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  #1  
Old 08-10-2006, 02:00 PM
1969-280SE
 
Join Date: Aug 2005
Location: Mt. Horeb, WI
Posts: 16
69 280SE Camshaft Saga

Wrote almost a year ago about a lobe wearing off on my camshaft. Finally found and purchased a used camshaft from Adsit. In the process of getting intimate with this vehicle, I learned a fair bit. The original problem was due to a valve adjust shim getting cocked, which cocked the rocker arm, which caused a bad wear pattern on camshaft. Turns out for some reason the valve required more clearance then the 2.5 mm shim would allow, so the dip that owned the car b4 me ground some of the end of the rocker arm off (valve end). This is probably what cocked the shim since the grind job left the end of the arm with a transverse angle. Anyway now that i am reassembling with new rocker arm, wondering why this valve is sitting high and what to do about it. Must have been a valve replacement originally, the the other user get the wrong valve, or is the valve too deep into its seat? It looks ok. Anyone got anything to say about this?

Thanks

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Old 08-10-2006, 10:15 PM
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The "hockey pucks" that go between the rocker and the valve stem come in different thicknesses, so you might be able to gain some clearance that way.

I have heard of valve pulling up into the head, but never a good explanation of why it happens.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 08-11-2006, 09:31 AM
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gimme a low-tech 240D
 
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Yeah, for example the rocker arm grinding previous owner shoulda just picked up say a 2.45mm shim at the dealership to replace the 2.50 shim if he wanted to adjust valve clearances. I believe the hockey puck valve clearance adjust system is unique to your engine model, but could be wrong.

Meanwhile anybody who would deliberately grind polished and plated surfaces of rocker arms down to core metal underneath oughta be shot. And if you see any other rockers with a patch of dark metal shining through the surface oughta replace em immediately.

The hockey puck system is actually kinda cool. MB shops all carried trays of different size shims. And you just mixed and matched em up to adjust valve clearances.

Last edited by 300SDog; 08-11-2006 at 09:42 AM.
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Old 08-11-2006, 09:41 AM
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You still do the adjustment with the ball studs, but the different "pucks" are there for cases like this. You can also shim the ball stud to increase the height.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 08-11-2006, 09:45 AM
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gimme a low-tech 240D
 
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Okay gotcha, then ball stud travel was limitted and hence different size shims? Seen and heard of this legendary unique MB valve adjust method but never actually owned a 108, 112 or 111 coupe so aint done it myself.
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  #6  
Old 08-11-2006, 10:57 AM
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I preffered to use new rockers when changing cams for several reasons. The most important reason in my opinioon was there would be a slight wear pattern or slight scoring to match the individual lobe after enough milage on the rocker. That might start an earlier heavy wear on another cam. To get around this I started sending my cams out to have the damaged lobe repaired so I only had to purchase one new rocker. I specified to have only the damaged lobe turned after repair. That of course was if the cam and original rockers in general otherwise looked pretty good. An ethical and knowledgeable seller in my opinion should have offered you the rocker arms off the same engine with each numbered for it's lobe to circumvent this problem. Other than that the rockers are generally just junk parts if not sold with the used cam. I also noticed as well some deeply recessed seats on quite a few mercedes gas heads before lead free gas was introduced. Suspect the heads had been done too many times for a burnt valve because the owners had not adjusted the valves regularily..Every ten thousand miles back then I believe and mercedes meant it. It is logical to assume that one or two thread interference fits that may have been a little looser on the adjusters than the majority where the ones that always burnt a valve. The earlier engines were notorious for closing up their valve clearances as the adjusters had not enough of an interference fit to hold long term. That was eventually rectified by making the interference fit so tight I had to remove the rocker to get movement of the adjuster and re install rocker in some cases . Really became almost a trial and error situation on some to adjust the valves. Perhaps thats why the system on your valves using the hockey pucks might be a little different. But to be honest I do not really know. We also found there was not enough surface hardness depth to restore the rocker wear surface. We even tried a light radius grind in a good machine shop as an experiment once to no avail. Probably my experience as a hobby mechanic and resultant history from it is general knowledge anyways. Or my experience might be unique but I really suspect not.
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Old 08-13-2006, 11:42 PM
t walgamuth's Avatar
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when grinding seats and not replacing them it is normal to take some material off the top of the valve stem to keep normal adjustment range.

tom w
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  #8  
Old 08-13-2006, 11:54 PM
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Tom,

It's normal to square up the ends when doing a valve job. nessary on American iron with stamped rocker arms.


Michael

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