compression testing

[usmcruiser]

Okay I have seen every one saying that you need to check the compression of the engine wet and dry. But I have no clue how to do this. what is the difference between wet and dry.

I feel kind of like an ass asking but the only way to learn is to ask.

So how do you check engine compression?

Thanks,

 

[Ullr]

Dry - pull plug and check compression.

Wet - pull plug, add a a little oil through the spark plug hole, check compression.

the difference, if the compression number goes up when you add oil your rings are leaking, the oil temporarily plugs the leak. edit: well, soemthing in the cylinder is allowing air to pass on the compression stroke, not necesarily the rings

 

[fyton2v]

wet is when you squirt a bit of oil into the cyl you're testing. dry is when you don't.

 

[Poser]

Before checking compression...I would warm the engine up, and adjust the valves if they have not been done recently...

Good luck!


-Steve

 

[cabron]

also remember you dont need much oil for the wet test. A few drops should be fine. Also open throttle plate.

 

[Poser]

a few drops will only make the top of the piston wet....

 

[72FJ40LandCruiser]

also remember you dont need much oil for the wet test. A few drops should be fine. Also open throttle plate.

I always thought you should use about a teaspoon?

 

[fyton2v]

I always thought you should use about a teaspoon?

I just use a funnel.

When I tested mine last time I used my wife's turkey baster... and forgot to tell her. Do you guys have any idea how hard it is to find a store with a turkey baster on Thanksgiving day? It's hard.

 

[usmcruiser]

So do you just screw the gauge into where the spark plug was then manualy turn then engine over a few times and record what it says?

Then do it again after putting a tablespoon or so of oil in the cylinder?

 

[Ullr]

So do you just screw the gauge into where the spark plug was then manualy turn then engine over a few times and record what it says?

Then do it again after putting a tablespoon or so of oil in the cylinder?

Yes. You can get a remote starter for about $12 so that you don't have to have someone crank the engine for you. A tablespoon of oil will do it, turkey baster works great too

 

[2mbb]

So do you just screw the gauge into where the spark plug was then manualy turn then engine over a few times and record what it says?

Then do it again after putting a tablespoon or so of oil in the cylinder?

"manualy turn the engine", meaning turn the engine over using the starter motor. That's where the remote starter comes in handy. Its a momentary switch that you connect to the starter to allow you to crank the engine from under the hood. I usually let it turn over five or six times per cylinder, to get the pressure to stabilize on the compression gauge. I disconnect the coil lead at the distributor and ground it. I also remove all the spark plugs, so there is less resistance for the starter to turn against. I only do the wet test if I think my compression is low or otherwise not correct.

 

[andrewfarmer]

You should also hold the throttle wide open so there is no restriction on the air going in.