Making a long story short: Bumped into a guy with an older 380SE at the gas station. He mentioned that I was wasting my time replacing the chain rails with plastic OEM parts, and I should be using Aluminum rails. Furthermore, he stated these rails are not available through Mercedes, but only to shops through very few suppliers. Anybody got any info on aluminum rails or ever used them? My local MB dealer parts dept has no idea of what to look for. I have a 1989 560SEL with 127k miles on the original plastic rails, and I am going to change them with the chain and tensioner in short order.

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1989 560SEL
1971 Cutlass convt. (sold)
1978 Olds Toronado (sold)
the rest are boring

If everything that people design worked perfectly then this is a good idea also. Have seen several of these aftermarket rails broken & metal all through engine. The plastic rails will last 5-10 years with good chain & tensioner.

Thanks MB Doc. I think the MBenz engineers just MIGHT have some experience designing these parts, so I will trust their judgement on the choice of plastic for the material. It has been my experience that if something is designed to be soft and wear, replacing it with something harder ususally causes a different failure. While the chain links are much harder than the aluminum, I would be concerned about wear particles from the aluminum floating around. I expect having stray aluminum running through the internals of your engine is at least as bad as stray plastic. I am going with OEM components, as my first intuition told me to.

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1989 560SEL
1971 Cutlass convt. (sold)
1978 Olds Toronado (sold)
the rest are boring

I think MB's design engineers were out to lunch when they designed those rails. They play no active part in the running of the motor. The rails are there to keep things in line when the chain goes slack.

The Aluminum rails were the designers choice in the original v8s 3.5,4.5, and 6.9. I would gladly use the original MB Aluminium rails if they were still available. I haven't seen the aftermarket replacements so I can't say. I can make a good guess though; that the aluminum rails wouldn't fracture like a beer bottle no matter how old they got. When the rails get about half the color of a beer bottle they are about as fragile. The only way you could grind up a aluminum one would be to run to motor in constant chain slack.

I doubt anyone on these forums would do that.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

The key here is the word aftermarket rails. I have seen what MB DOC has said. The aftermarket rails will fail. I have had the Aluminum ones have the rubber that is bonded to them come off. When this happens, no one knows. They drive the car until it makes a noise, TOO LATE.
I will agree that the FACTORY alum rails were nice and rarely failed....But we can't get them anymore.


I have seen Plastic aftermarket rails fail with 20k miles on them. Just be sure to use the Mercedes Original rails, and you will have the best product I have seen.

I hope we will all agree on this.

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM