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M116/117 V8 engine - whos changed their valve stem seals?

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Just a quick one, I'll expand on it later...

Who has changed their valve stem seals to cure smoking engine and was it successful / how long was the problem solved before returning again?


My local european car guy, not a MB specialist but all expensive european car dude (does the work on my car I can't do myself) (well anyway he drives a W140 and thinks the 116s are great, so he can't be too bad)...

I said I wanted to change the valve stem seals on the M117 in the race car, and his opinion was that it was wasted time and money without doing the valve guides at the same time, or else it'll start smoking again soon.

This comes from the M117 VSSs being a harder plasticy type material which is easily damaged/worn/cracked etc. if the valves are wiggling around loosely in their guides.  This is in constrast to, say, a Mistubishi engine which has a relatively soft rubbery VSS which will effectively stop smoking in a Magna even if the valve guides are fairly worn out.

The other concern is how quickly the VSSs start to fail again if the valve guides are worn... if it does it in 500km then there's a problem... bu if it takes 20,000-30,000km then I consider that acceptable since the Team116 car will cover only about 1000km/year* tops and be running high-quality engine oil to boot.

* Granted that this 1000km/yr will be covered at high revs under racing conditions I would expect VSSs, as well as everything else in there, to have a pretty difficult and short life..


To GUARANTEE that you do not have this problem for I would say as long as for 200K miles, I would recommend valve seals AND valve guides!

I have had heads rebuilt out of vehicle for both my 110 and 100 engines by a machine shop. They replace ALL the valve seals but only replace the BAD or worn valve guides.

I know people who have replaced the seals  with head in car but you must be careful to keep the valve from falling into the combustion chamber after removing the valve springs and valve spring keepers!

Good luck,
Joe Perkins
Berkeley, CA

Thanks Joe.

Not exactly what I was asking by I appreciate your input.  Yes I know the best is to get the guides done at the same time... 

What I'm after is anyone's real-world experience of changing the VSSs without doing the valve guides.

I've changed VSSs without removing the heads on other non-MB cars, you just run compressed air into the spark plug holes to stop the valves falling in...


I was thinking along the same lines as Joe, however, I only got stem seals.

My 350 used to smoke on start up as oil leaked past the VSS.  A quick puff of blue.  Depended on how long the car stood.  If not used for a long time (couple of weeks) it would be ok as if the oild would seep past rings back into the sump.  Stand for a an hour or so and the oil would leak into the cylinders. 

Most noticeable was going down a hill and throwing the car into a low gear.  A second or so later an embarassing blue plume would develop.  When cruising and putting the foot down, i wouldn't notice any smoke unless it was fuel related, timing etc ie hints of black smoke.

So, March 06 I had VSS replaced, guides left in.  I wished I had both done but anyway, the difference was great. ie no smoke.  Fast forward a couple years later and about 11,000km.  It has not returned to being smokey like before.   I've only noticed oil smoke under two conditions recently.

1. Full accelerator, cold engine.  (I know I shouldn't)  The smoke is part fuel part oil related but not thick
2. On a forced overrun when engine is hot.  ie down hill and shoving A/T into L.  Slight bluish smoke especially when engine is warm.

Another thing to keep in mind. I'm experimenting with oils and am running thin synth that has diluted too.  Due to be changed any moment I get my arse into gear.  I have noticed though that new oil reduced any chance of smoke.  No doubt whatsoever.  Stands to reason as it's thicker.  No idea what you'd use in the raceing version but generally, Ive noticed that thick new oil will cut down the smoke.


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