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914World.com _ 914World Garage _ stripped spark plug

Posted by: Gearren Sep 18 2005, 04:02 PM

Well it all happed yesterday while I was just taking the car out for a spin. It was running good, until the car ran BAD all of the sudden, to find out the one of the spark plugs shot out of the cylinder head, neadless to say, the threads are stripped out! So I bought a rethreading kit, and I am going to try to rethread the plug hole while the head is on the engine, in the car. I have head that if you use a heavy grease on the tap, it will catch most of the metal, its worth a try. But what kind of grease should I use, and also, what should I put on the insert so that is will stay in the head and not allow any blow by occur, any ideas, loctite, HB Weld, epoxy, what is the best stuff for this application?

Posted by: spiritedTreiber Sep 18 2005, 04:35 PM

If you have an air source, it would be a good idea to roll the motor over so that the damaged cylinder's intake valve is open and exhaust shut. Then put the air line/tip in the intake, pin the butterfly open, and carefully work on the hole. The air will push through the intake runner and out the sparkplug hole, helping even more with stopping shavings from gettin in the engine.

When you go to put in the insert, I would use red thread locker. IMHO.

Any one else have any other ideas?

Posted by: dmenche914 Sep 18 2005, 05:03 PM

What kind of thread repair kit do you have? I avoid the Helicoil type (the spring looking insert) as i have found them to back out when replacing / cleaning the plugs. Use a spark plug repair type for aluminum heads. Timesert (Timecert???) is a good brand, and there are others.

really the best bet is to pull the head. Any bit, just one bit of metal chip gets inbetween the cylinder and the piston, and you'll start scuffing away at the engine. Yes it is done, but for best success, pull the head. Especially if you engine is expensive or you expect to have it last a long time. If you engine is aready worn and tired, in need of a rebuild, and you just want to get it thru another spark plug change period, then rebuild it, than the risk is not so bad, as you won't lose as much if you do drop a chip. (which could ruin the engine very quickly if you are unlucky)

That said (I will be pulling my head to fix my stripped plug on my car, rather than risk the chance of a chip) air pressurization is sound advice, as is sticky grease on the tap, frequent backing all the way out with the tap, cleaning it, re-greasing, repeat, ( at least clean each 1/4 turn). when done a small diameter hose taped to a shop vac hose to suck out any potential debries. say a prayer, and you might be on your way.

I am a bit paranoid about tapping with head in place, also with the real spark plug inserts, you need to do a slight counter bore. (the tool that is in the kit does it) again a chance of chips left in the cylinder. Also you can be more dead sure on tapping square and true with head off, rather than working on it with engine together thru the sheetmetal. Then again, folks do get away with it with no problems, it is just a gamble that you got no chips in the cylinder as you drill/tap, and counter bore. All these machining steps in a cramped engine bay at odd angles in a hole you can't see with a hand drill verses doing the job on a mill or drill press with head set up on blocks to assure a perfect perpendicular hole and no chance of chips in the cylinder

again, i have had several helicoils (and some cheap chain auto store inserts) come out with plug changes, use a quality insert never a "spring" type and use one that requires the bottom be upset into place (like the Timesert) (Note Helicoils are great in some applications, use them for exhaust studs, but for some reason they want to stick to the sparkplugs rather than the head)

good luck

Posted by: Gearren Sep 18 2005, 05:24 PM

thanks. so I should use red loctite on the insert, but will it withstand the heat. And also what could I use for the grease on the tap.

Posted by: DJsRepS Sep 18 2005, 06:17 PM

What ever you do just dont drop a Chop Stick in there. Old 914 club thread.

Posted by: SGB Sep 18 2005, 06:19 PM

I got someone else to do mine. Old time air-cooled guy, said, "well, we could do it that way, (drop the engine & pull the head) but why? I trusted his ability to do it right. He did just as described- 1/4 turn then clean, air blowing thru intake, etc. He told me he just used wheel bearing grease. Who knows if any shrapnel escaped? That was one of the reasons I let someone else do it. I didn't wanna know...
Anyway, my engine already had 65k miles. My insert backs out with the plug, but thats OK. I figured I would lock it in when I rebuilt the engine next time.