To Helicoil or not?

[49er]

Has anyone had previous experience with Helicoil repairs to the spark plug holes on their GS's.

Do they hold when running higher than stock compressions? Are they prone to screwing out of the hole when the spark plugs are being removed?

I've done Helicoil repairs on other places, but never to spark plug holes. I'm working on a head that needs one plug hole repaired. If they aren't reliable fixes, I'll look at modifying another head instead.

Any thoughts/past experiences please!

[kirkn]

Yes, I've had experience with Heli-coil on spark plugs and also with Thread-serts on spark plugs.

Both worked perfectly, no issues. Neither were on higher-than-stock compression, but I can't imagine that would make enough difference to matter. I mean, the stock threads do blow out when one bumps compression, so I don't think a Heli-coil would either.

I'd do it in a minute, if I were you, with no concerns a'tall.

Good luck with it.

Kirk

[simon kuether]

You can get a spark plug repair kit . It's got a tap and a bunch of these threaded tubes that have a small flange on one end . They're threaded inside and out and as they are not a coil , like a "helicoil" they're good for compression .

Cheers , Simon .

[49er]

Thanks to the feedback guys. I will do the repair and proceed with the blueprinting.

Cheers, Ian

[Nessism]

Here in the US Timeserts are the cats as$ for repairing spark plug holes. There are some cheaper substitutes available that work okay as well.

[ddaniels]

Solid threaded inserts are way better than helicoil in my opinion, and I've done both. And if you're going to do the repair with the head still on the engine, don't forget to goop up your tap with axle grease really good before tapping. Catches most, if not all of the shavings so they won't fall down into the cylinder.

[49er]

Ok, I'll try the Timeserts.

Head is off the engine, so no problem with shavings going where they shouldn't!

[bwringer]

Solid threaded inserts are way better than helicoil in my opinion, and I've done both. And if you're going to do the repair with the head still on the engine, don't forget to goop up your tap with axle grease really good before tapping. Catches most, if not all of the shavings so they won't fall down into the cylinder.

Agreed. Helicoils suck, but I've seen excellent results with solid inserts. There are several brands.

I have no idea how something as crappy as Helicoils became the most common thread repair.

Protip: On 8-valve GS engines, the thread for the drain plug is the same as the spark plugs (14mm diameter X 1.25mm pitch). So you can use easily available spark plug inserts to repair your drain pan when it strips out.

[rustybronco]

Wallowgreen (Martin) just repaired a spark pug hole on his GS250 with a timesert.
not at all cheap to do, but an effective repair.

[Flyboy]

Must agree, I have had a spark plug come out on my IT250, repaired it with a helicoil, did not last, spat out the helicoil and plug, in short time, I think it has to do with the two different metals, steel insert/ally head heating and expanding at different rates, that leaves the helicoil loose.
Inserts are best, as they are peened in place.

[blowerbike]

i have had problems with heli coils others have installed but as far as the ones i have done...i have had zero problems/high compression/40+ lbs boost/cam caps/1150 VC holes.
a lot depends on the person installing them.

[Nessism]

Nothing wrong with helicoils but they are not the proper insert for a spark plug application.

In the aircraft industry helicoils are extremely common and considered more robust than threads in straight aluminum.

In my opinion Timeserts are the best for a spark plug application because they are solid inserts and are expanded into the hole to lock them in place. The cheap solid inserts as sold at auto parts stores are better than helicoils for spark plug thread repair but are not as good as a real Timesert.

[ddaniels]

Nothing wrong with helicoils but they are not the proper insert for a spark plug application.

In the aircraft industry helicoils are extremely common and considered more robust than threads in straight aluminum.

In my opinion Timeserts are the best for a spark plug application because they are solid inserts and are expanded into the hole to lock them in place. The cheap solid inserts as sold at auto parts stores are better than helicoils for spark plug thread repair but are not as good as a real Timesert.

I haven't used timeserts, but have used the cheap ones sold in auto parts stores. I could not get it to stay in when I unscrew the spark plug. But, as long as the plug is in there, it's fine. Still in there now, but I imagine I'll have to do something when I change plugs.

[chuck hahn]

Dale..as you may recall i had to do the #3 cylinder on the 1000. I used a SPARK PLUG THREAD repair kit from Napa. Cost 49.00. You just use the supplied tap and go right thru the existing spark plug hole, put the insert onto the tap and use that to put the insert into the cylinder. Then just remove the tap and your done. took the shop vac and duct taped a small vinyl tube into the small adapter and sucked the shaving out of the cylinder..put in plug and it has been perfect since. Use a long screwdriver to be sure the piston is at the bottom of the cylinder before running the tap in too!

[Road_Clam]

Solid threaded inserts are way better than helicoil in my opinion, and I've done both. And if you're going to do the repair with the head still on the engine, don't forget to goop up your tap with axle grease really good before tapping. Catches most, if not all of the shavings so they won't fall down into the cylinder.

I frequently use threaded inserts as well. Problem is you typically need a large screwdriver blade to install the inserts (unless you know of a different style than I use). I would speculate that the slots would cause the sparkplug gasket to not seal correctly and cause compression bleed.