Cold starts, timing chain 300SDL - PeachParts Mercedes-Benz Forum

#1 04-30-2002, 03:43 AM

This winter, my 300SDL started very easily (1 crank after glow light) but once started it would run rough, and if I plant my foot on the gas pedal it would shake and smoke and -slowly- climb in RPM's. If I were to let off, occasionaly it would stall. This would be temps below 35 or 40F.

About 2 weeks ago I put in 6 brand new Bosch glow plugs thinking the old ones were getting weak.

Tonight it was about 40F, she started easily but there was still some roughness and she was hesitant to revv and was giving off some blue/grey smoke (not much), just like this winter.

I remember this being an indication of a stretched timing chain. As far as I know, the original chain has 270K miles on it.

My car will be in the shop for some front-end work, do you think I should get the chain done as well? He quoted me a price of ~$350 for the chain, is this a good price? It is just to roll in a new one, no guides or anything.

Thanks

sixto · #2 04-30-2002, 07:08 PM

You should probably get a new tensioner along with the new chain. That might be part of the $350.

Sixto
91 300SE
87 300SDL
81 300SD

HGV · #3 04-30-2002, 08:14 PM

I have similiar syptoms. How difficult is it to replace the timing chain? I should of done it when I did a valve jo. Any suggestions?

henry

sixto · #4 04-30-2002, 08:21 PM

Henry,

Have you checked the chain stretch recently? Do that first.

Sixto
91 300SE
87 300SDL
81 300SD

HGV · #5 04-30-2002, 08:41 PM

How do I check chain stretch? I have not looked in the manual, I assume it is there.

Henry

gsxr · #6 04-30-2002, 11:06 PM

To check stretch, you line up the TDC mark on the cam with the TDC mark on the #1 cam bearing, then read off the crank indicator. You need to do this several times because of "eyeball" error, when you get consistent results it's probably close. There is a more accurate procedure in the manual to use a dial gauge on the #1 intake valve. I did this AND did the eyeball method. The eyeball method was within 1/2-degree of the dial indicator.

Note: The TDC indicator on the crank is adjsutable over a 3 degree range. The chain stretch check assumes your pointer is still accurate. It's tempting to loosen it when replacing the water pump b/c it's in the way. Just an FYI. It's a MAJOR pain to re-set, you need to get a dial indicator on the piston top. Much easier with the head off, a real challenge with the head on.

My TDC indicator was 1 degree off. After setting that, my chain stretch is 4 degrees - right at the limit allowed by the manual. Dr. Booth on the mbz.org diesel email list (also MBCA Diesel tech advisor) says any less than ~4-5 degrees has little, if any, effect on engine performance. I haven't replaced my chain yet so I'm not sure.

A new chain was ~$70. MB makes a neat tool to make replacement a 1-man job, it's ~$20. The hassle is the rivet. The tool is ~$200, or you can rent it for ~$40. Only the valve cover needs to be removed (well, maybe the fan clutch too so you can access the crank bolt). I've been told you can use a sledgehammer as an anvil, and a ball peen hammer to set the rivet pins, but I'm real nervous about trying that on an interference engine that costs $7500 for a rebuilt, $8000 new (wholesale), and $11,000 from the dealer. (And that's a bare longblock!)

HTH,

#7 05-01-2002, 04:31 AM

I talked to my mechanic today, and descibed the symptoms and he seems to think its typical of an old injection pump that is showing its age.

What do you guys think? Splurge for a new chain or not?

jcd · #8 05-01-2002, 10:15 AM

Turbo, let me know. I need to have a few things done that are over my head. I seem to recall that you had a shop you used in the past with good luck.....let me know.

JCD

gsxr · #9 05-01-2002, 10:45 AM

Well, with 270k on the engine, replacing the chain would be nice as a preventive maintenance item. $350 seems a little steep but I've heard worse ($500-$700, which is plain robbery for a ~2 hour job.) If you have it done, let us know the results. Just don't be too disappointed if it doesn't cure the problem...

Regards,

#10 05-01-2002, 11:47 AM

John, after some thinking, I don't think its the timing chain. But if it is the original timing chain, it should be replaced, unless you want to replace the motor one day. A timing chain with 270K is a ticking time bomb, stretched or not. A stretched timing chain will result in hard starts, for the valves on the 603 are hydraulic. Your injection pump sounds like it need adjustment or overhaul. Fuel delivery in these things is crutial...

sixto · #11 05-01-2002, 01:08 PM

turbodiesel,

Everyone I talk to about my symptoms (hard start, rough idle, smoke when idling) says to have the IP checked. Pacific FI is within 30 miles of me so that's the route I'll be taking when I confirm that compression and chain stretch are not issues.

The more familiar you become with the 603, the more you realize what an engineering marvel the 617 really is.

Sixto
91 300SE
87 300SDL
81 300SD