Valve Seals Replacement - DIY???
 

Is replacing valve seals a DIY job? Does the head need to be removed to do this or just the valve covers.

I have read more and more that MB recommended valve seal replacement at about 100k or when symptoms like oil in air cleaner or at valve cover vent to air cleaner show.

Thanks for any feedback.

Valve Stem Seals
 

1984 300D TURBO 143,000
VALVE STEM SEALS, GO WWW.MERCEDESSOURE.COM THEY HAVE GUIDE BOOK
AND KIT DIY

Thanks, Ray. Have you used this kit?

http://**************.com/node/760

If the valve seals need changed at 100 k a lot of us 123 owners are way overdue and in deep trouble. I do not think oil showing up where you have mentioned it is any certain indication of valve seals being required. How many miles do you get to a quart of oil just might be a better guide. .

I know what you mean.... but it does kinda make sense that any oil seeping thru the seals end up around the pcv or the air cleaner. Theres lots of talk about blowby and its cause being rings.... but it seems that the first thing to look at are the stem seals.

A leak down test seems to be about the best way to check.

Blowby is mainly from the rings. If the valve guides are so worn that they allow that much air past them, it's time to rebuild the head before you drop a valve. Not just that, but there is no pressure in the manifolds to contribute to blowby at idle.

Oil seeping by the seals is going to end up in the combustion chamber or exhaust and not in the PCV system or air cleaner.

Am not questioning any of the above feedback on this. I recently read from an MBCA book that worn valve seals cause oil to occur inside the air cleaner or oil to leak out of the PCV hoses on the cam cover.:)

I've never heard of the valve seals causing oil to come out of the PCV hoses on the cam cover. that oil is caused by pressure in the crank case that carries the oil. the valve seals are a rubber ring like cup around the valve inside the spring above the valve guide (the bore the valve goes through to the combustion chamber) they are there to minimize the amount of oil getting to the guide, so that you do not burn oil. but they do alow oil to get past them because you need oil to lubricate the valves. the valve stem to valve guide clearence is very small, and if you were to be getting to much oil into the guide, because of a bad valve seal, and you were getting it into the combustion chamber, and burnign it, that means you need to have your head re-machined. the valve stem to guide clearence would be warn, oversized and the only way to correct that is with machining.

Hunter, Brian, got any opinios on this??

I agree with Lance on this. The seals just prevent the last bit of oil from leaking down the guides. They won't prevent any compression pressure from escaping into the valve cover if the guides are worn.

The real question is why you are considering seal replacement? Is it oil consumption or blowby that you're trying to fix?

For reference, the SD has all new guides and seals. Didn't affect the consumption one bit. It still drinks one quart every 2K, just like it did before the head was replaced.

I thought equal forces cancelled. The intake valve guide would intake air when the valve was open. The exhaust guide would exhale it a little later so to speak. This nice applecart is upset by the constant turbo pressure acting on the intake valve guide though. Then again Lance did read it in mercedes literature apparently.
To counter all this. I have not one single refference of a person having valve cover discharges because of bad guides or stem seals. Perhaps it has remained unknown this long as a contributor to the overall problem. Yet somehow I still feel the combustion byproducts going past the pistons are the prime source of too much blowby and oil in the breather line. .
Maybe Lance could post the refference material as something may be learnt. I for one would not change the valve stem seals for this problem at this point of my limited knowledge. Yet I have to keep an open mind as it may be contributing to some unknown extent. Also if this were true when you had bad intake valve guide seals no oil could go down them. This may be an additional factor to our generally low rate of valve stem seal changes on these engines. Rather than just the lack of constant vacuum in the intake manifold. That low milage engine with massive blowby I own for example. It was on unheated vegatable oil. The compression rings are coked. There is absolutly no doubt about that. At high speed it would not suprise me if it blew most of its oil into the breather.

True, but the exhaust valve guides typically suffer the increased wear.

I think the discussion is moot, however, unless the guides are much larger than spec (.004" or more).

No oil consumprion, no blowby. Just oil stains around breather on valve cover.

this typically is a diy job just make sure you dont let a valve drop into the cylinder or loose the timing.