Sadness... Broken Timing Chain on '81 - PeachParts Mercedes-Benz Forum

Lambrettaman · #1 02-01-2012, 02:47 PM

My timing chain on my 1981 300TD with ~330k miles on it broke last week. This was the original factory chain. Car otherwise ran great. No oil consumption, no loss of oil in the incident.

I was accelerating lazily from a stop light when I felt a shaking in my right foot through the accelerator pedal and heard a clanking scraping noise and then the engine died.

The cam broke and it took out a couple towers.

My mechanic is recommending a motor transplant because it would cost about as much to get in and replace the cam and towers and chain. He's concerned that the teeth on the gears might be worn and that a replacement chain could be damaged and cause another failure.

Thoughts?

I'm thinking that my 6-year stint as a 123er is coming to a close. This car is in really nice shape. I'm amazed at the paint and chrome on these fabulous cars.

Part it out? Sell it as a project?

ngarover · #2 02-01-2012, 02:59 PM

really tough call that only you can make based on the condition of the rest of the car. If it is great, you can always find a donor car to get an engine out of whose body is crap etc.

vstech · #3 02-01-2012, 03:23 PM

in AZ, I am certain the vehicle is flawless... maybe interior fade, cracking etc...
I agree with your mechanic, put a replacement engine in there... save the head from your car, heck, go get a motor from any 82-85 diesel, and have your mechanic rebuild your head with new valves, and parts from the donor motor, and be ahead of the game with better compression up top!

vstech · #4 02-01-2012, 03:24 PM

if you decide to sell the car, many members here would snatch it up. ebay the thing with the blown motor for a rust belt MB'er looking for a great chassis.

Lambrettaman · #5 02-01-2012, 03:30 PM

Good advice from all of you... It's nice to hear from folks who appreciate these machines. It has amazed me ever time I work on it. And you're right, it has lived an easy rust (almost) free life. 1981-2006 in Socal and 2006 on right here in dry, sunny auto preservation land. I think MB Tek fabric is one of the most amazing fabrics ever used.

benhogan · #6 02-01-2012, 03:44 PM

Quote:

Originally Posted by Lambrettaman

Good advice from all of you... It's nice to hear from folks who appreciate these machines. It has amazed me ever time I work on it. And you're right, it has lived an easy rust (almost) free life. 1981-2006 in Socal and 2006 on right here in dry, sunny auto preservation land. I think MB Tek fabric is one of the most amazing fabrics ever used.

what caused the chain to snap again? describe what happened for the benefit of the less informed (like me!)

Lambrettaman · #7 02-01-2012, 03:48 PM

Quote:

Originally Posted by benhogan

what caused the chain to snap again? describe what happened for the benefit of the less informed (like me!)

Absolutely NO idea. Oil was fine. Mileage had increased in the past few months from 22.5mpg to 24.5 mpg. I was very good about changing the oil regularly. Did the valves once per year (I now know I should have been inspecting the chain). Vacuum was a bit low at 15mm, but working, so I don't think the vacuum pump was the cause. We just did a 800 mile trip to Colorado for skiing over Christmas. It ran like a champ on the trip. Maybe it was just time...

benhogan · #8 02-01-2012, 03:54 PM

the vacuum pump can cause a motor to fail? how?

vstech · #9 02-01-2012, 04:01 PM

the vacuum pump is driven by the chain, it's opposite from the IP, and it's got bearings, and steel parts that can fall into the chain and cause timing to skip, resulting in valve contact with pistons, or debris can get in the chain, and jam a gear, or cause the chain to rise and bind in the block or valve cover... messy...

Orv · #10 02-01-2012, 04:02 PM

Quote:

Originally Posted by benhogan

the vacuum pump can cause a motor to fail? how?

On some cars the bearing in the vacuum pump can fall apart and drop hardened steel ball bearings into the timing chain gallery. They can get caught in the chain and cause problems immediately, or sit in the oil sump until they wear through the pickup screen and get pulled into the oil pump, jamming it.

benhogan · #11 02-01-2012, 04:07 PM

Quote:

Originally Posted by vstech

the vacuum pump is driven by the chain, it's opposite from the IP, and it's got bearings, and steel parts that can fall into the chain and cause timing to skip, resulting in valve contact with pistons, or debris can get in the chain, and jam a gear, or cause the chain to rise and bind in the block or valve cover... messy...

is this for the 61x and 60x engines?

vstech · #12 02-01-2012, 04:13 PM

yup

Stretch · #13 02-01-2012, 04:23 PM

If you love the car don't let it go.

Lambrettaman · #14 02-01-2012, 04:27 PM

Quote:

Originally Posted by Army

If you love the car don't let it go.

I don't want to. I have a love of old vehicles. 4 1960s motorscooters, a '74 step van, and a '97 BMW E38 share the garage with this one.

whunter · #15 02-01-2012, 06:10 PM

Quote:

Originally Posted by Lambrettaman

My timing chain on my 1981 300TD with ~330k miles on it broke last week. This was the original factory chain. Car otherwise ran great. No oil consumption, no loss of oil in the incident.

I was accelerating lazily from a stop light when I felt a shaking in my right foot through the accelerator pedal and heard a clanking scraping noise and then the engine died.

The cam broke and it took out a couple towers.

My mechanic is recommending a motor transplant because it would cost about as much to get in and replace the cam and towers and chain. He's concerned that the teeth on the gears might be worn and that a replacement chain could be damaged and cause another failure.

Thoughts?

I'm thinking that my 6-year stint as a 123er is coming to a close. This car is in really nice shape. I'm amazed at the paint and chrome on these fabulous cars.

Part it out? Sell it as a project?

FYI: The 1981 300TD has an OM617

This is why I replace the timing chain around 200K.

To answer your question, if you are lucky:
* Pull the head.
* Replace the camshaft and towers.
* Replace valve guides and valves as required.
* Replace the timing chain and rails.
* Reassemble.

A replacement engine is another option.

.