Mercruiser 3.0L core plug

Mercruiser MCM 140, 3.0L, #5568367

Pulled the engine for various reasons (leaking front oil seal, worn engine mounts, and then after the winter engine would not turn over). Got the engine in the workshop, filled the cooling system up and had a leak from behind the flywheel. Pulled the flywheel cover off and found the top core plug behind the flywheel had come out, and got trapped between flywheel and cover, hence engine would not turn over. Removed plug and engine turned fine. Lucky!

I have since torn the engine right down (head off, valves out, pistons out, checking mains, thrust and bottom ends etc), thought I might as well as I have come this far.

Anyway, the parts I have ordered for the rebuild have started to arrive, and today I received the replacement core plug.

The old one was bronze and the new one sent to me is steel! I pointed this out to my supplier and they said its the correct part? The core plug further down the block is steel but that covers the camshaft, I would expect bronze to be over the cooling port. Is my parts guy right?

A couple of questions on refitting the plug;
1). I know you positon them (after thorough cleaning of the block bore) then hit the centre with a punch to expand it, but do you hit it once hard, or several times?
2). What size punch?
3). Should I use any sealant on it?

Once refitted I will pressure test the block in case there are any other leaks as I guess the block froze during the winter to pop the plug (I know they are not 'freeze' plugs but they often come out because of freezing). I have been looking closely now that the block is stripped out but so far no sign of any cracking on block or exhaust manifold.

Tks.

Re: Mercruiser 3.0L core plug

I know you checked it well.... but I would double check it again for any signs of cracks. Especially on the inside of the block.

And yes - you are right that steel is NOT the way to go. You want brass core plugs.

To install them, coat the outside with a little permatex #2 or Aviation sealant and find a socket a little smaller than the diameter and tap them in.

Re: Mercruiser 3.0L core plug

mrsaundep said:

1). I know you positon them (after thorough cleaning of the block bore) then hit the centre with a punch to expand it, but do you hit it once hard, or several times?

Click to expand...

Never heard of hitting a core plug in the center with a punch to expand it, you should drive it in with an appropriate sized socked, one that fits a bit loose in the cup. I alway use Permatex "Aviation" Sealant to seal core plugs.

Your supplier is full of "it" on the steel core plug, you need a brass core plug as the steel one will rust out.

Re: Mercruiser 3.0L core plug

OK........ so are we entering the Twilight Zone of something

Fishermark and fishrdan both replied at 12:58 with the same advice...

Weird

Must have something to do with that Startron alien add off to the right

Re: Mercruiser 3.0L core plug

Weird

Click to expand...

Ayuh,.... Don, 'n I did it ALL the time...
Look at the times when our posts are back to back...

Is my parts guy right?

A couple of questions on refitting the plug;
1). I know you positon them (after thorough cleaning of the block bore) then hit the centre with a punch to expand it, but do you hit it once hard, or several times?
2). What size punch?
3). Should I use any sealant on it?

Once refitted I will pressure test the block in case there are any other leaks as I guess the block froze during the winter to pop the plug (I know they are not 'freeze' plugs but they often come out because of freezing). I have been looking closely now that the block is stripped out but so far no sign of any cracking on block or exhaust manifold.

Click to expand...

Ayuh,... Yer Parts Guy, is really a parts runner fillin' in for the Real Parts Guy....

Ya Need the brass core plug...
And,...
As the Guys stated, the Core Plugs are a resistence fit, No need to expand 'em, after installation...
Matter of fact, they go belly In, from the start, keeps 'em centered as you beat it in...
I do throw abit of gaslket sealer on the edges though...

Yer overall Plan sounds solid,...
I like the pressure test,...
Look inside the block, from below, along the wall that has the waterjacket, behind the drain plug...