty sure for a stock 8.9-1 is 150-160psi. You are off 5 lbs (3%) with perfectly matched cylinders.
Sounds like a very healthy engine unless my figures are wrong. Do you have a running issue?
I can't get combustion in the rear cylinder. I have spark I have fuel no combustion
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Leak down test issues
