Just did a compression test yesterday and I would like to know what is a good compression. Each cylinder compression was at 160 PSI and higher. I have a stock LG4.

Thanks!

 

LG4s in good shape should show around 180-190 psi on all cyls.

Look for consistency among all 8; no more than 10 psi or so from lowest to highest. That's more important than the absolute number itself.

 

So basically if they were all in between 160 to 170 PSI it’s in decent shape? The reason I’m asking is because I’m thinking of taking the heads off and sending them a shop to have them rebuilt (valve job /smoking at start up) but I wanted to make sure the bottom end was still in good shape.

Here is how I did the test. I could not start the engine to warm it up because the carb is being rebuilt. Took all the plugs out and disconnected the electrical connector on the distributor. Check compression one by one. Is it a big thing that the engine was not warmed up?

Thanks!

 

Re-test all the cylinder and after all they are all in the range of 175 PSI. I wasn't cranking the engine enough. I guess I can consider the bottom end in good working order.

 

If it smokes on a start, then it's a seal issue and not valve failure. Seals can be done on the engine.
Also with a cranking pressure check, was the engine cold or hot and was the throttle being held wide open during cranking.

 

The engine was cold and I couln't held the throttle wide open because like I said the carb was not on the engine. Without the carb on I guess you can actually say that the throttle was wide open can you?

 

If they were all 170-175 psi on a cold motor, I'd call it good.

Readings will be somewhat higher if the engine is warmed up; because then it's taking in cool air, and warming the air up after it's already in the cyl, which adds to the reading. If you had a stock LG4 and the readings were 160 psi on a hot engine, that wouldn't be so good.

 

Thanks RB83L69. I'm glad that the bottom end is still good.