1941 A-How many lbs. psi on compression test?

Tue Feb 03, 2009 6:15 pm

Got the A out of the shed to start getting it ready for it's rebirth. It was missing and running badly the last several times I had it out. The block had a small freeze fracture behind the carb and was leaking anti-freeze, so I thought I was dealing a similar fracture on the head deck of the block. Either that or I had valves sticking.
First thing on my agenda was to observe the valves with the valve cover off. Everything was moving smoothly. I know it makes a big difference if it is at operating temp. and this was not.
Second objective was a compression test. I didn't have the proper adapter to screw my compression gauge into the spark plug hole so I just tried wrapping it with electrical tape :oops: and shoving it up against the hole as best I could. I know this is not going to be extremely accurate but I really expected to find # 2 and 3 cylinder (freeze cracked) with 0 compression and this set up would be good enough to tell me that.
My results were very pleasing.....I think. :? All the cylinders came out within about a .5% of one another. That's pretty good cylinder balance in my book. The thing I don't know is how much pressure should each cylinder render? This is a gas tractor from the midwest , so it shouldn't have any whacky compression ratio pistons (high altitude or distilate).

OK you salty dogs, help me out..........please

Thanks,
Steve

Re: 1941 A-How many lbs. psi on compression test?

Tue Feb 03, 2009 11:15 pm

As long as the compression is even on all 4 cylinders, the tractor runs fine and does what you want - don't worry about it.

Just guessing. 100 psi would be in the ball park, good. 80 marginal but still satisfactory. However, I have a WC Allis and without looking you could find any one of 7 different piston sets (compression rations) for the original engine. Don't know about an IH 41 A. I have a distilate set in the WC and a fresh engine overhaul. Hand cranking, 70 PSI is the best I can get.

Re: 1941 A-How many lbs. psi on compression test?

Wed Feb 04, 2009 5:13 pm

With my screwed up method of checking compression I got 46 to 48 lbs. on all the cylinders. I didn't think that sounded like much pressure.

Steve

Re: 1941 A-How many lbs. psi on compression test?

Wed Feb 04, 2009 9:08 pm

With 46 to 48 pounds of compression it should barely be able to move itself, and blow a lot of oil smoke.

Re: 1941 A-How many lbs. psi on compression test?

Wed Feb 04, 2009 9:40 pm

Time for a dry and wet compression test. You do not need one of the mechanics quality testers - one of the cheaper ones will do just as well - provide you with the needed information.

NAPA has loaner tools. Perhaps some of the other autoparts store have loaner tools. Know a local mechanic?

Re: 1941 A-How many lbs. psi on compression test?

Thu Feb 05, 2009 7:37 am

Steve,Stop by and pick up my Compression tester so you can get some accurate reading .

Re: 1941 A-How many lbs. psi on compression test?

Sat Feb 07, 2009 6:48 am

John *.?-!.* cub owner wrote:With 46 to 48 pounds of compression it should barely be able to move itself, and blow a lot of oil smoke.

I'm taking it that these are bad numbers, but is there any reason why all four would give reading so similar?
Steve didn't say if these were wet or dry tests, but are these numbers way out of spec for a dry test?
I can understand low readings on a couple of cyinders, but the part about all of them being so close is confusing.
The only thing I can think of is using electrical tape to seal the spark plug openings gave artificially low numbers, and the true compression is a lot higher.
What do y'all think?

Steve, if you are able to get a gauge that fits, please let us know what results you get.

I've got a feeling he has good compression on all four cylinders, but I am definitely not a mechanic!

Re: 1941 A-How many lbs. psi on compression test?

Sat Feb 07, 2009 10:25 am

I'm taking it that these are bad numbers, but is there any reason why all four would give reading so similar?

The only thing I can think of is using electrical tape to seal the spark plug openings gave artificially low numbers, and the true compression is a lot higher.

I've got a feeling he has good compression on all four cylinders.
Could be a couple of reasons that the compression numbers are so similar. My thought is that the electrical tape is a big part of the problem. Also, that the true compression readings - dry then wet will be higher.

The fact that the current compression numbers are "even" is a good thing. If the results from the full compression test result in low "even" numbers - then I would suggest starting the engine and operating for a while (a number of hours). Adding Seafoam to the crankcase and gasoline. See what happens.

Re: 1941 A-How many lbs. psi on compression test?

Sat Feb 07, 2009 5:50 pm

I should add a couple of hints to this mystery. The engine is hanging on my engine stand and I was cranking it by hand with crank. This was a dry test.
I am going to test it again tomorrow with the correct adapter on a compression gauge and I'll squirt some oil in the cylinders and do it again. I'll fill you in on the results after I'm done.

Steve

Re: 1941 A-How many lbs. psi on compression test?

Sat Feb 07, 2009 9:22 pm

hook up a battery and starter, hand cranking turns it to slow.

Re: 1941 A-How many lbs. psi on compression test?

Sun Feb 08, 2009 8:44 pm

battery crank compression test, for sure. but with the motor already in a stand, i would not hesitate to look inside and see what's up. where you stop depends on what you find and if your block can be welded.