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Core Plugs

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settimo velo

Contributing Member
What material are Mercruiser core plugs made from?

Of my twin 1993-95 manufactured V6 engines, one has all brass core plugs and the other has one brass (which looks new) and three of what appear to be galvanised steel (as they are magnetic). They all appear to be in good condtion.

Did Mercruiser ever supply engines with steel core plugs? I thought they would've fitted brass and I am wondering if I should go to the trouble of changing them, whilst the engines are out of the boat?
 
BRASS only..........salt water will rust them in short order........

I cant say if they ever supplied them with anything but brass.......never looked that close, besides the engine blocks are usually painted black so you would not see any difference.

Sounds "fishy" to me....Maybe the motor in question had a cold weather issue and the previous "owner" repaced them with the wrong type.
 
Should be all brass. Either they were replaced with the wrong ones, or the block has been replaced with an automotive one. If that's the case there may be other items that don't meet marine requirements.
 
Thanks for confirming that ... I will replace them with brass. 2 look easy to get at but the third is just above and behind the starter motor so I think the starter will have to come out to get at the core plug. Any tips on how to remove and replace core plugs would be appreciated. Is it as simple as knocking a hole in it so that it can be levered out with a screw driver and then knocking the new one in square with say a suitably sized socket on an extension bar?
 
yeah, just knock one side inward. then a pair of long nose locking pliers can grab it and drag it out. I have dropped one in before - not all that hard to fish out, especially if steel
 
kghost said:
look here, Item 2 expansion plug, disregard the text in the box (piston rings etc) it is a carry over from previous item.

http://www.mercruiserparts.com/Show...99&bnbr=140&bdesc=CYLINDER+BLOCK+AND+CAMSHAFT
Click to expand...

So, there are 10 expansion plugs I need to have a look at - 8 off item 2 and 2 off item 4. I looked in the Mercruiser Service manual but this does not have a lot to say about core / expansioin plugs, other than giving some advice on how to extract them. So far I have only found 4 - 2 on the front under the cylinder heads and 1 on each side adjacent the oil filter and starter motor. It looks like item 4 is somewhere on the upper back part of the engine, I will try to locate these when I'm in the workshop this afternoon. Does anyone have a diagram or can anyone tell me where the other 6 expansion plugs are to be found? I'm guessing that I'll probably have to remove the bellhousoing and flywheel to find them?
 
As Kghost said, "Bingo". To check all the plugs, it's easier to pull the engine, as there are 2 behind the flywheel and chances are, if you see one on the side of the block, there may be others elsewhere too. Be aware there will be one right behind the camshaft at the rear of the block. That one isn't a freeze plug, but it plugs the cam bore and is OK if it is steel cause it doesn't see the water jacket. BUT, if it's rusty, I'd change it too. Don't forget to check the small plugs in the heads, also.
 
Core Plugs.jpg

Job done! ... I found 5 steel core plugs that I have now replaced with brass. Fortunately the 2 behind the flywheel were found to be brass, so that saved some time. Interestingly the 5 steel ones all looked to be in servicable condition, free from any signs of corossion. Maybe the block has not seen much salt water or has been regular flushed with fresh water after use, so whatever the core plugs are plated with seems to have held up really well.
 
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