Compression Test

ktkamm

ktkamm

Member
Did my first ever compression test (never too old to learn at 59). I have no previous information regarding the engine on this newly purchased AA truck. Readings were: 1-55, 2-45, 3-34 and 4-55. From what I have read on this forum and from other resources, this would be c/w probable blown head gasket between cylinders 2 and 3? Of interest, spark plug in # 1 looked fouled, however the others were clean. What might that suggest?

Looks like I need to order a head gasket and pick up some stuff to loosen up the bolts on the head. I think I will also plan on changing out the threaded studs. Anything else I might consider doing while in there?

Thanks,

Kieran
 
Try a new head gasket. They should all be within a close range.

Is you engine smoking at all? Any noise or power problems? Water in the oil, or oil in the water?

I would like to see the compression more in the 60's range.

What type of compression tester are you using?

Good luck.
 
As long as your on a learning curve it's time to learn how to do a leak down test before you pull the head. It will tell you what is leaking. If the motor has sat for a long time it could be valves not seating.
Do a leak down and report back.
 
mine is mid 60s. I went with the copper sandwhiched gasket and used a gasket shellac. hightack by permatex 5$ at local auto parts. I have heard since then Indian head gasket shellac is the good stuff. I used a file to take down a bulges I had around my studs probably from over torque. and ran a small hone around to take any extra debris or corrosions
that could be a bump on the block and head surface. check your head for flat. I used a carpenters 24 in square if you can pass paper between your straight edge and head I would get a new head. 55ft radial torqure pattern from center 30ft-45ft-55ft
 
how did it run like that? im guessing ok. mine would wet down 3/4 but ran decent until those cyls shut down. i didnt get a test number before the head gasket job.
 
I had 94 in $1, )=0 in #2, 85 in #3 and 94 in #4, Pulled the plugs on 2 and 4 and put some Marvels Mystery Oil in there, cranked it a few revs with the key off and drove it to coffee the following morning. Came home and did a compression test. 94 psi in all four holes, I'm a happy camper. I have no prior history on the engine as the prior owner had passed away and his son could only tell me he remembered helping dad put an engine in the car some ten + years ago. No clue where he got the engine. Have driven it two years now with no issues.
 
As mentioned I would check head torque and do a leak down test. Not very
likely that the gasket would blow between 2 & 3, 1 & 2 or 3 & 4 yes.

Bob
 
katy said:
Did you do it the correct way?
Click to expand...

My guess is that "the correct way" is the way YOU do it. Right? ;)

Problem is, if you ask 4 Model A guys the "correct way" to do it, you'll get 4 different answers...all swearing ANY way else is absolutely wrong!

With those numbers, I'd suspect a couple of burned or at least leaking valves. As suggested, do a leak down test BEFORE you take it apart so you know what the problem is.
 
daveymc29 said:
I had 94 in $1, )=0 in #2, 85 in #3 and 94 in #4, Pulled the plugs on 2 and 4 and put some Marvels Mystery Oil in there, cranked it a few revs with the key off and drove it to coffee the following morning. Came home and did a compression test. 94 psi in all four holes, I'm a happy camper. I have no prior history on the engine as the prior owner had passed away and his son could only tell me he remembered helping dad put an engine in the car some ten + years ago. No clue where he got the engine. Have driven it two years now with no issues.
Click to expand...

Are you running a stock head?
 
Correction to #6, MMO was put in all holes with a generous shot in the 2nd and 3rd. I also add 4 oz. to the full tank whenever I remember to do it. That is about every third tank full. Also keeps the throttle stuff responsive in the carburetor. Good stuff.
 
Thanks for all the input. I did the compression test by first warming the engine up for about 20 minutes. I then removed the distributor cap and all four spark plugs. Used a compression gauge I purchased at the local NAPA store, and screwed the hose end into the spark plug hole adapter. Turned the engine over 4xs with the starter and took the highest pressure recorded. Did the same thing x 2 for each cylinder. Results consistent.

I attempted my interpretation of a leak down test. Using the above adapter, I changed out the compression gauge for an air hose nipple. Tested each cylinder by first attempting to get the cylinder at TDC, then hooked up the air hose which was in turn hooked to a small compressor. Could not see any air bubbles in the radiator. Cylinders 1 and four seemed to hold the pressure but unable to do that with #s 2 and 3. With ear up to the exhaust pipe, sounded like I could hear the sound of air. Not sure if that helps with additional advice as to which way to proceed.

Thanks,

Kieran
 
WHN said:
Try a new head gasket. They should all be within a close range.

Is you engine smoking at all? Any noise or power problems? Water in the oil, or oil in the water?

I would like to see the compression more in the 60's range.

What type of compression tester are you using?

Good luck.
Click to expand...

If the engine was running OK prior to your test and you have no problems with oil or water where they should not be.

I go along with the recommendation to try Marvel Mystery Oil in your gas and putting some in the offending cylinders. Easier than replacing head gasket.

Are you using HD oil? Sticky valves or slow valves are common in old, seldom used, engines.

If you can get all cylinders to the mid 50's things could be OK. Mid 60's would be great for a stock head without a lot of carbon build up.

Keep us informed, great cars.
 
Thanks Bob. When doing the test, I knew that was the case, however, in retrospect, I think I had the choke wide open (mixed that up in my mind with the throttle).

Unfortunately before reading all these replies, I went ahead and removed all the nuts from the head, took out the distributor and removed the neck from the pump. Would it make sense to put it all back together, torque all the head nuts to 55lbs and redo the compression test and also try the MMO in the cylinders?

Thanks again for all the help!
 
When and if you go to take the head off.
Leave the bolts on the studs, raise them off the head a couple of threads, install all plugs, leave the plug wires off, crank the engine.
Helps to loosen the head.
 
At this point I would remove head. If you have "any" valve issues, easier to lube with head off. Also now you will settle any head gasket questions.

Clean carbon off head and block.
 
94 psi in all four holes ................ what head are you running ? stock is like 55/60 on a good day .
 
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