Strange noise from front of engine
 

I have a rattle or clank type noise coming from the front of the engine in my 83 300sd. I checked all that I can think of that would cause this noise, alt, water pump, fan, ps pump. I replaced the vacuum pump thinking that must be the cause of the noise, and with 250k on it I was worried about the bearing on the arm. When I replaced the pump I found the cam part that is bolted to the timing device to have one of the lobes pitted. So i replaced it with a used one from a parts car I have. Thinking I had found the problem I put the thing back together, but the noise is still there, although it seems less loud and less frequent. the noise has no pattern It is most noticable at idle and probably less noticable at higher rpms due to other engine noise.
I am wondering if the timing device could be worn and causing this noise? or is there somting else that could be the culprit.
Oh, I replaced the timing chain around 1k miles ago with a new tensioner. This noise was present before that and did'nt change after the new timing chain.
Anyone have any ideas?

Have you checked the crankshaft pulley? It's secured by six bolts which sometimes loose torque and/or break. Also, check the balancer for security.

X2

I had a noise that I could not identify, coming from the front of the engine as well. It sounded like a kernal of popcorn bouncing around. It went on for a month or so and finally revealed itself when my alternator froze up. I think it was a bearing going bad. I had a few warnings when the alternator light would flicker briefly. You could try loosening or removing the alternator belt to eliminate this possibility.

Alternator is new, replaced last week. So i know it is not that. I will check that crank pulley today, although I would think if it is loose it would make the noise more constant. I might take the belts off and see if it still does it.
Thanks

Just to add some more information to this post. Here are some pictures of the vacuum pump cam plate. I thought for sure this was the problem... Oddly enough the bearing roller on the vacuum pump had no signs of damage at all.
http://www.peachparts.com/shopforum/...1&d=1227014234


http://www.peachparts.com/shopforum/...1&d=1227014234

every 617 I've heard does that.Less when hot,or running biofuels.

Maybe just to clarify some, It sounds like there is a marble in there and every now and then it jumps around. Sometimes a second or 2 between rattles, sometimes a bunch in a row. very irregular noise pattern. I am going to take a video and see if you can hear the noise on the vid.

Yep,I've heard it on youtube.But when I run at least 5% svo,its gone.Just remebered,when I take a high speed run for 30 mins.Its gone for days.Maybe carbon glowing and preignition.

Did you use a mechanics Stetoscope or as I like to use a wooden Broom stick and listen to suspected areas?

The pitted plate should be replaced even if it is replaced with a used one.

I did try the stethoscope method, and I didn't come up with anything nothing I checked seemed to be making the noise.
I did replace the pitted plate. Just posting some pictures.
I tried taking a video but you can't really hear the noise on the video. I might be paranoid, but I don't want to have a catastrophic failure because I ignored something that was warning of a problem.

I have a very similar noise in my 78 240D, though, its coming from what appears to be the back of the engine, loudest where the trans mates with the engine. I heard that it could be a loose clutch plate or fly wheel, but it too goes away when the engine is hot or has been driven 10 or more miles.

I had a noise that might be similar to the one you are describing in my 617 and it brought the house down. Check the chain and tensioner for the oil pump. It is different then the timing chain. You can get to it by taking the oil pan off. Don't drive it until you know this is not the problem it isn't worth replacing your engine!

Can I get to this by just taking the lower pan off? should do a oil change anyway so it might be a good time to look in there.

thanks

An irregular tinny clatter at idle is very often a worn fan thermocouple. Check fan for play. Remove the fan belt and running for half a minute or so will confirm.