Compression Testers

[Marty Rogan]

I would like to buy a compression tester. What should I look for in a

tester? Are there a couple of brands that are better than others? Where is

a good place to buy one?

What is the thread pitch and size for the spark plug hole?

Send along any other info that you would think helpful.

I have seen it done a couple of times, but did not get a good look at the

tools.

TIA,

Marty

[kmack]

Marty,

I haven't bought one yet, but I know others that have and have used them.

Most will come in a sort of kit, with different adapters for the spark plug

holes. The spark plugs on the L series engines are 14mm. I don't know the

thread pitch, sorry. The tester kit should have an adapter for this size as

it's a pretty common plug size.

Where to buy one: Sears, PepBoys, AutoZone, Advance, O'Riley's, etc....

PepBoys and Sears will probably be on the high side of the price range. I

have seen the testers for sale at Harbor Freight's website for $29, but I

haven't seen them in the actual store here in town. Worth checking out

though.

The process for using it is straight forward and simple. Plug the tester

into one cylinder, crank the engine over a few times (get at least 3 full

compression cycles) and the guage on the tester reads and locks the highest

pressure reading. Write it down and compare with the other cylinders and

diagnose your troubles.

Good luck.

[24OZ]

I haven't got or used one either but i have been told that there are 2 types. One has a connecter that screws into the spark plug hole and another you just push the connector into the spark plug hole and keep pushing while someone turns the engine..

I've been told to avoid the push in ones and go for a screw in one. Screw in ones are supposedly more accurate then push in ones as there is less chance for air to escape and therefore false readings.

[tanny]

Yes, the screw in type is much easier and you can test the compression without a helper. Victor. Be sure to warm up the engine before you test and take out all the plugs.

[Bambikiller240]

Originally posted by 24OZ

I've been told to avoid the push in ones and go for a screw in one. Screw in ones are supposedly more accurate then push in ones as there is less chance for air to escape and therefore false readings.

AMEN! Get the one with a threaded fitting, not the one with a rubber end that you press into the spark plug hole.

I want to say thread is 14mm X 1.25; but I may be wrong. It is a very standard metric size though, so you should not have a problem findin one that will work for you. I've had my Craftsman one for 25 years. Works great.

[beandip]

For sure the screw in type is the one to get. As far as the thread pitch I dont know but I bought a color tune and it is a 14mm:classic:

[Marty Rogan]

I'll definitely will go with the screw in type kit, as I will want to be able to do this myself.

Someone said that you should take out all 6 spark plugs for the test? I would have thought you would only do one at a time.

Also, I have understood that you should not have more than a 10% difference between the highest and lowest reading. Is there a bottom level reading where you would you should not go below, even if all six are relatively even?

TIA,

Marty

[tanny]

By taking out all the plugs, the engine will turn faster giving quicker read, easier on starter. Not absolutely necessary, but getting engine to operating temp is. Must adjust valve clearances before doing the test. Victor.

[Marty Rogan]

Ok, I understand. Just wondered if putting less load on the engine would affect the compression reading.

Marty

[72zcar]

yes, you must remove all the spark plugs for a accurate test. If not and there is a head gasket leak between cylinders you can get a false reading because the cylinder next to the one being tested with the spark plug left in will compress and show the inaccurate reading. Removing all spark plugs is a must...

[Bambikiller240]

Se FSM or Haynes manual for min / max specs on compression for your engine.