broken timing chain on 617.912 - PeachParts Mercedes-Benz Forum

Mauidieselpetr · #1 08-31-2006, 05:53 PM

Aloha from Maui,
i can have for free 1979 300D from friends, it has broken timing chain while running. I'm reading my factory manual, but can't find out how to install it (it only shows with old one in place).How to time everything together? Most importantly, is there enough space between pistons and valves that they didn't hit each other?
I hope we can save another MB diesel.
And fill it up with biodiesel.
Thank you for your time and help
still learning
Petr

Old300D · #2 08-31-2006, 06:03 PM

I'm sure you'll have to completely rebuild the head. Diesel engines have 21:1 compression, guaranteeing you will have valve to piston contact if the chain jumps.

t walgamuth · #3 08-31-2006, 06:41 PM

when mine broke the pistons and head were ok but the valves went up and broke the cam and two of the three cam towers. they "while you're in there" we did a complete rebuild. if you just repair the damage maybe it would be only 2000 or so if hired done. you have to pull the head to do it right, i think.

probably cheaper to find a good used motor, if possible.

tom w

Carson357 · #4 08-31-2006, 08:45 PM

we had one in the shop like that once, the tech was able to get the chain back on with some difficulty, the pistons and valves were fine, similar to above post, the valves were pished straight up and broke the cam and the bearing towers, he replace the damaged parts, retimed the engine and pump, and it ran fine, no issues at all,. he did not remove the head.

bgkast · #5 09-01-2006, 12:57 AM

How do you know that the pistons and valves were ok if you did not remove the head?

02HD677 · #6 09-01-2006, 03:52 AM

If you are running a 617 at freeway speed and break a chain? ... guaranteed the engine becomes a rebuilder ... cheaper to find a good used engine ... if you can anymore. If chain breaks while at idle ... good chance just valves, camshaft and camshaft bearing tower(s). BUT you will never know about any potential collateral damage that might have resulted down below (plastic or metal chain-guide pieces falling down to the bottom, etc) unless you take the engine apart. Best rule of thumb is to just find a decent engine and keep the broken one for parts by wrapping it up in a nice cozy blanket with plastic/tarp and put it under a tree out in the back forty!

Carson357 · #7 09-01-2006, 04:08 AM

Quote:

Originally Posted by bgkast

How do you know that the pistons and valves were ok if you did not remove the head?

because the car ran fine after the repairs compression was normal, and is still running fine today (repair was in 1998), we suggested to remove the head, but the customer wanted to fix the damage first. i cannot say all are this lucky, but this is what i personally know of the one i saw.

Diesel Giant · #8 09-01-2006, 08:24 AM

It is possible to get away with no significant valve or piston damage, however I have not yet seen one with NO valves bent at the very least.

mplafleur · #9 09-01-2006, 10:42 AM

Finding a used engine is a crap shoot. A friend spent a good deal of time and money replacing an engine instead of rebuilding. After a month of headaches, that engine is now toast.

I think it is better to rebuild if you can do it yourself. You get the satisfaction of finishing the job and you get a practically new engine. A known quantity that will give you more peace of mind.

babyjames · #10 09-01-2006, 10:47 AM

What about interchangeability r.e. turbo vs. N/A, cylinder head wise. I just bought a '79 TD with a snapped chain. I have an engine w/a bad bottom end, but what appears to be a good head, from an '82 TD (turbo). See where I'm going?

Any potential pitfalls involved with putting the turbo head on the N/A bottom end?

Thanks,
Jay.

babyjames · #11 09-02-2006, 11:40 PM

I realize the cam profile is very different, and would replace the cam in the turbo head with the proper cam for a n/a bottom end.

Externally, are the dimensions for the cylinder heads the same?

Jay.