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Compression test diagnosis???

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Morris

Morris

Yoda
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I pulled my 79 off the road a coupla months ago because of some weird compression readings. Basically 150 for all holes but #1 which showed 80. A real bummer on a fresh rebuild. I squirted some oil in #1, and compression came back up. Okay, I can handle replacing rings. But I just checked compression again after the car has been sitting for a while and fired (but not idled) a few times, and #1 is still holding strong.

Now, my high quality Harbor Frieght compression tester has been known to occasionally give wierd readings, so I am wondering. How long will a couple squirts in the cylinder maintain compression? Is it possible I do not have to tear down my engine after all?
 
Might just want to run it for a while...and borrow another tester to compare to. Rings just might need more time to seat. And the repeatibility of the tester is suspect.
 
Oil on rings should be effectively gone after you run it for 30 sec.
 
Morris, do a leakdown check before you tear into anything. That is a much more important and accurate test, and if there <u>is</u> a problem, you can isolate it exactly.
Jeff
 
Leak down test is awaiting me gettin off my butt and building a leak down tester. /ubbthreads/images/graemlins/wink.gif
 
C'mon, Morris, surely you know somone with one of these gems? To me, it's one of the primary tools in the diagnostic box. The compression gauge is way down on the list except for field expedient checks.
Jeff
 
Morris:

[ QUOTE ]
A real bummer on a fresh rebuild.

[/ QUOTE ]

How many miles on it??

Borrow another guage from AutoZone, etc.

Go to www.justbrits.com and in Various Articles is a 4 cyl. Comp. Test Form. Do the testS, fill out , scan and send to me. I will plug in your numbers and send back.

/ubbthreads/images/graemlins/cheers.gif
Ed
 
Ed, would you please enlighten me on what you can prove by a simple compression test, rather than doing a leakdown?
At best, a dry/wet compression test is going to show you whether the rings are sealing properly. Whereas, a leakdown test will isolate a leaky valve, blown head gasket, bad rings, etc. On my race engines, even though the compression pressure numbers may be good, and within 10% of each other, by doing a leakdown, I can determine the state of the engine much more accurately.
Is there something I've missed?
Jeff
 
Thanks Ed. It's gonna be a couple days before Santa gets to work on his sled again.

Jeff, I need to move closer to you or get some better friends, because none of mine have even heard of a leakdown test.
 
Whoa. Leakdown testing is about as good as it gets without OBD-II... or maybe a smoke tester (really is such a thing, too!).
 
I have several smoke alarms, will that work? hehe
 
Keeping my vacuum guage here in case of emergency.
 
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