Topic: Best way to check compression with the engine out of the frame?

[raymond182]

Greetings, got me a 'basket case' 1971 CB 500, the engine is complete but, is not in the frame. Before opening it up I would like to run a compression check. Should I just hotwire the starter and get it done? Thanks.

[WHALEMAN]

It would be a cold test not as good as a test warmed up. Dan

[raymond182]

At the very least it would tell me if any cylinders are really bad right?

[goon 1492]

It would get you in the ballpark at least, I would reccomend fabbing up a bracket or small engine stand that would mount ot the workbench at least to help hold the engine still for you. You will probably use that engine stand again in the future too.

[bryanj]

Leave carbs off,exhaust off, all plugs out and use HEAVY leads from a big battery and it will tell you if you have one or more bad cylinders as long as one is good

[raymond182]

Got it, thanks guys!

[MRieck]

 A leakdown test would work much better especially with an engine out of the frame.

[raymond182]

Leakdown? Explain please

[XN]

This explanis it better than I could write it...

http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/index.html

[HondaMan]

Shade-tree method:

On a cold engine that hasn't been run in a long time, this method works pretty well:
1. Take the "starter-driven" reading cold, all 4 cylinders. Look for more than 10 PSI difference between them as an indication of poor sealing somewhere.
2. Pour/squirt/dribble about a teaspoonful of light oil like WD40 into each cylinder and let is sit for 5-10 minutes. Repeat test #1. The number will be higher. Look for an improvement in that low cylinder: if it now matches the others, the rings are leaking somewhat in that cylinder. If it is still low, the valves are leaking.

Since it hasn't been run in a while, the actual number might be in the 90 PSI range. If it's more than that, so much the better. Later, you'll find higher numbers when you can warm it up and take the readings.