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Stripped sparkplug threads

A

Anonymous-0

Well-known Member
Got a McCormick Deering 10-20 with a stripped spark plug hole. A local machinest could not find something to fix it with.A local industrial supply house quoted $750 for a "kit" to fix it.Does anyone out there know of an affordable repair option. It's a7/8 plug.
Thanks,DAVE
 
Spark Plug Port Thread Repair Kit - 7/8-18
by Heli Coil Products

Description
Spark Plug Port Thread Repair Kit - 7/8-18 Heli-Coil is the original spark plug port thread repair, with kits offering the highest quality and most durable repair available. Contains piloted reamer tap p/n 549 (no drilling necessary), installation tool p/n 548 and 10 inserts. Note: Do NOT use Heli-Coil wire inserts to repair taper seat spark plug ports.

Price
$159.95
Amazon
 
I would take the head to your local auto machine shop to see what they charge. They should be able to get the correct heli coil kit. Hal
 
I had a head that somebody broke the plug out and took a hacksaw and cut it out but they got into the threads. One machine shop told me the head is junk, took it to another shop, they drilled it out about twice the size of the plug and filled with a threaded patch and then threaded a hole in that patch for the plug, but it was twenty years ago. It was not expensive either.
 
If the head is off, have it fixed the right way, not heli-coil. Heli-coil is good for non-critical threads but not a spark plug.
 
So, in your humble opinion, what are heli-coils good for?

It seems to me that any threads that are stressed enough to fail WOULD be critical.

Heli-coils are routinely used on head bolts, and if those aren't critical I don't know what are.
 
I've put heli coils in spark plug holes before, it works great. And it sure as heck does not cost 100 bucks! The local machine shop (Martin and Otterback) did it for like twenty bucks while I waited.

Wayne
 
use a spark plug instert. A heli coil will leak around the seal. also once you mess the head up using the heli coil. Things get expensive. the right tool for the right job, it isn't a expensive repair yet
 
Any Machinist that can't fix a ruined thread ain't worth going back to. First thing we learned in Navy School for Machinist is how to repair bad threads. Heli Coils Bore out and put in a plug with very tight threads then center punch around it to lock it in. Weld it up re-bore it and re-thread it no big problems here.
Walt
 
The threads aren"t what seals it"s the gasket and flat surface on the head where the spark plug seals on that 7/8" x 18 thread per inch plug. Same on a taper seat it seals on the seat. Helicoils work fine and there are many other brands of thread repair inserts out there too. Check for thread repair inserts with mcmaster.com fastenal.com motionindustries.com helicoil.com Call around and find a REAL machine shop that already has the thread repair kits. You need the proper size drill, special tap, thread insert tool and thread insert is why they aren"t cheap.
 
You need to go to an AUTOMOTIVE MACHINE SHOP
or place that does heads, valve grinding, etc
They will do it correctly, and it's not an
expensive fix.
 
I used to use heli-coils with great success, but have now switched to EZ-Lok as listed below... You can get them with Locktite on them and when the head warms up, the locktite sets up.See their site for instructions and ECT. They will send you a FREE sample and that is what I done. I figured out what size for my stripped plug.. Didn't even have to buy one to fix a head....JB
EZ Loks
 
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