Helicoil or Tap

[Concrete-crusher]

Hi whilst putting my gearbox back today I have stripped the thread on two of the 4 bolts that hold the gearbox mount to the chassis it looks like its originally a square nut welded to the thin mild steel chassis plate.

So is it better to drill and tap these to a larger size or drill and helicoil to the original size

Either way I need to buy the tools to do it

Steve

[nmauduit]

I would not use a helicoil there, the thread length is not very long nor is the material width to hold it : if good enough for tapping the next size up I would try that first. If that fails you could try inserts (worse come to worse, welded from underneath).

[Bud English]

There's not much thickness there to work with. Heli-coils come in various lengths based on a multiplier of the nominal thread diameter, with the shortest ones one times the thread diameter. I believe those bolts are 5/16" and I'm not sure you could make the 5/16" length coil work in the stripped captive nut.

EDIT: Woops, you beat me to it.

[mbell]

I used helicoil on mine (5 speed mount), which worked ok. Snapping the tangs of was a pain thou.

Any tap you put in there is going to bottom out on the body. I was able to get enough thread for the helicoil but not sure you could get a thread all the way through with a standard tap.

I'd check the different drill size for the types of hole and see which options gives you a fall back option. E.g. can you try 3/8" thread and then helicoil back to 5/16" if that doesn't work out or the other way round?

[alan.barker]

You can not tap 3/8" then fit 5/16 Helicoil.
For a 5/16" Helicoil you need the special Helicoil Tap.
The best thing is to buy a Helicoil kit that consits of : Helicoil Tap + Pilot/tapping Drill + Fitting Tool + Tool to break off the Helicoil Tang + a selection of different length Helicoils.
The ideal thing to do is drill a hole in a piece of scrap metal the same thickness as the Captive Nut in the Chassis.
Tap the hole then assemble a Helicoil counting how many turns you need. You can then trim the Helicoil to the length you need. Continue to turn the Helicoil until it comes out the other side of the scrap metal.
You now have a Helicoil the correct length to fit the tapped hole in the Chassis.
The Helicoil needs to be fitted a quarter of a turn down from the top surface.
DON'T use Loctite on the Helicoil.
Alan

[nigelrbfurness]

Easiest is to tap the next size up. If that fails, a bit of art with the Mig to weld up the hole then redrill and tap the correct size. Shouldn't take more than an hour or two.

[alan.barker]

If the thread has stripped it will be almost the correct tapping size for the Helicoil Tap
Alan

[webrest7]

Helicoil in mine .
No problem.

[Hawksfield]

Hi

Try the next size tap first as even for a helicoil you have to get a finish tap in
If that fails look at the other options.

[Concrete-crusher]

Well the helicoil route was a complete failure , every time I tried to insert the helicoil it just sprung inward on itself.

Interestingly the tap that was supplied with them seems to be 3/8 unf so I ended up just using larger 3/8 unf bolts.

Tapped hole

Wasted helicoils

Steve

[alan.barker]

Steve,
Sorry for my silly questions but.
Did you tap the hole with a Helicoil Tap. It's not possible just to use a normal 3/8" Tap. The dia will be wrong.
Are you using the correct Helicoil Insert tool
The Insert Tool should stop the Insert closing in. It just fits inside the Insert.
When fitted the Insert should be about a 1/4 of a turn below the surface.
You need to trim the length of the Insert before fitting.
Good luck
Alan

[Concrete-crusher]

Hi Alan

I used a kit which came with the correct size drill bit , tap and insert tool. or should have done.

The insert tool was a loose fit into the coil . and the tap did allow a 3/8 unf bolt to fit , so maybe the kits wrong.

Anyway the 3/8 unf bolts fitted the tapped thread so problem solved for now ,

tomorrow its time to pay the engine back in.

steve

[c.garde]

Hello all,

Allow me to point to " timesert "
A bush insert system , you can also get the bushes in oversize.
As an amateur this is to me a far better solution than helicoil with the inbuild risk of loose coils.
Helicoil has been used with success by pros through ages but being better at screwing things up rather than screwing coils in I feel much more confident using timesert.
It comes at a price but you will reward yourself with a big smile after having tried it .
Have a look for yourself on the WWW.

Best regards
C.Garde

[nmauduit]

Hello all,

Allow me to point to " timesert "
A bush insert system , you can also get the bushes in oversize.
As an amateur this is to me a far better solution than helicoil with the inbuild risk of loose coils.
Helicoil has been used with success by pros through ages but being better at screwing things up rather than screwing coils in I feel much more confident using timesert.
It comes at a price but you will reward yourself with a big smile after having tried it .
Have a look for yourself on the WWW.

Best regards
C.Garde

yes, but Timesert requires even larger diameter bore, so in that specific case there would be very little left to hold it up... welding would probably end up being necessary to keep everything together sooner rather than later.
I usually use Timesert where the thread is more likely to require maintenance assembly/disassembly, esp. in cast alloy (e.g. to replace exhaust studs by screws in the head...) - they are more costly than helicoil.

[alan.barker]

I'll try to answer 2 things as i see it imho.
Maybe a 3/8" unf fits because 5/16" and 3/8" unf are the same tpi 18 but the effective dia is not the same and it's the effective dia which is the strength.
For the "timesert"or "keysert" i would use something like that if the Helicoil or Armstrong Insert got stripped at a later date.
This is only my personal way i see things.
Alan