Low Compression - keep trying or rebuild?
 

I'm finally getting started on the 34 pickup I inherited from my Grandfather. I had hopes of getting the 59A engine that is currently in the truck running without major engine work, but hope is fading. The initial compression test was pretty dismal, but compression has improved somewhat by squirting oil into each cylinder, cranking it over and letting it sit for a few days. Currently compression (in psi) on cylinders 1 to 8 is 70, 65, 40, 35, 40, 60, 42, 25. I know it ran when it was parked, but that was 1972, and I can't vouch for how well it ran.


My question: should I throw in the towel and rebuild it, or try additional steps to bring up the compression. Suggestions for other things to try are welcome.

Re: Low Compression - keep trying or rebuild?
 

Could be stuck rings / valves . I'd stick new oil in it , add water and fire it up . Run it for 1-2 minutes, shut it down , check oil water let cool and repeat . Do it a few times , see if the compression comes up . Heat and movement should give you the answer you need .
If you hear any thunks shut it down .
If you don't want to do that. At least remove the intake and heads , examine and check condition. If it all looks good reinstall and go back to first suggestion of running for a minute or two .

Re: Low Compression - keep trying or rebuild?
 

My 34 has a stock engine,that has low compression, it would not pull a maggot off a pork chop, but it runs very nice,is a smooth as ,and will run a 60 mph all day on the hiway,
Lawrie

Re: Low Compression - keep trying or rebuild?
 

Did u use the procedures outlined in posts here and other places for "steps to start an engine that's been sitting a long time" before u turned it over the first time?

Re: Low Compression - keep trying or rebuild?
 

Like posted, could just be rings or valves not sealing due to long storage. Try something like MMO in the cylinders and let it set a bit. Run it a bit to see if it continues to improve.

Re: Low Compression - keep trying or rebuild?
 

Go for the gusto! Fire that puppy up!....

Re: Low Compression - keep trying or rebuild?
 

we will assume that the engine was warm, the throttle was wide open, all plugs removed and you let it spin for 4/6 revolutions. if this resulted in that low a compression then you can try a couple of things--what was the vacuum when the engine was running? 20 inches? if not do you hear a popping sound out of the carb or tailpipe? indicates a valve problem. I would soak the engine with a mixture of acetone/ATF after a few days then I would squirt some oil down each spark plug hole, put the plugs back in and fire it up. and see what happens

Re: Low Compression - keep trying or rebuild?
 

Probably should have done what alanwoodieman said before turning it over the first time. Now that that horse left the barn u should do it now. I recently used a combo of wd40 penetrating oil, kroil, atf & diesel fuel in all cylinders & let it marinate 4 a week. Engine turned with starter motor easily after not being started & stuck for 20yrs. Drained all put new Plugs, oil & filter & she fired up. ran a few times 4 5 minutes. did compression check & all were 118 to 123, still runs fine. Good Luck!

Re: Low Compression - keep trying or rebuild?
 

I drove my 40 with 65 lbs of compression on 7 cylinders and 35 lbs on one for ten years. Get it running and then decide what your goals are. A poor compression driver is a lot better than a car you cant drive.

Re: Low Compression - keep trying or rebuild?
 

Thank you everyone for your words of encouragement. I am following the Van Pelt instructions for starting an engine for the first time, and have not tried to fire it up yet. I still have to get some ignition parts (new condenser) and get some gas to the carb (rusted out gas tank). The engine turned by hand easily, so I have just squirted oil into the cylinders through the spark plug holes and turned it over with the starter. Based on what you all said, I'll get the parts I need and give it a go. The radiator is disconnected currently and I am trying to decide if I should replace the water pumps before I put on new hoses and reconnect the radiator. One of the pumps turns easily by hand, the other is a little stiff but can be turned. There is also a lot of flaky rust visible in the pumps.

Thanks again everyone for your suggestions.

Regards, Jim

Re: Low Compression - keep trying or rebuild?
 

What do you mean by "soak the engine with a mixture of …" ? Could you be more specific? Any additional info is much appreciated.

Regards, Jim

Re: Low Compression - keep trying or rebuild?
 

MMO is one agent you can use, but a mixture of acetone and automatic transmission fluid is also good. These two and several other suggestions were provided in the previous post. The idea is something that will penetrate into tight spaces such as between the rings and the piston and around the valve stems. The method you used to check the compression is only good for a rough measurement. To get a better reading need to follow the recommendations posted above. You can fire up the engine without any water in it, but can't run it for very long.

Re: Low Compression - keep trying or rebuild?
 

if you have sticky rings and valves then Marvel Mystery Oil is your friend. Put a good dose in each cylinder and let that marinate for several days while turning the motor over by hand a couple of times in the interim.


I did this with a modern OT motor that had been sitting idle for several years that I bought for an old truck project. When fire up day finally arrived I found that the compression was so low that it wouldn't start. I used the MMO process and after a few days i removed the spark plugs and spun it over with the starter to blow out the excess oil, put the plugs back in and she started!! on about 5 cylinders, but the longer it ran the smoother it got and after about 15 minutes it was purring like a kitten, and after 25K miles it still does.
Good luck......

Re: Low Compression - keep trying or rebuild?
 

50% acetone
50% automatic trans fluid of your choice

Re: Low Compression - keep trying or rebuild?
 

Not all ATF is equal. Some brands mix more readily than others. You may want to test some first.

Re: Low Compression - keep trying or rebuild?
 

Compression ratio is calculated as 15 divided into compression psi pressure. An 8:1 cylinder would be 120/15. An 6:1 cylinder would read 90psi. You highest reading of 75psi means CR of 5 ??? If I recall correctly it takes a CR of 4 to ignite the gas. So either you have a not really working engine or a bad pressure gauge. More likely the latter.

Borrow a friends gauge and make certain you have a fully charged battery and turn the starter over for 4-5 revolutions and get new readings.

Re: Low Compression - keep trying or rebuild?
 

A friend used a product called Penetrol on a Model A and it worked GR8. Anyone else use it or know if it is still available?

Re: Low Compression - keep trying or rebuild?
 

After reading this, I don' believe that you have gotten the true compression readings from your engine. I suggest that you try to beg, borrow, or steal another (hopefully good) compression gauge. Then follow "alanwoodieman"s procedure exactly. Do it twice, once with each gauge. Then come back and tell us what you got. You might be pleasantly surprised

Re: Low Compression - keep trying or rebuild?
 

I'll see if I can track down another compression gauge. This one is a brand new Bosch brand, so I would hope it's accurate, but you never know.

Re: Low Compression - keep trying or rebuild?
 

Make sure you block the throttle open when making the test.

Re: Low Compression - keep trying or rebuild?
 

1. Charge the battery if the battery is not fully charged.
2. Disable the ignition system.
3. Disable the fuel injection system if applicable
4. Remove all of the spark plugs.
5. Block the throttle plate wide open.
6. Start with the compression gauge at zero, and crank the engine through 6 compression strokes (6 puffs).
7. Make the compression check for each cylinder. Record the reading.
8. If a cylinder has low compression, inject approximately 15 ml (one tablespoon) of engine oil into the combustion chamber through the spark plug hole, recheck the compression and record the reading.
9. The minimum in any one cylinder should not be less than 70% of the highest cylinder.

Interpreting the readings.

• Normal: Compression builds up quickly and evenly to the specified compression for each cylinder.
• Piston Rings Leaking: Compression is low on the first stroke. Compression builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
• Valves Leaking: Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you ad oil.
• If two adjacent cylinders have lower than normal compression and injecting oil into the cylinders does not increase the compression, the cause may be the head gasket leaking between the cylinders.

The above from > http://gregsengine.com/cylinder-comp...n-testing.html

Re: Low Compression - keep trying or rebuild?
 

Thanks petehoovie. Had done the first 8 steps. The last 4 bullet points are really informative.

Regards, Jim

Re: Low Compression - keep trying or rebuild?
 

If it were me, I'd look at it like this:

I could pull the motor and rebuild it.

Or I could get it running and drive it.

Driving it will do one of two things.

It will improve with driving, any smoke or other bad symptoms will clear up and it will run as well as any other running flatty.

Or it will not run well, it smokes bad, runs rough, and smokes like a trooper.

If the latter, you pull the motor and rebuild it. You're no worse off than if you had done that in the first place.

If the former, you pat yourself on the back, compliment yourself on your judgement and revel in the fact that you saved yourself a load of expense and time.

It's a win / no loss situation, you may as well just fire it up and stop worrying.

Mart.

Re: Low Compression - keep trying or rebuild?
 

^^^^ that’s some AWESOME, PRACTICAL advice right there^^^^^.......Mark

Re: Low Compression - keep trying or rebuild?
 

Excellent advice!

Re: Low Compression - keep trying or rebuild?
 

I have to agree. When I got my '40, 40 years ago. It seemed tired. I built a new motor, and before I made the change over, it got better and better. That motor sits on a stand still waiting for the other one to decline.

Re: Low Compression - keep trying or rebuild?
 

Compression is over rated.
https://youtu.be/1l-oUqnHBTU

Re: Low Compression - keep trying or rebuild?
 

And when the test is done, don't forget to take the brick off the accelerator before pushing the starter button! Don't ask.....

Re: Low Compression - keep trying or rebuild?
 

I’d pay money to see the look on your face when the motor started!!!....Mark

Re: Low Compression - keep trying or rebuild?
 

Also, if it was mine, I'd pull the oil pan, clean all the crap and sludge out of it (there will surely be some) before you start it. In many cases the old oil will have coagulated and turned into a nice thick layer of goo (depending on the type of oil that was in it). Don't pump all that crap through the engine . . . or worse, ruin the bearings because they're not getting a good supply of oil on initial start up.

Water pumps: You'll need a good set anyway . . . so if it was mine, I'd have 'Skips' water pumps rebuild your originals -- he does an excellent job and you'll be very thankful that you used him. When I had the water pumps out of it, I'd try flushing hot water through the engine (from the upper radiator hose location on the heads). See how much rust and other crap comes out of it.

Ignition: - just take it off, clean the points with a point file, gap them and put a quality capacitor/condenser in it. Don't use an old vintage condenser - most of them have gone bad. Don't worry about losing your timing - the distributor used an offset "tang" so it will index when you put it back on. You may want to check the vacuum brake in it - taking it apart, making sure it is cleaned and operational, etc..

I would crank it over with 5 new quarts of oil in it, with the plugs out of it and do your compression tests. You can even crank it with 12 volts to really turn it over fast (I do this to get the oil pressure up). Before you start it - make sure you have oil pressure.

It may actually run quite well after it warms up a bit and things get a chance to "loosen up and seal". You will probably need a new fuel pump - I'd recommend having CharlieNY (on this site) rebuild your original --- so it has the proper springs and diaphragm materials in it. Most of the "new" pumps have the completely wrong pressure settings. Once you've done the compression tests, started it and ran it through a few heat cycles - then recheck the compression and see what you have.

You may be surprised on how this old girl might run . . . I know I was with the 59AB in my 32 Cab - it had sat in an unheated garage for 55 years - I cleaned the oil pan, put a new oil pump in it, pulled the heads and put new gaskets in it, new water pumps, new ignition and fired it up. It ran pretty well for the next two years that I drove it. (While I built a new engine for the car). One thing others have said - it is a LOT more fun having your truck running and driving, while you find another engine to build for it. Just having something to drive gives one a LOT of motivation to continue on the project! It ALWAYS helps me!