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Discussion Starter · #1 ·
I've done some reading about both of these tools but if I had to choose between one or the other, which would you recommend? Compression tester or cylinder leakage tester?

Thanks - Tim
 

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An air compressor is needed for a leakdown tester. However many newer production small engines have some sort of compression release for easier starting and this will affect the results of both compression and leakdown testing. One needs to know if an engine has the compression release feature before performing either type of diagnostic testing. However, this info is not easy to extract from operators and/or maintenance manuals.
When doing service work on any engine with overhead valves, I assume that it has a compression release designed into it and deal with it from there. I did service a snowblower recently that has a Techumseh L head engine with a compression release. During my initial diagnostics, fuel, oil, spark check, compression check, I got only 40 PSI during the compression check which is due to the compression release feature of the engine. Having electric start makes no difference, still have a compression release.
Mad Mackie in CT :mrgreen: :lol:
 

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Discussion Starter · #4 ·
Thanks Bob and Tom. I'm planning on conducting a leakage test on my B43M in the near future. In preparation for that, I was looking at a dual gauge cylinder leakage tester that will need compressed air - not an issue as I have a compressor. Any suggestions/tips before I attempt the leakage test?

Thanks - Tim
 

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On Onans I always do a compression check first. If it shows lower than I'd like, I followup with a leakdown test. I have a Harbor Freight version, works fine and is priced right, almost as cheap as putting one together from the hardware store.

On those engines with compression releases, just start with the leakdown.
 

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Hi Tim,
A B43 Onan does not have a compression release so you won't have to deal with it.
For years I have done leakdown testing on piston engines in aircraft at 80 PSI in and then read the leakage rate. I have also done leakage testing on small engines and did them at 60 PSI in. Now they are doing testing at 100 PSI which makes figuring the percent of leakage easier. I personally would not put 100 PSI into a small engine during a leakdown test, but this is my opinion. Finding TDC and keep it there during the test sometimes can be challenging on small engines as access to the crankshaft can be difficult on most, with a propeller it was easy. On an engine several years ago I had a breaker bar and socket on the flywheel nut holding the piston at TDC but the piston was not at TDC and the flywheel nut loosened from the force on the piston!!! After retorquing the flywheel nut the test went fine!!! A second pair of hands while doing this test is good to have providing that person understands whar you are doing and holds the breaker bar and socket securely and safely. I recommend a two gauge tester and I agree with Kenc, do a compression test first. So to do this type diagnostic testing you really need both type gauges.
Mad Mackie in CT :mrgreen: :lol:
 
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