Mercedes Primary Chains

Stoutgoose

Stoutgoose

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I need a pair of primary chains for my RGS. I think I read somewhere that Andy has retired; is it still possible to obtain the German/Mercedes type primary chains?
 
IIRC the manual says to replace the primary chains at 16,000 miles. I have also read that you should replace when you can no longer tension them correctly. Which is correct or is there some middle ground?
 
Stoutgoose said:
IIRC the manual says to replace the primary chains at 16,000 miles. I have also read that you should replace when you can no longer tension them correctly. Which is correct or is there some middle ground?
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Some opinions say that in normal use, the primary chains are for life. Not the twin single chains.

Paul
 
Thanks Paul. Which primary chains do you mean; triplex/duplex? The twin singles were fitted to the later bikes at the factory I believe?
 
Unless newer chains are made of indestructium, there's no real reason to ignore the factory-spec 25000km change interval. ALL chains will wear, there's no getting around that. Leaving a worn chain to run on otherwise within-spec sprockets will eventually wear these as well, replacement of which poses far greater problems and expense. A worn chain is far more prone to breaking than an un-worn, it eventually cannot follow the sprocket teeth properly. The large wrap angle at the clutch sprocket is most affected, there are a lot of teeth engaging with a lot of links, the slightest length differential will make itself felt. If the primary chain had a removable connecting link, the wear would be quite visible, reckon nobody would then propagate leaving them in there for life. Timing chain connecting links are a good indicator for chain life/wear.

The primary chains can be tensioned "correctly" until the adjuster screw falls inside the primary housing, but they're past their best long before. Sticking to the specified interval may be a pita for those that still do big miles, but, most of us are not needing to renew chains very often anymore. Perhaps a chain for each of my twins and triples will see me through the remainder of my riding career, which I'd rather end on an intact bike than have the engine laying in a box with a hole punched through the primary housing.

piet
 
Stoutgoose said:
Thanks Paul. Which primary chains do you mean; triplex/duplex? The twin singles were fitted to the later bikes at the factory I believe?
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Yes, the twin chains fitted to the last triples. They wear unevenly and become extremely noisy.
Let me reformulate after Piet's comments.
Yes, factory recommended interval for change was 25 000 km. I've put duplex Mercedes chains in all my big Laverdas and I doubt that I'll be needing to change them again in my lifetime. Some may be over the recommended change interval. If you have recently become a proud new Laverda owner, change all chains as a matter of course.
(Just in case, I have some spare twin cases:) )

Paul
 
Thanks Paul. I’ve owned a 750GT for three years and have recently bought a lovely RGS that has been well maintained, but hasn’t had the timing or primary chains replaced in a while. Like you say, putting the Merc chains on now will most likely cover my mileage for at least the next decade.
 
You should check what is currently fitted to the RGS before ordering a duplex chain. Early RGS had triplex chain and sprockets fitted, these will accept the duplex. If however, the 2 single chains on dedicated sprockets are fitted, the duplex will not fit, not even if you hit it with a stick or swear at it.

If good quality single chains are fitted and kept properly tensioned, the uneven wear will hardly make itself felt between renewal intervals.

Although the Mercedes duplex do run noticably quieter, there's not THAT much difference to either a triplex or 2 x simplex chains when new. We put up with them for decades before the duplex arrived on the scene, can't be all bad. ;)

piet
 
It has two single row simplex chains fitted. I’ve misunderstood about the Merc chains, are duplex all that’s available? If so, what are the best simplex options?
 
It was recommended to me that I replace the clutch cush rubbers at the same time, which I did and the noise was noticeably less than the chaff-cutter it previously was 😁
Also with the cush rubbers out, it is possible to change the simplex chains without removing the drive sprocket 👍
 
One of Andy's (chain man) recommendations was that a chain should be replaced if has more than 1% stretch (that is if it's 101% of its original length). With the primary drive cover off, you can estimate the stretch in the primary chain by putting a straight-edge across the top of the two sprockets and pressing down in the middle of the top chain span to see how far it sags. A stretch of 1% in the primary chain is about 24mm sag. That's quite a lot of sag. I reckon the tensioner would be getting near its limit of adjustment by then.

If Andy's limit can be relied upon then it means the chain can be pretty sloppy and still be OK. But I reckon most people would prefer to replace a chain before it got anywhere near the 1% limit.

How do I know the sag vs stretch relationship? Basic geometry - I did the calculations in a spreadsheet years ago. I just added it to the forum library.

Triples - Primary chain stretch chart - History

www.laverdaforum.com www.laverdaforum.com

Note: I did the calculations using the primary chain specs (sprocket centre distance, tooth numbers, etc.) for Laverda triples, but I'm 99% sure the twins use the same primary drive (albeit with a different tensioner) so the chart would also apply to the Breganze twins.
 
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Andy said:
It was recommended to me that I replace the clutch cush rubbers at the same time, which I did and the noise was noticeably less than the chaff-cutter it previously was 😁
Also with the cush rubbers out, it is possible to change the simplex chains without removing the drive sprocket 👍
Click to expand...
Reading the manual, I’d need to use the special tool to lock the primary drive sprocket and remove. What would be the process to follow if doing it without removing the drive sprocket?
 
You can undo the bolts securing the cover plate on the clutch drum this will allow you to slide the sprocket off the cush drive rubbers as you ease the sprocket off the drum the chains will become slack and you can remove the large sprocket and carefully remove the chain from the crankshaft sprocket without undoing it.
When you are reinstalling the new chain it wouldn't hurt to ensure the nut on the crankshaft is locked up tight !!!!
 
mauricejota7604 said:
You can undo the bolts securing the cover plate on the clutch drum this will allow you to slide the sprocket off the cush drive rubbers as you ease the sprocket off the drum the chains will become slack and you can remove the large sprocket and carefully remove the chain from the crankshaft sprocket without undoing it.
When you are reinstalling the new chain it wouldn't hurt to ensure the nut on the crankshaft is locked up tight !!!!
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Thanks, that sounds very straightforward. Are there any gotchas to be aware of? I have ordered a pair of Merc chains from Jason today.

Having reread the manual, there’s no change interval for the timing chain; just the tensioning check. My bike is on 72,000km. The primary chain was last changed at 32k and the timing chain never, although the link has been replaced several times.
 
Stoutgoose said:
Thanks, that sounds very straightforward. Are there any gotchas to be aware of? I have ordered a pair of Merc chains from Jason today.

Having reread the manual, there’s no change interval for the timing chain; just the tensioning check. My bike is on 72,000km. The primary chain was last changed at 32k and the timing chain never, although the link has been replaced several times.
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There is no interval for changing the primary on twins as you've noticed.
The one on my long suffering SF2 probably has around 130 000 km. I see no reason to change it though I'll do so if I rebuild the engine.

Check regularly however the camchain tensioner wheel.

Paul
 
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