Rack damper bolt adjustment question and cold idle problem... - Page 2 - PeachParts Mercedes-Benz Forum

lietuviai · #16 12-21-2003, 03:21 PM

Thanks Peter for the easy to follow details on checking the chain. This will be the next thing I will check when I get the valve cover off. Good thing about the v/c gasket is that I have been able to re-use it the last couple of times but just applying some permatex on the surfaces.
One more thing, is there anything you can suggest for my noisy injectors, is it time to replace them or can I just replace the one that is the source of the noise?
~DJ

ILUVMILS · #17 12-21-2003, 06:23 PM

Hi mbshop, I was told about doing "cold" valve adjustment about fifteen years ago while attending MB technical training. Since the cam bearings are made of different material than the cylinder head, they each expand and contract at different rates. This can result in valves not closing completely when cold, resulting in low compression. I've seen several cars over the years suddenly develop a hard start condition when mercury drops. Checking the chain stretch is a good idea. Adjust the valves when cold, and check the chain while you're in there.

mbshop · #18 12-21-2003, 06:37 PM

well, i'm not to sure what is best as far as cold or hot
valve adj. over thirty years on mb's and your still the
first for me on cold adj preferance. i think that adj them
regularly is more important than cold or hot.
linkage adj and lubrication is also important. i have seen them hang up on the shutoff position because of no lube.

george

psfred · #19 12-21-2003, 07:30 PM

George:

The factory manual recommends valve adjustment be done with cold (room temp) engine. Different spec for very cold outside temps.

DJ:

Check the chain stretch first, as late injection timing can make injector knock worse. If you need to replace the chain, drive it a while and then decide on the injectors.

If one knocks badly, I'd have the whole set checked. They should all wear at about the same rate, so should all be in comparable condtion. Worst case is that they will need nozzles, about $50 each.

Peter

lietuviai · #20 12-21-2003, 08:04 PM

Peter, I really appreciate the advice. Chain stretch will be on the top of my list.
~DJ

mbshop · #21 12-21-2003, 08:32 PM

ok, i'll be man enough to admit i pooched this one.
room temp it is.
for me being a tech and then a shop owner this was
basically impossible if i wanted to get the work done.
so for many years i have done them hot.
still gets the job done.
thanks

george

psfred · #22 12-21-2003, 08:45 PM

George:

The only real difference is the actual clearance needed. I'd certainly do them hot (60C) rather than cold if I had a shop -- doesn't take long enough to have the customer leave the car overnight.

My friend Hans tries to get cars in and out in a single day whenever he can -- diagnose and order parts, then get the car in the morning and return it that evening. Not always possible, but I'd bet he doesn't let them cool off overnight just for a valve adjust!

Oh, and for the rack bolt adjust:

Engine must be HOT, not just "not cold" -- drive it and adjust before it cools off. Put in gear and turn bolt in slowly until the idle just start to smooth out. Lock bolt, run idle up IN GEAR, then check again. Must be in gear, if you adjust in neutral, it will still shake.

If you have cold start problems, you will have to tolerate the rough idle until you need to have the IP rebuilt -- the actually problem is the spring on the OTHER end of the rack, and to get to it, the IP has to be completely disassembled and re-calibrated. Most of them never need any other work, so they shake at idle.

Peter

engatwork · #23 12-22-2003, 08:46 AM

On my '85 model I had a cold start issue (it sounded like it was running on 2 cylinders at cold idle - real weak sound and it would surge) and after reading through this thread backed the rack dampener out 1/4 turn and the cold start issue is resolved - smooth idle when hot now too.