1992 W124 300D - is it a interference motor
 

Hi,

Will the valves hit the pistons if the timing chain brakes ? that is to say is it a interference or a non-interference motor ?

Thanks

do you want pics of the carnage, or just my word that it does indeed hit?

I don't know of any diesel that is non-interference.

-J

interference... Yeap definably interference!!!

In my limited experience if a diesel car is at idle that has hydralic lifters there seems to be enough give to just need a new timing chain or belt.

At speed the senario is always very different. Fortunatly a lot of timing belts on diesels seem to fail at start up or shutdown.

my kubota tractor has a compression release lever, it pulls the exhaust valves open for smooth cranking without compression. it might only pull them open a little, but the piston does not hit the valves on it.

Your Kubota pops the valve open a hair during the compression stroke, and closes it before the piston reaches TDC. Clearance in any diesel is in thousandths of an inch, if you had a valve hang open more than just a bit, it'd get smacked.

Hmmm I thought I looked at it with the valve cover off, and it seems to have a lever that holds the exhaust valves all open... now I gotta go pull the VC again and look it over.

One of my best craigslist e-mail arguments ever was with some crazy person that thought 300E (m103) motors were non-interference. :D She was selling a 300E as "needs only a timing chain". I said "it will need a lot more than that if it broke the chain" and so began the arguement. :D :D

There Seems to be a concensus here...thankyou all

What exactly occurs typicaly when the chain breaks ?

Does it bend the valves ?

or

Does it crack the head ?

or

Does it break the piston(s)

in my experieince with gas engines it usually is limited to bending the valves

thanks

Bent valves, if you're lucky. Typical damage seems to range from bent rods to broken cams and cam towers, cracked pistons, broken head bolts, etc.
The last gasser I had lose a belt was an 85 Honda Accord, it pitched the belt at about 4500rpm. Bent valves, broke the cam, shattered one piston, and split a bore. Very bad day.

Makes you long for the days of Engines that had only Timing Gears and Pushrods istead of Timing Belts or Chains.

I managed to drop a Screwdriver into the Timing Belt on the Volvo (I had long ago removed the several piece Timing Belt Guard).
It happend at idle speed and I bent 2 Valves and Cracked several Tappets. What made it really sad was this was about 2 years after I had rebuilt the Block.
My carlessness could have ruined a lot of work.

ALL automotive diesels are interference engine. With a 20:1 compression ratio, the combustion chamber is so tiny that there's no way around it.