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Old 04-26-2019, 05:43 PM   #1
AJCoholic
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Glow plug thread repair


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I have been wanting to get a kit for repairing glow plug threads - ive stripped a few out over the years but mainly I have bought used engines where the threads were damaged or stripped and I sometimes was able to out in my own home made insert, sometimes it was junked.

Heli coil is pricey to get set up and I cant seem to find the correct size easily. I came across these “time-sert” inserts on eBay not too long ago, and decided to give them a try.

The kit comes with the following: a drill to bore out the damaged plug hole, a counter bore that follows the drilled hole and counter bores the top lip to a predetermined depth, a custom 32 pitch tap that is proprietary for the new insert, and an insert driving tool (that looks like a tap but has no cutting edges) that both inserts the new copper clad steel insert, and expands the insert to make it tight in the hole.

I tested the system today on a “test engine”, a Saito .82 cylinder. It went well - but the truth will be in the use once back together and a new plug installed and run.

This is a slick setup. The inserts are reasonable, once you get the toolkit. Much less time spent than when I make a custom one-off insert.

Unlike a heli coil, which must be put exactly perpendicular to the surface of the existing plug seat, because these have a flange, if the new plug hole is slightly off the old one, it wont matter - the insert seals against the counter bore and also the threads, and the glow plug seats on the insert’s flange.

Here are some photos...







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Old 04-26-2019, 06:11 PM   #2
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Re: Glow plug thread repair

AJ, I started using them in automotive back in the mid 90's, (remember the adds "100K miles before the first tuneup"?) and recommended them ever since. Much better for this kind of app than Helicoils.

I looked at this kit years ago, but a bit pricey for the few I would have needed it for. Hope you can make better use of it.
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Old 04-26-2019, 06:14 PM   #3
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Re: Glow plug thread repair

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Originally Posted by Cougar429 View Post
AJ, I started using them in automotive back in the mid 90's, (remember the adds "100K miles before the first tuneup"?) and recommended them ever since. Much better for this kind of app than Helicoils.

I looked at this kit years ago, but a bit pricey for the few I would have needed it for. Hope you can make better use of it.
I actually saw your thread on RCG I think.... after I was doing some research on them. BEing in woodworking, I dont come across things like this too often lol.

They do look promising. I bought 15 inserts to try out.
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Old 04-26-2019, 06:15 PM   #4
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Re: Glow plug thread repair

It's a cool system Andrew . I have a similar set for cars and motorcycles been using it for 20 years . mine has a set tool that punches the edges of the insert into the base material . The tap is 2 stage so you just thread it in the old thread and it cuts the larger new thread , it keeps alignment very square , pretty slick . To repair glow plug holes I was drilling and tapping a fine thread bolt . I would flush the head of the bolt off in the lathe drill and tap 1/4-32 , this way I could use the hex to tighten the insert .
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Old 04-27-2019, 08:17 AM   #5
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Re: Glow plug thread repair

Roger, do you thread the bolt in before you drill and tap it? Then face it off flush. I was thinking of drilling and tapping first and then screwing it in, but it would be loose. A .001" press fit is what I had planned, but would want a shoulder just to be more positive that it would not blow out, or spin when tightening. I want to make a few brass inserts in standard heads to use turbo plugs on two strokes using that method. I do have one 4 stroke that has a iffy thread though too. The Timeserts are great, after the initial first expense. ;-( I don't think helicoils would seal well enough.
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Old 04-27-2019, 09:18 AM   #6
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Re: Glow plug thread repair

Quote:
I don't think helicoils would seal well enough
Plugs don't seal at the threads. The brass/copper gasket does that.

I found Helicoils good for single-use apps and when in aerospace manufacturing we added them in magnesium housings to reinforce the stud base lock. These would remain in place throughout service life and since they would remain relatively temp stable were fine.

The problems start to occur with high temp and mechanical stresses, basically the definition of what occurs inside a combustion chamber. Over time, repeated cycling caused physical movement between the alloy base metal and the steel insert. Wear meant they eventually lost the ability to lock together under tension and the coil would start to loosen. Either it came out with the plug upon removal, or worst case, threaded inwards when the new plug was inserted. Unfortunately, unless it fell inside the jug and required disassembly, it was impossible to tell you may have only a few thread engagements. That condition usually did not last long.

The post-installation lock system on Time Serts did not allow for the insert to move....Period!
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Old 04-27-2019, 10:14 AM   #7
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Re: Glow plug thread repair

On A K&B.40 RR I used a 1/8th Pipe thread plug. I tapped the head from the inside and screwed the plug in from the inside. I drilled a 3/16" hole through the centre of the plug. I modified a 3/8" drill bit so part of it will fit in the 3/16" hole and sharpened the shoulder of the drill bit so it would reshape the head of the 1/8" plug to match the cylinder head. Then I drilled the hole the proper size for the 1/4'X32 tap and tapped the hole.
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Old 04-27-2019, 01:17 PM   #8
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Re: Glow plug thread repair

I put in 10s of thousands of Helicoils. They were considered an upgrade in the defence industry. I never thought much of them. The washer on a plug would have to seal on the aluminum part of the head. There is a lot of air space between the plug and coil, and then the coil and head. A turbo plug seals at the tip. It really makes a difference especially on the smaller motors which I like for some odd reason. The tapered pipe thread seems like a good alternative. I never thought exactly of that. I even have lots of 1/8 npt taps and dies I could make brass plugs from. I have some measuring to do.
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Old 04-27-2019, 01:22 PM   #9
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Re: Glow plug thread repair

The point of my post was to let others know of this pre-made solution lol. Yes I’ve made many plugs and fixed a lot of engines. But nothing as quick and simple as this.
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Old 04-27-2019, 01:34 PM   #10
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Re: Glow plug thread repair

Yes, quick and simple. It doesn't require a lot of meat around it for a repair either if there is not much room. I am maybe on another wavelength having used the turbo plugs. I am kind of thinking that any repair I do may as well be for them. I am not so sure if the 4 strokes would benefit though. On your other repairs, were they just a press fit, or knurled, threaded, stepped or anything fancy? You know you could likely take over Clarence Lee's job. Everyone would love you.
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