Case Colt Ingersoll Tractors banner

Leak Down Tests

2740 Views 6 Replies 4 Participants Last post by  robynrj

There's been a lot of posts that I've read over the time that says: Do a leakdown Test and get back to us.

I don't recall a reply other than a comment about being in the green zone.

I know that there are a variety of testers on the market that have different markings on the gauge.

My question is what is a decent reading in PSI ?


1 - 7 of 7 Posts
There's been a lot of posts that I've read over the time that says: Do a leakdown Test and get back to us.

Compression test tell you how high compression will go hopefully 90 psi are above is good after 120 psi and above there can be problem valve train like compression release this is notice when reading around 160 are above.

Leakdown test to see how well engine hold pressure by using aircompressor leakdown tool have orfis so incoming air be about same as normal ring gap leakby.

Two gauges one measure incoming air pressure other how much leak off the persent shouldbe no more than 30% off incoming air you hear are see a leak above 20% like coming out muffler that exhaust valve coming in carb that intake valve leaking are from head gasket leak to outside are bubbles in coolant if water cooled. Crankcase venting to much air ring or piston leaking.

0 to 20 % give you life range for engine like 18% you got one more season with that engine then overhaul are trade time.

I use compression testor and 3 of my 5 sences to tell me how read parts on teardown. Leakdown test just reverse of compression test so why not use faster compression tester.

Which leakdown tester to buy start out one harbour freight unless in engine rebuilting business then get one with better guages and valves so be lifer. If do warranty work you need leakdown tester if don't you don't.

Some people helping other on internet beenfit with leakdown test report. Greem zone is 0 to 20%
See less See more

Wow are my numbers out

I built my own with the help of an article which I have since never found.

I built a tester with a 0.040 orifice and two calibrated 160# gauges.

I run 100 psi( Some say 60 works ) and I got a reading of 86 psi and could hear leaks at both valves. I put a 1" plug in the exhaust and got a reading of 90 so I built a plate for the intake and that gave me a reading of 92.

So I got 8 % if I can lap the valves tight. Maybe valves leak a little and I end up with 10 % leakage.

Compression is 135

Maybe the testers orifice is to big. :)

It's a K321AS from a 224-79

Thanks Gator

See less See more
While a compression gauge reading maybe faster, if low, what do you know? Low compression!! Add little oil to cyl and if increases its ring issue. Using leakdown you know if going by rings or intake/exhaust valves...or head gasket. A 15% just tells you your lossing power and will continue lossing till it affects you early warning. You may run for years like that....depends on maintence, amount used etc. Should be tested with 90+ it sees during compression stroke. So, thou it may take couple minutes longer, you know issue. If calling B/S/Kohler/Kaw etc factory on oil use, power issue, you better have leakdown, not compression reading. Bob M
I have to agree with Bob on this one I went thru a 2 year marine and small engine school ans they don't even have a ompression tester on the tool list but we used leak downs everyday so now I use it on every thing really helps you pinpoint where the problem really is
Thanks Guys

Looking like my 321 is good for awhile. :)

What % would a brand new K-321AS be expected to have? Would the valves seal 100% ?

A brand new K has been run at the factory 10-20 mins. so I'd expect 5-10% leak could be possible.... valves tight but rings not. After 50+ hrs I'd expect under 5%. This would be most small engines really. Bob M
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.