LCGB Forums

Apology's if this has been covered before but i've got a stripped thread on one of the M6 chaincase studs on an engine Ive just aquired can anyone recomend a Helicoil kit or am I best getting the hole welded up and re tapping .
Also is the thread M6 x 1.0 pitch ?

Yes, 6mm x 1mm pitch. No problem with helicoil if done correctly

As mentioned nothing wrong with Helicoils, but re weld and tap is the best option, check ALL the others especially the one under the kickstart and bottom rows! You may need more than one, as a right pain when later on another one goes during rebuild.

Helicoils are fine for crankcase studs , if the hole is a tad large then helicoil to M7 and use an M7/M6 repair stud

Some facts about wire thread inserts, the correct generic term (commonly called Helicoils though that is a brand name)

• They are used extensively as the primary means of creating a threaded hole in very critical, stressed areas such as in racing vehicles & aerospace.
• They are designed into & fitted from the outset, not just as a means of repairing a thread.
• They are considered stronger & far more durable than the parent alloys that they are fitted into.
• In the event of a thread failure, they are normally replaceable as an easy fix, far quicker than other alternatives.

Of course, that’s not to say that Boeing etc have never, ever got their mate from the pub to weld up a stripped hole in a wing section, but I think it very unlikely....

Thanks chaps.
So a thread repair kit seems at this point the way forward is there a specific depth re-coil /VCoil /Heliccoil I should look for?

Also if I did go down the mate down the pub route (as I have a mate who it turns out is a dab hand at welding aluminium)
What's the best way to re -face the engine case?

M6 x 2D would be the helicoil to use(12 mm) although 1.5D(9mm) would probably be ok. Easiest is tap to M7 and use a M6/M7 repair stud but not aware of a long one if it's for a tailpipe mount?

Warkton Tornado No.1 wrote:Some facts about wire thread inserts, the correct generic term (commonly called Helicoils though that is a brand name)

• They are used extensively as the primary means of creating a threaded hole in very critical, stressed areas such as in racing vehicles & aerospace.
• They are designed into & fitted from the outset, not just as a means of repairing a thread.
• They are considered stronger & far more durable than the parent alloys that they are fitted into.
• In the event of a thread failure, they are normally replaceable as an easy fix, far quicker than other alternatives.

Of course, that’s not to say that Boeing etc have never, ever got their mate from the pub to weld up a stripped hole in a wing section, but I think it very unlikely....

Very true.many years ago i used to supply helicoils by the hundread to Motor Racing Development ,who were behind Brabham (formula 1,2+3) cars, a mate worked there and told me they used to helicoil every ali thread , as it was harder to strip than just an Ali threaded hole.
if your stuck i have a M6 x1. helicoil tap, drill and inserting tool.

Just to add to the other advice received, particularly martyn dwanes , I’d also meant to add that welding Lambretta alloy components has mixed results, in my own experience.

The alloy used often has metals in it that contribute to achieving the excellent die casting results. Unfortunately, that zinc (?) content can cause porosity of the weld. As can any trace of oil that may have been absorbed into the surface.

Then there are the knock on effects that welding can cause. Distortion, stress & the need to machine back spring to mind.

Even in the unlikely event that a wire thread insert will not fix a stripped thread, there are similar ‘oversize’ options that will work. The Acme & Keenserts even offer the advantage of utilising standardish taps to create the threaded hole:

Thanks for all the replies and kind offers of loan of kits .
I Phoned a insert stockist today to find out what sizes they stocked and got some useful info I wasn't aware of.
The taps contained in the kits are special and cut a unique thread for the insert the angle of the pitch helps the insert "bite" into the hole your repairing which makes perfect sense .
I'll have a better look at the weekend but it looks like someone has wound and M7 bolt in the hole instead of doing a proper repair
I'm totally on board with the thread insert idea
It seems salvageable and I have options but as WT says welding will be the last resort.
Will post the outcome.

Phil D wrote:Thanks for all the replies and kind offers of loan of kits .
I Phoned a insert stockist today to find out what sizes they stocked and got some useful info I wasn't aware of.
The taps contained in the kits are special and cut a unique thread for the insert the angle of the pitch helps the insert "bite" into the hole your repairing which makes perfect sense .
I'll have a better look at the weekend but it looks like someone has wound and M7 bolt in the hole instead of doing a proper repair
I'm totally on board with the thread insert idea
It seems salvageable and I have options but as WT says welding will be the last resort.
Will post the outcome.

Fortunately, M7 & M6 are the same 1.0 mm pitch, so an M6 wire insert (Helicoil) tap will clean up the M7 because it is about 'M7.25' if that makes sense...

I know this trivia only because I have 'converted' M7 holes down to M6 many years ago when, frustrated by the quality of end plate studs & nuts available, I decided that high tensile M6 socket head cap screws would be a better opotion...

Thanks for that WT1 so theres a good chance I may get away with running an M6 Helicoil tap down the hole and
an M6 Helicoil will work, would you use a dab of Loctite on the insert ? for a belt and braces effect.

Phil D wrote:Thanks for that WT1 so theres a good chance I may get away with running an M6 Helicoil tap down the hole and
an M6 Helicoil will work, would you use a dab of Loctite on the insert ? for a belt and braces effect.

You shouldn't need to use Loctite when winding in the insert, but I've done it & know that other's have, too. I first witnessed it when Martin Cook kindly repaired an M8 cylinder crankcase stud hole @ Mamby Wheels.

You should get away with just adding a spot to the fastener to be used, if it is a stud, to stop the inconvenience of it coming out.

BTW if you find that the insert has gone in but not seated correctly to the freshly threaded hole, you can carefully use an M6 tap to re-seat it. I couldn't believe that this trick would work & had visions of the tap breaking or causing the insert to come out with it, but it does work, as I've found on a few occasions.

I hope this helps especially as the kits nowadays are so affordable if you check out Recoil's site:

http://www.recoilshop.net/shop-recoil/t ... r-kit.html

Thanks for the kind offers of loan of repair kits, I decided to buy one as more than likely this will happen again.
I also got some longer inserts as the ones supplied aren't really deep enough.
South Essex Fasteners supply small amounts (10) for a few pounds and are really knowledgeable.

Now I know to a lot of guys on the forum this repair is a walk in the park but I would urge anyone who thinks they can't manage it because they are not good at fixing stuff give it a go it's very satisfying .
The tools required are widely available and cheap .
Thanks lads for the spot on advice