602 Crate - Low Compression On 2 Cylinders

[smokinjoe3]

I have a 602 crate motor that has 13 nights on it. I just changed valve springs and noticed it had a severe miss. Started by changing plugs, wires, cap, rotor, module and even tried unplugging the MSD box to make the miss go away. None of that worked so I got the compression tester out and #3 cylinder read 90 and #6 read 125, all other cylinders checked out at 150. The motor ran like a top the last time I had the car out to the track. Does anyone have any ideas on what is causing the low compression on the 2 cylinders? I am assuming it to be either rings or bad valves but really am hoping it isn't. Thanks in advance!

[rubbinsracin]

Sounds like rings.

[smokinjoe3]

What would cause the rings to get wore out after just 13 nights? The motor never ran above 220 degrees and the spark plugs seem to be burning ok. Also, does anyone know of a decently priced certified crate motor rebuilder around southwest Iowa?

[racinjj]

Are you sure you did the valve spring change correctly and didnt slap some valves on the pistons and bend them? Seems suspicious that this would happen right after you change springs.

[smokinjoe3]

It acted like it was missing before we changed valve springs so I dont think that is the case, I did not do a compression test prior to changing springs though. We pressurize the cylinders with air when changing the springs out to prevent them from dropping. With valve covers off everything seems to move up and down as normal and all rocker arm nuts are pretty well even across the head. I think its odd to have problems after just 13 nights on a motor, never had any issues with it at all. I really thought the Crate motor was the way to go in a sportmod but maybe I was wrong!?!

[Dirtrunner35]

If you have a port on the carb for vacuum , put a vacuum gauge on it and see if fluters

[smokinjoe3]

If it flutters or doesnt flutter what will that tell me? I will try this tonight, I am pretty sure my carb has a vacuum port on it.

[Dirtrunner35]

Flutters mean a burnt valve or valve spring issue

[usafracer]

Put 2-3 squirts of motor oil in each cyl just before you test it. If the psi goes up then it's rings. No change its valves.

[smokinjoe3]

Put 2-3 squirts of motor oil in each cyl just before you test it. If the psi goes up then it's rings. No change its valves.

What test are you referring to? Compression test or vacuum gauge test?

[usafracer]

Compression test.

[smokinjoe3]

Found out it was an intake valve hanging up causing low compression. Simply put air to the cylinder and smacked the valve a few times with a brass hammer, re checked compression and it was back to 150. Must of been a piece of carbon causing the valve to hang open just enough, did the same thing to the other cylinder and had the same results. Everything checks out and the motor seems to run great!! Thanks for all of your input, its apprecaited.

[jsf74]

have been doing that in airplanes for years. good luck.