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Not very happy - wife even less so!


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Hi Mick,

now your being naughty. You have introduced corrosion.

The ali alloy didn;t corrode because of the UNF stud form. And then upon unwinding the nyloc nut of course the stud will come out - thankfully.

 

With all that corrosion if you pulled the stud with enough force the stud would easily (compared to sound metal) pull out.

 

But!!!!! I bet if the stud was put back in the corroded hole the hub would perform OK. I don;t know how many would need to be badly corroded before the hub went flying. However none so far have done that.

 

But we are drifting off the point. ST designed it with UNF studs and they have performed very well - perhaps against the norm but work they have.

 

Roger

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“I've often seen the studs just unwind along with a portion of grey powder which used to be alloy 50 years ago, doesn't appear to have had excess torque to me , just corrosion and insufficient thread root strength to retain the studs and hub”

 

Wouldn’t that corrosion occur no matter the thread type? Granted, it might take longer with unc. The point I’m making is that when putting on or taking off the hubs is very difficult unless the hub is being presented at precisely the right angle to the trailing arm by virtue of the close tolerance holes. I can’t see a situation where, even with corrosion at the stud / arm interface of one or two studs, that would result in the studs coming out under tensile loads in service (like driving).

 

Ive seen studs corroded in the way you describe mick, but they won’t fall out unless corrosion is affecting more studs resulting in the assembly not being ‘close tolerance’.

 

Where’s me coat.

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Thanks everyone for your suggestions and comments. Seems its not as big an issue as I'd feared so I'll proceed with stripping and checking repair options with a lot more confidence :)

 

Gavin

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Dave,

 

I think both you and Roger are correct (and come to think about it so am I) because we have 6 x 5/16th studs in direct shear the actual force applied to the studs is easily coped with, so they won't shear.

 

The other force is transitional (lateral forces when cornering) because of the close fitment of the holes on the studs the hubs are amply supported and the retaining torque could probably be reduced from what it is, there simply isn't enough torque along the stub axle plane to wiggle the hubs up the studs (they are only about 5 thou clear on each hole.

But engineering practice still dictates that if you have a nut on a stud it should be able to be tightened to a specific torque (even if pathetic), so my money would be on a slightly coarser threaded stud into the trailing arm, hence the 3/8th UNC is my choice gaining maybe another 20 years on top of the 50 years original life !

 

Mick Richards

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You can't be serious ! :wacko:

 

And Black pepper !

 

Mick Richards

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On this subject, can anybody advise me of the length the studs are supposed to be, and also,

Where can the appropriate 5/16" UNC studs be purchased from?

Cheers, Paul.

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Speak with Mark at Southern Triumph Services in Bournemouth, he should be able to sort you out.

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Hi Gavin,

not the end of the world :o

 

Firstly remove the hub

Then screw in a 5/16"UNC (course thread) bolt to see if it can hold reasonably tight - it is only 16 lb.Inches of torque.

If it does then simply replace with decent studs.

 

If the thread has gone then consider 5/16"UNC helicoil - this is the simplest first step - as if you cock up you have another chance later on. (3/8"UNC)

As Mick states it MUST be square to the plane of the hub face. Ideally a jig that holds the drill/tap.

I made one from 1/4" ali alloy plate that 6 x 5/16" holes on the PDC with one hole bigger to take the drill/tap guides. see my pics.

 

 

Roger

 

attachicon.gifP1030513aa.jpg

 

 

 

 

 

Hi Roger.

 

Thanks for all the info, most helpful as usual. Can you conform the torque value of 16lb.inches? And, is this for the studs or the retaining nuts?

 

I can't seem to find values for either in my Haynes manual.

 

Kind regards

Gavin

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Hi Roger.

 

Thanks for all the info, most helpful as usual. Can you conform the torque value of 16lb.inches? And, is this for the studs or the retaining nuts?

 

I can't seem to find values for either in my Haynes manual.

 

Kind regards

Gavin

Gavin,

 

If you download a brown book ( from the links displayed a while ago on this forum) , all the torque settings for the TR6 are in the front.

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Hi Gavin,

sorry about that - I was getting UNC/UNF & Inches and feet all muddled up.

 

It is apprx 16 lb.ft.

 

The studs go in as far as they can and simply nipped up. The Nyloc is then torqued down. It is a very low figure. Don't over-do it.

 

Roger

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Thanks all, for the healthy subject and discussion which I am sure most would agree and I would like to see more of this in TR Action.

I have often thought why Leyland came up with this but was convinced they knew what they were doing and the testing would have been stringent.

I did work for BSI in my past life and the testing of any component was very good.

Regards Harry

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I've just had the same problem on my TR, the aluminium thread had corroded. Drilling and tapping to 3/8 UNC was a straightforward fix. One of the holes had already been repaired with a 3/8 UNF stud which seems to work equally well, however I don't know anybody who supplies a 3/8-5/16 UNF stud. Using a 3/8-3/8 stud would require opening up the hole in the hub assy to accept it.

It strikes me that the problem, apart from over tightening and stripping the thread, is dissimilar metals corrosion between the aluminium hub and the steel stud. Copper grease would seem to be the best way to avoid this. Loctite is intended primarily to prevent the thread from coming undone, something that doesn't seem to be an issue with these studs.

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"I still maintain that they went unorthodox"

 

Not arf pop pickers ! I reckon they were on the "wacky baccy" why use an UNF with attendant root material compromises when a similar sized UNC would do the job better ? I reckon the studs wouldn't "unwind" when you've got 16 lb ft dragging the threads into contact with one another.

But bear in mind these were the same genius's who developed the Stag engine with NO holes in the centre of head and block relying on thermos expansion to help the coolant flow from the back to the front. Then developed a head retention system with 11" ANGLED studs with 2 threads and one nut and 5" set bolts at 90 deg running alongside them and then 3" set bolts at 90 deg along the cylinder head edge which compresses a thinnish 1" thick head section and ALL of these fastenings are supposed to have the same torque and clamp the head equally, not a chance in hell.

 

Mick Richards

Well said Mick! I At that time I worked for Coopers/Payen and we refused to guarantee our head gasket because of that design! let alone the single row timing chain which failed on 2 occasions when testing our head gasket on our engine test bed and wrecked their engine. We were not too popular with BL.

 

Bruce.

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Hi Mick/Bruce,

this will be my last comment on on the use of UNF studs in the TA.

 

This lunchtime I had lunch with a dozen of my BA retired engineers - we do it every on the 1st Tuesday of each month.

 

I posed the question - when would you use a 5/16"UNF thread in place of a 5/16"UNC thread in an Ali alloy casting.

 

A number of chaps said you wouldn't.

And then one bright spark chimed in with - if you don;t want vibration to undo it' No prompting from me.

 

So I will stick with ST designers. I think 40 or 50 years without undoing is pretty good.

 

 

Roger

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"if you don;t want vibration to undo it'"

 

I am undone...I concede.

 

Mick Richards

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Thanks all.

 

On further investigation I find that all of the thread is missing from one holes in the trailing arm and that left in the second looks pretty sad so I'll be replacing them all with the 3/8" UNC kit from CDD as recommended by many. Fortunately I'm able to borrow a jig from someone locally so it should be fairly straight forward :unsure:

 

Roger, I know you said that you wouldn't be commenting further, but I presume that back in the days there was no such thing as thread locking compound, hence the concern about UNC studs vibrating loose? Regardless, I will be using Loctite of some description on the new studs, although I'm not sure this is recommended for use in alloy as I believe it can pull the alloy threads out if the studs are subsequently removed :unsure:

 

Regards

Gavin

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