13 replies to this topic

[JonnyAlpha]

Hi;

 

I have a couple of threads in the Gearbox Casing (Transfer Case Side) that have been bodged with UNF bolts.

Following advice I bought a Chronos 5/16x18 Helicoil Thread Repair Kit.

 

I have drilled out the old threads using the supplied HSS Drill, but the supplied Tap seems way too big (the taper end is bigger than the drilled hole).

 

The drill is stamped 21/64 HSS and the Tap is stamped STI3/8-16 HSS.

 

Is the Tap too big and what size Tap should be used?

 

The Helicoils are also just under 10mm making them a 1D Helicoil, the threaded hole is 23mm deep, should I be using longer Helicoils? Should the Helicoil sit flush with the top of the drilled hole and should I be using Thread Lock when inserting the Helicoils.

 

Also two of the holes are blind and one is through so should I have a bottoming of plug tap?   

 

Sorry lots of questions

[nicklouse]

First you say Helicoil is it or is it a different make? 
 

and is the tap thread the same as the outside thread of the insert?

[GraemeC]

The numbers don't look right - I've never studied it, but I would've thought the TPI of the tap should be that same as the finished thread size, just a different diameter

 

Edit - on my original Helicoil set, the tap isn't marked with its actual size, it is marked as a 5/16 UNC Helicoil tap (which makes sense as it probably a special size to achieve the TPI). The drill bit is 8.2mm

Edited by GraemeC, 05 August 2020 - 03:52 PM.

[GraemeC]

I suspect you have the tap for 3/8" UNC inserts

[JonnyAlpha]

First you say Helicoil is it or is it a different make?

and is the tap thread the same as the outside thread of the insert?

It’s a Chronos Thread Repair Kit

[JonnyAlpha]

First you say Helicoil is it or is it a different make?

and is the tap thread the same as the outside thread of the insert?

The OD of the coil is 9.95mm and the OD of the Tap is 11.71mm

[JonnyAlpha]

The numbers don't look right - I've never studied it, but I would've thought the TPI of the tap should be that same as the finished thread size, just a different diameter

Edit - on my original Helicoil set, the tap isn't marked with its actual size, it is marked as a 5/16 UNC Helicoil tap (which makes sense as it probably a special size to achieve the TPI). The drill bit is 8.2mm

The drill is 8.3mm

[GraemeC]

OD of my tap is 9.9mm

[nicklouse]

 

First you say Helicoil is it or is it a different make?

and is the tap thread the same as the outside thread of the insert?

The OD of the coil is 9.95mm and the OD of the Tap is 11.71mm

 

then that aint right looks like you have the tap for a 3/8ths

[JonnyAlpha]

 

 

First you say Helicoil is it or is it a different make?

and is the tap thread the same as the outside thread of the insert?

The OD of the coil is 9.95mm and the OD of the Tap is 11.71mm

 

then that aint right looks like you have the tap for a 3/8ths

 

 

Having had no response so far from the supplier and wanting to crack on, I Just ordered a V Coil Set and some 2D inserts,

[Spider]

The Tap they have supplied you is for 3/8" thread repair. They have supplied you with the wrong one.

[JonnyAlpha]

The Tap they have supplied you is for 3/8" thread repair. They have supplied you with the wrong one.

 

Thanks Moke - they emailed me to say they have just shipped the correct one. I will now have 2 sets

[JonnyAlpha]

Correct Tap arrived in the post along with another V-Coil set that I ordered and some 2D 5/16 x 18 UNC Coils.

 

A bit nervous as I'd never done this before and did not want to mess up the gearbox casing. Threaded the hole, inserted the coils, no just need to turn them in 1/2 turn and break off the tang (Is that what the small punch is for?).

 

Hole Tapped:

 

 

Helicoil fitted:

 

 

Job done:

 

[GraemeC]

Yes, the punch is to snap the tang off