leak down test
Seasoned HDF Member
Joined: May 2008
Posts: 21,146
Likes: 12,713
From: South Carolina
A lot of people don`t understand what a leak down test is, and what the numbers mean.
Most leak testers are el cheapo junk, and will have readings that won`t be the same as another tester of the same type.
The leakdown rate doesn`t tell you a lot, since it is just the difference between the air supply pressure and pressure after the orifice, which is not standardized or calibrated (except on units approved by FAA).
A leakdown test is a great tool, but you must have a baseline to compare it with.
Buy a leakdown tester, test the leakdown yourself when the engine is just broken in.
Now when you take a subsequent leakdown test (using the same tester) you will know how much difference there is.
In my opinion, a leakdown test performed at dealer using some junk Chinese tester is just generating numbers that don`t mean anything.
Do a compression test.
Most leak testers are el cheapo junk, and will have readings that won`t be the same as another tester of the same type.
The leakdown rate doesn`t tell you a lot, since it is just the difference between the air supply pressure and pressure after the orifice, which is not standardized or calibrated (except on units approved by FAA).
A leakdown test is a great tool, but you must have a baseline to compare it with.
Buy a leakdown tester, test the leakdown yourself when the engine is just broken in.
Now when you take a subsequent leakdown test (using the same tester) you will know how much difference there is.
In my opinion, a leakdown test performed at dealer using some junk Chinese tester is just generating numbers that don`t mean anything.
Do a compression test.
Last edited by Dan89FLSTC; Oct 23, 2021 at 03:19 PM.
Cruiser
Joined: Mar 2017
Posts: 196
Likes: 91
From: Hamburg
To judge an engine I prefer the following way:
- Do a compression test. If it's not noticeable enjoy the ride. If yes, go ahead.
- Do a leak down to know why the compression is low. The leak down helps you indicate the source of the failure:
- Intake: While carburator or bridge removed, you can hear the air escaping.
- Exhaust: While exhaust removed, you can hear the air escaping here.
- Piston rings: Hear the escaping air makes sound in our oil tank.
- Head gasket: Use a brush and some soap. If you see bubbles, the head gasket is blown.
- Crack anywhere (cylinder head, combustion chamber): Same as #4.
Seasoned HDF Member
Joined: May 2008
Posts: 21,146
Likes: 12,713
From: South Carolina
If you want to do the leak down in a 100% way, you've to open the primary and block the sprockets with a steel.
Doing a leak down by blocking the engine just with the clutch can be fail because if the clutch slips just a little way, the intake/exhaust beginns to open and you get a false positive.
Doing a leak down by blocking the engine just with the clutch can be fail because if the clutch slips just a little way, the intake/exhaust beginns to open and you get a false positive.
There is no reason to pull the outer primary cover and waste a quart of primary lube and possibly a gasket just to perform a leak down test, the clutch should not going to slip by putting 100 psi into one cylinder, transmission in high gear holding brake....
If it does, you probably do need to pull the outer primary cover....To replace the clutch.
You don`t really need 100 psi either, 80 psi will be just as accurate.
People use 100 because they don`t remember how to compute percentage of 80...
Last edited by Dan89FLSTC; Oct 28, 2021 at 09:42 AM.
Thread
Thread Starter
Forum
Replies
Last Post
