Upshur's opposed twin engine

[Sparky_SC]

Help!!! I buggered up a sparkplug thread. It should have been 1/4-32 but I pooched it. I have too much work in the cylinder head to scrap it, so I'm looking for a Helicoil kit that will let me save the head. Who can help me find a Helicoil kit that will get me out of trouble. I only need one Helicoil but the kits I've seen have 25 or 30 Helicoils in the kit. I need to buy the drill, the tap, and a driver (maybe). Can somebody line me up with a kit that has the least number of Helicoils in it. ----Brian

Car parts stores or Amazon are the cheapest. Drill bit is one included in a full 1/64 step set which you probably have. These small kits usually have 5 inserts.

 

[Jasonb]

Chances are the small copper washer on a 1/4 x 32 plug won't have enough surface area to seal against if you put the larger helicoil in. Any other options to try and seal it will likely end in loss of compression.

May be better to tap it out to something a reasonable size 3/8 or 7/16 and make an aluminium insert to screw in with the aid of Loctite.

 

[Gordon]

1/4-32 is probably going to be a problem. That is not a common size. 1/4-20 and 1/4-28 but not 1/4-32

 

[mnay]

1/4-32 is probably going to be a problem. That is not a common size. 1/4-20 and 1/4-28 but not 1/4-32

Brian,
I would suggest you drill and tap oversize and make your own threaded insert and loctite it in.
Then you could use steel material for the insert. I have made this repair on my projects lots of times.
You can also put a grub screw in the outer thread to secure it in place.
Good luck. I am following along.
Mike

 

[stanstocker]

1/4-32 is probably going to be a problem. That is not a common size. 1/4-20 and 1/4-28 but not 1/4-32

MSC at least doesn't list any 1/4-32 thread repair inserts. I think the practical repair will be as JasonB suggested, use Loctite retaining compound to secure a shop made plug.

 

[Jasonb]

Oh, that rocker stud hole may be in the way.

Might actually be an advantage as you can redrill and tap it then the stud/screw will help stop the plug screwing out

 

[Mike1]

When I built my Wyvern gas engine I had a similar problem, I did a similar repair as the one Jason suggested but instead of Loctite I used JB Weld smeared on the threads the repair was a success.
Mike.

 

[Jasonb]

Brian, you have stripped 1/4 x 32 threads in other engines. Is it heavy handedness or are you using the wrong tapping drill and not getting a deep enough thread ? What plugs are you using, if something like a V3 they have very short thread length so more likely to strip than a standard length VR2 Either way be careful with the other head.

Also looking at Helicoil data for 1/4 x 32 you probably don't have the length for a helocoil.

 

[Brian Rupnow]

It was my own fault. I used the wrong size tap drill.

 

[Brian Rupnow]

We have a carburation system!!! Very simple but ingenious carburetor. I'm happy with this. I still have a couple of carb parts to make, but they are not big jobs. Then, on to the rocker arms.