914World.com [Powered by Invision Power Board]

Posted by: monkeyboy Jul 27 2014, 01:21 PM

I pulled my motor out of the car to work on my Fuel Injection project.

When I pulled the motor I did a compression test. Cylinder 3 and 4 are at 115-120 PSI, and 1 and 2 are at 130 PSI.

Is that difference anything to worry about?

Leakdown is only 2-3 % on any cylinder.

Should I yank the heads and check the deck height since I have it apart, or is this not enough to worry about on a stock 2.0?

Posted by: malcolm2 Jul 27 2014, 01:27 PM

You did the test with the engine out? Someone will correct me if need be, but shouldn't that test be done cranking the engine, usually in the car? Maybe I mis-read and you did the comp. test before you pulled the engine.

Posted by: monkeyboy Jul 27 2014, 01:29 PM

I have an engine stand. An old bell housing with a starter on it. I can spin the motor out of the car.

I also had the whole induction off so there were no restrictions.

Posted by: euro911 Jul 27 2014, 01:45 PM

Perform a valve adjustment and a compression check again, Jim

Posted by: monkeyboy Jul 27 2014, 01:47 PM

Mark, I took the rocker arms off. I will try it again with no valves opening.

Would 15 PSI be enough to tear off the heads if it is indeed the case?

Posted by: euro911 Jul 27 2014, 02:42 PM

If you have the motor out and partially disassembled, half the battle is over.

If you have the time and a little play $, pull the heads and barrels, inspect the cylinder bores and check your rod play.

If the cam and lifters (and cam bearings) are OK too, you can re-ring it and lap the valves and seats (although your leak-down #s look ok). 15 #s is low though … it's only 8.5% of your highest compression reading (130 psi). I'd pump more in there to obtain a more accurate reading.

You've got a little homework to do.

EDIT:

I think I misunderstood - were you referring to the 130 vs 115?, or using 15 # to check your leak down?

130 is 13% higher than 115 and you'd like to keep lower than 10% difference

Posted by: monkeyboy Jul 27 2014, 02:48 PM

QUOTE(euro911 @ Jul 27 2014, 01:42 PM)

If you have the motor out and partially disassembled, half the battle is over.

If you have the time and a little play $, pull the heads and barrels, inspect the cylinder bores and check your rod play.

If the cam and lifters (and cam bearings) are OK too, you can re-ring it and lap the valves and seats (although your leak-down #s look ok). 15 #s is low though … it's only 8.5% of your highest compression reading (130 psi). I'd pump more in there to obtain a more accurate reading.

You've got a little homework to do.

Wait. I did my compression test and got 115, 120, 130, 130.

My leak down test was done at 100 psi and there was only 2-3 % leak down on any cylinder. I think I'm good there.

I'm not tearing into the bottom end. I have another motor that I'll build while I drive this one. I was just wondering if the 15 psi difference in compression would be worth tearing apart the top end.

Posted by: euro911 Jul 27 2014, 03:03 PM

See my edited post (above)

If you're building a new motor, I wouldn't worry about it now.

Let's see what you get when you re-test popcorn[1].gif

Posted by: monkeyboy Jul 27 2014, 03:05 PM

Got it. I'll keep you posted. Thank you.

Posted by: monkeyboy Jul 27 2014, 04:17 PM

Changed out the rocker arms and readjusted the valves. Brought everything between 125 and 130 PSI.

Thanks Mark.

Printable Version of Topic

Click here to view this topic in its original format

914World.com _ 914World Garage _ Compression question