Oh happy day...broken guide rail
 

I am somewhat "restoring" my 86 420 and in the process sprucing up the engine compartment. So I took the nasty valve covers off to get them coated. I got to looking at the timing chain and guide rails. First of all, they are dark brown, which I know means replace them, and then I shine a light down the drivers side of the engine (down the chain) and there sits a piece of a broken lower guide rail. The top ones are all there, so it could only be a lower one. I've looked up previous posts on chain and rail replacements, but they mostly talk about the uppers.

Now, the lowers require dismantling the entire front of the engine and timing cover, correct?

Is this anything for a gutsy mechanically inclined DIYer with factory service manuals to tackle? Or is this something to trailer it to the shop for? Any idea what that might run for someone else to do it?

Are you sure it is a lower rail? The single rail on the right bank and one of the rails on the left bank are long, much longer than the short rail on the left bank. Could possibly be an end from the long rail.

As I recall, the rails should almost touch the cam sprocket, not have a large gap there. Take a closer look.

http://www.pe.net/~mktangas/rails~in.jpg

see how close the upper rail comes to the sprocket. Looks pretty much the same on the other side, except there is only one rail.

unless you got a lot of time and all the tools, you can try it yourslelf, but I'd say take it to the shop, I just had to get the timing chain rails and sprockets replaced on my 190, two day job in the shop.

XP

Mike, I hope you're right!!! I went back out and looked, the drivers side rails are definitely intact. I can see the broken off piece, and the tip looks exactly like those of the exposed rails. The tensioner arm looks like it has a blunt end, but then I looked up a picture of it on FastLane and it looks like they come that way. The other rail on the passenger side is intact on top, and you really can't see the bottom too well, so my only hope is if it is the bottom of that rail that the broken piece came from. I called an MB shop and they said that lower rails "rarely need replacing and that they are willing to bet that it is an upper" I hope you and the shop are right!! If it is only the uppers, I think I can tackle this with the step by step instructions on this forum and my service manuals. I'm not payin the astronomical price the shop wants!! For the money I save in labor, I can pay for my service manuals, buy a nice torque wrench, maybe even a complete tool set :)

More pictures here
 

Try these for a sense of what the upper rails look like.

I had always heard that the lower rails were usually immersed in oil and would last about 300k as a result. How many miles on your 420?

Well what everyone is saying about the lowers being bulletproof is encouraging. I'm just praying it is a piece from an upper. I'll have to do a little more investigating. The car has 165,000 on it. And thanks for all the pics:)

Hi mbjtc

Have never done this myself but good luck - the info on this forum is pretty detailed on the job the link thomaspin posted is absolutely terrific.

If you have a reliable parts supply (and I mean reliable) when you have the new rails in your mitts and are able to compare with the rails you take out - then your knowledge of the true position will be confirmed.

I expect by then you will have the confidence to tackle whatever is necessary in this area ;-)

Best of Luck (and keep us posted)

WHEW!!! Today I ran out and got one of those little grabber claws (the ones where you push the button like a syringe and little claws come out), and I fished out the broken piece. I also bought one of those little telescoping mirrors and got to examining my car. The upper rail on the driver's side, inboard side of the motor, is snapped off at the bottom below the lower pin where you can't see it, but with the mirror I could. So that is a relief!! I guess I'll be printing out a lot of pages from this forum! Here I go!....:p

Thomaspin,

Unbelievable website. Your pictures (not just of guide rails) are truly beautiful. Are you a pro? This needs to be in the permanent DIY file. Well done!

Thanks jba007!
 

I am anything but a pro - doubt my back could take this sort of thing all day long....

LOL.

not that your mechanical skills are in doubt, but i meant, "are you a pro photographer?" ;)

No, not a pro photographer
 

I enjoy taking pictures too much to want to do it for a living....