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RogerH

TRailing Arm Stud Alignment jig

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Hi Folks,

a friend of mine requires his TA stud holes rejuvenating.

Has anybody got an alignment jig I could borrow/hire/ for a week. I promise not to break it.

 

I will save me making one

 

Roger

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Worth noting that some specialists can offer studs with a larger, coarse thread for T/A, much better in the soft alloy casting than the small fine thread Triumph used originally. From memory, these studs are 3/8" UNC into the T/A with the original 5/16" UNF thread for the hub securing nuts.

 

Sorry I can't help with the jig.

 

Nigel

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Roger

 

I used an old hub. Bolt it to a couple of the old threads and drilled out the others, then fixed the new studs in and swapped over. The hubs are pretty tough and allow for you to drill square which important. Worked a treat for me. I have the hub that I used if you want to borrow it. I also used the replacement studs that have one side course thread and one as original.

 

Cheers

 

Roger

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Roger,

 

Use bigger 3/8th UNC studs with the original 5/16th UNF thread on the hub side. The 3/8th UNC thread in the trailing arms is coarse against the original 5/16th UNF threads used there, and it doesn't require as large a parent hole as the other popular fix of using the 5/16th UNC Helicoil with a 5/16th UNF interior thread inside it.

 

As regards the use of a jig when you are repairing all the stud holes It is almost mandatory. If you were just repairing an odd thread you may get away with hand drilling out the trailing arm with a pistol grip drill (I know your particular hand and tool skills will keep the stud hole square in both planes). But if all holes are being drilled and more importantly tapped it's all too easy for a small couple of thou lean on a couple of opposing plane studs to prevent the hub being fitted afterwards without redrilling the hub out larger to allow clearance on the studs. Not to arduous I hear people say but of course it does introduce a bending motion (and consequent possible failure points) onto the studs where the hub hole axis and stud axis doesn't coincide as being parallel.

Sorry if I had a jig I'd loan you it.

 

Mick Richards

Edited by Motorsport Mickey

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I promised to make some of these studs for Mickey, according to his special recipe.

I've got everything needed and will get to it shortly.

 

I now have two die-heads mounted on MT2 arbors.

https://www.flickr.com/photos/90670218@N04/sets/72157646485503192/

 

PM me, Roger if you want to know more about this.

Edited by AlanT

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Thanks everybody for your ideas and suggestions.

 

I think I shall make my own jig - it is fairly straight forward. I have the metal and machinery.

 

I'll feedback on how it works out.

 

Roger

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Just as an aside here: do not use Würth Time-Serts for this job- they can pull out.

I have used the 5/16" UNC Recoil kit for many years, without a jig; the drill bit supplied is driven by hand with a tap wrench & cuts true.

Just take reasonable care with it and the tap.

The studs can be replaced by caphead bolts, which will take 22-25ft/lb comfortably.

I can vouch for their strength- one of our racers once caught a kerb hard at Pembrey circuit & ended up beached with a smashed trailing arm. The bolts held. We replaced it with an unmodified one, sent him out again, and he performed exactly the same stunt again. All 6 studs out, more damage & a long ride home...

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Hi Folks,

if I was doing the job I would probably give it a go by hand but my chum doing the work is an office type bod - but usually quite capable.

I actually enjoy making things so this jig was fun.

 

The body of the jig does not need to be that robust (that Patton jig looks like a Rolls Royce of a jig) as it is simply holding and aligning the guide that takes the wear.

1/4 ali plate is used.

 

The studs are on a 4.25" diameter. I used a pair of dividers to mark the six points on the circumference where the stud holes will be.

Thankfully as there are 6 holes these are at 60 degree around the centre - this forms an equilateral triangle so the divider measurement is the same as the radius 2.125"

 

The positions marked, The holes were started with a centre drill to get them as close to the mark as possible.

I do not have a pillar drill but my mill works well for this sort of thing.

 

With the holes sorted the moment arrived to place it over the TA studs - bingo. It could not have been more accurate than if I had used an index plate and CNC machine.

 

The intention was to leave three holes at 5/16" for alignment. and open out the other three to take the alignment guides.

I then realised that I only needed one hole opened out - too late.

Anyway a hole was opened to 9/16" dia. (to allow micro adjustment possible)

The guide will be 1" deep x 1" diameter this should sit well on the flat plate. The end of the guide is turned down 1/2" diameter x 1/4" deep.

This guide fits into a small plate with a 1/2" diameter hole in it that is attached to the larger alignment plate.

The reason in using this secondary plate is to allow for any misalignment in the drilling process in making the plates.

The guide and secondary plate are then placed over a known good stud and then screwed down and fixed.

 

I now need to make a number of guides -

Tapping drill size for 5/16" helicoil

Tap size for 5/16 helicoil

3/8 tapping drill size for 3/8 UNC.

etc

 

These simply pop into the secondary guide plate and bobs your uncle.

 

I'll try and put a pic on here later.

 

Roger

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Hi Harry,

I knew that somebody close had one but couldn't for the life of me remember who. Many thanks for the offer though.

 

Roger

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Hi Folks,

here are a few pics of the TA stud jig.

The cylindrical lump is the drill/tap guide and may be any diameter needed. These would bemade from steel to give them some durability.

 

Nice and simple

 

Roger

 

 

 

 

 

 

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Hi Simon,

you can certainly borrow the jig when my chum John has sorted his - that is what it is there for.

 

The guides are drilled to accept the 5/16UNF tapping drill and helicoil tap. I don;t know if 5/16 UNC use bigger drills/taps.

 

5/16 UNF will out last any owner by about 40 years.

 

You will need to order a dozen 1.5D helicoils

 

Roger

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Roger,

 

Drill size for 5/16th UNC Helicoil is .328 thou (outer tapping size for the helicoil), this is 16thou MORE than the .312 (5/16th) hole required for a 3/8th UNC PARENT thread tapped into the alloy casting. Conveniently when the 5/16th UNF thread in the trailing arm strips it often leaves a hole of about the .312 thou dia there which should accept the 3/8 UNC tap nicely. I'd still use your jig though, it's the tapping which often puts a lean on a stud rather than the drilling.

 

Hence my favouring a stud of 3/8th UNC thread (it will be about a 300 thou deeper thread also) into the trailing arm, with an original 5/16th UNF thread pattern as original on the hub size.

 

Mick Richards

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Hi Mick,

the owner of the TA has chosen to replace the original studs with the same (plus the helicoil).

 

I can see where you are coming from with the 3/8UNC stud.

 

Roger

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Hi Simon,

you can certainly borrow the jig when my chum John has sorted his - that is what it is there for.

 

The guides are drilled to accept the 5/16UNF tapping drill and helicoil tap. I don;t know if 5/16 UNC use bigger drills/taps.

 

5/16 UNF will out last any owner by about 40 years.

 

You will need to order a dozen 1.5D helicoils

 

Roger

Hi Roger! It is general engineering practice in the UK to use course threads only in soft metals as course threads are deeper per size and there is more thread engagement on the flanks of the thread form. I know that Triumph got it wrong here but I suspect that it was a DO mistake when originally drawn up. Another point when doing this repair, only use a new HSS Drill bit and thread tap(s) as carbon steel types often bind when drilling and tapping and the hole is oversize and not round. One final point the jig-bush should be made from harden steel to counter off centre drilling.

 

Bruce.

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Hi Bruce,

Roger managed 30 + years "in front of the mast" at BEA before his more laid back apparition took over, I think he may know about British engineering practice Lol :ph34r::lol::lol::lol:

 

Mick Richards

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Hi Bruce,

see my post on Gavins thread http://www.tr-register.co.uk/forums/index.php?/topic/65602-not-very-happy-wife-even-less-so/

 

I do not think that ST got it wrong. If they did they would have corrected it on the TR5, TR6 Stag or whatever.

How many hubs have come off because the studs are broken. Even the dreaded corrosion has taken decades to work its mischief.

 

Good engineering practice is a generalisation. There are always exceptions.

 

The 5/16UNF has proven itself to be adequate. The question should not be they got it wrong but why did they choose UNF and got it so right.

My point is the shallower angle of the thread.compared to the UNC.

 

Roger

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