Repair stripped plug threads without removing head?

[jimbrizzolara]

I have a 1957 Big Twin that has stripped threads on both spark plug holes. Besides already being fed up with this motor the compression release system would have to be dealt with in order to remove the head. Is it possible or feasible to repair the threads without removing the cylinder head?

[frankr]

Why fear the comp relief?  Just remove the two screws from the long stainless steel bar.

[Bob Wight]

Some folks have done this repair without removing the head by using lots of grease on the drill bit and thread tap to catch all the chips, but that’s too sketchy to me.  I’m with Frank on this one – easy enough to pull the compression relief off, pull the cylinder head and do it right.   And use the thread repair kit made specifically for spark plug holes.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[jimbrizzolara]

You’re correct Frank, looks like I could leave the compression release on. Any tips on doing something before I loosen the head screws to lessen the chance of breaking them?

[retiredoz]

I have a cylinder head with good threads that you can have for the price of shipping from Seattle.  Call/text  fourtwofive 765 threeonetootoo.

[olcah]

Thread repair kits are fairly pricey and they do not always work (in my limited experience).  My advice is to talk with retiredoz about another head.

[Mumbles]

This thread repair kit by Heli Coil is meant for spark plugs and works great if the instructions are followed. The inserts are steel, not wound wire as used for general thread repair, and are locked into place with the included tool.

This fix can be done with the head on and using grease on the tap to catch any chips. No drilling necessary.

[crosbyman]

I fixed a 7.5hp  cyl head  years ago…worked perfectly !    the tool will crip/lock the insert just below the surface

 

just add Red thread locker if you are hesitant.

Joining AOMCI has priviledges 🙂

[rmhxruss]

The above Helicoil kit is good. Another is made by Time-sert solid style better than wound style.

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