3.0L Compressions is this a problem

[reavesga]

While tracking down a clicking sound coming from my 1974 3.0L Mercruiser I decided to check compressions. They were 120,100,90,120. Do the lower compressions for #2 and #3 cause problems? Is it time to overhaul? Clicking turned out to be a little rocker adjustment. Nothing big there. Thoughts on if it is time to tear down would be appreciated. If it is time to tear down anythoughts on tearing it down and putting in new rings or get short block instead?

 

[Rick Stephens]

Probably too expensive of a block to purchase. Better to ring and valve yours. Still costly, being as how the 3L is not used in autos. But short blocks cost you your first born.

Merc states 100 minimum. And lowest should be maximum 70% of highest. So the 90 psi is a bit low. Be fun to ring and valve it if it's in good shape.

Rick

 

[Fun Times]

Did you run the compression test hot or cold? After your repair, it may be worth re-testing just be sure. Also try injecting some oil in the cylinder/s to see if there are any changes.

Some compression tips for you if needed, http://www.freeasestudyguides.com/compression-test-injecting-oil.html

 

[jhobbs26]

heads up on the rocker adjustment. check to make sure the stud isnt pulling out of the head. Had this happen to mine. I ended up pulling the head and having a machine shop put in screw in studs on all valves. You can use a straight edge and the tops of all the rocker studs should all be level.

 

[reavesga]

Pulled the plugs and put some Lucas oil in cylinders. Then turned it over a few times to work the oil in. Then rechecked compression. 100 psi cylinder came up to 120 psi. 90 psi cylinder pretty much stayed at 90 psi. Sp guessing rings for sure and possible valves as well. I am assuming there is a link on here somewhere for what to do on a rebuild. I might as well dig into the rest of it if I pull the motor.

 

[Grub54891]

Compression did not change when you did the wet test? That would suggest a valve issue, not rings.
And no need to pull the engine if all ya need is a valve job. Just remove the head and bring it to a machine shop.

 

[Rick Stephens]

+1 Grubs


Do a valve adjustment before assuming anything.