Rocker Arm Ball Studs

[MikeSimon]

I think I asked this question before, but I cannot find anything using the search function!

I installed all new ball studs. Because of the concern that was expressed by a couple of forum members about the threads in the aluminum head being stripped when removing the lower part, I replaced only the uppers (the actual ball studs). Several of them are not screwing in tight, i.e.: are most certainly well below the specified torque for valve adjustment and thus prone to move during operation. What can be done? Is there a thread "locker" that would result in increased torque, but NOT "lock" the thread? I am talking between the two steel items, NOT between the balls stud base and the aluminum head! Are these things designed NOT to come out and will lose their grip once removed? 

[Minerva]

I think I read somewhere here that you can deform the threads on the screw in piece to get more of an interference fit. From memory I squashed them in a vice to make them slightly oval
I replaced them completely and even though they were tight coming out if the head there was no thread damage, most of the new febi rocker balls were too loose in their new bases.

[wwheeler]

Were the new ball studs tight in the new bases as shipped? Reason I ask is because I know for a fact that about 3 years ago, there was a batch of ball stud assemblies from Mercedes that had defective threads. The stud assemblies as shipped were loose and could be turned by hand. I had the new complete assemblies installed on my new 220SE engine and had to remove them and received good replacements. As far as I know, the problem has been fixed.

On my 280SE engine, I did the same as you and found that the torques were not consistent. Luckily, they were still tight enough to be in the range. I think that is why they only sell the assemblies and is the only way to assure even torques.

[MikeSimon]

I bought ball studs without bases.

[wwheeler]

Where did you get them from? How loose is loose? Can you turn them by hand?

[MikeSimon]

It was a couple of months ago. I compared prices for quite a while and then decided. have to check where I got them. I think they came from Germany. They are loose. You can almost turn them by hand. Not quite, but almost. Definitely out of spec. I would think the problem is with the bases, not with the studs?

[Benz Dr.]

That's definitely too loose. I usually replace the whole unit but I've also mixed and matched them when they weren't too worn.

[MikeSimon]

When you replace the whole unit, are you just out on your own luck that the threads in the head stay intact or is there something that you can do to prevent them from stripping.
One issue is, you never know what a PO has done to make the bases stay put. maybe someone "loctited" them in.

[wwheeler]

Yes, that is way too loose. 

I would think anything you do to the stud threads to make them tight is a one time deal. That is not good for this because they need to be readjusted every so often. While I am not a trained machinist, I know several tricks. There are many ways to have a mechanical lock on the threads and not sure what they used on these. Without that knowledge, it would be difficult to reproduce that on the studs.

I might suggest you buy one unit (stud and base) and check the fit of the studs in the one base you buy. If the studs are all tight, then your bases are worn. If the stud is loose, maybe the studs you bought are bad.

[MikeSimon]

Thank you Wallace. That may be a way to proceed. The problem really is, that you cannot work with a thread-locker à la Loctite, as the threads have to work back and forth. I was thinking of maybe distorting the threads of the studs ever so slightly or maybe using sort of a tape to tighten the threads. I really do not want to take the bases out of my head as I am afraid I will make things worse.
I had hoped someone else had crossed this bridge before me and had a word of wisdom.

[Benz Dr.]

I've removed a lot of them and only rarely was there any problem doing so. Cleaning the bottom of the base before removal can help but that's not always possible. If you have the head removed, you should be able to see if the base is moving up and out of the top of the head without any galling. There is a lot of threaded depth to the hole so it's a very solid base that everything threads into. Even if there's a bit of damage the threads can be cleaned with a tap and usually that's enough to fix anything. Use thread or pipe sealer on the base to prevent any oil seeping down and around the threads and torque them to spec which is about 55 ft lbs. 

The way the ball stud was made is actually quite interesting. MB designed an interference fit thread system. I think what they did was to machine the thread on the top end of the ball stud and then spin the whole part one flat so that the two threads are slightly out of sync with each other. This produces a threaded part that turns with some effort but is never so loose that it will turn on its own. Simple yet brilliant design.

You will find that the bottom part of the ball stud will usually turn into the base by hand until it gets to the top part of the threaded area and then it will only turn in with some necessary force. This the effect of the out of sync threads doing their job.

[MikeSimon]

Why do the parts for the 230/250SL have different part numbers from the 280SL? Is there a difference?

[Benz Dr.]

Yes, the ball stud on the 230 has a 14mm hex which will easily round off so the 280 was increased to 17mm. I believe the threaded portion is also larger on the ball stud.

[Pawel66]

If I may throw in my 2cents... from what I read the change was also the rockers. And this is important because the later rockers have a bit different shape - the bottom arch, so that they do not hit the top of the valve spring holder.

The 230 rockers had that arch more shallow and could hit the spring holder unclipping the whole valve assembly. It is clearly stated in BBB to use new type rockers for replacement.

Please check me if I am correct, I just thought it was important to flag that.

[Benz Dr.]

If I may throw in my 2cents... from what I read the change was also the rockers. And this is important because the later rockers have a bit different shape - the bottom arch, so that they do not hit the top of the valve spring holder.

The 230 rockers had that arch more shallow and could hit the spring holder unclipping the whole valve assembly. It is clearly stated in BBB to use new type rockers for replacement.

Please check me if I am correct, I just thought it was important to flag that.

I think you're right on that point. There were a lot of running changes on our cars and the 230SL engine is as specific as a 300SL. Probably why the parts are more than a 280.

[wwheeler]

If you replace the rockers, I would highly suggest getting them from Mercedes. I bought aftermarket rockers a while back to save money and the hardened surface that contacts the cam started to de-laminate. See attached. Yep, brand new.

Luckily I caught it before it wrecked my camshaft's lobes. I changed rocker arms for the same reason because I had new ball studs. I went back to Mercedes brand and never had anymore issues.