leakdown testing

[frankp]

I have several motors that I want to do leak down testing on. In the manual I have for the harbor freight tester I have, it says that one should warm up the engine before one does the test. I can't start most of the motors I want to test. Is it meaningful to leak down test a cold motor?

[KE4AVB]

Yes, The reason for the warm test is that the cylinder and rings will leak more when cold testing so you must allow for a little higher leakage rate.

To be honest most time when I use my homemade tester is to find leaky valves and head gaskets. Most times these engine won't even start for me in the first place. If I suspect leakage cylinder or rings after doing a leak down test I do a compression check. If then the compression is very low I do a physical check of the cylinder.

[bobodu]

I don't even use the gauges on mine. If the compression is that low...the hissing points to the problem.

[Merkava_4]

In my case it was the blue smoke that pointed to the problem. A 1969 B&S model 60102 horizontal shaft with a Vacu-Jet on a McLane edger. I swapped in a 3hp crank and connecting rod, Magnetron coil kit, and a standard size chrome ring kit. That chrome ring kit has 8 piston rings. Man-o-man does that kit work good! I can feel the increased compression when I pull the rope. The smoke is completely gone and the engine runs like a sewing machine. I'm proud of that little engine.

[frankp]

Thanks for the help. Someday I might know something so I can help this forum. You guys help my confidence.

[frankp]

Got a chance to use the tester. Never got a reading. The manual says to make sure the regulator is fully counter clockwise before connecting the tester to a pressured air source. also don't operate with air greater than 100 psi. my shop compressor was 140psi. As a result, the leakage gauge on the tester pegged, so I couldn't set it with more than 20psi. That's why I never got a good reading. The good new is I cleaned the carb and checked the spark and started the engine. Started first pull and ran great. That's the best compression tester I know.

[RoyM]

I hope you aren't running tools or a blow gun at 140psi, bad things happen. Put a regulator on it before you hurt yourself.

[frankp]

Hi Roy, I have a regulator on compressor which is set for 140psi. I don't run tools very often as I prefer to use rachet, but as I gain experience and need to speedup my production I plan to start using air tools more. I have them, just don't use them. Actually I am a bit afraid. What pressure do you recommend to set the shop compressor?

[Luffydog]

the compressor is built up to 140 then kicks off the i back my regulator down to 90-100 psi... but i would look at the manual and see what the recommend psi should be set at. most now just saying most but not all say recommended @ 100psi. just depends on the tools u have. now if u set it at 100psi then hook a paint gun to it youll have probs lol. for most paint guns are to be used at lower psi and if not will damage the can. but like i said for most between 90-100psi and should be ok but look to see what is the max psi rating for your tools........

[frankp]

Lots of my air tools don't have manuals. I'll set it at 90 and see how things work. I tried to call harbor freight technical support to see if I can readjust the leak rate gauge on my leakdown tester but they are closed. I'll try tomorrow. I took a quick look at the gauge before I left the shop but didn't see any calibration screw. I might be stuck and use Bob's method of no gauges.