1/4-32 HELICOIL OR SIMILAR PRODUCT

[Brian Rupnow]

I have managed to strip the 1/4-32 threads out of a bronze cylinder head. (For a 1/4-32 sparkplug.)--Does anybody know of a supplier for this size of Helicoil or similar product? I can find lots of 1/4" inserts with coarse and fine threads, but none that are 1/4"-32.----Brian

 

[Ghosty]

Brian,
They are hard to get, I had to special order to get a set.
Cheers
Andrew

 

[michael-au]

This maybe helpful

https://www.ebay.com.au/itm/294664806504

 

[Badhippie]

Brian McMaster Carr has them and so does
MMC direct

 

[DCRC]

I have managed to strip the 1/4-32 threads out of a bronze cylinder head. (For a 1/4-32 sparkplug.)--Does anybody know of a supplier for this size of Helicoil or similar product? I can find lots of 1/4" inserts with coarse and fine threads, but none that are 1/4"-32.----Brian

Brian,
Recoil brand has a kit 1/4-32, in the US I find them on Amazon for a kit, tap insert tool and a few inserts for $30.00us.
Dale

 

[ajoeiam]

I have managed to strip the 1/4-32 threads out of a bronze cylinder head. (For a 1/4-32 sparkplug.)--Does anybody know of a supplier for this size of Helicoil or similar product? I can find lots of 1/4" inserts with coarse and fine threads, but none that are 1/4"-32.----Brian

Given your abilities - - - you might need to just replace the cylinder head.
Other option would be to increase the size of the spark plug (assuming there's room to accommodate that).
The options presented previously (here) sound sorta pricey to me although redoing the head wouldn't be cheap either.
Be curious what you decide to do.

 

[Jasonb]

Given the small diameter of the washers on the 1/4" plugs and their small tightening surface I wonder how good a seal you would get against the helicoiled hole?

 

[Brian Rupnow]

Does anyone have a listing for a sparkplug with a 5/16" diameter threaded end? I have a 5/16"-18 tap and a 5/16"-24 tap. If I can find a sparkplug with either of those thread sizes I can retap my cylinder head to accommodate that thread size.

 

[Jasonb]

Didn't Steve Huck make you some 5/16" plugs to rescue the head on your horizontal air cooled engine?

https://www.homemodelenginemachinis...al-air-cooled-engine.33596/page-9#post-370385

 

[peterl95124]

Brian, I'd make my own, but not a heli-coil instead just a piece of metal. IE with the head upside down drill out the spark plug hole to 5/16", then without moving the table use a 3/8" flat end mill to open up the hole but don't go all the way through, you want a flange at the far end to hold the insert you're about to make. now turn and drill & tap an insert to go into that hole (maybe use steel so your less likely to strip the threads again). now you can loctite the insert in. they make reasonably high-temp loctite if you're worried about that, otherwise make the insert a press fit.

 

[DKGrimm]

Brian, I'd make my own, but not a heli-coil instead just a piece of metal. IE with the head upside down drill out the spark plug hole to 5/16", then without moving the table use a 3/8" flat end mill to open up the hole but don't go all the way through, you want a flange at the far end to hold the insert you're about to make. now turn and drill & tap an insert to go into that hole (maybe use steel so your less likely to strip the threads again). now you can loctite the insert in. they make reasonably high-temp loctite if you're worried about that, otherwise make the insert a press fit.

I did essentially the same on an aluminum head with a #10-40 spark plug. I used 6061 aluminum to make a threaded repair stud 1/4-40 on the outside and #10-40 on the inside. Used Loctite 680. Machined the spark plug seat. Better than new because it is a harder material than the casting.

I imagine you could use steel or bronze for the repair plug.

Don

 

[Brian Rupnow]

I have retapped the sparkplug holes for a 5/16" fine thread. I will make up a couple of my own sparkplugs for this job, as the only helicoils I can find to buy have 40 or 50 helicoils and a special drill and tap and cost more than I am willing to pay.---Brian