1987 3.0 mercruiser manifold drain port

[Starcraft5834]

Went to fire up engine after winter sleep, i drained block and manifold, tried screwing in manifold drain bolt, wouldnt catch..threads worn out.. anyone know size of that drain plug?. Or what the proper merc part # is?, i ordered plastic version thats advertised to fit "manifold/block" hole.. it fits block petcock hole which is lrager and not the manifold hole which I need..thank all

 

[Yegboats]

32802 2 (.125-7)

 

[Alumarine]

1/8 NPT I believe.
You can get the brass ones at any plumbing/hardware place.

 

[wrench 3]

Yep, 1/8 NPT.
It's not a good idea to leave the ones out that screw directly into the casting. The threads in the manifold tends to rust out over the winter. I've had to drill and re-tap a couple of them to 1/4 NPT. But run a 1/8 tap into the hole, not far enough to cut into the metal, and see what happens.

 

[Starcraft5834]

thanks guys,, found it on amazon prime,, will have it Friday, my bad, I should have asked here first,, I took a chance on "it fits oem mercruisers manifold/engine block drains" .. I did not realize till later that the manifold drain hole size on my motor and the block petcock drain hole size are two different animals..... the plastic version that I bought fits the block hole,, don't need that one...:fencing:

yea wrench I found that out,, I left it out after draining it, it rusted,,, it was the original screw, the threads were just about non existent... the new plug should grab in there ok

 

[Bt Doctur]

to use the plastic plug you also need the adaptor to screws into the block
but sierra 18-4218 is a all brass plug

 

[fishrdan]

I've had to run a tap through the drain hole to clean up the threads before, rust and junk made the plug tough to install like you are seeing, but after chasing the threads, the plug went in easily.