Compression test engine outside of car Options

[Hammy]

I have an engine I need to do a compression check on... The engine is about 2 feet off the ground, each side of the engine mount bar is supported on blocks and there are two jack stands under the rear of the case. I have a spare tranny and starter to use...
Anyways, will this be safe? Or not a good idea?

[Twystd1]

I have an engine I need to do a compression check on... The engine is about 2 feet off the ground, each side of the engine mount bar is supported on blocks and there are two jack stands under the rear of the case. I have a spare tranny and starter to use...
Anyways, will this be safe? Or not a good idea?

Hell, I would do it in a heart beat..... Just stick sumpin under the tranny tail. And have at it.

I usually do this with the engine and tranny on the concrete. The HEs hold it up.
The engine won't torque hardly at all. Have no worrys.

Make sure ALL 4 plugs are out. Throttle is wide open. And have at it.

Be aware that your compression check is being done on a COLD engine. And the accuracy of this won't be anywhere near perfect.

Yet it will tell you if you have a bad cylinder or cylinders. And that would result from valve issues or ring issues. or both...........

It will also tell you how close the cylinders are in compression.

If you get a low cylinder. Toss a couple squirts of oil into that one cylinder and see if the compression comes up. If it does. Thats a ring issue.

Might also be a good time to do a leak down test. Which is MUCH better than a compression test. If'n you have one.

Cheers,
Clayton

UUhhhh...... How long has this engine been sitting???? And is it a known engine?

[Hammy]

I have an engine I need to do a compression check on... The engine is about 2 feet off the ground, each side of the engine mount bar is supported on blocks and there are two jack stands under the rear of the case. I have a spare tranny and starter to use...
Anyways, will this be safe? Or not a good idea?

Make sure ALL 4 plugs are out. Throttle is wide open. And have at it.

Be aware that your compression check is being done on a COLD engine. And the accuracy of this won't be anywhere near perfect.

Yet it will tell you if you have a bad cylinder or cylinders. And that would result from valve issues or ring issues. or both...........

It will also tell you how close the cylinders are in compression.

If you get a low cylinder. Toss a couple squirts of oil into that one cylinder and see if the compression comes up. If it does. Thats a ring issue.

Might also be a good time to do a leak down test. Which is MUCH better than a compression test. If'n you have one.

Cheers,
Clayton

UUhhhh...... How long has this engine been sitting???? And is it a known engine?

Thanks Clayton..... That's exactly what I want to do, see if there are any issues. How much of a difference would a hot engine have compared to cold?
According to the seller it's been sitting 4-5 months. I literally just bought it. Not really known as far as condition, but said it pulled strong. I took a gamble, at the very worst I break even since I got a good price.

I have all the tin off and intake is all off, plugs are all out. Is this ok to test it this way (bare intake)? Or should I put it back on for the test?

[sww914]

I'd say leave the intake off, you're supposed to do a compression test with the throttle wide open anyway. It doesn't get any more wide open than that.

[Twystd1]

YUP... What he said.

I have seen stock, used 2.0s that ran bitchin and only showed around a 120lbs of compression. COLD.

A typical deviancy from hot to a cold test can be as much 25%. Possibly more.
And possibly less.

Post up all your numbers here and let us know what you find out.

By the way. If you have an air compressor. Or have easy acess to one. Bum, borrow or rent a leakdown tetser. You will be MUCH farther ahead of the knowledge game.

If'n you wanna know more about it. Use Google. Do a bit of homework on leakdown testers and their use. They are a great addition to any tool box if you play with used engines or need to test a "JUST BUILT" engine.

NOTE:
MAKE SURE YOUR ENGINE HAS OIL IN IT IF YOU ARE GUNNA SPIN IT. I DON'T CARE IF IT'S CRAP OIL. THE CRANK MUST HAVE OIL IN IT TO KEEP THE RINGS LUBED A BIT AND TO GUARANTEE THE BEARINGS AREN'T TOO DRY.

dats it folks...

Claytonobitch

[BK911]

Skip the compression test. Do a leakdown. It will tell you more and is much easier and safer. You can build a leakdown tester for about $15.

Like others have said, make sure there is some oil in the case. Spin the crank a few times, then have at it. Should take less than 5 minutes.

[Spoke]

Harbor Freight has one for $39.99. Is this one any good?

Harbor Freight Leak Down Tester

I too have an engine out of the car that I'm prepping for the red 914 and would like to do a leak down test on it.

Thanks,
Spoke

[Hammy]

Skip the compression test. Do a leakdown. It will tell you more and is much easier and safer. You can build a leakdown tester for about $15.

Like others have said, make sure there is some oil in the case. Spin the crank a few times, then have at it. Should take less than 5 minutes.

I have a small compressor I can use... Any info on how to build one?

[BK911]

Google is your friend, my friend.

This is similar to the one I use. I set my compressor to ~75psi and the leakdown regulator to 50. When you plug it in the new reading will be less than 50. Double the difference and that's the leakdown.

http://www.650motorcycles.com/LeakDownTester.html

Have fun!

[BK911]

This one is better, it has grainger part numbers:

http://www.kartingtechinfo.com/tech/leakd.htm

[Hammy]

Uh.....having a blond moment. How should I wire up the starter outside the car? All I'm getting is a click (known working starter/solenoid). I have a charged battery....

[Hammy]

Nvm got it figured out (IMG:style_emoticons/default/rolleyes.gif)

OK compression results:

1 - 125 psi
2 - 165 psi
3 - 140 psi
4 - 140 psi

This is a stock 1.7

Ok so major inconsistent. This is before I've even touched the valves and with the engine cold...
So what am I up against here?

[BK911]

You have to do a leakdown to see where the problem is. That'w why I don't bother with compression checks. A leakdown is easier to do and it tells you more. A compression test basically just tells you if you need a leakdown or not.

[Twystd1]

Set the valves and do it again.

Just for shits and grins. Put a quarter of a shot glass of motor oil through the spark plug hole of each cylinder. Spin it with the starter motor 4 or 5 revolutions. THEN give it another compression test.

Then post up those numbers. I would like to see what you get.

In a perfect world. On a used engine. ALL 4 cylinders would be within 10% of each other.

Lets see what a little engine oil in the cylinders will do to your test.

STILL, A leakdown test will give you MUCH MORE pertinent data.

But if thats all ya got.. Run with it.

Clayton

[GWN7]

A wet compression test should be used when cylinder pressure reads below the manufacturer's specifications. It helps you to determine what engine parts are causing the problem. Pour approximately 1 tablespoon of 30-weight motor oil into the cylinder through the spark plug or injector opening, then retest the compression pressure.

If the compression reading goes up with oil in the cylinder, the piston rings and cylinders may be worn and leaking pressure. The oil will temporarily coat and seal bad compression rings to increase pressure; however, if the compression reading stays about the same, then engine valves or head gaskets may be leaking. The engine oil seals the rings, but does not seal a burned valve or a blown head gasket. In this way, a wet compression test helps diagnose low-compression problems.

Do not put too much oil into the cylinder during a wet compression test or a false reading may result. With excessive oil in the cylinder, compression readings go up even if the compression rings and cylinders are in good condition.

Compression levels must not vary more than about 10 to 15 percent (30 to 50 psi). Look for cylinder variation during an engine compression check. If some cylinders have normal pressure readings and one or two have low readings, engine performance is reduced. If two adjacent cylinders read low, it might point to a blown head gasket between the two cylinders. If the compression pressure of a cylinder is low for the first few piston strokes and then increases to near normal, a sticking valve is indicated. Indications of valve troubles by compression test may be confirmed by taking vacuum gauge readings.

[Hammy]

I'm lookin for a leakdown tester...

New #'s after a valve adjust:

1 - 155-160 psi
2 - 175 psi (WTF?)
3 - 155 psi
4 - 155 psi

I didn't get a chance to try the oil trick yet.

More consistency now... But #2 is still reading higher than the others. Is this a problem and/or what's the problem?

[GWN7]

It's within 10%-15% of all the others and they are "up there". I'd just drive it.

[Hammy]

It's within 10%-15% of all the others and they are "up there". I'd just drive it.

(IMG:style_emoticons/default/smile.gif)

[Twystd1]

Like the other fellas said.........

Drive that bitch... Period.
The high cylinder in this case. Doesn't mean much for you because of cost and application.

This ain't a race engine. It's a used engine. The compression check tells me that unless something is wrong internaly. That sucker oughta run ok.

So there ya are...... Run it..........

If'n it pukes and dies... YEAH...!!!!! You get to learn how assemble to a Raby Kit...!!!!!

Hey Bruce... Where did you copy and paste that from...?????????

Cheers,
Claytonovich

[GWN7]

Copy & paste?...I know a thing or three (IMG:style_emoticons/default/smile.gif)


Google is your friend .....search for "wet compression test"

link was http://64.78.42.182/sweethaven/MechTech/Au...=7&modNum=6