Repairing spark plug threads on '76 35HP Evinrude?

tony_cliffy · #1 April 29th, 2003, 05:44 AM

Hello! I may buy a small boat with a 1976 35HP Evinrude on it. I will have to buy it 'as is' without checking how it runs (no way around this). A visual check revealed a moderate amount of darkened residue adjacent to both spark plug holes. I was able to remove one plug by hand and noticed it became wobbly as I removed it and the threads in the head are noticably stripped. When I hand-tightened the spark plug it seemed snug but the outer residue (glazed engine oil? varnished gas?) suggests there may be blowby? Regardless, fixing the threads is something I think should be done.

Is there a specific tool for cleaning up spark plug threads? They are not totally trashed as some I have seen and I am hoping running a thread cutter through there will improve the situation.

Thanks!!!

lakeman1999 · #2 April 29th, 2003, 06:03 AM

In the past, I have filled the threads (not the complete hole) that remained in a plug hole with JB Weld (after cleaning, and wire brushing) used a tap to recut threads, turn motor over to blow debris out of cylinder, put in new plug, started up, and run fine from then on with no problems.

tony_cliffy · #3 April 29th, 2003, 06:08 AM

Thanks for instructions. Sounds like a plan! I have never tapped a motor. Can I get just the tap for spark plugs or will I likely need to buy a whole kit?

jim dozier · #4 April 29th, 2003, 06:22 AM

Remove the head and insert a heli-coil into the stripped plug hole. A helicoil is probably better than the original threads. Basically you drill out the hole with a specified diameter drill and retap with a specified larger diameter tap and then insert the helicoil threads (which are a stainless steel spring). If you don't want to do this yourself a machine shop will do it for a reasonable cost (call around). It will be good or better than new.

Fixit · #5 April 29th, 2003, 09:37 AM

reccomend removing the cyl. head and purchase a helicoil kit from about any automotive dealer and repair the plug holes -- operation is relitively simple process, replace head gaskets w/new and clean cyl. head etc before reassimbling.

bhalsdorf · #6 April 29th, 2003, 09:48 AM

Go to your local Auto Parts store. They sell a kit to repair the threads. It includes a tap and helicoils. You are better off removing the head to do this as you can scratch up the cylinder walls badly with chips if you turn the motor over .

tony_cliffy · #7 April 30th, 2003, 08:44 AM

Excellent, wel-articulated advice gentlemen!

Thank you!