Compression testing an engine OUT of the car?

[AZhitman]

Can it be done?

I'm looking at an engine with 24K original miles, but it has been sitting for SIX years (was 2 years old when removed).

Want to make SURE it's not a bad motor, what can I do?

[elwesso]

just grab a battery and jump the starter if it has one on the engine... compression test that way.

[InsanityInc]

You have to use a starter. Compression numbers are all rated at ~300rpm.

[PoorManQ45]

Can't you just spin the crankshaft manually via the crank pulley bolt?

At max you'd only have to spin it four times to go through a complete cycle

[elwesso]

you had better be strong to turn the engine 300 RPM by hand......

*sigh*

[PoorManQ45]

Why does it have to be at 300 RPM?

Full compression should be reached during every power stroke

[AmoebAssassin]

Why does it have to be at 300 RPM?

Full compression should be reached during every power stroke

Not true, the slower you rotate an engine the more time compressed gasses have to leak past piston rings.

Remember that piston rings do not form a perfect seal against the cylinder walls and some of their pressure holding ability relies on proper oiling, which you cannot achieve without proper engine RPM.

[Q45tech]

Also the engine coolant, block, and rings [plus oil] must be at operating temperature to use the FSM compression spec.Why many higher mileage engine smoke and shake when cold until they warm up ----low compression temporarily.

[Ezekial]

mate just do a cylinder leakage test!

TDC and valves closed (compression stroke) on the cylinder you are testing

and listen or feel for air coming back out the inlet or exhaust port (valve seating problems or bent valves)

and listen or feel for air coming out the rocker cover breathers (rings problem, head gasket problem)

an engine that old though ... i think its safe to say you'd have to rebuild it before you put it back in ... i'd be checking all the valve spring tensions as well ... if it hasnt been turned over regularly in 6 years

[raremotive]

You can even start the engine out of the car for a short bit if you wanted.

There's two ways you can test. One that's mentioned above would get actual compression numbers and leak down. But that takes time to get the starter to work.

The other is a leak down test mentioned above, where you can bring a pressurized tank and you plug it in the spark plug hole. The hose is equipped with a pressure gauge. Let the pressure in by means of a switch valve. Turn the valve off. Watch the gauge for rate of drop of pressure. Only difficulty is finding when all valves are closed. Also on a engine sitting for two years, you are going to expect a little more than usual leakage, until you add some oil yourself.

[scoobas]

just get jumper leads see if you can start it, when the engines hot do a compression test with dizzy unplugged (so engine don't start) and use starter to turn, the engine may be seized, if it is drop the oil out and refill with diesel leave it for a few days and turn the crank with brute force then when it's turning smooth again start with diesel in it for a few minutes n she'lll be good as gold!

[ARKQX33V6]

Do a leak down test with compressed air, more accurate the compression testing and does not rely on internal sealing of rings but will tell you about the condition of the engine. Compression testing if done to a cold engine without a charged battery will indicate low PSIG. Since this motor is isolated out of a car and complete, was it stored correctly, was gasoline left anywhere near it, was it in the cold, was it oiled, sprayed. Are valve assemblies still under spring pressure, have rings split or turned.

An engine improperly stored can be a nightmare of problems not even a compression test or leak down test can see. Scored crank, water or condensate internally...on and on it can go.

But if all your interested in is can it make compression do a leak down test and at least listen to the engine as it talks to you.

[AZhitman]

Holy ancient thread bump!