SHOCKED With Compression Check

Cape Codder

Cape Codder

Well-known member
Today, I decided to check the compression on my newly rebuilt (462 miles) motor. I wanted to have something to have as a base for any further checks. The results SHOCKED me because they are #1 - 20 lbs., #2 - 25 lbs., #3 - 27 lbs., and #4 - 28 lbs. Could it be that the rings are not seated? Or is there some other reason? Give me some good news!

Thanks for your time.

Cape Codder
 
good news cape,
go get yourself a quality gauge and deep six that one.
opening the throttle never made much of a difference for me and definitely will not cause a loss of 50% compression reading plus your car would be running like dog poo
 
Last edited:
If it runs good I would be looking at the compression tester.Sometimes raw gas and oil gets up into the tester and gums things up while they sit in the toolbox.Unseated rings and low air volume will change numbers,but not to the kind of numbers you have.A few pounds off is one thing,but 30-40 pounds is another.You may have some tight valves being it is a new engine,but I would think it would be showing other symptoms.What made you feel you had to check the compression? Was something acting up?
 
Sometimes the rings need longer to seat, but I'd call the builder for an explanation as to your readings
 
I second the suggestions to try another compression tester. To have all 4 that low, but so close to each other seems odd.
 
Cape Codder, Why do you need a "BASE" for further tests?? If it's running good, leave it alone!
PROPER compression tests should be left to techincians that know their stuff & have done this for years & know how to analyze the results properly. Compression tests are generally only necessary to diagnose problems.
Some folks "tinker" too much, if you must "tinker", adjust your horn, check your oil & water, check tire pressure, & check your lug nut tightness, bathe your rubber chicken, scratch your butt, etc. Bill W.
 
BILL WILLIAMSON said:
Cape Codder, Why do you need a "BASE" for further tests?? If it's running good, leave it alone!
PROPER compression tests should be left to techincians that know their stuff & have done this for years & know how to analyze the results properly. Compression tests are generally only necessary to diagnose problems.
Some folks "tinker" too much, if you must "tinker", adjust your horn, check your oil & water, check tire pressure, & check your lug nut tightness, bathe your rubber chicken, scratch your butt, etc. Bill W.
Click to expand...

With all due respect, I disagree. I know and record the compression, valve clearance, plug gap, points gap, timing, dwell, cylinder head temp above each cylinder, radiator temp over ambient, and a half dozen other specs on every engine I own. If I have to work on it, and diagnose it, I want to know what I am starting with. When something goes awry I want to know that it was not like that a few months ago. Particularly when I am starting with an engine that I don't have the history on. One afternoon spent benchmarking an engine and comparing.those specs to the manual, brings me a lot of satisfaction.
 
QGolden said:
With all due respect, I disagree. I know and record the compression, valve clearance, plug gap, points gap, timing, dwell, cylinder head temp above each cylinder, radiator temp over ambient, and a half dozen other specs on every engine I own. If I have to work on it, and diagnose it, I want to know what I am starting with. When something goes awry I want to know that it was not like that a few months ago. Particularly when I am starting with an engine that I don't have the history on. One afternoon spent benchmarking an engine and comparing.those specs to the manual, brings me a lot of satisfaction.
Click to expand...

I agree.:)
It's just like preventive maintenance beats having to do repairs.
 
QGolden, We're NOT workin' on aircraft or rockets, just a FUN old SIMPLE Model A.
It's apparent that Cape Codders tests were NOT done properly, with that low a compression, it wouldn't even start & run. Bill W.
 
QGolden said:
With all due respect, I disagree. I know and record the compression, valve clearance, plug gap, points gap, timing, dwell, cylinder head temp above each cylinder, radiator temp over ambient, and a half dozen other specs on every engine I own. If I have to work on it, and diagnose it, I want to know what I am starting with. When something goes awry I want to know that it was not like that a few months ago. Particularly when I am starting with an engine that I don't have the history on. One afternoon spent benchmarking an engine and comparing.those specs to the manual, brings me a lot of satisfaction.
Click to expand...

I also agree. To me it's silly to pooh-pooh the idea of collecting reference information that may help in future diagnoses and general LEARNING. Yep, not only do most of these cars not run like a "rocket", the vast majority don't even run like a Model A should. Obviously there was a problem with his test or he wouldn't have come here looking for further advise. I vote for supporting Joe in his quest for more information as several already have.
 
Marco Tahtaras said:
Yep, not only do most of these cars not run like a "rocket", the vast majority don't even run like a Model A should.
Click to expand...
Marco, I'm SHOCKED! What qualifies you to make such a derogatory statement such as this? Have you seen & noticed the performance of "THE VAST MAJORITY OF THE MODEL A's?????? (I don't think so!) Our mission, here, should be to help & encourage each other.
I feel that an apology is in order to the novices & the seasoned Model A folks who DO know how to make a Model A run as well as it did when it was new! (And sometimes BETTER, even on a stock Model A!) Bill W.
 
Last edited:
Hi Bill,
I presume your reply was made in jest? Nothing Marco said was derogatory. I'll bet you lunch that the folks who keep their A's "running as new", spend a lot of time benchmarking their engines.
 
Yep, not only do most of these cars not run like a "rocket", the vast majority don't even run like a Model A should.

How true that statement is. I owned a Model A for a few years before I really learned how to maintain it properly. And drive it properly. Now that I have gained this knowledge I can easily tell a good runner from one with problems. Bill, you know if someone wants to establish a compression baseline on their motor, why not? It's cheap and keeps them out of the bars! Of course I do agree to try it with a known, good compression guage. I think it will come in significantly better than his current readings!
 
Yes the readings are low, but the consistency between them all is a good thing. Try squirting a little oil in the cylinder and doing it again.That could tell you if its a ring issue.
I really hope Marco and Bill are just shining each other on....
I love the information but I can do without the drama.
 
Marco's right. Once you hear and feel how good an original low mileage engine runs, you'll find there aren't many that can match it. So many have some noise or vibration that wasn't there from the factory.
 
You must log in or register to reply here.
Back
Top