300 SD valves adjustments - PeachParts Mercedes-Benz Forum

#1 05-21-2002, 11:50 AM

I just wonder how frequently one needs to adjust valves on 300SD.I had on mine 10 000 miles ago(16.000 km) and I started to hear them when on slow speed uphill.

gnolo · #2 05-21-2002, 12:17 PM

I guess it's every 20k or something like that.

By the way, does anyone know what happened if the valves are not adjusted regularly ? I am wondering that because on my 84 240D, the valves have only been adjusted 1 time (at 212 000 km) and never before.

P.E.Haiges · #3 05-21-2002, 08:05 PM

Ivo Tyl,

I was all set to adjust the valves recently on my '79 300SD with 200,000 total miles. It had been 25,000 miles since they were adjusted. I checked each valve with go/nogo feeler gauges before I loosened the adjusting nuts. All the valves we were within specifications so none needed adjustment. I will be interesting to see what the clearances are after another 25,000 miles but that will take another 2 1/2 years.

This doesn't happen every time because other times when I checked the valve clearance after 25,000 miles, some of the valves did need to be adjusted. In my opinion, the valves should never have to be adjusted more than every 25,000 miles. I think the above case proves that.

I suggest you set the valve clearance on the high side but not more than .001 inch over the nominal. Too much clearance is better than too little.

P E H

P.E.Haiges · #4 05-21-2002, 08:22 PM

Ivo Tyl,

One more thing: The valve clearance becomes less with use. Since you can usually only hear valves with too much clearance, I doubt that you were hearing valve train noise unless they were not adjusted properly in the first place. If you have any doubt, its easy to check the clearance.

Gnolo,

As the valves wear into the valve seat, the clearance becomes less. If the valves are not adjusted, the clearance becomes zero or less and the valves no longer make a tight seal. The first symptom is usually hard starting because of the lower pressure (translates to lower temperature to ignite the fuel) inside the cylinders caused by the valves leaking.

P E H

mikemover · #5 05-21-2002, 10:55 PM

Mercedes recommends every 15,000 miles.

Many owners observe this religiously, others are more flexible. I think as long as you're in the 15-20,000 mile range, you're probably OK. The valves tend to get tighter over time, eventually causing declining performance and mileage, and starting difficulties. It can eventually get tight enough to cause excess wear on the cam, valves, etc.

It's also a good time to check for timing chain stretch, particularly on a higher-mileage engine!

Mike

JPL · #6 05-22-2002, 03:42 PM

Mikemover;

The other day I was getting a valve adjustment and my mechanic 'peshawed' the idea of checking the timing chain when I mentioned it to him. He said that I wouldnt need to do that for another 58,000 miles. ( I have 142000 now ) Funny, he said " when you need it you'll feel it" which sounds kinda scary. I dont wanna 'feel it' when I am in the middle of a 200 mile run.

Just passin it on, cause I always thought that it is advised to check the timing chain stretch when doing the valves. I am interested in opinions here.

BTW, your 116 is really sweet. I am looking for one of those, but I am torn between restoring my CD, or just waiting for the right 116. As much as I want to, I cannot justify (or afford) to have both.

Later,
J

jcd · #7 05-22-2002, 04:33 PM

TXBILL,

I have the same phobia that you must have. I'm getting mine done this Friday by an Indy recommended by Turbodiesel.

I have done motor mounts, shocks, all fluid changes, am doing break master cylinder tonight and tie rods Friday. I am just hinky about the valve train.

Maybe with your FAQ page, I will take the plunge.

Hope the courier business is doing well.

JCD

#8 05-22-2002, 06:08 PM

I have been following the links here for some time now. This is the first time I have posted anything. This is a terrific source and has been most helpful to me as I have recently replaced the engine on my 81 300 SD with a used.
The used engine was sold to me as being in excellent shape, it may have been at one time but... Well I believe now that it had sat for a very long time out in the dry California sun. When I got it in I replaced the oil and water pump. I also replaced the gasket behind the oil filter, as that would be a tough change later. I noticed at that time that the gaskets were mosty dried up.
After the install it started leaking oil out of the rear main. I then had to pull the engine again and replace the rear main seal, which was brittle and had thrown off some chunks. That was only a 30 hour job...
Next the number five intake valve has been trouble. Broke two rocker arms before I finally figured out the valve is either sticking or the spring is not strong enough to return it correctly. In doing this little project I did have the uncommon privledge of setting the valve lash at least a half dozen times. Next will be to replace the spring. Have it in hand and that is scheduled for the long weekend.
The point here is that setting the valves can be a pain, but you know what they say, practice, practice practice...

#9 05-22-2002, 06:18 PM

TXBill and all,

Valve adjustment is NOTHING to be afraid of. It is about the most easy thing besides oil changes and brake pads on my 300D. Besides it is very cool to get to look at the workings of the OH cam. I know several here have posted on how to bend a cheap generic wrenches to do it but I went ahead and bought a set from Braun Tools. Doing this gives you one of those warm and fuzzy feelings that you just did "something big" even though the real pros here would get a kick out of that statement

P.E.Haiges · #10 05-22-2002, 06:23 PM

Old Deis,

All the 300SDs I have seen do not have rocker arms. Usually only push rod engines have rocker arms. You might be referring to cam followers which are between the camshaft and the valve. What broke on the cam follower? If the valve stuck open, the piston would hit the valve and close it rapidly. Possibly this is what broke the cam follower.

I had a chain jump one time and when the piston hit the valve it broke the cam in the middle of the lobe and the cam towers but it didn't break any of the cam followers.

P E H

P.E.Haiges · #11 05-22-2002, 06:42 PM

JPL,

You should always check the cam timing and chain tension when the valve cover is off. It is so easy that there is no excuse not to do it. It takes only a few minutes.

I found that my chain tensioner was jammed once, leaving the chain loose. Had I not checked it, it probably would have jumped and wrecked the engine.

The only way you will feel the chain is loose is when it jumps and the engine stops. I'd look for a new mechanic. Better yet, I'd do it myself.

P E H

#12 05-22-2002, 06:45 PM

My mistake. Yes they are called cam followers. Have two broken cam followers on my garage bench now. I am still not sure of the latest diagnosis on the problem here. I should know for sure after the valve spring has been replaced. The story goes that the springs can weaken if the engine sets for a long time with that valve in the open position. At least that is what the mechanics tell me. I did a search on the threads and did not find anything here either.
In any event with the lash set properly the "ticking" is still very pronounced. I used a stethescope and it is definetly coming for that same valve/ cam follower. Stop the engine and check the lash and it is just fine. So I am told most likely the spring is shot.

P.E.Haiges · #13 05-22-2002, 07:38 PM

Old Deis,

A quick check of a valve spring is to compare its length to the length of a new spring. If there is a significant difference the old spring is probably not strong enough to close the valve fast enough and the piston might be hitting the valve. There is very little clearance between the pistons and valves in MB Diesel engines.

P E H

mikemover · #14 05-22-2002, 08:16 PM

JPL,

I'd like to have a CD as well...I just saw a really nice white one today. I spend enough time and money on the SD right now....I sure don't need another car!

I'd keep an eye out on eBay and elsewhere...there's a lot of good rust-free cars around the south/southeastern US, and a lot of us forum members that could go take a look at them for you!

How much work does your CD need? I'd weigh the cost of that against the cost of buying a nice SD...and go with whichever will cost you less...The 123 CDs are great cars too! Diesel durability in a 2-door!

Mike

#15 05-23-2002, 01:03 AM

Yesterday. Replaced rear muffler,adjusted valves and changed glow plugs.Took about four hours.
Bill the only advise I will give. Take a digital picture of the linkage before you remove valve cover. I crossed tWO of them and it didn't have any power. Got the manual out and found problem. Also cleaned and lubed the linkage. Good luck. Charlie