COMPRESSION TEST // HEAD GASKET???

[Colorado Boat Nut]

I did a compression test today and it doesn’t look good <br />Mercruiser 120<br />I followed the instructions to the letter and this is what I got<br />#1 140 <br />#2 70<br />#3 70<br />#4 140<br /> I put oil in #2 and re-tested and I got about 100 psi and it looked like oil mist was blowing out of the #3 plug hole<br />Did the same with #3 and got the same results 100psi<br />No mist was blowing out until I added the oil.<br />i think it might be the Head gasket????<br />Wouldn’t I be getting water in the oil?<br />Would it be overheating or something?<br />What signs would the plugs be showing?<br />They always look a little rich, I pull them after every trip to see how they look<br />My main problem is low rpm’s I cant get over about 2500 rpm I reproped , <br />Carb rebuild and all the usual tune up stuff, good fuel timing and points to spec<br />What would you do??<br />Thanx for any ideas<br />CBN<br /><br />Please see my other post’s if you like<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=003009 <br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=003361

 

[The Marine Doctor]

Re: COMPRESSION TEST // HEAD GASKET???

Your head gasket is blown between 2 and 3.<br /><br />Remove the head...get it machined back to spec...and have them check the valves for cracks or seating problems.<---these arrive after a blown head gasket.<br /><br />TMD

 

[jimmmy]

Re: COMPRESSION TEST // HEAD GASKET???

I have exactly the same problem. Haven't been able to get over 2600 RPM with my 3 L Merc. Carb rebuilt twice and then they found cracked head gasket between #2 & 3. Had head machined. When reassembled....no difference. Tried going from 19 pitch prop to 17 and got it up to 3200RPM, but still a long way from 4400! Two mechanics (and $1800) have been unable to fix problem.

 

[Tacklewasher]

Re: COMPRESSION TEST // HEAD GASKET???

And if it is just blown between two cylinders, it may not touch the water jacket so there would be no reason for water in the oil.

 

[Colorado Boat Nut]

Re: COMPRESSION TEST // HEAD GASKET???

Well that’s good and bad to know, the head isn’t too big of deal to do, <br />now who knows the cheapest place to get the gaskets or what I can expect to pay locally<br />Does anyone sell a head gasket kit.<br /><br />Thanx for your help <br />COBONUT