TR6 Thread repair for trans cover bolt

[kyslugbug]

Transmission cover left rear bolt threads into the hole, but will not tighten.
I'll verify the bolt size tommorow. The size is roughly M8 125 70.
Do I tap it to the next larger size bolt (M8)?
What about Helicoil, Timesert, or Keensert?
Once repaired, what arbout torque setting?
Thanks!

 

[TomMull]

I think you'll find that it is 5/16 inch. The best fix would be a thread repair; Helicoil or the like. Once done, use prescribed torque. The threads will be stronger than the original.
Tom

 

[bobhustead]

Try the US size(not metric) before any mechanical repair. Any drilling or tapping needs to be done in a way that does not put shavings into the trans.
Bob

 

[Tinkerman]

Don't know about the TR6 but my TR3 had no metric threads, they were all SAE course and fine. I used Helicoil on a couple of bad tranny top bolts , worked fine.


Good luck, Tinkerman

 

[Tybalt]

Threaded fasteners for the TR6 are for the most part to the "Unified" standard which is interchangable with SAE standard fasteners, you can thank the lend lease program from WWII for that help in getting fasteners for these cars. These should be 5/16-24 and in three different lengths for the gearbox top cover. The forward long bolts should be 2 7/8" long, the rear long bolts should be 2 3/4" long and the ones on the side are set screws (threaded all the way) that are 1 1/4" IIRC.

About the only thing that I can think of right off hand on a TR6 that was metric from the factory is on the later cars where they went to the 16M front calipers that had metric sized mounting holes and metric threaded hydraulic ports. Despite having metric sized mounting holes, the mounting bolts were still Unified threaded shoulder bolts where the shoulder was 13mm to match the caliper and threaded 7/16-20 to match the existing caliper bracket.

 

[kyslugbug]

Yes. The bolt is 5/16" SAE and 3" from top to bottom. The last inch at the bottom had about 15 or 16 threads. Found a Helicoil Thread Repair Kit 5/16-18 by Stanley (5521-5). I measured the helicoil inserts to be about 3/8" long. Is this the right kit, or should the helicoils be longer? Also, does anyone know the torque settings for the cover bolts? Thanks!

 

[CJD]

3/8" is all that is needed. The hard part will be to prevent the drilling chips from falling into the case while you install the inserts. Most of the holes go all the way through. I put a rag inside the case to catch them. Use lock-tite on the insert and stake the top thread to keep it set in the case and not spin out with the bolt the next time.

14-16 ft-lbs for the cover to case.

 

[Geo Hahn]

Don't know about the TR6 but my TR3 had no metric threads...

Of course your TR3 has at least 4 parts with metric threads... right?

Hint: A TR6 will have 6 of those parts.

 

[Tybalt]

D'oh! Completely forgot about spark plugs being metric threads, a nominal 14 x 1.25 in our case....

 

[kyslugbug]

Will have rags and a small shop vac ready. Also, thanks for the torque settings.

 

[Got_All_4]

The threads are 5/16 24 or USS on my tranny. Get the longest thread coil insert you can find but the 3/8 would be fine. If the tranny case is empty then no concerns on the chips. If not check to see if the drill bit goes through the case cover hole. If so put lots of grease on the bit and drill it with the cover on. Same with the tap. The grease will help to keep the chips from falling into the case. Also put lots of grease on the tap threads and back out and clean it off often. Be carefully using a drill with the drill bit. I know that on Time Sert kits the drill bit is made to be used by hand with a tap handle. If it has a square end then use a tap handle otherwise if you use a electric drill it could immediately pull the bit into your work and possibly snap it off if you go too fast. Then you've got another set of problems.

 

[Tybalt]

The threads are 5/16 24 or USS on my tranny. Get the longest thread coil insert you can find but the 3/8 would be fine. If the tranny case is empty then no concerns on the chips. If not check to see if the drill bit goes through the case cover hole. If so put lots of grease on the bit and drill it with the cover one. That will help to keep the chips from falling into the case. Also put lots of grease on the tap threads and back out and clean often. The grease helps catch the smallest of chips.

Can't be both, it's either 5/16-24 or it's USS. The 5/16-24 is SAE superseded to Unified Fine aka UNF. USS thread pitch for a 5/16" fastener is 20 tpi. USS is superseded and corresponds to Unified Coarse aka UNC. Strictly speaking, both SAE and USS are considered obsolete terms for identifying fasteners as they were superseded when they were incorporated into the Unified Thread Standard. We really should be referring to these as UNF and UNC (and I do at work, gotta use the proper terms there) but SAE and USS were in common usage for so long that they are still hanging on for the time being. My bet is that they'll finally fall out of use about the time the keepers of the standard decide to stop using UNF and UNC and go to some new set of designations for fine and coarse threads.

 

[martx-5]

.... USS thread pitch for a 5/16" fastener is 20 tpi. USS is superseded and corresponds to Unified Coarse aka UNC..

That should be 5/16"-18 IIRC.

 

[Tybalt]

That should be 5/16"-18 IIRC.

D'oh! x D'oh! You did indeed "RC." That's what I get for posting late, when tired and in a hurry, the ol' brain starts fading out and can't tell my NAS from a hole in the ground....

 

[Got_All_4]

Ya sorry I miss spoke. Should have said 5/16x18 USS. I wrote what I was reading "after midnight". However USS & SAE are more communally used terms this day and age. I deal with that every day in my job too and we are not writing text books here so ether is correct.