Compression Check Help

[iwldntli2u]

Need help form all boat guru's.<br />1981 inline 4 Mercruiser 120<br />I just got done doing a compression check.<br />1# 115<br />2# 120<br />3# 118<br />4# 125<br />They all look good so I did a wet check and found most of them to only rise 2 - 7 pounds psi. My question is the vavle train is sounding kinda knocky Should I attemp to have the vavles adjusted or should I just pull the head and have the complete valve train redone? Any help will be apperciated.<br /><br />Thanks-

 

[FatBack]

Re: Compression Check Help

It's messy,but, this is what i do. Take the valve cover off get an old towel and wrap it around the head to contain the oil. Start the engine and adjust each valve by loosening till you hear it start clicking then slowly tighten 3/4 of turn. Do it on each valve. It is easier than rotating the engine by hand and all that top dead center stuff. But it is messy and you have to throw away the towel unless you got one of those fancy rocker arm covers with a hole in the top.

 

[FatBack]

Re: Compression Check Help

oh! Be sure and let the engine warm up first.

 

[FatBack]

Re: Compression Check Help

It also helps to turn the idle down a little too. Turn it back up when you're done.

 

[Seaboo2]

Re: Compression Check Help

I agree... Either have the valves adjusted or do them youself. The way Fatback described is not the correct way to adjust the valves (although it works, works well and I highly recomend it.... That's the way I adjusted valves when I was into hotrodding cars.... If oyu have a good ear you get a more powerful tune that way).

 

[iwldntli2u]

Re: Compression Check Help

Thanks guys you are awsome. Anyone else is welcomed.

 

[Boatist]

Re: Compression Check Help

Ski Rob<br />I agree you can do it that way but there is some danger. My 1980 OMC 140 is 1 turn down from zero clearance. You need to find out if 3/4 turn or 1 turn.<br />Anyway what you are doing is centering the hydralic lifter in the center of it travel. This will give you good valve lift with no danger of not closing if everything works right. Problem is if any problem with lifter, like a stuck lifter or lifter that does not have full travel then you may adjust to a point the valve does not close.<br /><br />So here the way I do it. I warm engine good and slow idle then adjust valve down slowly until engine missis then back out until runs smooth then one more turn out. If all the lifter working correctly then will end up with the same adjustment, but if have a stuck lifter or lifter without full travel this way will leave lifter loose instead of tight and burning the valve.<br /><br />Only thing I do not know is if your adjustment should be 3/4 turn or 1 turn. The GM 1980 181c.i. 3.0L is one turn.