Annoying rattle in reverse

[ChadF]

I need some expert advice.

I recently bought my first 500e and LOVE the car. It is a '92 with 69k miles. It is my daily driver and goes like a train. Recently it has started making an annoying noise though. I start it in the a.m. (i.e., it's cold) and after a brief warm-up, put it in reverse. As soon as I shift into reverse, I hear what sounds like a rattle or vibration under the hood. I have localized it to under the left valve cover. It's not loud but it is noticeable - both inside and outside the cabin. It goes away when I shift back into park or into drive. It also stops after the car warms up. At first I thought it might have been some looseness in the air filter assembly. But after removing that, it seems pretty clearly to be coming from under the left (drivers side) valve cover.

So here are my questions:

(1) Any idea what is making the noise or how it can be remedied?
(2) Any recommendation for a shop in Fort Worth, Texas? Hate to take it to the dealership.

Any help / advice would be greatly appreciated.

Thanks,

Chad

 

[KarlC]

I'm not an expert but there are plenty here, welcome aboard. Post some pix and details of your car when you can.

 

[ChadF]

Thanks. I am planning on doing so soon. I would like to get some new wheels first but may have to put that plan on hold for now. Probably need advice on wheels too. But first the rattle must get sorted.

 

[Jim]

Towards the rear of the engine there is a thin sheet baffle fitted inside the valve cover; it could be split or loose. You cannot see it via the oil filler.

Jim

 

[gsxr]

I'm stumped too. First, try pulling the plastic cover over the spark plug wires - make sure the noise isn't something simple.

I can't think of what might cause a rattle inside the valve cover, but if you're certain the noise is internal, you'll need to remove the valve cover to investigate. The rearmost/lower bolt is very difficult to access, so start with that one... if you can get that out, then remove the rest of them. You'll need a new gasket, and always install it dry (DO NOT add any sealant to the gasket when installing). Hopefully the last mechanic didn't try to "help" by adding RTV or other gunk, which will take you forever to scrape off the sealing surfaces. The little copper washers under the v/c bolts are important, I always replace them since they're cheap, but don't put the bolts back without them. The FSM procedure is at this link. If your PCV tubing is old, it may be fossilized, so don't be surprised if those snap when trying to remove them. I just went through that same exercise on my E420 and had to replace all the PCV pipes, so I can provide a part # listing if you need it. While the valve cover is off you can inspect the upper chain rails and, if so inclined, check timing chain stretch as well.

On a side note, driver's side is left, passenger's side is right... MB refers to left/right from the viewpoint of the driver facing forward.

BTW - welcome to the forum!

 

[Jim]

GSXR (Dave) gently reminds me that the oil separation chamber is in the right valve cover not the left. My only excuse is a wicked bout of jet lag. The left valve cover does not have the oil separation chamber. Sorry for my mistake.

Jim.

 

[ChadF]

Jim and Dave,
Thanks very much. I will try to open up the valve cover see what's what. How can I tell if the upper chain rails are in good shape? Or measure any timing chain stretch?
Thanks for the help.
Chad

 

[gsxr]

How can I tell if the upper chain rails are in good shape?

It's a visual inspection. If any of the rails are broken, most likely they are all brittle and in need of replacement. Check out the link below for photos of what I found on a low-miles spare motor I bought a couple of years ago. I replaced all the upper rails prior to installing it in my car to test out:
http://www.w124performance.com/images/M ... re_engine/

Or measure any timing chain stretch?

There are holes in the camshaft flange which will align with holes in the cam bearing tower. There is a special tool which is just a dowel pin that slides through both holes when they are lined up. An appropriate size drill bit would suffice. With a brand new timing chain, all four camshafts should line up with the holes (i.e., you can "pin" all four cams at the same time) with the crank at 45° BTDC. With a stretched chain, the reading at the crank will be a degree or three past 45. I check at the left (drivers) exhaust cam and right (passenger) exhaust cam. Usually the right side will be double the left, i.e. if you measure 43° at the left (2 degrees stretch) the right side will likely be 'pinned' at 41° (4 degrees stretch). While there is no official spec for the M119 as to how much stretch is acceptable, I consider 2° left / 4° right about the limit of acceptable; at 3° left / 6° right (or more) it should really get a new chain.

The factory procedure is at this link - note it only says that the cams should be able to be pinned at 45° BTDC, and doesn't say what to do if you can't, etc:
http://www.w124-zone.com/downloads/MB%2 ... 5-2230.pdf

For reference... my "spare" motor with the busted rails was 3.0/6.0 left/right and I rolled in a new chain. My '94 motor measured 1.5/3.0 and I plan to leave it alone. My '92 got a new chain courtesy of the previous owner, and my silver E420 measured zero (wow). Haven't checked the other (black) 420 yet. If you replace the chain, it's usually a good idea to replace the tensioner as well... cheap insurance.

 

[ChadF]

Dave, thanks for this. Don't suppose you'll be in Fort Worth anytime soon?!
SO is it that hard (time, skill, etc.) to replace the upper guides? I mean, it looks like they simply bolt on . . . but I have never come close to doing anything like this. Checking the timing chain stretch seems a little more complicated but not terribly difficult either. Think these are things that someone who has never even changed his own oil could do? (which something else I want to try to do!) So the pics of with the guide pieces in the engine, did the engine run in that condition, i.e., with all those pieces floating around in there?

 

[gsxr]

Checking the chain stretch via pinning the cam(s) is relatively simple, the hardest part is being able to slowly turn the engine a degree at a time (far easier with fan clutch removed, but that's a chore in itself).

Acutally replacing the chain rails is a long process because you have to disassemble & remove the cam advance mechanism and all cam sprockets. It is an advanced DIY and may take a couple of weekends of work or more. On a scale of 1 to 10, changing the oil is about a 2, pulling valve covers a 4, checking chain stretch 5, replacing the upper chain rails 7.

The engine can run with those pieces floating around, they just sit there, if they're in a bad spot they may wear and the little pieces end up in the oil pan. That's another good check for rail problems - pull the lower pan and see if there's any rail debris. The scary part is that engine only had ~77kmi on it!

 

[ChadF]

Okay, short of visual inspection, is there any way to tell if the guide rails are worn out / broken OR the timing chain has stretched to a dangerous point?

 

[gsxr]

Okay, short of visual inspection, is there any way to tell if the guide rails are worn out / broken OR the timing chain has stretched to a dangerous point?

For the chain rails, it's either visual inspection, and/or pulling the lower oil pan at the next oil change to inspect for any signs of debris. For the chain stretch, the only way to check is to pull at least one valve cover and measure the reading at the crank with either of the exhaust cams pinned. None of these jobs are particularly fun though!