The Stovebolt Site Forums The Shop Area Engine Shop I need some more sage like wisdom

I'm almost ready to fire off my truck.. Thought I would check cylinder compression before putting spark plugs in.. I found something I wasn't expecting.. All odd cylinders have no compression and the even had about 40psi.i I knew the truck hadn't been run in years so I am not surprised with low compression but all odd having none...

I'm at a loss... I'm sure some or all lifters might be stuck but not sure if that could account for this issue

Do not try to start the engine. If you indeed have stuck valves you could very easily bend a pushrod. Take the valve cover off and tap each valve with a hammer (don’t get heavy handed) to make sure they are all free. A shot or two of penetrating oil will help. Once you are sure all valves are moving do your compression test again. You may get lucky and find all is good to go. Hope they aren’t already bent. Good luck

Does turning the engine over cause damage also.. Because I did that for the compression test

Yes, best now to oil the valve stems and tap them with a rubber hammer or a 2 x 4. If bent, need to pull the head. Usually the pushrods bend before the rocker arms break.

Ed

Well I dont claim to be a sage, but hopefully the information below could be considered sagacious.

Before you start tearing everything apart, first try to roll the pushrods with your fingers. This can be done with only removing the valve cover. You will need to rotate the engine to get them all in a (loose) position off of the cam lobe. Bent pushrods if present will be evident. Oil the valve/valve guide contact areas liberally. Be careful with the hammer on the rocker arms, they are cast iron and crack easily.

Martin,


When you say tap the valves, do you mean tap the rocker arm on the pushrod side?

Paul,

Thanks for the information. I will roll the pushrods and see if any are bent. Other than stuck lifters, is there any other reason the compression test shows nothing on all of the odd numbered cylinders?

No, to do it properly and safely you need to remove the rockers. It can be done by striking the rockers but if you do it that way be sure to use some sort of shock insulator between the rocker and the hammer. 2X4 will work. Try Paul’s suggestion first.

Anything that rotates the engine is potentially damaging, unless the intake pushrods are completely free.

When the guys are saying tap the valves, they mean on the valve stem to be sure that the valve isn't seized up in the head. You want to tap to insure that each valve will come off it's seat when you eventually turn the engine over.
[on edit] I see you've already turned the engine over for a compression test. You could have valves that are stuck in the open position, which would cause low compression. Tapping on the stem could free them up.

OK... Just a note... I pulled the oil pan to clean it out and pulled the valve cover to find TDC before doing the compression test... Even though it hasn't run in years.. The top end and bottom end still had oil.. I Even pulled a rod bearing cap and the journals still had oil in them

I use a plastic dead blow hammer to hit the rocker arm above the valve stem. As I am striking each one, I am watching for rapid rebound of the valve and a soothing clunking sound of a healthy valve contacting a healthy seat. You will need to manually turn the engine over a few turns in order to test all of the valves, as some of them will not be on their seats due to the camshaft.

Thanks 52carl. I will give that a try