How do you do it? I've got to go out and buy me a compression gauge...but how do you check it on each cylinder? Do you have to tear anything off or is there some other way? I'm ABSOLUTELY clueless here..but I'd like to check mine to see if it'll work right..not to mention that someone I know said that he's gonna talk to his Uncle for me..his Uncle owns a local performance shop, and supposedly if I let him document ALL of it and take plenty of photos of my car and feature it to promote himself, he'll cut me an insane deal on a nitrous kit and computer controller for it..WITH install...as in $100 or less possibly.. Needless to say, I'm not expecting anything to happen with this..but you never know. But point being...gotta check the compression out for that...not to mention I'd just like to know how healthy this engine is to begin with....this heavily vibrating idle and rough topend is starting to bug me.

-Brooks

 

1. Remove all your spark plugs (can't avoid it this time)

2. disconnect coil wire

3. Insert compression gauge into spark plug hole

4. crank engine (you will hear it cycling). have engine cycle 4-5 times

5. read gauge -- write down cylinder # and compression #

Repeat steps 1-5 5 more times

 

I had to take all the plugs out??? OOPS. Maybe that's why I got such high readings...

 

When I do it, I have someone watch the gauge and record the first reading, and the last reading. i.e. the first cycle and the fourth cycle. This way helps you tell wether or not you have bad rings or valves.

 

When you say crank engine..I assume you mean hold the key full forward to start and let the engine just turn over? I'll grab someone to help me with this...but I probably won't do it any time soon. Those spark plugs are a pain to get too, and I kind of didn't put enough dielectric grease on my plug boots...even though they're Taylor's and should be high quality...I'm paranoid since the last 2 times I tried to remove boots, they both ripped open. Manifold heat killed em. Dont have any boot protectors.

 

The hardest one to get the compression tester into is the number 3 hole, unless you get the hold in type. I have the screw in compression guage and it makes it a one person job that way. I really hate the hold in ones, i don't think they are really accurate. By the way, you can't tell if it's the rings or valves that are bad by just checking the compression. you have to do a leak down test to figure that out. All this does is tell you if you have compression.If you have a healthy seal, each cylider should be between 140 and 150 psi. If you find one that is dramatically low(100 or below) then you have a problem.

To do a leak-down test:
1. remove sparkplug in cylider to be tested.
2. Hand crank motor to TDC on same cylider.
shoot compressed air into spark plug hole. If you have the compression tester with the screw in hose and quick diconnect, you can hook you compressor right to it.
3. listen fo air escaping out of Intake, exhaust, and look for bubbles in the radiator and listen for air escaping from the oil cap.

Air from Intake = Bad intake valve
Air from Exhaust Pipe = Bad Exhaust valve <- I've had this problem
Air from Oil cap = bad rings
Bubbles in Radiator = Blown Head Gasket

Good luck

 

You don't have to remove all of them. You'll get different readings but it's still OK. Hell, you can even do a running compression test where you actually start the engine on 5 cylinders while checking comp. on the 6th one.

 

Screw in gauge is the best type for this.
And obtain a remote starter or make one.
You can do one plug at a time, no true need for removing all plugs at one, yet, THAT WON'T HURT EITHER!
DEFINETLY DISCONNECT COIL WIRE.
i aways did thetest per cylinder twice.
WHY?
Checking myself, that's all.
My last 3.4 I got at 50K miles was 150lbs per cylinder all across (upon tightening/adjusting the valves).
The one in my Firebird was a 44K mile mill & I got 175PSI at 5 cylinders & 200PSI at one.
I was content.
My 211,500 2.8 outta my Blazer, I got max 50PSI after I swapped headgaskets & heads.
Well, it was dead, Jim & but got my money's worth outta that 2.8 mill!
Atleast I was able to make Blazer move under own power (Instead of pushing it every other day!) across street for street sweeping in Communist Soviet Monica
And I did drive it into position for towing to my new home in the Big San Fernando Valley
So that job was worth it, just to lessen the pushing effort.

 

don't konw about an automotoive application, but on our planes we can simply listen to the parts mentioned above for air escaping after we crank the motor over. but, now that i think of it, we can hand crank the motors w/ the prop which places the engines at TDC for each cylinder, which would make it much easier. I'd say, hand crank the motor (if possible) to TDC for each cyl. And you should be able to hear any air that's whizzing past valves, rings, head gaskets, etc. Good luck again, and sorry this was worthless, but i've typed it now, so i'm gonna post it. lol.

 

Hmmmm that's probably better....



Actually you can... By squirting some oil into the spark plug hole and retesting it. If the reading goes up = rings. If the reading stays the same = valves

 

Now...proper compression readings should be between 140 and 150 right.....I assume it's bad if it's lower or higher.. Lower...bad seals or something or maybe deformed pistons, etc? Higher....some sort of buildup in the chambers??

 

140-150 sounds good. Any "low ones should still be within 10% of the others

EX: assume you do this and get these results

1 140
2 130
3 135
4 145
5 140
6 140

#2 is the lowest but is still acceptable

140/10=14

140-14 = 126 minimum

Feel free to correct me if I'm wrong guys!

 

Thats what I was told was 10% "tolerance".

As for 140-150 readings. Wouldn't that depend on how warn the engine is?? But I would say if its lower then 90 all around. Time for new block, rebuild, something.

I got readings from 125 to 85 on my old s10 block. Thats way off. Hence the reason I'm doing 3.4 swap