merc 140- leaking head?

[jimmytee]

1986 Mercruiser 140. Compression test #1-90 #2-70
#3-110 #4-120

Underneath the manilfold by #2 you can see rust where water has been dripping down. Doesnt seem to be any water in the crankcase.....head gasket? warped head? manifold or gasket?

 

[jimmytee]

Re: merc 140- leaking head?

should have mentioned, the engine does start and run and oil pressure seems normal at lower rpm.....did'nt want to rev it up too high....

 

[ziggy]

Re: merc 140- leaking head?

check out the 2nd part of this compression test service bulletin. the air leak part.... i did that and it helped me decide what i thought was wrong with my engine. beware. for me it was all down hill after the air test.i had a cracked block in one of my headbolt holes that i had to see to diagnois, but i did diagnois a bad headgasket between one and two, and i think that was correct......good luck.
oh, and my engine ran too. i had 2 low cylinders. the front two out of 6 in my case....

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

 

[MJ76]

Re: merc 140- leaking head?

The compression test tells you that something is wrong, but not what. There are a number of things that can cause a loss of compression. A leakdown test will tell you where the air is escaping to - through a valve, past the rings and into the crankcase, past the head gasket and into an adjacent cylinder or cooling passage.

 

[cobra 3.0]

Re: merc 140- leaking head?

My head gasket and manifold gasket failed after having similar conditions you describe on the same engine and year, but an OMC.

Upon taking off the head and manifold, I could clearly see a blown head gasket and manifold gasket at the same place (between # 2 and 3 pistons). Apparently, this is a common area of eventual head gasket and manifold gasket failure.

I could also see very slight glazing on all four cylinder walls, but decided against pulling the engine and rehoning the cylinder walls and changing the rings. I just didn't want to pour that kind of time and money into a 20 year old boat unless I absolutely had too. It wasn't using/burning any oil anyways, so probably wasn't that bad.

I had the head resurfaced on a head plainer and the manifold also resurfaced with a surface sander at an engine shop. I checked the head for leaks at the valves by pouring gas into/onto the valve area and waited to see if it leaked. It didn't, but if it did a valve job would have been in order too.

I reassembled the whole thing with new gaskets from BRP and everything works just fine.