spark plug threads in block

backyardmechanic4you · Dec 13, 2008

I just bought a project motor, a 1967 mercury 50hp short shaft.When I got it home I realized that one plug hole has bad threads in it and another one has a larger size thread than the plug.My Question is are these inserts replacable or since there is no removable head on these motors, did I just buy a parts engine?

mthieme · Dec 13, 2008

Re: spark plug threads in block

It's possible someone before you use a helicoil insert to rectify a previous thread issue.

jimg984 · Dec 13, 2008

Re: spark plug threads in block

NAPA Auto Supply has the inserts and tool you need,,, good luck

Chris1956 · Dec 14, 2008

Re: spark plug threads in block

You should pull the crank and pistons out of the cylinders, and drill, tap and install the solid inserts with some epoxy.

jimg984 · Dec 14, 2008

Re: spark plug threads in block

Yes, Chris has given you the correct producer for taping for insert,,, but can be done with removing crank and pistons a stiff heavy grease applied to the tap and erea to be tapped will catch most of the metal,,also as the tap turns it moves metal to the outside of erea,,, also you may position the engine so the spark plug hole will be pointing down,, ( redneck and shadetree method lol}

Chris1956 · Dec 15, 2008

Re: spark plug threads in block

Jimg has recommended a standard practice for the repair. The problem with this procedure is that some slivers of aluminum may get into the cylinder.

Laddies · Dec 15, 2008

Re: spark plug threads in block

The process that jimg describes is the one Mercury recommended about 1969 and we have used it ever since with no problems.

jeff_smith_0423 · Dec 15, 2008

Re: spark plug threads in block

I recently did one - any shavings that get in the block can easily be removed with compressed air

backyardmechanic4you · Feb 6, 2009

Re: spark plug threads in block

Thanks guys , just realized that there were replies, I thought that replies would show up in private messages, so I thought no-one replied.It turns out the previous owner or owners have tapped these holes with two different styles of inserts, one a helicoil from NAPA and the other I found at princess auto. Both purchased for under ten bucks ( alot cheaper than the ford kit). The compression seems okay, hard to check with a pull start.I've added a 1974 distributor and now all I have to do is find a coil and switch box and fire her up.Thanks again for the replies!

kandil · Feb 7, 2009

Re: spark plug threads in block

The safe way to do it is to take it to a shop to braz new aluminum to the whole and re thred it or find a used one.
Helicoil are very dangerous for spark plugs you can kill your self if the plug projects out from the compression inside the Cly good luck and be safe

jimg984 · Feb 7, 2009

Re: spark plug threads in block

the insert from NAPA is not a helicore,,,,,,,,,, it s threaded male/female insert

spark plug threads in block

Cadet

Captain

Chief Petty Officer

Supreme Mariner

Chief Petty Officer

Supreme Mariner

Banned

Chief Petty Officer

Cadet

Chief Petty Officer

Chief Petty Officer