The Benz Dr.'s, Strange but true.

[Benz Dr.]

Srange but true; a new feature brought to you by the Benz Dr.

  Well, back to work a little bit but not better yet. Still have radio iodine treatment in late Feb before they leave me alone for a while.

 So, lets talk about 113 engines, or in this case those that have the ball stud valve adjusters with roto caps. This covers a lot of different models including all the engines used in the Pagoda cars.
After rebuilding a number of these units I've found some rather interesting results if everyhing isn't right inside. One thing I've found is that the rockers have to maintain a certain geometry relative to valve height. Once you run out of adjustment on the ball stud you are in trouble and the engine will likely start to smoke. You can use thinner thrust pieces under the rocker arm but I've seen little by way of help doing this. This is usually caused by worn out valves and seats.
During rebuild it's probably wise to replace all the valves if they're worn. The valve face has a small ridge or raised area that will be removed from the valve griding process. You can grind valves about 3 times before this raised area is removed. The intake valve tends to wear out faster due to the thin sectional area of the valve face. Both valves when new have the same relative amount of raised area but the exhaust valve is much thicker so you can grind past the raised area and they'll still work.
New valves are easier to install than valve seats and should be your first choice during rebuilds. I usually install new springs which also improves overall performance. I measure the depth of the valve in the head from the stock or new position and then subtract the tickness of the head if it's been plained. So, if the head has been plained .010 and the valve sits .015 deeper than stock I use a .020 piece of valve spring shim stock to retain spring tension.

Why the engine smokes:
 After looking at this for several years I've found conclusive evidence that points to rocker arm position. Once the end of the rocker arm sits too high on the valve stem the engine will smoke. Even on fresh rebuilds where you have all new valve guides and seals they still smoke. Sometimes it will be all the time and other times it will only happen at idle.
I recently cured this by installing shims under the cam bearings. I added .030 under each bearing and within 3 miles the smoking cleared right up. This engine had a warped head and the only way to repair it was to machine the areas where the cam bearings sat. This lowered the camshaft which removed all the adjustment on the ball studs. I believe that the position of the rocker arm has a lot to do with how the valve is pushed down. Once you run out of adjustment the rocker tends to push the valve sideways and instead of a smooth movement it might be that it starts to bind up. I've never had an engine with proper valve rocker geometry that smoked after rebuild. Anything that didn't have this critical dimension was a prime candidate for a mosquito fogger.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Cees Klumper]

OK Dan, makes perfect sense. One thought - besides raising the camshaft with shims, could an alternative also be grinding a bit off the tops of the valve stems?

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[Ben]

But is the only sysmptom, apart from the smoke, the fact that you have run out of adjustment ?

The reason I ask is despite a rebore and new pistons, all valves cleaned up and refaced,new guides and new seals etc.. my motor still smokes a little occassionally !

I guess what you are saying is that the valve does not travel down the bore of the valve guide centrally, then it starts to chew it up, make the guide more oval shaped. Do the guides need replacing if your theory is correct ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

[TheEngineer]

Last year I got a new head and was left with the old head to play with: I installed a one inch travel dial indicator and determined opening angles between the 08 camshaft and the 09 camshaft. In the process I got involved in the change of geometry when there is wear outside of specifications. The rocker arms are quite short and when everything is right, they push on the valve stem describing a short arc. But when there is excessive wear resulting in the need for extreme adjustment of the ball stud, the arc becomes offset. That results in rocking the valve stem sideways and compromises the sealing ability of the valve stem seal. Just like Dr. Benz says! So, don't skimp and replace valves when they are outside of wear limits. Remember: It is much cheaper to to the job right the first time than to do it over again. The perfect example is my engine: It was completely rebuilt: 1st oversize pistons, new everything, even painted. But it wasn't run-in in properly. Whoever did it, was too easy on driving it. As a result cylinders 5 & 6 never seated. Now I have to do it all over again.

[al_lieffring]

quote:Originally posted by cees klumper

OK Dan, makes perfect sense. One thought - besides raising the camshaft with shims, could an alternative also be grinding a bit off the tops of the valve stems?

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

Cees

I encountered a motor (I think it was an m129) once where someone tried to shorten the valve height by grinding the top off the valve stems. It caused the roto caps to bottom out and push against the spring cap instead of the valve stem. The engine made a pequliar noise that I had a terrible time tracking down.

Al

66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket

[Benz Dr.]

In this case the top of the head was badly warped. We machined the area under each cam bearing so that it was even with the bottom of the head. The center two had a lot of material removed while the ends were only slighty cut in. The head also had a lateral warp - this was the only way to save it. Let's just say I went way above the call to save this engine. We had to remove two head bolts with a boring mill.

BTW, the 280/A head is no longer available as a new part. Core charges are about $1,000.00 while used heads that are useable can be $1,800.00. They were only produced for les than 3 years so there aren't a lot of them out there. Kind of makes that rustly old 108 sedan look good for 200 bucks.

At any rate the engine seems to run well now. I still have to break it in yet and finish some other things around the car for spring delivery. Anyone who was at the clan party may remember this car that was in the main shop.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061