Checking compression

[Boston Habba]

Have pulled the power head from my 1987 175hp V6 OB. It's sitting on my work bench. How do i check compression without reattaching the power head to OB.<br /><br />Thanks

 

[CU2NITE]

Re: Checking compression

I don't think you can, I believe there is two heads on your motor, one on each side. Get new gaskets torque them down and run the compression test. The test is done through the spark plug holes while the motor is cranking(not running). Good luck and let us know.<br />CU

 

[The Marine Doctor]

Re: Checking compression

Set the powerhead and bolt it in place so that the bottom of the crank will not touch anything and it won't bounce around.<br /><br />Once you feel that its stable...connect a battery directly to the starter and a good ground on the block. It should then turn over and allow you to check the compression.<br /><br />TMD

 

[jdkzrt]

Re: Checking compression

If you do it on your bench, I'd like to hear how you managed accomplish this.

 

[Xcusme]

Re: Checking compression

I don't think he removed the 'heads' ...he removed the whole power head.....

 

[CU2NITE]

Re: Checking compression

I think your right, my mistake!

 

[Boston Habba]

Re: Checking compression

Yes the powerhead is off. Before I pulled it, the compression was good. I just want to make sure that everything is OK before I put the head back on.<br /><br />Some Background. It's a Merc 174hp V6 1987. Engine was stalling at low speed, hard to start, backfiring. While doing a cpmpression check found water in #1 cylinder, replaced the head gasket on that side but found small nicks in head, cylinder and piston looked ok. Couldn't find any debris in cylinder and the cylinder an. Replaced head gasket. Checked compression all 6 between 120 and 125. Seemed like I had it fixed until I tried starting it. Had all of the same problems and one new one. Engine made a distinct metal on metal knock or rapping sound. Mechanic who heard it said, "somethings broke, get a new powerhead". Don't have the $$ so I'm opening it up to see what's up.

 

[trumanlake]

Re: Checking compression

Pull the exhaust cover off and look directly in the exhaust port to the side of the piston and see what it looks like. If it was like my 200hp when I blew a head gasket, it should probably show signs of scraping and probably a little black on the sides. By looking at the top of the piston and the cylinder walls it looks good, but.....it was toast! Bore one and sleeve.