The Stovebolt Site Forums The Shop Area Engine Shop Compression test done, now what??

I just got done running the compression test on my burb. It has a mid-60s 250 in it. I got a new compression tester that you actually screw into the sparg plug holes to get an accurate reading. That and the remote start switch that I picked up made it a pretty easy task.

The results were:
1. 108
2. 140
3. 132
4. 135
5. 150
6. 140

Cylnders 2-6 seem pretty consistent. I am concerned about #1. Seems awfully low/inconsistent with the others. Also, when the engine gets up to speed there is a ticking noise from that area. I'm thinking it could be a hole in the head gasket or maybe a valve issue.

All that being said, I'm wondering if there is any problem with picking up a new gasket set and taking the head off to have a look. What should I be looking for? I'm afraid I'll overlook a major issue and not even realize it.

Once I'm done, can I just clean everything up and put it back together? Are there any issues/mistakes to avoid? The engine is pretty grimey and has a slow oil leak so I know it could use new gaskets all the way around. I'm thinking about just working my way through the gasket set to tighten everytyhing up. Anything special I should remember/do on the oil pan gasket or any others for that matter?

Sorry for the long list of questions.

Leak down test. That will tell you exactly what is borked. You might be able to get a loaner for autozone, or buy one for $50-100. I have the HF one and it works well.

Google leak down test and read up on what to look for. I would skip trying to figure it out with a vacuum gauge... they are only indicators of a problem... you got one, you need to figure out what end of the cylinder is the problem.

You might have a worn valve/guide, worn rings, a hole in the piston. Hard to tell without putting air in the cylinder and seeing where it comes out. With a reading that low I don't think its a head gasket... your exhaust would show smoke and after sitting your oil would have antifreeze in it.

Pfarber;

Hooah. Thanks. I'll have to try that.

I'll check Oriely's and see if they have a loner. If not, I'll go back to Harbor Freight to see if they have one. I just came from there. I got myself a new torque wrench for when I put everyting back together again.

Larry, I didn't relise you were in KC, I am out in Lee's Summit, we are neighbors!
#1 is low, the rest are just fine. Check the valve springs on #1 cylinder and make sure they are not broke. Next, grab the valve and spring and see if you can wiggle it around, you should not be able to. You can also try tapping the valve stem with a hammer (after you remove the rocker arm) and see if the valve is seating all the way. It could have carbon holding the valve slightly open. When you tap the valve, you should hear the valve shut pretty solid.

When you had the engine running, did you hear a miss or pop out the tail pipe or in the carburetor? Exhaust valves not sealing will make a constant miss sound in the tail pipe, intake valves let you know through the carb.

Leaking or broken rings will generally smoke while driving, most of the time you cannot see it, but you notice the oil level in the pan has dropped. Try adding a spoon full of oil or more to the cylinder and retest the compression. If it rises, then the rings are probably worn. A easy test with out spending money is retest that cylinder and not release the compression on the gauge, then put your ear up to the carb and listen for air hissing, then move to the tail pipe. If you hear anything, thats where the problem lies, if all is quite at the pipe and carb, listen real close down at the head, air escaping from the cylinder will hiss deep down in the block and you should be able to hear it. You may have to crank the engine some more to build compression again. A leak down gauge does the same thing only it has dials to show how fast its leaking. In your case it doesn't really matter how fast, you are only after wheres its going.

Joe

Larry, just figured out you can't listen for a leak using the compression gauge. I had one that would work like that, but it was old and probably broken. Rig up a air hose if you have one or use part of the compression gauge and blow air into the cylinder. You might have to rig up a spark plug adapter to your air source.

Joe

Joe;

Thanks for the tips. We need to get together. I'll send you a PM.

I have to give a shout out to a fellow Bolter. Joe H came by my house yesterday and spent about 3 hours working with me on my Burb. I think I learned more in three hours than I have in the last ten years. We diagnosed the idle/acceleration problem, set the timing, cleaned and lubed the distributor and cleaned and reassembled the carb. All in driveway in the weather at about 40 degrees with a whipping wind. It was fascinating to watch a real pro at work!! To top it all off, he even took my carb home with him to run it through the industrial solvent tank where he works so we can get it really clean. We pretty much decided that gunk somewhere in the carb is the root of my acceleration problem. Stovebolters are a great bunch!!!

Well-done! Enjoy driving your better-tuned truck.

Now you can "pay it forward".

-Michael