TR6 TR6 trailing arm stud upgrade?

[ichthos]

In my last post concerning torque, Ron suggested using course threaded studs. I was told that fine threads actually hold better since there is more surface area making contact on both surfaces? Please correct me if I am wrong.

Also, Goodparts does sell upgraded 3/8 inch, grade 8 studs with matching nuts (stock are 5/16"), but they look like fine threads. Tinster's story about his wheel falling off makes me nervous. His advice is especially good for me since I have twisted off bolts, especially low torque bolts in the past, when I have tried to tighten by "feel" (which is why I use a torque wrench religiously now).I admit I did not find my rear axle bolted to aluminum to be comforting to begin with. Would putting in those upgraded studs really make them any safer? Who would I take my trailing arm to to to get this done, and what would be the cost? My car has been on blocks since August, and I will probably be snowed in for the next 2-4 weeks. I don't mind waiting to get this done if it makes sense to do so. Your opinions and comments are always appreciated.

Kevin

 

[ichthos]

I just thought of another questios also. Would putting in larger studs change the torque values I would use when tightening the nuts?

 

[crj7driver]

Not sure about how the GP kit is installed but the rule of them is you want to use coarse threads on aluminum and fine on steel for the most strength.

Just looked at the picture, it is pretty small, but the threads that go into the trailing arm might be coarse. I would be very interested to hear what Richard has to say about them.

 

[RonMacPherson]

My recommendation(suggestion) was based on some basic metallurgy engineering. If you have any questions that can't be answered here, and hopefully they will be, you might explore more and improve your understanding of metallurgy and nuts and bolts.

Carroll Smith, who in my mind, was the auto racing guru, wrote a very informative book-Nuts, Bolts, Fasteners and Plumbing Hardware. See if you can get a copy. I think you will find it explains a lot.

In essence the larger stud you can go, the better, in both diameter and depth of thread, even to the point of going through the arm and mounting nuts on the back.. Yes your torque value will be increased, any basic high school auto repair, or military auto tech manual will give you general guideline for sizing of bolts and torque value.

But, remember you will be torquing dissimilar metals. So your torque value will be the lower value in any chart. Also dissimilar metals, i.e., steel into aluminum is the main reason I recommend coarse thread. If you were going steel to steel then fine thread may be better. But steel stud to aluminum begs coarse thread contact for expanding the torque stresses....

 

[TR6BILL]

How about installing inserts on each 5/16th stud? Two of my studs are installed with HeliCoils (the DPO installed them with JBWeld, that's scary!). Plan on replacing all of the remaining 10 studs with new ones and HeliCoils this week. There has been much discussion on this and other forums about using Timeserts, some saying they are superior to HeliCoils. From what I know and have read, HeliCoils are plenty strong enough for this application (understand that I am a toilet PhD) and are much easier to find. A kit will cost you about 60 bucks. The HeliCoil is stainless steel wire that is self-aligning. I put mine in with some Loctite. They are fairly easy to install.

 

[crj7driver]

To add confusion to the subject. Is there any difference between running a helicoil, timesert, keensert etc. vs running a 3/8 stud with course threads. In both situations you have larger coarse threads in aluminum. The only real benefit I can see regarding the insert is if you need to remove the stud, it will be steel on steel and not risk the possible bonding between dissimilar metals.

Am I missing anything?

 

[BobbyD]

The Keen-serts have tongs that get driven in after you thread it into the hole. Those tabs are what really lock it in place virtually eliminating any chance of stripping in the TA. They don't recommend using anything like Locktite. The stud can then be tightened into the Keen-Sert without fear of stripping the aluminum TA.

 

[Tinster]

OK - I-ll back away.

Helicoils are totally safe inserts and everyone should use them .
There is certainly plenty of excess Trailing Arm aluminum thickness
to drill out for the new Helicoils.

I probably had a bad dream that a rear wheel come off due to Helicoils
stripping out at 40 mph.

My blunder, sorry gang!!
This is what happens when a non-mechanic makes a technical statement.

now, back under my rock for a while.

'croak!!"

d

 

[DougF]

I made my comments about Keen Serts and Heli Coils in the other thread on trailing arms.

The only advantages Heli Coils have over Keen Serts are they don't require as much material removal for installation, better availability and lower price.

With trailing arms, Keen Serts eliminate all concerns with electolysis. They were originally designed because of problems with crossthreading of sparkplugs in aluminum heads.

 

[martx-5]

As mentioned, the problem with Keen Serts is the size of the hole and tap needed to install them. A 5/16 Keen Sert requires a 7/16-14 tapped hole. I don't think that the TR6 trailing arm has that much material to work with.

And Dale, a <span style="font-style: italic"><span style="font-weight: bold">properly</span></span> installed Heli-Coil in aluminum is far superior then just threading a stud or bolt into the aluminum alone. The aircraft industry has been using them for years. They are also a proper fix when threads in aluminum or any other metal gets stripped. The key is to do it correctly. It's obvious that whoever did the repair on your TR6 did not do it correctly. I've repaired hundreds of stripped threads in aluminum, cast iron and steel using Heli-Coils and have never run into problems with them pulling out.

It's unfortunate that you had the experience that you did, but it was NOT because of inferior technology on the part of the Heli-Coil...it was due to a bad technician.

 

[ichthos]

I wrote a quick little note to Richard Goodpart to see what he says about the studs. I'll let you know what he has to say if he writes back. At a very basic level it makes sense to me that a larger and/or longer stud would have more surface to secure itself into the aluminum area unless it was so big that it compromised the aluminum. That book sounds interesting, Ron. I am going to try and get a copy. It is easier to make choices when I have a full understanding of how things work. One of the problems I have with the upgrade is that there is no way I will attempt this. That means I will have to find someone good I can trust locally, which isn't always easy. Does anyone know of someone who can do this in my area? I am in the Olympia area, but I am willing to drive a ways if necessary.

Kevin

 

[RonMacPherson]

Any competent machine shop should be able to drill, tap, insert insert, larger studs. etc...

See if any work with trucks(big rigs, etc.) or aerospace or hot rods... Those usually have more experience(other than some old guy who is 95 years old, been working on cars since he was 16, etc...)

In over 35 years in the auto repair industy I have seen one(out of several hundred) helicoils fail, and that was not due to installation... Believe it was one of the first "imports" and not a true helicoil... that was for a steel into cast iron, head bolt hole in an Acura V-6...

 

[BobbyD]

As mentioned, the problem with Keen Serts is the size of the hole and tap needed to install them. A 5/16 Keen Sert requires a 7/16-14 tapped hole. I don't think that the TR6 trailing arm has that much material to work with.

Herman van der Akker who makes the Toyota 5 speed conversion kit is the guy who turned me on to KeenSerts as he's done them in all of his and his kids' TRs. The hole is an "X" drill size (.397") and the tap is 7/16-14. I did one of mine last year for a stripped thread and there was no problem having sufficient material.

I figure if the Aircraft industry is OK with these things holding airplanes together, we shouldn't worry about using them on our cars..........providing they are installed correctly. My guess is that a very common mistake is that people see, for example, that a 7/16" tap is required.... so they drill a 7/16" hole for the tap to go in. A 7/16" tap requires different size holes depending on coarse vs fine threads and in either case, it is not a 7/16" hole!

 

[ichthos]

I checked on Ebay, Ron, and the book you mentioned by Caroll Smith (a new addition) is being offered out of the UK. Not cheap, and I will check elsewhere, but I think I am going to get it. One last question: since the stud holes are not damaged in my trailing arm, would my best upgrade be to go to the larger size stud with courser threads, or would I do better to put in the Keen-serts? Would a machine shop be able to tell me the new torque values?

 

[RonMacPherson]

Bes? I can't tell you.

I can advise, that to me it would depend on the condition of the aluminum.

Here in Hawaii, anytime I see ANY oxidation, it needs to be done away with. So that would require inserts or larger size studs.

You in the Pacific Northwest, I dunno what shape your t/a's are in. Might want to lug them to the machinist for his advice. After all that is his profession, and if you get a reputable one, there should be no concern..

 

[Tinster]

And I'll shut up about technicals things, since I've no knowledge
or skills when it comes to things automotive. I'll stay over in
the Pub and discuss weather and food and fishing and bikini babes.

I'll leave this technical arena with with one final thought-

When a rear wheel comes off your car at 40 mph,
going thru a bend in the road- you will NEVER
EVER again trust Helicoils or any other insert.

Now over to the Pub to see what's cooking!!

dale

 

[Brosky]

Dale, what it the matter with you lately? Can't anyone have an opinion or knowledge that is contrary to yours? We all know that your wheel fell off. It was more than likely caused by a faulty installation. Period.

Do you think that anyone here would intentionally set themselves up for the same thing? Hermann and Richard Good both recommend this type of PREVENTIVE modification and I haven't checked Kas's site, but he probably does too.

HeliCoils are put in spark plug threads everyday. How many repaired cars do you see with holes in the hood from spark plugs blowing out that are under explosive force many times per second?

 

[sail]

II have never dealt with a machine shop but with no drill press looks like I need to find a good one for this and the next thing or two or three. When I do and replace the 5/16th studs since they are all good stud holes can I assume they know what size HeliCoil to put in. And would it be a different coil for either existing fine thread or coarse?

 

[TR3driver]

Helicoils are different for coarse or fine threads.

One advantage of the Keen-serts that I've not seen mentioned : Helicoils require a special (expensive) tap for installation, while the Keen-serts use ordinary taps.

However, an old mechanical engineer once told me that Helicoils should be stronger in aluminum, as the coil can deflect slightly to spread the load over all of the aluminum threads. The rigid Keenserts wind up concentrating the load on the outermost threads, which is exactly where you don't want it.

Whether that actually makes a difference in practice, I can't say, but I've always used Helicoils and they have always worked well for me.

It's actually pretty easy to install a Helicoil without a drill press, since the stripped part of the hole is already the size that you are drilling, and will act as a guide to some extent. Of course you still need to exercise care to hold the drill square, but it's not terribly difficult. I've even gotten away with not drilling at all in aluminum, using the special tap as a reamer to (slowly) remove the excess material at the bottom of the hole. There are also guides available to help you hold the drill square (tho I've not tried them myself).

Keep in mind that these cars have already survived three times their design lifetime; so you don't really need to engineer them stronger. Just restoring to original should be all you need, unless you are making other modifications that increase stress on the rear suspension (like that 302 Ford under the hood).

 

[BobbyD]

OK Guys.......here's a simple solution. I've been working with Rick Patton, of TBI fame, on a precision machined jig that would make the drilling, tapping and installation of inserts and studs foolproof........and I get the be the fool to test it! Basically I had asked around how people have done this process and most had either step drilled it or made up a simple jig to help with keeping everything aligned. So I came up with an idea for a precision jig, asked Rick his opinion and he immediately improved upon the idea and has made a few of them up. I have no financial interest in this other then getting to be the guinea pig for the first installation. If you're interested, you can email Rick at his web site www.pattonmachine.com I also just added lots of pictures to my site so you can see the jig in action.

This is all done with the TA on the car and with a portable drill.