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Message started by Dave on 11/22/15 at 08:31:51

Title: Thread Repair
Post by Dave on 11/22/15 at 08:31:51

I just installed a Heli-Coil to repair some stripped threads on a cylinder. The right rear head cover bolt is a long 130mm bolt, and it appears someone installed a shorter bolt and pulled about 5mm of threads out of the cylinder.

If you look close in this photo, you can just see a tiny sparkle down in the hole were the first thread is - the threads are supposed to go all the way to the top.

http://i67.tinypic.com/2dkir9w.jpg

The Heli Coil kits are affordable and can be found at a lot of auto parts stores and good hardware stores - or online. Unfortunately the kits in stores only have the short threaded inserts that are about as long as the diameter of the insert, and for the 6mm head cap stud repair you need one that is 18mm long......I bought the longer ones from an eBay seller. They claim you can just use more of the shorter inserts - but I just didn't feel good about doing that in a cylinder.

http://i64.tinypic.com/14u9ulv.jpg
http://i65.tinypic.com/fu6nhu.jpg
http://i66.tinypic.com/2zge0t1.jpg

For the 6mm you drill out the hole with a 1/4" drill bit, then use their tap to cut new threads, then use the installer tool to place the new insert in the threaded hole. The wire thread piece is sightly larger than the hole and the insert tool winds the piece a bit smaller as you install it, and when you stop turning the tool the wire expands and locks into place.

http://i65.tinypic.com/rml9g6.jpg
http://i65.tinypic.com/22i5pd.jpg

I used a drill press to drill the hole and start the tap so that I could be sure it was done straight....that is a really long bolt and it needs to be straight. For this cylinder stud repair the cylinder will have to be removed from the engine - this is the passage that the oil uses to get up to the top to provide oil to the cam and rockers...you don't want any metal shavings blocking the flow.

Title: Re: Thread Repair
Post by KennyG on 11/22/15 at 23:12:12

Dave,

HeliCoils are really lifesavers.

I have used them all of my life, and as far back as 1959 I recall using one where the intake manifold fastened to the head on a my brother's AJS twin,

Kenny G