Repairing a damaged thread

[Richard Russell]

I have managed to strip a thread in the RHS cylinder head of my R1100GS by overtightening one of the valve cover mounting bolts. In fact it stripped with so little effort I wonder if it was already damaged. Or maybe I'm just hamfisted.

The cover is still oil-tight, thanks to the remaining three bolts and the small amount of tension provided by the damaged thread. Obviously it needs sorting though.

I wondered about an epoxy thread repair kit (since it requires a relatively low torque) or a helicoil (but I have my doubts about the suitability of a handheld drill for drilling out the hole).

I noticed that the damaged hole is not directly in the cylinder head, but seems to be in an insert of some kind. Is it removable? If so, how?

Grateful for any advice,

Richard Russell

 

[Rob Farmer]

Russel,

Been there done that!!

A helicoil is the best way of repairing the damage. Mine appeared to have an insert in the head, it's a dark ring round the thread, this mark is actually caused by the rocker box seating onto the head and leaving a dark ring, if you clean it with solvol it will disappear.

The clearance drill that comes with a helicoil kit is only used for clearing out the old thread, it's best to take the sharpness off the edge off the drill because they are bloody sharp when new and can grab and dig in. Just get somebody to 'Eye up' the drill for you and go in slowly. its scarier thinking about it than actually doing the job. Just remember to allow for the distance between the tip of the drill and it's shoulder when drilling the hole and that the helicoil extends slightly when inserted.

The Helicoiled repair will be stronger than the original.

 

[Richard Russell]

Thanks Rob. Top advice!

After a few days of failing to find a supplier of helicoils, I managed to get hold of a "Recoil" kit today. Looks very similar to the helicoil kits, but with no drill. Although I bought a 1/4" drill to go with it, I didn't use it as the instructions said drilling wasn't necessary if the thread was completely stripped.

The only problem I had was that the bar on the tap wrench was too long, and fouled on the rocker assembly. A smaller chuck-type tap wrench worked fine.

I've also bought myself a decent torque wrench, so I'm hoping not to have to use the other 9 inserts

Cheers,

Richard

 

[sjwb]

It is always advisable to use a 'clearance' drill prior to tapping the insert thread. As a rule of thumb, the OD of the original thread is the size of drill that you should use For example, a stripped M8 will need a diameter 8mm drill. It is the same for Imperial threads.

 

[Rob Farmer]

My 6mm Helicoil kit came with a 6.3mm clearance drill and cost £17. I got the kit from:

J.L Engineering
284, Loughborough Rd
Leicester
Leicestershire
LE4 5PH

Tel: 0116 266 7074

They stock just about anything you would possibly need for engineering work including lots of different length helicoils. It's just a small shop, looks derilict, thats run by a biker and his mate. Very helpfull, in a piss taking kind of way. I think they do mail order.

 

[cookie]

that's a good price. i recently bought a "used once" 6mm recoil kit from a mate for £16. he paid £32

no drill with recoil kits either.