View Full Version : compression test

09-22-2005, 10:24 PM
how do i do a proper compression test on my stude? i've been wanting to learn, i've read a few things about how to but would like any input from you guys.

09-22-2005, 10:43 PM
i remember there was a site that has all the studebaker engine specifications but for the life of me i cant remember how i found it, or where it was. i just moved into a new place so right now my shop manuel is now where to be found.
the engine is a 170 ohv, 63

09-22-2005, 11:30 PM
Have you got a compression tester (gauge)?
I usually prefer to have a helper to turn the key since the time my gauge blew out of the plug hole and past my ear at about 90 mph.
Pull off your coil wire so the engine can't start,check one cylinder at a time with your gage.Hold it in tight against the plug hole.

09-23-2005, 12:06 AM
I use the kind of guage that screws into the spark plug hole so you don't have to hold it at all. It just goes fingertight by twisting the rubber hose. Do the test twice on each cylinder. The first time, just screw in the guage and rotate the engine one revolution. Remove the guage and record the reading. Next, put a couple of squirts of oil into the cylinder and repeat the operation. Record that reading. If the difference is a lot, you probably have worn out piston rings. If the compression is low on one or two cylinders and not the others, you have some other problem with those cylinders, maybe valve problems or head gasket problems. You can tell a lot with a compression guage.

09-23-2005, 12:55 AM

I don't rotate the engine only one revolution when testing compression; I crank it until the gage stops rising, and I think that is pretty much standard practice. It takes a finite amount of time for air to rush into and fill that rubber gage hose, and there's not necessarily enough time available on one compression stroke. Typically the gauges will make a big jump on the first stroke, a moderate one on the second, and the subsequent ones will be incremental. I usually crank for about 4 or 5 revolutions. Basically you are stabilizing the gage at the peal pressure the cylinder is capable of making at cranking speed.

Same drill for a "wet" test.

Gord Richmond, within Weasel range of the Alberta Badlands

09-23-2005, 08:08 AM
Take all plugs out, Screw the compression gauge into a sparkplug hole, I use a remote starter switch ( not expensive and it is a breeze to use ). Rev the engine several revs and take a reading. I have been told to do this on a hot/warm engine. Take a reading on all holes. The oil trick is a good idea for a second time through.

Mike Van Veghten
09-23-2005, 10:20 AM
VERY important...........

Lock the carbuetor fully open, you might remove the coil wire also.

09-23-2005, 10:51 PM
mike what do you mean lock the carb fully open? do you mean keep it at wide open throttle. wont that just flood the engine?butch

09-24-2005, 09:51 AM
For a compresion test flooding is not an issue, good question. If all plugs are out does the carberator need to be 'wide open'? Yes, ground the coil by puling the big wire off . I pull it out of the distributor and ground it.

09-24-2005, 10:23 AM
I always remove all the spark plugs,the coil wire, and hold the throttle open.
I like the engine cranking without compression resistance, except on the cylinder being checked..
If you did NOT remove the spark plugs, your starter motor is fighting against compression and the carb is seeing manifold vacuum and fuel is being pulled in. There won't be any vacuum per se` to allow fuel to go into the manifold.
This way the readings will all be similar and the battery will last longer, and the starter will see less strain.

quote:Originally posted by cosmo

mike what do you mean lock the carb fully open? do you mean keep it at wide open throttle. wont that just flood the engine?butch

DEEPNHOCK at Cox.net
'37 Coupe Express
'37 Coupe Express Trailer
'61 Hawk

09-24-2005, 10:54 AM
ok, i think i get it. thanks alot guys.