Update : Forgot my plug....

[UNCC Grad]

1989 3.0 Mercruiser

I recently found out that my compression numbers were 75 psi and 50 psi in #1 and #2. I did a wet compression test and the compression only went up 10 psi in each cylinder (#1 and #2) so I pulled the head thinking the head gasket or valves. Sure enough, the head gasket was gone between #1 and #2. I checked each cylinder wall and found no scoring and the pistons look good except #1. It's burnt around the edges and looks somewhat ragged, but I think the rings are holding fine and it's not that bad. I'm definitely not doing anything with the lower end at this point...it's just not in my budget.

Can I check my head for flatness myself? I read somewhere about filling the valves with rubbing alcohol to see if they are leaking by? I'd like to avoid taking the head in to the shop because I don't know if I can trust them to tell me the truth and I'm afraid they would see me as easy business since I am unfamiliar with how to diagnose heads and valves.

 

[Fishermark]

Re: Update : Forgot my plug....

If you have a very straight "straight edge" you could check the head and block to see if it was warped or not. A machine shop would probably do a quick check for free.

You can check the valves for leakage, but you can also lap them in yourself fairly easily. Borrow, buy, or rent a valve spring compressor, (many auto parts stores have a loaner tool program for free), take each valve out one at a time and use valve grinding compound and lap the valves. (It's easy to do, but hard to explain here! I'm sure if you Google valve lapping you would find the proceedure). Put new valve stem seals in and try it out! A little elbow grease, but very little money.

 

[180shabah]

Re: Update : Forgot my plug....

Sure you can check for flatness, you need a straight edge, but it has to be perfectly straight. That ruler from JMart won't cut it.

 

[Don S]

Re: Update : Forgot my plug....

The biggest problem is that this whole thing didn't have anything to do with leaving the plug out. My guess is the comperssion has been low for a while. You really need to check the block and head, right where the gasket blew. Usually they are eroded away from combustion and exhaust gasses moving between the cylinders, and it doesn't take long.
Get a straight edge and check side to side between the cylinders. More than a few thosands of an inch and you need a block or head.

 

[UNCC Grad]

Re: Update : Forgot my plug....

I've decided to take the head to a shop and have it milled since I don't have a good enough straightedge to check for flatness. I gave the block a good feel and it feels flat with no wear but I'll be able to tell more after I clean the block well tomorrow.

Thanks for all the help guys!

 

[Don S]

Re: Update : Forgot my plug....

It's good that the block feels good, but check the block with a metal square also, and turn the square over and see if it's the same. The 3.0L engines had some problems with head gaskets blowing in later years because of timing and advance characteristics of the EST distributor. So when you get it back together, make sure you have the proper initial timing and advance timing which could be the problem with your head gasket.
I still think if you had all the moisture out of the distributor, the engine would still run and you would be off boating and destroying your block in the process. That one time of leaving the plug out for a while did NOT damage your head gasket. May be one of the few time a near sinking has a good outcome.