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[PeteF]

Also make sure the tap is aligned properly - it's all too easy to tap the thread crooked even when you've got a straight hole especially in aluminium.
Time spent making a jig is time well spent! If you make a drilling jig you can then drill it out to guide the Helicoil tap.

[ChrisD]

Good points, gents, and thanks for all the input.

I have an offcut of 1inch of aircraft aluminium alloy that I’ve drilled to bolt onto the head using the remaining studs, with a hole centred where it needs to be in order to be the hole guide for the bit that comes with the Recoils. Under that ally plate is a plastic barrel cover (made from plastic kitchen sheet) that is also held by the other studs, to stop bits falling into the crankcase.

Since the stud that pulled is the one where the breather is (the only stud where the threaded section actually holes out into the crankcase) I’ve also made a tool that sits in that breather slot and is covered with grease, to catch any bits of ally falling down the drill&tap hole. I think I’ve covered all bases with drilling the hole. Aligning the tap is the next step, as you note PeteF. If the tap is long enough, then a similar hole guide should be fine. Yes, a proper drilling jig would be nice too.

I shall also buy our hosts squared stud set. Since only one of the threaded holes in the crankcase is damaged, and the head has always been an issue to remove (even with hardened washers etc) I guess that’s the one it was catching on. So that stud, at least, must be removed before pulling the head again (now why would that be necessary?). Indeed, on testing this, the head comes off easily without the pulled stud.

Cheers, ChrisD

[Mark M]

Don’t forget to run a clearnce drill through the stud holes in the cylinder head each time you re-fit it to clear the impacted alloy. 2mm over stud size is plenty. The stud spacing can be a bit random as well! REgards, Mark

[ChrisD]

Gents. Yes success (sort-of). Following comments about the thread size for the cylinder head bolts (5/16” BSF) and my re-reading of the Indian workshop manual, I purchased the relevant Recoil kit. My centering alloy block worked a treat to drill the 8.2mm hole at right angles to the casing head. Then the hole was enlarged to 9.5mm, a “just-touching” fit, so that the tap went in straight and finally a tad larger to allow the insert to fit OK. The result is that the recoil went in just great – perfectly centred and vertical and the tang broke off smoothly and was captured by the magnetic device supplied. Recoil do indeed make a great kit and its well worth the money!

BUT the new squared-head bolt wouldn’t fit.

So I checked further and discovered that the cylinder studs on my 1996 Classic are BSC not BSF – I said a few choice words along the lines of “^&@%#*@$&*^(@*”. So now I am getting my friendly machinist to turn me up a special stud with a squared-off 5/16" cycle thread at one end and 5/16" BSF at the other.

Hope the rest goes better and I hope this @%&#$@&$^& makes others read the manual more carefully. Cheers, ChrisD

[vince]

Hi, I nearly got caught the same way as twins use bsf and I thought bullets were the same, luckily the guy at our host corrected me at time of purchasing the helicoil. Redditch had ano obsession with fine threads in alloy. Vince