MY 1990 SL HAS BROKEN ( PLASTIC) GUIDES . My son , a budding mechanic has dismantled everything that we can see to get to the chain and now e are looking at it wondering what we do next. we have fished out the broken bits of black plastic, but how do we now know what piece needs replacing and who do we do it? it is not obvious.

I am not sure about a 1990 model(I think it's a m119 motor), but on the older v-8 models when a timing chain rail broke it tended to bend the valves on the left side head. I would remove both valve covers and check for damage. You will need a crimp tool to crimp the master link on the new chain. You might check with a shop for estimate on repair. By the time you add up parts, tools, supplies, pepto-bismol(sic), and asprin you might want to have a qualified shop finish the job for you.

do you have the manual for the car? That would have been an excellent first step;-)

I agree w/ the post above, you will be Very lucky if you didn't bend a valve or two in the process of breaking the guide.

I'd wager you will need to pull all the accesories off the front of the motor to gain access to the guide rail pins that hold them in place.

Again, the manual would be the way to go.

jonathan

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When I needed to change the timing chain and guide rails on my 116 engine I subscribed to www.pindelski.com. Though I had the CD manual, the pics and hints on this site were well worth the $30 I paid for the yearly subscription. Timing chain slap led me to change the timing chain. I discovered 2 broken guide rails but no damage to the valves, so dont get discouraged.

One of the things you can do is order the new parts - you're going to need them no matter what. They will often shed some light on what's going on. Get a manual somewhere - AllData for example. You should take the oil pan off - probably find some more plastic crumbs there. If plastic parts made it to the oil pan you will probably find some stuck up in the oil pump intake pipe. This needs to be cleaned out - not too hard once you find it.

wow, thanks all of you for your response and advise. This is the first time I have posted and I was supprised to get any thing.

An earlier post got me thinking that maybe you didn't grenade the motor. Did you have the car die and not restart? or was the chain making noise and you decided to do exploratory surgery? If the the bits of the guide didn't get ground up by the chain and the car was still running then you probably didn't bend any valves.

Please forgive me if I mess something up. I hope someone will correct any mistakes I have made.

Things you will need:

Timing chain
Guide rails (4)
Tensioner
6mm bolts and assorted washers and nuts
Strong zip ties

The tensioner is located on the passenger side of the block on the forward end of the engine. Looks like a really big nut.

You have to take off the alternator and powersteering brackets, which are mounted to the head.

There are some holes in the front of the heads which house these pins that you have to screw the 6mm bolts into and using washers/socket/nuts/whatever, get them out of the block. The hold the guides in. Make sure not to let one drop in.

You can actually replace the entire chain without taking off the front engine cover. Zip tie the chain in multiple spots on one of the cam sprokets. Then, grind one of the links out in the middle of a cam sproket and attach the new chain to the feed end. The engine turns over clock-wise as you are looking at it with a 27mm socket. You can move the cam sprocket about 1/8 of a turn at a time before removing and replacing the zip ties. You MUST keep the chain and the sprocket teeth in alignment.

I want to say the order of events that I took were:
Remove tensioner
Pull passenger side sproket with chain zip tied on (22mm socket?)
Replace passenger side guides
Replace passenger side sprocket
Repeat on driver's side
Put in new tensioner
Roll in new chain

thanks for all of your advice . I am in to this now with a visiting mobile mech that seems to be sensible. I now need the service manual , but cannot find one. I have been to the Pindelski site and that looks good, but it doesn't seem to include my 1990 500SL as a model ( which I believe is a chassis #129.066 ? can some one tell me how I ask a question of this site , as all it has is info. and subscription:

Check it out:
http://www.books4cars.com/result3.htm?finddesc=SL500

You can also get the service CD's right of MBUSA's website, they are usually pretty cheap.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

FWIW -

My M116 motor had two broken guides and killed the driver side head. I'm going to pick up an M117 (560) late this week so long as the top end is okay.

From seeing what damage can result, I'd recommend the upper guides every 100K. Maybe the chain too.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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