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W126- 1989 US 560 SEC (117.968 ) - Valve Stem Se... [Benz Repair and Maintenance Tips]
Requested and Answered by Buckrey on 04-Apr-2005 03:15 (6328 reads)
W126- 1989 US 560 SEC (117.968 ) - Valve Stem Seal Replacement.

The classic symptom of bad valve stem seals is, if when starting the car, after it has set for a little while (say over night), clouds of smoke appear from the exhaust and then stops after a few seconds. What happens is, while the car is setting, oil leaks down the valve stem past the seal and accumulates in the cylinder chamber. When you start the car, that oil is burned off out the exhaust pipe.


The valve stem seal fits over the valve stem and seats over the top end of the valve guide. (refer to Fig-1) The valve guide is a sleeve thatís pressed into the cylinder head, the valve stem rides in this sleeve. The valve stem seal keeps oil from passing down between the valve guide and valve stem into the combustion chamber. The valve is held closed by a set of 2 valve springs (one inside the other). The springs are compressed down over the valve stem and held in place by steel disk on top of the valve springs call a "valve spring retainer". The retainer is locked to the top of the valve stem by two small halve cone shaped steel wedges called "valve cone halves" or "valve keepers".

In order to get to the valve stem seal, most of what Iíve described has to be removed (16 times, be thankful you donít have a 32 valve engine). If the cylinder head was removed from the engine and setting on a bench, this job would be a breeze. We could simply compress the spring using a conventional spring compressing tool, remove the various components (keepers, spring retainer, springs and stem seal), then put them back together. But weíre doing this job with the head still on the engine. The problem with this method, is once the valve spring is remove the valve will drop out of the cylinder head. On a bench, no problem, but on the engine, bad news.. The valve drops down into the cylinder and the head has to come off to get itÖ

In order to keep the valves from dropping, we use an air compressor and pump air into the cylinder weíre working on. With the valves closed and the piston at TDC (Top Dead Center) for that cylinder, the air pressure inside the cylinder will keep the valve up and in place. We can now compress the spring (using a special tool), remove the keepers, spring retainer and springs. The valve stem seal is now exposed and can be removed.

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Posted: 2009/4/10 20:50  Updated: 2009/4/10 20:50
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