Timing belt failure - thankyou merc. Engineers.

oigle

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The same technique is used on MB chains,,and this does speed the process up.

I normally say that the teeth on the cam wheels should be looked at after say 140k miles,,if the are sharp with no flat on the top of the teeth, then they should be replaced as there is the danger of the chain riding a tooth.

For wear in the chain,, if the engine is put onto its timing marks, then the max at the camshafts should be no more than 3 mm and this is on the average 100 link chain

Yes, the teeth must show some flat on top. I recall the cam gear on the Nissans had 3 installation positions and we had to check the cam timing mark to see which one to use. It was fairly critical for optimum performance. If the new chain couldn't be properly adjusted using the last of the last of those positions, then it was obvious new parts were required - gears etc. Milled heads presented a problem in this area at times as they changed the chain length from drive gear to cam gear and retarded the timing. We once had to redrill a cam gear to give it an additional more advanced position. Ah the fun and games with modified engines!!
 

Number_Cruncher

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For the older diesels there are offset woodruff keys available to adjust the cam timing to correct for chain wear - I'm not sure if they are available for newer engines like the OM606 and the CDI engines which followed it though.
 

Cole@MBS

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I expect you've seen some do mega miles too?

264000 miles was the last one i see that had snapped!!

Higest i have seen without having a new chain is 475000 miles, E220 cdi!!
 
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HERBIEMERCMAN

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thankyou guys, i am much happier now, i will examine the chain sprockets for wear.

technology is fantastic when you think that members from the otherside of the globe are participating in our club.

thankyou malcolm for the tech info. herbiemercman.
 
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HERBIEMERCMAN

HERBIEMERCMAN

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hi russ, ( rf065), thankyou for the url for the timing belt replacements, it is very good. herbiemercman.
 

OlafMaxwell

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The difficulty was that originally timing chains were not great and prone to early wear and failure and with associated tensioer problems, belts were much easier to change. Older FIATs always had these and they worked well, as long as they were chnaged. neglect does lead to serious engine damage although as far as I know some of the Fiat petrol engines are still non interference.

Technology moved on and oils improved. Chains now seem to last longer and do usually give audible warning when things go wrong.

I wonder what is the life of the timing chain in the 320cdi?
 

Weather Man

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1984 380 SL
380SL's 1981-82-83 for U.S. delivery had a single chain. European models had the duplex chain. Failure mode is to rattle or chatter on startup, indicating the tensioner has lost tension due to oil leaking out.

The fix is as above, examine the teeth of the cam sprockets which can be done with a dental mirror through the oil fill cap. Wear will lead to stretch, in effect. In addition, the plastic chain guides can fail due to heat and age; typically the driver's side upper goes first and this can also be seen with a mirror as wear on the block or cam cover, in the form of slices the chain has made, two parallel grooves.

When I had the tensioner and guides replaced on my '84 which has a duplex chain, the driver's side upper had snapped and the broken piece was in the oil sump! I got it just in time.
 

Alex Crow

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hi weather man,

when i read your post about the single row chain on the 116 engine i was somewhat sceptical to say the least. a little research later and i am agog. how did MB think going from a duplex in the iron block 350 116 to the single in the aluminum block 380 116 was a good idea? but only for the US market, really struggling here. it seems that many have been converted to duplex over the years, and that later models were duplex.

presumably the 420 116 engine was duplex? come to think of it, it was probably only available in later years.

the similarities between these aluminium and steel block engines is great. they shared engine numbers for a start, 350, 380 and 420 were 116 and 450, 500 and 560 were 117. the timing gear train parts were largely the same, but the later engines had different, more reliable tensioners. neither were the locking type though, could have been a good idea. i have rebuilt 5 or 6 over the years due to chains jumping when the rail gets between the chain and gear, or just because it is too slack - this only happened on start up. broken rocker covers at the front is a clue.........i am not a fan.
 

hiram

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I had a 1977 capri 1600 and the belt went and through shere good luck on my part not a pick of damage, and these are known for causing valve and head damage.
 


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