Compression Check

[dirt1bike]

I was told that I had poor compression in cyl. #3 on a 4.3L OMC after replacing a head gasket. The boat overheated due to a worn rubber water propellor. I overreacted and pulled the motor. When I pulled the heads off everything looked OK. No scour marks on the walls, no gaps around the piston, everything looked OK. Could a bad adjustment on the valves been responsilble? The main question that I have is can I do a compression test with the engine out & sitting on the floor? I would think that it would be OK? Any thoughts will be greatly appreciated

 

[Backlash]

Re: Compression Check

Hey Bart,<br />Yes you can test the compression on the engine without re-installing it in the boat. Yes valve maladjustment could cause low compression. If the valves are adjusted too tight, they won't fully close & low compression will result. How low was the compression in #3? How does it compare to the rest of the cylinders?<br />Backlash

 

[its-a-sweater]

Re: Compression Check

BART,<br /><br />THE 4.3 GM ENGINE HAS HYDRAULIC LIFTERS. IF THE LIFTER WAS COLLAPSED IT WOULD KEEP THE VALVE CLOSED NOT OPEN. THERE IS NO VALVE ADJUSTMENT PER SAY. IT IS SIMPLY A TORQUE SPEC. ON THE INSTALLATION OF THE ROCKER ARM NUT.

 

[clanton]

Re: Compression Check

Heads still off? Check the valves.You also need to adjust the valves after you reinstall the heads. Clymer manual has instructions, same as 350 chev 3/4 turn on rocker arm nut, after all slack out of pushrod, with lifter on bottom of cam ramp.There is chart in manual for adjustment, set engine TDC adjust half of the valves, turn engine 360 degrees adjust the other half.

 

[dirt1bike]

Re: Compression Check

Thanks for the input. I do have the heads off and will re-install in the next few days & re do the compression check. Can I test without the push rods installed which should then keep the valves closed? I had the heads redone so they are OK. I was confused about the comment on the hydraulic lifters. My OMC manual mentioned the adjustment as descibed above. Maybe that is for a different 4.3L. Again thanks for your responses.<br />Bart

 

[its-a-sweater]

Re: Compression Check

Sorry for the valve confusion. I didnt mean adjustment like a solid lifter or overhead cam where you would use feeler gauges.<br />All your doing by turning the rocker arm nut down is setting an initial backlash. The hyd. lifter takes up the rest of the slack.

 

[clanton]

Re: Compression Check

If you do compression test with pushrods out, cylinder will not get air thru intake valve, very low compression. Look real close in the Clymer manual for the V6 specs easy to miss.

 

[Joecol]

Re: Compression Check

If you find that the valves are OK and adjusted properly then I would start looking at stuck piston ring or rings in that low cylinder. Just a thought????