improved trailing arm studs

[Casar66]

Have found two different improved set studs, one from goodparts, the other from CDD. The later are twice more expensive. Are there other differences?

 

[RogerH]

2 minutes ago, Casar66 said:

Have found two different improved set studs, one from goodparts, the other from CDD. The later are twice more expensive. Are there other differences?

 

Do you need to repair/replace the studs.?

If you need to repair damaged threads why not helicoil to 5/16UNF and use the original studs. 

They will only last another 40 or 50 years.

 

Roger

[Casar66]

Because that has happened already, done by the pre-owner. Unfortunately with M8. And one time with a M10! At least for the later a member of this Forum (Peter) will turn me one. 

My favorite was that method, pictured below. But the diameter will be 12mm overall and I do not know if there is enough material at the trailing arm.

[RogerH]

Oh dear!!!

 

Roger

[Casar66]

and, Roger, what do you think, will be 12mm too much for the trailing arm?

[Motorsport Mickey]

The problem is the alloy threaded material in the trailing arm is gained by small square alloy blocks being placed in the inside edge before the trailing arm was cast and then the holes being drilled and tapped into them.

Unfortunately the employee chosen to position the blocks was a 18 year old YTS employee who had only done the job over the last month Oh...he was also drunk ! 

Even the 3/8 th UNC threads will occasionally break through the walls of the misplaced alloy blocks ! so I think your 12mm threads will certainly cause some problems.

Mick Richards

 

Edited October 30, 2020 by Motorsport Mickey

[Casar66]

I feared that.

[RogerH]

There is just not enough material there

 

Roger

[Casar66]

But back to where it started: are there differences apart of the colour?

[astontr6]

1 hour ago, Casar66 said:

Have found two different improved set studs, one from goodparts, the other from CDD. The later are twice more expensive. Are there other differences?

 

The top stud has 2 different thread sizes on it and the larger one is a course thread and looks to be unplaited? The bottom one has fine threads on both ends and looks to have a parkerzed finnish. I am not certain that is good for aluminium?  I would be using the top one only as alum. requires a course thread. Although others on this forum do not think so?

Bruce.

[Casar66]

Iam not sure about the differrent threads, means that I think that both have the same threads if you count the twists.

[astontr6]

3 minutes ago, Casar66 said:

Iam not sure about the differrent threads, means that I think that both have the same threads if you count the twists.

The top one has a larger course thread I suspect 3/8" UNC and UNF 5/16" on the other end ?

Bruce.

[Motorsport Mickey]

The CDD hybrid studs with 3/8th UNC on one end and 5/16th UNF on the other allow you to often tap the stud holes without having to drill them, the tapping size for 3/8th UNC is .312 Thou which is neatly 5/16 " the outside size of the tapped UNF stripped threads. Counter intuitively the tapping size for a Helicoil for the 5/16th UNF threaded holes in the trailing arms is .328  (it has an outside thread with an inside thread inside it) and needs 16 thou more in an area where every thou is precious.

Also the 3/8 th UNC end is about 3 threads longer than the standard 5/16 th UNF stud and this can be drilled deeper and give you threads into virgin material, that's my choice.

Whatever you decide in this area remember the clearance stud holes in the hub are drilled about 5 thou larger than the 5/16 th studs, so if you helicoil the trailing arms back to 5/16th it absolutely needs to be tapped in square in 2 planes otherwise the hubs will not fit over the studs. I'm not even sure there's enough material on the hub flange to take 12 mm stud form and it's outside diameter.

Mick Richards  

Edited October 30, 2020 by Motorsport Mickey

[Casar66]

Quote

The top one has a larger course thread I suspect 3/8" UNC and UNF 5/16" on the other end 

Like the goodparts as well. But I do not know is it UNC or UNF.

 

[Casar66]

Quote

so if you helicoil the trailing arms back to 5/16th it absolutely needs to be tapped in square in 2 planes otherwise the hubs will not fit over the studs. I'm

? 

[Motorsport Mickey]

47 minutes ago, Casar66 said:

? 

When the holes are drilled out and tapped to take a helicoil even if the original smaller 5/16th UNF size they need to be absolutely vertical in both directions (planes),  if the studs lean over only the smallest amount the fit of the holes on the hub will prevent the hub fitting over the studs because there are 6 of them. If the studs are fitted leaning over it is tempting to "open" out the holes in the hub by drilling a bigger size that will allow it to fit onto the studs, but that then places a bending force on the studs and stresses them. That is not good long term from an engineering position, perhaps some pictures might help.

http://www.pattonmachine.com/TAK.htm 

[Casar66]

Now I got it! Thank you. I had to enlarge a hole of a (new) hub already, the M10 stud´s diameter was just to big for st standard hole. I hate this style of repairing.

 

[AarhusTr6]

14 hours ago, Motorsport Mickey said:

The problem is the alloy threaded material in the trailing arm is gained by small square alloy blocks being placed in the inside edge before the trailing arm was cast and then the holes being drilled and tapped into them.

Unfortunately the employee chosen to position the blocks was a 18 year old YTS employee who had only done the job over the last month Oh...he was also drunk ! 

Even the 3/8 th UNC threads will occasionally break through the walls of the misplaced alloy blocks ! so I think your 12mm threads will certainly cause some problems.

Mick Richards

 

Hey . . I was on YTS . . £25 quid a week if I recall :-)  made a man of me . . but dont think I delivered much on hindsight,,,,

[barkerwilliams]

I have CDD ones, as I recall came with the loan of a  jig,  drill, starter tap & bottom tap, not just the studs.

I would not like to have tried the job without the well made jig.

Probably took less than 30 minutes per side start to finish.

Alan

[JohnC]

I did mine using a hand drill and Mk 1 eyeball. I was blissfully ignorant of the risk I was taking. But, as they say, "better lucky than good"! If I ever had to do it again I would make a jig.

[Andy Moltu]

If all else fails you could get someone to TIG weld the holes so you can drill, tap and helicoil again.

[Casar66]

yes, that's the last exit.

[astontr6]

On 10/30/2020 at 11:02 PM, Motorsport Mickey said:

When the holes are drilled out and tapped to take a helicoil even if the original smaller 5/16th UNF size they need to be absolutely vertical in both directions (planes),  if the studs lean over only the smallest amount the fit of the holes on the hub will prevent the hub fitting over the studs because there are 6 of them. If the studs are fitted leaning over it is tempting to "open" out the holes in the hub by drilling a bigger size that will allow it to fit onto the studs, but that then places a bending force on the studs and stresses them. That is not good long term from an engineering position, perhaps some pictures might help.

http://www.pattonmachine.com/TAK.htm 

Hi Mick!

That company's method looks to me to be the DB for TA thread repairs using those Keen Inserts. The only problem I see is obtaining AF thread types here in the UK unless you work in the Aerospace Industry like BAe. Roger did British Airways Eng. use them?

Bruce.

[RogerH]

Hi Bruce,

I never came across any type of insert either at BEA or latterly at BA.

However I was only on the shop floor for three years after my apprenticeship. I then went into NDT.

Having said that I seem to recall inserts in Magnesium castings - Fuel control units and the like.

If you think Aluminium is dodgy to tap into try Magnesium sometime.   I don;t recall using them on the aircraft fuselage.

 

Roger

[Motorsport Mickey]

1 hour ago, astontr6 said:

Hi Mick!

That company's method looks to me to be the DB for TA thread repairs using those Keen Inserts. The only problem I see is obtaining AF thread types here in the UK unless you work in the Aerospace Industry like BAe. Roger did British Airways Eng. use them?

Bruce.

Depends very much on the actual trailing arm Bruce, as pointed out there is considerable variation in the locating block positioning and I've seen some horrors (when buying spare trailing arms for my Stag) especially when "gung ho freehand" drilling and tapping has lead to a lean which leads to the thread breaking through the material wall around almost half of the diameter.

I'm not sure that a helicoil or even these solid inserts will remain in position if a maximum exertion of side force is put through them (happily because there's 6 of them they support in a push me-pull me way). Hence my preference for the 3/8 th UNC hybrid stud into the remaining parent material which if in it's original 5/16th UNF stripped condition offers the maximum remaining material to tap into.  The 5/16th stripped dia holes (.312 thou )being the tapping size for 3/8th UNC taps, and smaller than the 5/16 Helicoil size (it's a fine interior thread inside a coarse exterior thread) of .328 thou, 16 thou bigger on dia. Those that remain unstripped are easily drilled out to 5/16th, and also the virgin material under the bottom of the stud can be drilled and tapped 3/8th UNC (you'll note the hybrid 3/8 UNC -5/16 UNF studs are long on the UNC side) offering another 3 threads of full dia material there.   

Mick Richards  

Edited November 1, 2020 by Motorsport Mickey