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Author Topic: Best way to check compression with the engine out of the frame?  (Read 1348 times)

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Offline raymond182

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Best way to check compression with the engine out of the frame?
« on: January 07, 2009, 05:41:05 AM »
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.
« Last Edit: January 07, 2009, 06:39:11 AM by Bob Wessner »
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WHALEMAN

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Re: Best way to check compression with the engine out of the frame?
« Reply #1 on: January 07, 2009, 06:22:12 AM »
It would be a cold test not as good as a test warmed up. Dan
« Last Edit: January 07, 2009, 06:38:57 AM by Bob Wessner »
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Offline raymond182

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Re: Best way to check compression with the engine out of the frame?
« Reply #2 on: January 07, 2009, 06:24:22 AM »
At the very least it would tell me if any cylinders are really bad right?
« Last Edit: January 07, 2009, 06:38:31 AM by Bob Wessner »
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Offline goon 1492

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Re: Best way to check compression with the engine out of the frame?
« Reply #3 on: January 07, 2009, 06:34:29 AM »
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. ;)
« Last Edit: January 07, 2009, 06:38:10 AM by Bob Wessner »
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Offline bryanj

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Re: Best way to check compression with the engine out of the frame?
« Reply #4 on: January 07, 2009, 07:05:04 AM »
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
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Offline raymond182

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Re: Best way to check compression with the engine out of the frame?
« Reply #5 on: January 07, 2009, 07:18:32 AM »
Got it, thanks guys!
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Offline MRieck

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Re: Best way to check compression with the engine out of the frame?
« Reply #6 on: January 07, 2009, 10:11:26 AM »
 A leakdown test would work much better especially with an engine out of the frame.
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Offline raymond182

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Re: Best way to check compression with the engine out of the frame?
« Reply #7 on: January 07, 2009, 12:48:18 PM »
Leakdown? Explain please
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Offline XN

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Re: Best way to check compression with the engine out of the frame?
« Reply #8 on: January 08, 2009, 02:22:55 AM »
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Offline HondaMan

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Re: Best way to check compression with the engine out of the frame?
« Reply #9 on: January 08, 2009, 05:32:07 AM »
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.
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