107 1982 500SL dry start sound
 

My euro model 500SL makes a slight knocking sound on start up, some times. It goes away very quickly and does not come back. This seems to happen only some of the time, and it does not matter how long the car sits. I just changed the oil after about 800-1000 miles, and I used 10W-40 max life with new MB filter. No change. what could this be?

My car does the same thing... until the oil pressure rises to 3 then it stops... is this bad, are we going to ruin engines, or is this completely normal for older cars?

500sl knocking sound
 

both cars sound like the timing chain is stretched and they will knock until the chain tensioner fills with oil and extends all the way out.time for a new chain and tensioner. david poole european performance dallas tx.

Concur, it sounds like a tensioner issue. If the dry tapping continues longer than a few moments I would also consider replacing the oil drip tube plastic bits and making sure the drip holes are clean and free of any blockage.

Interesting... I listened for the sound this morning... and nothing... I will have my guy look at it and see what needs to be done...

My car only has 118k miles on it if that makes any difference... I dont think its due for a timing chain replacement... can the tensioners be adjusted?

my car has 116K miles. I have been getting quotes from local shops and they want $400-500 in labor, so I think I might try doing it myself.

If I do the job myself of replacing the chain and tensioner should I purchase any special tools? the shops in town have said that a special tool is needed for doing this job.

http://www.samstagsales.com/mercedes.htm


this website has some tools fo the job, do I really need them or not?

I've replaced the tensioners on both the 4.5 and the 560. Both took a very special tool...a 12 or 14 mm socket. Two bolts are all that hold them in. The new tensioner spring will have a bit of resistance, it does take a little bit of oomph to press it into place while threading in the bolts, even more so if this is an older model that requires priming the tensioner. You have to push it in flush before starting the first bolt. Do not try to get it close and then pull the tensioner against the block by tightening down the bolt. You'll likely strip the threads from the block.

I have been advised by a local mechanic to replace the guides at the same time, since they are a weak point. This of course means that the whole front of the motor has to come off. Is this job really needed or should I just replace the chain and tensioner.

The mechanic that I am talking to now has said that all the guides, except for one can be replaced, without dissasembly of the front of the engine. Should I be concerned about the one guide that is not being replaced?

No, your mechanic is giving you good advice. The guides most prone to failure are up top, and the most critical one is the left inboard, but most elect to change all the top guides and tensioner guide when doing the job. It's do-able as a DIY job but you can easily get into trouble if you skip a tooth or drop the chain into the engine while rolling the new one in. If you can get it done by a reputable shop that will do the chain, tensioner, guides and cam oilers for $800-$1000 parts and labor that is a fair price, even up to $1200 if you really like the shop and trust they will do good work. Over $1200 then find someone else.