Thread: Comp. testing motor on floor, safe or not??

First Happy Holidays everyone, I have one lowport engine that I bougth as spare, it came from a crashed G20 and the guy that sold it to me told me it was running when he pulled off but I want to know the state of health before I do anything with it. So I wanted to know if it will be safe to attemp a compression test with the engine in the floor. I know it doesn't sound safe

How are you going to attempt to perform a compression test? By hand? Do you not have an engine stand?

If it's a spare, why not just pull the lower/upper pans to check the crank, and pull the head to check the pistons and whatnot? It'd be a good time to go ahead and replace gaskets and whatnot. Have you popped the valve cover yet to see how the valvetrain looks?

Well somebody local needs the engine and if I open the head its going to need a new head gasket. Under the valve cover looks good no sludge or anything. I just want to be sure its withing specs if I sell it, I dont have an engine stand the engine is sitting in some a thick cardboard in the floor.

I don't know how easy it's going to be for you to do an engine compression test on the floor. You may just sell it as is, or ask the buyer to purchase it with a 24 hour return policy. It shouldn't take them a whole 24 hours to drop it in and test it out. Also shouldn't give them enough time to joy ride it and blow it.

Cold compression numbers suck anyway.

C

Hadn't thought about that. Can't say I disagree with you at all. The motor at operating temps would be more accurate, as any type of metal tends to expand when heated. Good call, Chris.

cold test shows a ton about the motor, if all 4 cylinders match and so on you know that the pistons/rings and such are all good and there was no major failures. But, you have to turn the motor to do it, so that means cranking or hand cranking the motor. It MUST be on a stand to do that.

Brent

Other than catastrophic failure, do cold numbers really tell you much? Even on good motors that are consistent across all 4 cylinders when warm, I've gotten varying readings when they were cold.

C

yeah I forgot about that the FSM specifies that engine must be warm up and I dont think hand cranking will cut it, it has to be tested at 300 rpms with a fully charged batteries. I'll take tekkies recomendation give a 24-48 return policy, I got the engine for real cheap anyway, thanks for the input thou.

How about a leak down test? The engine would still be cold, but it could be safely done if you have access to a compressor. It might provide some useful information.