Cam wearing

[jeffc280sl]

I noticed a slight wear mark on one of my exhaust cam lobes.  This mark is located on the high part of the lobe with a similar mark in line with it on the round part of the cam.  The mark is a little off center of the lobe and this section seems to be the tightest when inserting a feeler guage.  Could this have been caused by a metal burr and should I take the rocker off to inspect and possibly replace if it is marked in the same line?

Thanks

Jeff C.
1970 280SL 4-speed

[jeffc280sl]

As I adjust the valves I can move the rocker arms just a little and this changes the the valve adjustment by .001 - .002in.  I suppose this is common.  Any comments?

Thanks

Jeff C.
1970 280SL 4-speed

[Ben]

All I can suggest is that you remove the rocker and clean it all up. Do you know how long this mark has been there, when did you last change the oil ?

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

[George Davis]

Jeff,

One of my cam lobes has a scratch, too; it doesn't seem to be causing any harm.  I'd probably feel them both carefully to see if there is any raised metal that might continue scratching the other surface, but if there is no raised metal, it probably won't get any worse.    I'd guess there isn't any raised metal, but it's something to check for peace of mind.

Regarding the slight change in clearance as you move the rocker, that's probably due to wear at the contact points.  As you move it, the contact point moves onto a less worn section, slightly raising or tilting the rocker and changing the clearance.




George Davis
'69 280 SL Euro manual

[ja17]

Hello Jeff,
The rocker arms and camshaft have a hardened surface.  The cam or rocker will wear fairly quickly after the hardended material is worn through. However some scratches of minor wear should not cause a problem as long as the hardened surface is still intact. You can usually see the different color of the metal. The hardened surface is chrome-like while the base metal is darker.

You should remove and check any rocker arm under a camshaft lobe which is showing unusual wear. Wear lines are not unusual but rockers showing wear past hardened metal should be changed with new or good used. It is always best to use new rocker arms on a new camshaft, just so the wear lines on the old rockers do not transfere to the new camshaft!

If I notice an extremely loose valve clearance during a valve adjustment I always remove the rocker for inspection. Often times in this case the rocker will be badly worn.

As far as valve adjustment technique, I like to tighten the adjustment until the feeler guage is locked in place then slowly loosen until the feeler guage can be drawn out with a fair amount of resistance.


Joe Alexander
Blacklick, Ohio

[jeffc280sl]

Thank you Joe, George and Ben

I change the oil often so I don't suspect that to be an issue.I'm going to keep an eye on the mark which is light in colr versus dark as you mention Joe.  Adjusting valves takes a little longer to master then I first thought.  I was reluctant to tighten them too tight.  The more I read and listened to the engine I realized they could be tighter and removing the feeler gauge with a "fair" amount of resistance was the way to go.  I've now made very minor adjustements for the third time.  It's amazing how much quieter the valves are then before. Souings like a new engine.  Very smooth, fresh oil as well.  I recommend making the effort to everyone. I'm very pleased and greatly appreciate all of your help.  I think I'll do it every season as I think you do George.  I only drive 2-3K miles each year.

Thanks again for your help.

Jeff C.
1970 280SL 4-speed