Slack primary chain

Please can I ask for some advice concerning reasons for a really slack primary chain? Bike is a 1974 Commando Mk2a

Just recently, I started noticing a rather scary grating sound coming from the bottom end..

I took the primary chain case cover off to see if there was something going on in there and sure enough, the primary chain is really slack.. so slack that it has been eating away the stator studs as it bounced around. Hopefully, this is the cause of the grating noise that I could hear when I revved the engine.. i.e. the primary chain was suddenly tightening up and gnawing away at the studs/posts

I’ve looked at the gearbox adjusters and it doesn’t look like they have moved at all (e.g. no scraped paint). The rear chain is also just fine and hasn't tightened up with the primary chain slacking.

Thinking it might be the gearbox adjuster that has slipped forward, I also tried to loosen the top bolt that goes through the gearbox housing and it will not budge.. which leads me to believe that I don’t think the gearbox adjuster has moved forward causing the primary to slacken

Can a primary chain simply wear so much that there is this much play? Time for a belt drive??
Thanks for any advice
Mike


Slack Primary Chain. I removed & checked the clutch while in there



Pushing down on the chain to measure the slack

The chain has gnawed away at the posts but it doesn't look too serious. The chain also appears undamaged.

Gearbox Adjusters don't seem to have moved

It not normal to hear chain clash but Its common to see chain teeth notches on mount posts but is unusual for triplex chain tension to change much over short few 1000 mile intervals, so either chain been wearing more than realized or tranny bushes going away or both. Got to have lots of cold slack though yours seems like maybe double slack needed. Try to wiggle clutch basket for a clues. Correct tension protocol is drawing triplex back with drive chain then gear box froward to set triplex final tension, then diddle drive chain again. IF ya can lift links out of rear clutch valleys likely chain is shot. Do re-check once hot on next ride out.

Can a primary chain simply wear so much that there is this much play? Time for a belt drive?? (/quote)


Perhaps time for a new chain. Normal slack should be about 3/16 to 1/4 inch up/down movement at mid run of the chain. Have you been maintaining proper oil or ATF levels in chain case?

The simple answer to your question is YES, especially if it has been run dry. To continue to run the chain in a worn condition risks breakage and lots of damage to whatever gets in the way when the chain let's go, and also puts increased wear on the sprockets.

Slick

texasSlick said:

Can a primary chain simply wear so much that there is this much play? Time for a belt drive?? (/quote)


Perhaps time for a new chain. Normal slack should be about 3/16 to 1/4 inch up/down movement at mid run of the chain. Have you been maintaining proper oil or ATF levels in chain case?

The simple answer to your question is YES, especially if it has been run dry. To continue to run the chain in a worn condition risks breakage and lots of damage to whatever gets in the way when the chain let's go, and also puts increased wear on the sprockets.

Slick

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+1.. where is the evidence oil, or have you cleaned out the cavity..

Thanks for the advice guys,

Yes, I cleaned the cases out before I took the pics as it was pretty dirty and I wanted to see what was going on, but there wasn't too much oil that came out when I removed the primary case. So that's probably contributed to the wear & tear. I'll pay closer attention to this in the future!

The clutch does wiggle/rock but only just a little. It doesn’t move from side-to-side / up-and-down though, so hopefully that’s good news concerning the bushes.

The chain also does lift off the clutch sprocket teeth quite a bit so again another sign of wear.

I’ll order a new chain and let you know how it goes
Thanks again

1/4" cold slack scares me once hot. My fail safe way is cold adjust so can't be made to touch anying then check hot and creep up tension staying conservatively loose. No biggie to run loose as long as not abraiding cases but only takes one sheep date or hot over tension event to leave a permanent fault in your shafts. Triplex chains usually throw halves, thirds and quarter pieces of link rollers for a while before any damage done but when in doubt whip out the wallet. Must investigate to better understand the care and feeding of a Commando and nothing like having a new and old chain to really tell, though how far back the gear box moves gives some clue too.

How long will a chain last under-oiled?

Racers have seized/broke dry chains before a race was over though some get away with sealed chain. Uk racers said same thing, if oil was thicker than 20 grade. Public use dry would last somewhat longer by keeping speed=heat down.

So 100-200 miles would be expected before serious damage occured?

Pleeeeeze don't be ordering in a new chain to replace that toasted one. Order in a belt system. Smooth. Dry. No vibrations. Loveliness.

Mike T said:

............I’ll order a new chain and let you know how it goes
Thanks again

Click to expand...

Not sure if you've seen the thread posted here about chains, but Andy here on the forum, is in the chain industry and has a good deal for those of us here still using primary chains. Stronger and cheaper than n.o.s.

cjandme said:

Mike T said:

............I’ll order a new chain and let you know how it goes
Thanks again

Click to expand...

Not sure if you've seen the thread posted here about chains, but Andy here on the forum, is in the chain industry and has a good deal for those of us here still using primary chains. Stronger and cheaper than n.o.s.

Click to expand...

Definitely check out AndyChain.....there is a lot of crap out there posing as chains these days....Andy's recommendations will be cost effective.

The 1/4 inch measurement I gave is for CAM CHAIN!! Sorry. I would set about 3/8 to 1/2 cold, or follow the Hobits method.

Slick

I thought 1/4 inch sounded a bit tight!

If chain already mysteriously worn slack it may not last 20 miles dry on free way use but could make it 100 more miles taken easy. A new chain might last 200 miles dry hyw use before about shot throwing pieces and maybe 500 miles before actually breaks. Btw Mike T. long knows how to properly adjust Commando chains.

Get one of Andy's duplex chains - i have a belt system in one of my bikes and Andy's chain in the other - for the cost i'd much rather go with the chain as while the belt is nice, unless you have to replace both the sprocket and clutch hub i'd stick with chain as it will last a long time (20,000 miles on mine now) - you should be checking the chain slack when the chain is hot too, and check every couple of thousand of miles or so -

andy@the-chain-man.co.uk

cjandme said:

Mike T said:

............I’ll order a new chain and let you know how it goes
Thanks again

Click to expand...

Not sure if you've seen the thread posted here about chains, but Andy here on the forum, is in the chain industry and has a good deal for those of us here still using primary chains. Stronger and cheaper than n.o.s.

Click to expand...

I know it's a very hot topic, but I intentionally run my primary WAAAAY overfilled (according to the level plug in the cover, not conventional wisdom.) with ATF, enough so the bottom run of chain is just covered when peering in the inspection plug. Oddly enough, the oil stays inside, the "dry :lol: " clutch works flawlessly and I can have peace of mind there is no undue dryness YMMV

Excellent, thanks for all the advice and information about Andy, I just sent him an email

remember the chain andy sells is a duplex, as opposed to the triplex that is stock. its actually stronger than the crappy triplexes available nowdays - so when fitting it only goes on 2 rows of the teeth leaving one exposed. No big deal, but if you fit another one down the road in another 20K miles or so put it back on the same 2 rows the older duplex came off of to account for even wear on those 2 rows

Mike T said:

Excellent, thanks for all the advice and information about Andy, I just sent him an email

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"its actually stronger than the crappy triplexes available nowadays"

Is that statement based on an objective test of some sort? Sounds more like an advertising claim. It MAY be true but I wouldn't buy a duplex chain for a triplex application without some DATA proving that it is better than current triplex and equal (or better) than oem triplex that, from my experience, has yet to need replacing in street use with proper lubrication.

yes -

have you seen Andy's threads - if not contact him. Having said that - i run these duplex on my norton and laverda's (each of which which have triplex's as stock and over 100 hp) in each of the bikes with NO problems - i think the current triplex chains are of poor quality is where this comes from

mike996 said:

"its actually stronger than the crappy triplexes available nowadays"

Is that statement based on an objective test of some sort? Sounds more like an advertising claim. It MAY be true but I wouldn't buy a duplex chain for a triplex application without some DATA proving that it is better than current triplex and equal (or better) than oem triplex that, from my experience, has yet to need replacing in street use with proper lubrication.

Click to expand...