correct bolt size needed for gearbox-engine

[Casar66]

Hi guys,

I am wondering what is the correct bolt for mounting the gearbox to the engine. On my car all the bolts are mounted with the head on the gearbox side. The Triumph manual says something different, there the bolts come from the engine side. Anyway, I will continue to do it wrong.
But I am missing one screw. It is one of the 3 upper ones. The position is about 11 o'clock. I can install it from the engine compartment without removing all the stuff. The correct size is 5/16 UNF x 13/8. I think that is correct (found it on the Rimmer site). But since the Brexit, it makes no sense to place such a small order, so I'll try to get the screw here. But the store is asking me UNF with 18 or 24 threads per inch. What is right?
Have a nice easter!
Cas

[Waldi]

5/16 UNF has 24 TPI (threads per inch), always.

Be sure to install the two special  “alignment” bolts with the correct boss-diameter in the 2 designated locations.

Waldi

[Casar66]

I would prefer "full threaded" screws. These should fit anyway. Or am I wrong?

[BlueTR3A-5EKT]

9 hours ago, Casar66 said:

Hi guys,

I am wondering what is the correct bolt for mounting the gearbox to the engine. On my car all the bolts are mounted with the head on the gearbox side. The Triumph manual says something different, there the bolts come from the engine side. Anyway, I will continue to do it wrong.
But I am missing one screw. It is one of the 3 upper ones. The position is about 11 o'clock. I can install it from the engine compartment without removing all the stuff. The correct size is 5/16 UNF x 13/8. I think that is correct (found it on the Rimmer site). But since the Brexit, it makes no sense to place such a small order, so I'll try to get the screw here. But the store is asking me UNF with 18 or 24 threads per inch. What is right?
Have a nice easter!
Cas

Buy them from Moss Paris?  

https://www.moss-europe.fr/

While you are at it get a printed TR5/6 parts catalogue from them.   It includes a sketch of which bolt goes where 

 

Edited April 7, 2023 by BlueTR3A-5EKT

[Casar66]

 Moss does not have it, originally it is a stud not a screw (#112 in the drawing)

The screw (#113) is too long ) I guess it 5/16 UNF x 2" and the shipping and handling is ridiciously expensive.

[Casar66]

I have ordered these one (they could be quite short) but the try is worth it:

 

 

 

 

[John Bracher]

When I put my gearbox back in, I ended up making these studs, and the 'alignment' bolts, from longer bolts and a suitable sized die, so I could use the shanks as the location.

The shank tends to fit/sit better in the alloy bellhousing, I think, than threaded sections.

[TonyC]

Cas,

Those 2 bolts Waldi refers to are important. They locate the bellhousing and act like dowels presenting the gearbox at exactly the correct orientation to prevent clutch engagement / release problems which have been well documented. They have a shoulder which locates into the engine back plate and through into the gearbox, and they are bigger than all the others. Fit these first.

Brown book, Haynes and all others I have referred to advise fitting all bellhousing bolts with heads facing into the engine compartment and threads towards the rear.

The three studs at the top are 5/16 UNF (20TPI) . If you are struggling to get the correct studs with the blank unthreaded section in the centre then remove heads from 3 x 5/16 UNF bolts. They screw into blind holes so as long as length is OK you won’t have any problems. I cut a screwdriver slot into one end of the stud so you can fit / remove them easily with the gearbox attached.

Hope it helps.

TonyC

[TonyC]

Cas, sorry 5/16 bolts / studs are 24 TPI not 20 as I stated.

TonyC

[Casar66]

Thanks, Tony. The gearbox is already mounted. And yes, of course I have used the special two alignmentbolts.  I bought the car with heads on the wrong side already. 

I have removed and reinstalled the gearbox four times during this period. With the bolt heads coming from the wrong side. Also have seen this happen with many TR's. I don't think it makes any difference.

[elclem1]

If you buy from rimmers  under a value of £100 they will ship without you having to pay customs duty small orders are ideal. Clem

[Casar66]

yes, but they have not the bolts I need. I need bolts with hexagon head instead of studs for the three on top. I hope that the one I have ordered will fit. Most important part is the length of the unthreaded section. If it is too long, the screw cannot apply a strong connection between motor and gearbox. When I have mounted the gearbox I have not noticed that the tree upper bolts had three washers as to shorten the unthreaded section, better I did not understand why they have that many washers. Now I know. And on one screw, I left out two of the three washers, with the result that I heard a bright ringing when driving. That was just the one washer that vibrated due to the threadless section on the screw being too long. 

So I unscrewed the bolt and shortened the thread. But because of the tight space (I didn't want to remove the whole interior again because of the one screw) in the engine compartment, I shortened too much. The screw is absolutely seen long enough, but with too little thread section.
When I read this I get the crisis. So much babble because of a bolt. 

[Casar66]

for anyone who is as stupid as me: the bolt mentioned above fits perfectly.