Mercedes-Benz Forum - View Single Post - M103 Rough idle and vacuum leak
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post #113 of (permalink) Old 01-08-2018, 10:05 AM
H.D.
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Date registered: May 2014
Vehicle: 1988 300CE
Location: Germany
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Quote:
Originally Posted by Strassenkreuzer View Post
... with emphasis on cylinder #1's lobes. Is there anything that can be done to make the oil dripper more effective? It's my understanding that this is the weakness that causes the premature wear on these lobes. ...
There is something that can be done to keep it from becoming less effective … make sure that it doesn‘t get clogged by old dirty engine oil !

This is a perfect opportunity to caution against the seemingly logic idea of enlarging the oil dripper holes. That affects the oil pressure and can severely reduce the oil flow through the bearings (crankshaft, connecting rods, camshaft, rocker arms). … Baaaad idea !!

The main cause for the premature wear is actually a quality problem with the inductively hardened surface of the lobes … or more precisely, with the hardening process in the camshaft production line. With a little luck your camshaft is still okay, even with 200,000 miles or more on the clock … if you‘re less fortunate you have worn lobes (even with very frequent oil changes).

A quick answer to the question why the intake cam lobes are usually hit hardest is: they are hit harder … LOL … has to do with the camshaft‘s direction of rotation.

Quote:
Originally Posted by Strassenkreuzer View Post
... How do you determine that valves need replacement without dismantling the entire upper part of the engine? ...
When I replace valve stem seals I grab the valve shaft with my fingers … with the piston of the respective cyclinder sitting high enough to prevent the valve from falling so deep that the valve stem completely disappears into the valve guide … and feel how it sits in the guide. And I visually check the part of the valve stem that moves in and out of the guide during operation. … Then I compare these impressions with the intended future of the engine/car. … If you have never done that, I suggest to have it done by an experienced and trustable mechanic.

Quote:
Originally Posted by Strassenkreuzer View Post
... So just what is a "failing lifter"? If they're hydraulic, I can understand that perhaps the mechanism is worn and needs replacing because there are oil and springs involved. If they're not hydraulic, then how does a lifter wear out? And if one replaces one lifter, shouldn't I replace all twelve? ...
They work hydraulically and they fail hydraulically if their mechanism wears. If you hear a suspicious ticking sound coming from the valve train area (when the engine is cold) I suggest to replace all 12 lifters when you replace the valve stem seals.

H.D.
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