some compression testing advice

Dutie

Dutie

Senior Member
Wanna do my first compression test. Have a pretty good idea but would like to first run it by some more experienced minds. I am thinking let it warm up some, plugs out, key off, engage starter from under hood and check gauge. The car is a 31 deluxe roadster and is my avatar pic. The engine is stock with a high compression head, maybe a comp. test will give me an idea of how high. Motor has been redone in 97 and has about 2500 mi. since a full restoration. Had this car about ten years and have it running great thanks to a lot of members who have helped out from timing to corn head grease. I am an older fella but a good learner.

thanks again dutie :)
 
Sounds like you're just checking for the fun of it? Sounds like you have it figured out, might want to hold the throttle wide open also, and cycle 5-6 compression strokes. My old engine has only 45, 50, 50, 50 PSI. I call it compression-depression, you have been warned! 8^)
 
I have found no difference between WOT and a closed throttle on compression checks. It won't hurt to put a brick on the throttle to hold it open, however. You may want to try both ways (closed and open) and report your findings back here.
 
Dick Steinkamp said:
I have found no difference between WOT and a closed throttle on compression checks. It won't hurt to put a brick on the throttle to hold it open, however. You may want to try both ways (closed and open) and report your findings back here.
Click to expand...

Same here no difference..... just pull the throttle lever down if you feel better having the throttle open....i usually go 3 bumps
 
One can tell just by the way an engine idles, and the sounds of it if the motor is tired.. a nice smooth running motor at a low idle the compression test will be fine.
All gauges are not created equal
 
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Dick Steinkamp said:
I have found no difference between WOT and a closed throttle on compression checks. It won't hurt to put a brick on the throttle to hold it open, however. You may want to try both ways (closed and open) and report your findings back here.
Click to expand...

Yep, the same with me. I don't worry about the throttle, but do have all the plugs out. A while back someone was checking compression with only one plug removed.

If you have a low cylinder, then do the leakdown test to see if the air is exiting out the tail pipe (ex. valve), or the carb (intake valve), or out the oil fill pipe (bad rings).
 
Oh, you have no idea. I am a native and I remember when there was NO smog. Sun burnt days of playing in shorts and no shirt in the summer without a care. Now they have polluted everything we have, air, water, food. It's like we are being embalmed before we die so all the funeral parlor needs do is bury us and charge more for that!
 
Compression decreases with an increase in altitude, less air density to suck in, less to compress. When the readings are not similar from cylinder to cylinder, put a squirt of motor oil in the hole, less than a teaspoon. This will make an improvement when redoing the test on that cyl. IF the rings are bad. The oil won't improve the readings if the valves are leaking.
 
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Trying Burping and Farting at the same time Bill, it will cause a vacuum and not create
any smog saving our air.
Thanks
 
Thanks to all the barners who took time out to reply. Will run it for a while Saturday outside, just to cold out there for me and Francis today...only 17. and real windy, afraid my top might blow off you know. Will keep in touch and thanks again Dutie:)
 
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