Mercedes-Benz Forum banner

A 1 1/2 Row Timing Chain???

2K views 35 replies 12 participants last post by  isthisdave 
#1 ·
I know there is a lot of debate on this forum about the relative value of replacing single row chains frequently vs a full blown double row conversion. Not wanting to spend either the money or the time to do a full conversion, I recently completed a replacement of a single row timing chain on an '81 380 SL. And much of the credit goes to the advice on this forum - Thank you!

After the job was finished, it got me to thinking some weird thoughts. I needed to use the master link from a double row chain to tie the old and new chains together as I couldn't find a single row master link with spring clips. Then I needed to make a tool to rivet the single row master link. And now I have about 20K miles until I need to do it again.

So, since the guides are the same for both the single row and double row chains, the tensioner is the same, and the link spacing is the same, would there be any advantage to using a double row chain and double row upper sprockets without changing the lower sprocket? Would the double row chain resist stretch any better if driven by only a single row at the bottom?

Inquiring minds want to know!!
 
#2 ·
I don't know if the front or back set of teeth on the double row sprocket line up with the single row sprockets BUT there are two additional sprockets you are forgetting about....see pic. If by chance they did line up you would have 3 single row sprockets pulling a double row chain. I have no clue what the implications would be if this were physically possible but it seems like all that rotating mass without support at high rpms would not be a good thing.
 

Attachments

#4 ·
Gilliac, you pose an intriguing question that I cannot answer. However, for some reason your inspired idea of using a double row chain on single row lower sprockets makes me think of the rear seat arrangement on the 107. Although it is theoretically possible to fit two normal human beings in the second row, what would be the long term consequences of such a practice?
 
#5 ·
Panzer, Don't know that I would consider the idea "inspired"!! But as to the long term consequences, I am now stuck with changing out the timing chain on some relatively short interval (20K?) and still have some forum members saying this is a time bomb. Just wondering IF this might be a LITTLE more reliable than a standard single row chain. Never thinking it was the equal of a full double row conversion. Would still do the 20K changeout until the thing dies from some other cause. Just would have less "single row angst".

I am assuming (yeah, I know!) that if the guides are good, on an engine with less than 80K miles, and a history of regular oil changes, that stretching of the chain is more likely than worn sprockets to cause the chain to jump off the sprocket tooth engagement. I think I will buy a new double row chain and test it in tension to failure, once loading both rows equally, then repeating the test loading just one row. The pins MIGHT carry some of the load to the extra set of plates, might not. But if they did, it would reduce the "stretch" of the chain. It would of course do nothing for the wear on the single row crank sprocket which carries all of the load to drive the chain.

Looking at the chain path, it appears that the single row chain lines up with the rear most path of the double row chain and there is the same unsupported areas in the one, one and a half and two row setups. And the use of a double row sprocket on each cam would reduce the wear at the two highest load driven components (camshafts).

Depending on the tensile tests, I will probably do this the next time I change the chain. The change to a complete double row chain would require removal of the engine and at least $1000 in parts, and if I ever have to remove the engine, I think I would try a conversion to something more modern. It is just a driver, not something that will ever be extremely valuable, nor is it what i would choose to build a street racer. So maybe something like a Buick 3800 V6 with about a 50% HP bump.
 
#9 ·
On my '83, the single row failed just out of warranty. I think it was about 30K. Mercedes covered it.

The new chain failed at about 80K. That's when I had the conversion done. I don't remember the cost but it wasn't cheap.
 
#10 ·
failure mode?

I have no idea, this is my first 380SL, and AFTER I bought the thing I found this website and read the cautions about single row timing chains. From what I have read (ZERO personal experience) the common failure modes are:

1. Stretch of timing chain until it jumps off camshaft sprocket (probably passenger's side due to engine rotation)

2. Failure of plastic guides (oil, heat and age make them brittle)

3. Failure of little plastic parts that hold rocker arm oil tube in place.

Two and three can be fixed somewhat easily without removing engine, chain stretch seems to be cured by a double row chain (at considerable expense) or frequent changes of the single row.

So I got to wondering what I could do to prevent/reduce chain stretch without a full conversion ($5K conversion on a car I paid $8K for just doesn't seem right!)

Guess I will just do the every 20K waltz. If a new one lasted 30K maybe i have a 50% safety factor (HOPE HOPE HOPE!)

German Engineering - What can you expect from people who invaded Russia in the winter -twice!

Gil
 
#12 ·
The double row chain has another bearing point, making it at least 50% stronger. The forces pulling the chain along are no different, so the double row chain has more bearing area to distribute the load and wears slower. Stretch is just wear of the bearings, so stretch on the single row chain is magnified by the greater effective forces per unit bearing area, and so it wears faster, and because it is not as strong it breaks sooner than the double row chain. By sooner I mean a double row chain with the same amount of stretch (wear) is still stronger than a single row chain.

Of course double row chain engine owners need not be too puffed up because guide and tensioner failures can break a brand new chain of either design. So you still have to manage this issue closely. :eek

It does seem that a better solution to the single row problem would have been a more robust chain design and a return to metallic based guides. :thumbsup:
 
#13 ·
The double row chain has another bearing point, making it at least 50% stronger. The forces pulling the chain along are no different, so the double row chain has more bearing area to distribute the load and wears slower. Stretch is just wear of the bearings, so stretch on the single row chain is magnified by the greater effective forces per unit bearing area, and so it wears faster, and because it is not as strong it breaks sooner than the double row chain. By sooner I mean a double row chain with the same amount of stretch (wear) is still stronger than a single row chain.
I was going to say that.








Yeah...right.
 
#14 ·
While I have seen pictures of damage caused by failures in the timing chain system, I have never seen a picture of a broken dual row chain. For that mater I have never seen a picture of a broken single row chain. Not saying it didn't happen just that I haven't seen it documented.
 
#15 ·
It's a bit odd. Lots of successful engines, old and new, from various manufacturers have single-row chains. I understand Mercedes switch was in pursuit of weight reduction uniquely for the US market, as the ROW engines continued with double chains.
I wonder what happened to make Mercedes' design effort such a dud? I suppose somebody shaved their design margin of safety too thin.
 
#18 ·
Shooting from the hip here, but I was under the impression that they thought they could get away with the single chain because of the reduced compression. Single chain, different sprockets, and some other stuff probably cash meaning a bigger profit margin per car sold.

But alas, the teutonic nature of these engines meant that it was not meant to be.

The fact they failed under warranty is depressing. I would be blown away if my nearly brand new 380SL in 1983 blew up right before or slightly after the warranty ended.

I know that's what happened to @Jyuma. I would have been furious.

And another note, I love how in @PanzerPuff's chain replacement video that he puts the old chain into a giant WTF. I didn't notice that until the 2nd time I watched it.
 
#16 ·
Original posted by Rowdie
For that mater I have never seen a picture of a broken single row chain. Not saying it didn't happen just that I haven't seen it documented.
I have never heard anyone even say what the cause of failure was of a timing chain. I have heard of several and from time to time see craigslist or ebay postings for cars with broken chains. I broke a timing chain on my 240D, which was due to a tensioner failure. My guess is chains don't break due to wear, they break because of peripheral failures (guide, tensioner, oil tube, etc.). Perhaps those who have had a failure could chime in with the cause, if they know what the cause was. I would like to hear of chains that broke solely due to wear (guides, tensioners, oil tubes, etc. in good condition).
 
#31 ·
I would say the single row chains do not have a strength issue. Its probably more of a stability issue and also the fact that a single row chain will wear into the chain guides at 2 time the rate of the double row chain. Old Ferrari's used a triple row chain. They may have revved a bit more but they were smaller engines. Oldsmobile Tornado and Cadillac Eldorodo used a 4 row, same pitch chain to drive the car.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top