# repair glow plug hole in head?



## jack620 (Sep 22, 2013)

A friend has stripped the glow plug thread in his RC car's engine. The "head", if I can call it that, is an aluminium disc that is sandwiched between the cylinder liner and the large cooling fins that sit on top of the engine.

I could make a completely new part, but I fear it will only strip again and he'll be back to have it repaired in due course. Would it be feasible to make a 1/4-32 tapped steel insert and press it into the glow plug hole (after boring the hole slightly larger)?

Chris


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## mu38&Bg# (Sep 22, 2013)

That head has serious detonation damage. Make another if the rest of the engine is any good. Make sure you're using the proper tap drill or maybe go a bit smaller for more thread engagement. Threaded insert kits cost 100USD. I've seen people make solid inserts as well.  A glow plug doesn't need much torque. Use a nutdriver to install and make sure it's not cross threaded.

Greg


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## stevehuckss396 (Sep 22, 2013)

Having nothing to loose I would drill the head and retap with a fine thread. Make a threaded insert and locktite it in. Then re-thread the insert 1/4-32.


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## lohring (Sep 22, 2013)

Repair inserts are not too expensive, but check on the cost of a new head button first.

Lohring Miller


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## petertha (Sep 22, 2013)

I'm not involved in RC car engines specifically, but point of reference, brand new ones for even the high end, Gucci screamers are sub-$50 from what I can tell. Not sure what engine that came from, but doesn't have through holes, might be just as easy to make one from scratch.

http://www.amainhobbies.com/product...1713_1848/products_id/204079/n/OS-Head-Button

I haven't had much long term luck with inserts. The best success was an aluminum insert threaded into the aluminum head button with HT locktite. Steel seems like a good idea from a thread toughness perspective, but will expand differentially to aluminum. The head/button is hottest part of the engine.

Head threads last a long time if you dont commit the cardinal sins:
- overtightening (develop a feel or use setable torque wrench if you must)
- tightening in a plug (even moderately) when the engine is hot
- dirt & debris in the threads
- running high compression/nitro/pipe setup/oil content/or any other setup ..resulting in excessive high temps & detonation as was pointed out


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## Wizard69 (Sep 22, 2013)

lohring said:


> Repair inserts are not too expensive, but check on the cost of a new head button first.  Lohring Miller



A big plus for Timeserts, we use them extensively at work.    Note too that the kit will come with several inserts and that you can order a lot more if needed at a lower cost than buying the kit.   The only gotcha is that the material being Timeserted needs to be thick enough to support the full length of the insert.    The way that the inserts are locked in place with the thread forming tap requires that the lower threads engage the parent metal.   

This isn't an uncommon problem with model engines, you could easily make a tiny business out of these repairs.


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## kf2qd (Sep 22, 2013)

Only problem with most commercial sources of parts is that these are 1/4-32 threads. And the internal shape of that head is important. Any sharp corners and the detination can get worse due to hotspots. That head button should be a fairly inexpensive part. Both curves are important. Could try making one out of 7071 series aluminum.


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## Capt,n John (Sep 22, 2013)

Get a Heli coil tap & tap the head for a Helicoil.   Good device to have, so you can repair your engines...and make alittle fixing other heads for people. You could make enough to pay fpr the tool.  Just a Idea.   John


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## jack620 (Sep 23, 2013)

Thanks gents. The time-serts look great, but the kit is $100, so I might try Steveshuckss396 idea first.


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## Wizard69 (Sep 23, 2013)

jack620 said:


> Thanks gents. The time-serts look great, but the kit is $100, so I might try Steveshuckss396 idea first.


  You will need a mechanical lock as the head will likely get hot enough to degrade the Loctites bond.  It should be noted though that the timesert kits start at around $70, the $100 kits normally come with a bottle of Loctitie 266 which apparently Timesert recommends.   Here is Loctites explanation of 266: *"Loctite® 266&trade; High Temperature, High Strength Red-Orange Threadlocker is fast fixturing, and resists oil and mild surface contamination at temperatures to 450°F. Locks fasteners up to 3/4" (20 mm) in diameter."*.  In this case they are suggesting a high performance, heat resistant Loctite, not your run of the mill stuff.   So if you go Steve's route I'd still suggest investing in this Loctite.


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## Lawijt (Sep 24, 2013)

What engine you are talking?? All those spots in the head are there because a broken bearing or a broken glow plug. Such engines don't like a empty tank. The glowplug will too hot than & breaks. The treads hammering the head.
Or there are not enouch shims unther the head. That is also a big problem.
Maybe the engine is not worth too repair.
I race about 20 years with 1/10 & 1/8 scale racing cars from SERPENT. I have Novarossi engines tuned by JP in France. They are very good. But very expansive.
Also I found the color too clear. The head have too be a much darker colour. So maybe the engine run very lean.

Barry


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## jack620 (Sep 24, 2013)

Wizard,
thanks for tip on the high temp Loctite.

Barry,
I don't know what brand the engine is- I only have this part. I think the engine is made in China. I think you are correct that the engine isn't worth repairing.


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