Helicoil hell

[thatHurt]

Me and a mate are doing up a rather abused 82 xl500. The major mod so far is the front end off a 92 crm250 which gives us better shockies and a front disc brake.

We have hit a slight problem with the engine though. Oil is bubbling out at serveral places (when running) where the rocker cover meets the head. On closer inspection it appears rocker/head bolt holes have had helicoil inserts put in and not very well.

What's the best option - get the holes re-threaded and bigger size bolts? Any other options?

Cheers

[Motu]

Fit new Helicoils correctly.

[thatHurt]

Is that the best option? Don't know too much about helicoils. Would getting it re-tapped be better just more expensive?

[Crisis management]

Listen and defer to Motu's comments....

Helicoils, correctly installed, are better than a thread cut in the parent alloy, and utilise the existing / correct size fastener.

Good luck!

[thatHurt]

helicoils it is then. Anyone want to explain quickly why that's the best option - very curious.

[Motu]

Because there is probably not enough meat to drill out the helicoil thread,which will be one size up on the original,and then tap out bigger again - so if it was a 6mm originaly you will need to go out to 10mm, not very likely.So if the helicoil threads aren't damaged just put new ones in.

[thatHurt]

thanks Motu - we'll give it a shot

[Crisis management]

Ok,
Lets assume that we start from a thread that has stripped and requires repair. You have the choice of either installing a Helicoil to restore the original thread, drill out and tap to a larger diameter thread, also drilling out the mating part to accept a larger fastener, or welding up the stripped hole and drilling and tapping back to original sizes.

Two options allow the use of the original fastener, which is preferable, as that size fastener will fit the mating part and not be liable to overtightening / distortion.

Of these two, its easier and cheaper to fit a Helicoil, its a hardened steel spiral that replaces the original thread and returns full strength to the component.

Does that help?

[thatHurt]

yep - thanks

[terbang]

Found a couple of dodgey threads in my 1100 recently. M6 as usual and I suspect I'll find some more in 25 YO casings.
Anyone know a supplier in AKL that I can get a Helicoil kit?

[Drum]

How much are these helicoil things? Can you do them yourself, or do you need to go to the shop?

[Motu]

Saeco.....

[Madness]

They are available from all Engineers Merchants, Transmission & Bearing suppliers and some specialty automotive places. They are generally sold in kit foorm, containing the oversize tap, a few Inserts & an installation tool. The tap is the expensive part, making kits around $100. Replacement inserts are relatively cheap at around $1 - $2 each. The inserts are diameter & pitch specific, so if you have one or two holes to repair of an uncommon size/form sometimes an Engine Reconditioner visit is the preferred method.

Edit:
Solid Inserts are also available in most common sizes. There isn't huge demand in NZ for them so not always available, Re-Coil make two kinds, Keyserts & Ensat Tappers. These have a heavier wall and are both different in their application. See your Engineers Merchant for more coz I can't be stuffed typing anymore.