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  #1  
Old 12-22-2008, 10:27 AM
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Rocker Removal and Repositioning

A friend, with lot of experience working on MB's and other cars, and I were removing the rockers on different sides of a 380sl engine when I noticed that he wasn't keeping track of where each rocker came from. However, when I admonished him for it and told him the MB manual says they should be replaced in their original position, he confidently replied that it doesn't make any difference because -- if i recall correctly -- "the cam lobes glide on a layer of oil that evens out any differences each rocker surface may have." So I was wondering what the experienced mechanics in the group had to say about this. Thanks very much in advance.

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Old 12-22-2008, 11:47 AM
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He in INCORRECT!! always keep the rocker arm on the lobe that it has been against!
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  #3  
Old 12-22-2008, 03:06 PM
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Quote:
Originally Posted by M.B.DOC View Post
He in INCORRECT!! always keep the rocker arm on the lobe that it has been against!
Thanks, Doc. I thought so. But now that the rocker positions have been lost, is there any way of correcting the situation, other than getting new rockers, and what will be the result of putting the rockers back in different positions?
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Old 12-22-2008, 03:38 PM
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People seem to get the idea that it doesn't matter because they or someone they know has gotten away with it in the past. I have also gotten away with mixing camshaft lobes and lifters in the past and have not lost a lobe as a result.

However, any time you mismatch the used parts, you have a chance of wiping the lope clean off the camshaft. This may happen as soon as five minutes after the engine is first started. Or, as stated above, not at all.
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Old 12-22-2008, 03:51 PM
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Matt,

What do you mean by "wiping the lobe clean off the camshaft?"

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Originally Posted by Matt L View Post
People seem to get the idea that it doesn't matter because they or someone they know has gotten away with it in the past. I have also gotten away with mixing camshaft lobes and lifters in the past and have not lost a lobe as a result.

However, any time you mismatch the used parts, you have a chance of wiping the lope clean off the camshaft. This may happen as soon as five minutes after the engine is first started. Or, as stated above, not at all.
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Old 12-22-2008, 03:52 PM
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Originally Posted by mbboy View Post
Matt,

What do you mean by "wiping the lobe clean off the camshaft?"
Exactly that. No lobe left. It looks just as ugly as it sounds.
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Old 12-22-2008, 04:47 PM
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Hmmm? Never thought that such a thing could happen, Matt. Does the lobe just fly off the cam and, if so, what is the likelihood of that happening ? Also, any suggestions as to what I should do, given that the rockers are all mixed up. (I hate to think about having to lay out over $200 for 16 new rockers considering they're all in very good condition.)
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Old 12-22-2008, 05:03 PM
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The lobe is part of the cam, so no, it doesn't just fly off. What happens is that the friction slowly reduces the cam lobe to dust. As for the chances of it happening, I really don't know. As I said, I've gotten away with this in the past. I also know of one instance of a brand new lifter taking out a brand new cam (but that may have been due to improper prelubricating).

The chance is reduced to nearly zero if you use new parts or matched used parts and proper camshaft assembly lubricant. With new parts, you should break in the surfaces if possible, following the manufacturer's procedure. Typically this involves running at 2K RPM (and no less) for 20 minutes, then changing the oil.
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Old 12-22-2008, 05:07 PM
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Let me add that I am uncomfortable recommending that you use the old lifters to save $200. Let me further add that I would check the price of the camshaft before deciding what to do. I would venture to guess that a new camshaft is very expensive, but a good used one may be available.

If you lose a lobe, it will probably be immediate and not at some random time down the road (although this is still possible). Your engine can run without one camshaft lobe, but it won't run very well and you won't feel too good about running it once you find the metal bits in the pan.
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Old 12-22-2008, 06:17 PM
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Quote:
Originally Posted by Matt L View Post
Let me add that I am uncomfortable recommending that you use the old lifters to save $200. Let me further add that I would check the price of the camshaft before deciding what to do. I would venture to guess that a new camshaft is very expensive, but a good used one may be available.

If you lose a lobe, it will probably be immediate and not at some random time down the road (although this is still possible). Your engine can run without one camshaft lobe, but it won't run very well and you won't feel too good about running it once you find the metal bits in the pan.
Just wondering: What's the possibility of matching rockers with cam lobes based on wear patterns or lack thereof?

Thanks again for any help,
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  #11  
Old 12-23-2008, 09:47 PM
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Ive set up a used cam with used cam followers, but I'm pretty sure that the person I got it from marked the followers very carefully.

The reason for doing this right is because the parts must be absolutely parallel in their mating surface so that the oil film can ride in between without scraping the oil film off, and so that the maximum area is available to distribute the load. It's hard to believe how important this is on a microscopic scale. If they are non-parallel or rounded in different shapes (and all of this is probably in the ten to hundred-thousandths of inches), you will find out pretty quickly. The parts are like butter with those kinds of pressures after you get past the case hardening.

I agree, if they are significantly off, you will find out soon.

In any event, I would use assembly lube liberally and change the oil sooner rather than later. There are varying opinions on whether or not this stuff is bad to leave in.

When I was a boy, there was an extremely cool exhibit at the Museum of Science and Industry in Chicago, where you could spin a several-ton disk with your 10-year-old little finger with just a few microns of oil as a bearing.
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  #12  
Old 12-24-2008, 08:46 AM
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mbboy, for reduced wear use Mobil 1 in your engine after you replace the camshaft.
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  #13  
Old 12-24-2008, 12:35 PM
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If you have a laser temp gun, you may want to check each rocker after the engine has run for a few moments. If one is severly mis-matched , I would expect that be hotter than the rest and therefore suspect.
This is just a thought , as I have never tried this [ b/c I would never mis-match], but it is a possible that could save you the trouble of wearing the cam out real fast...worth a try...
I would be interested in any results, if you do try it.
Those guns are great..............
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Old 12-25-2008, 10:16 AM
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Thanks very much for the responses -- all of which are predicting a negative outcome to one degree or another. Interestingly, the guy who machined my heads -- a German immigrant who began working on MB's in Berlin over 40 years ago -- confidently told me that I shouldn't have any problems putting the old rockers back in different positions, as long as they're not too, severely worn.

Similarly, another local Indy who's been working exclusively on MB's for decades told me he doesn't even bother marking rockers any more, and the only problem I might have is excessive chatter from one or more valves -- which an adjustment or individual rocker replacement can usually solve. In addition, a tech who's been working at the local dealer for 30 yrs echoed those opinions. So, experienced people seem to have very different opinions about this.

Since I'd obviously like to minimize the potential cost and aggravation of destroying one or both cams, I'm asking whether people here would recommend replacing the original rockers -- which have 180k miles on them -- with new Febi-Bilstein rockers at app. 16@. Or giving the old rockers a shot, lubing the cams liberally, and switching to synthetic, to minimize the excess friction the mismatched components would produce?

Another thing i'm now wondering is whether polishing the cam lobes and/or old rockers will reduce or eliminate the probability of prematurely wearing out one or more cam lobes?

I realize that if money was no object, the ideal thing to do would be to replace the cams and rockers, but it seems to me that it would make more sense to try the old rockers or new rockers first.

Thanks very much in advance for any additional advice anybody can give me, and best wishes for a Merry Christmas and Happy, Healthy New Year


Last edited by mbboy; 12-25-2008 at 01:46 PM.
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