Hi:
I am a new member and have a 1986 560SL (140,000 miles); and looking for advice with diagnosing a valve problem. I think my problem may be either worn valve stem seals or valve stem guides. My problems/symptoms are:
- burns some oil, I get a puff of blue smoke when starting cold on cold days
- 3 of the plugs are fouling, presumably from oil leaking down the valve stems
- engine runs smooth with clean plugs
- recently failed the emissions test on high hydrocarbons

I am trying to confirm my suspected diagnosis and determine if its seals or worm valve stems. I understand I can replace the seals without removing the heads, but stem guides need the head to be removed. Obviously I would prefer not to remove the heads if possible. Is there a test (compression or leak test) that would help confirm which way to proceed? Also, a friend told me to replace the timing chain guides/tensioner while doing this. Is that recommended?

Any advice/suggestions would be appreciated.
thanks
Neil

Neil...doing a 560 here too.
Smokes from left bank on start up only...I had the complete exhaust off.

Will replace all valve stem seal first and then run it up for a few days.
The oil burning in this machine stopped up the cat's. Got 10 psi back pressure.

The valve guides and valves are most like in good shape even at high miles, and 140K is not high..

Make sure the blowby is reasonable and the breathers are working.
With the valve covers off,you can determine if the plastic guides are in need of replacement....tedious job, but if okay, roll in a new chain.

There's no way off checking guide seals ....I just replace them.


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Thanks for the advice - How do I check if the blowby is reasonable/working? I am also curious as to how you figured out that you had 10 psi backpressure in the cats?

I think I will go ahead with the seal replacement. I need to get a spring compressor that works on this head. Any ideas where I might get one?

From what I can see, the plastic chain guides look OK with no visible wear. I a not sure if they have ever been changed (I have only had the car 18 months). However a mechanic told me that replacing the guides is a "must do" at 120 to 150k miles. Any thoughts on this??

Neil...
I have a pressure gauge that taps into the down pipe(s) ..a MATCO tool.
Basically, a pointy stick and a machine steel threaded hollow port nipple.

I gas weld the hole after tests.

I use a KD tools for valve springs.
http://www.mytoolstore.com/kd/kdengi13.html

I do believe there is a special tool for the Merc' heads. I think KLANN make one. Me ? I'm cheap ! KD does fine.

Guide go hard over the years....If you plan on keeping the car for a while, maybe new guides is a good thing, at least good for the comfort of knowing they are new.
To do them is a job for........Mercedes man...well,nearly.
They are a tedious job...

Need a tool to pull the guide retainers, front crank pully bolt.
Need to swing the a/c compressor mount free.( Real nightmare )
Lower the sway bar.
Remove the belts/fan boss.
Remove the radiator.
Best to remove the hood too.
Cover the fenders with thick cloth.

Buy two new oil spray bars while your in there too.... along with new plastic retainers.

You'll need front oil seal/ timing cover sealer/valve cover seals/rags to stuff down the oil drain holes..........etc.

Shouldn't take ....a few weeks !

.

__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Blowby is reasonable if there is little puffing out the oil cap while idling warm.

The only way to check a motor is a leak down test.
Another special tool.


.

__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Thanks for the link to KD. I am cheap too and the only thing I saw was a $130 tool on ebay (El Paso Tools). The KD3087 looks the most like the one in the Merc manual/CD. Is this the one you are using? looks like it uses leverage from the cm shaft.

The plastic guides can't really be judged by visible wear. They turn brown and get brittle over time. My tensioner arm had worn grooves. The danger is that the chain will be loose (either from the hydraulic tensioner getting old or the chain stretching), the chain slaps the brittle guides, the guides break off a chunk, the chunk gets wedged inbetween the chain and gear, the chain breaks/skips, and the pistons hit the valves, the valve cover breaks, the cam bearings break, etc. Very ugly and expensive to repair.

From what I've seen on this site, 100K seems to be a good mileage to do this. Your mileage is getting to the scary zone if this has never been done. Although I had 88K when I did mine, the car was 19 years old (like yours) and I did determine that the hydraulic tensioner was definitely not up to snuff after removing it and comparing it to a new one.

A "timing chain job" is not really a difficult job (I'm a data analyst and I did it) but it is lengthy, tedious, and not tolerant of mistakes. Some specialized tools are very helpful in order to accomplish it unless you are very resourceful. There is a lot of information on this site, and in the MB CD manuals. Usually, the tensioner, chain, upper guides, and tensioner arm are replaced as a set. This may be overkill. I analyzed this stuff quite a bit and I suspect that the chain gets blamed for stretching or breaking when in reality it is stretched or broken only AFTER the other things above have occured, and the heart of this problem is the tensioner itself.

While you are doing this, valve cover gaskets, oil tube connectors, all belts, and maybe even the water pump/thermostat/front hoses are good to do while you are in there and you don't know the service history of the car.

__________________
86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm