Selective Valve Stem Seal Replacement UPDATE

[rix116]

In a post a few days ago I told about my 74 450 SEL that burns oil like crazy
during the start up period. After cold starting, I'd drive a mile or two only
and there would be an "arrest me now" smokescreen. After a minute or two it would die down and drive "normal"- no visible smoke.
My mechanic suggested that I do a selective stem seal replacement based on only the cylinder(s) with fouled plugs.
Today I took out all the plugs. They are all dry and tan/grey- perfect
looking plugs with no carbon or oil deposits on them.
So there goes that plan.
The mechanic says maybe it is just the exhaust stem seals because the intake seals would suck oil into the combustion chambers and foul the plugs.

I got some great replies from you all last time.
Any new thoughts? Am I commited to doing all the valve stem seals?

[Tomguy]

I dont think "Selective" replacement is a good idea because I don't see why 1 would be bad and not another. I also don't see why an intake one would be good but not an exhaust. These are wear parts and they all wear the same and are all the same age. Also, unless you're putting a fairly large amount of oil into the cylinder at all times (in other words, it doesnt get a chance to burn off/out), you won't have fouled plugs. Unlike many American engiens of this era, MB ones have quite self-cleaning combustion chambers.

I think your mechanic is showing he's a two-bit mechanic (in suggesting "Selective" replacement, he's trying to take a lazy man's way out. Same with suggesting just doing the exhausts). The seals come in a set of 4 (4 intakes and 4 exhausts). You need 2 per car. No need to throw the intake seals out. You're gonna have the cyl at TDC anyway, possibly pressurized with compressed air as well. The exhausts are harder to do than the intakes. You would be best off doing every one. Then, in two months or so, if it started doing it again, you wouldnt need to go in and replace the rest. That'd take MORE time to do!

Find a new mechanic and don't do a half-assed job - you'll regret it later on when you need to go in and do the rest. These seals are over 30 years old and rubber. I don't know how 1 30 y/o rubber seal could be good while another's shot!

[wbain5280]

Since you are 'in there', just do them all. It really is false economy to just replace a few of them.

[rix116]

Thanks again. I had only hoped to do a shortcut if there were fouled
plugs that gave an indication of the worst cylinders.
Well, I will be doing the whole job.
1. Where is the best place to buy the seals?
2. I'd like to use rope in the chambers rather than
compressed air if possible. Any of you done this?
3.Mancini Racing, a supplier of Chrysler racing stuff has a
valve spring compressor that clamps to the edge of the head.
Anybody familiar with this type and whether it would work on the 450?

[CzarFC]

I had similar symptoms with my 560SEL. The smokescreen would go away after a mile or so. The problem was ultimatly shot valve guides. What happens is as the motor warms up, the loose guides expand and seal up their fittings and the severity of the leak lessens. My car would burn about a quart of oil every 100 or so miles.

I hope yours is less involved. Mine required a valve job, and while i was there I replaced the timing chain, air intake hoses, fuel injectors, and a couple of other goodies. I gotta say, having an almost-new 560SEL is pretty sweet, not alot of non-korean cars I could have bought for the same $$$


Good Luck!

[Tomguy]

1 quart per 100 miles is a LOT of oil. If he's only burning 1 per 500-1000 miles, it probably wouldn't be the guides then. That might be a good guideline to judge by?