Comet Chain Adjuster - Adjustment Criteria

Mickthevin

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Non-VOC Member
Chain adjustment

We always taught that when adjusting any bikes chain tension, the middle of the chain should flex approx 1.5 inches whilst on the centrestand so when the rider is on the bike and the weight of the rider is on the bike the chain will move approx half an inch

mick
 

Prosper Keating

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I was told years ago, and never found reason to doubt it, that primary chain tension (on Comets and bikes of similar layout) should always be set by "pushing" the gearbox forward, never by "pulling" it back. The reason is that the rear chain dominates, and pulls more on the gearbox than the primary does. If the gearbox is tight against the adjustment, as it will be when pushed, there is no slack to take up.

Use the front adjuster to tighten it appropriately. Tighten the rear adjuster snug against the pivot. Nip up the locknuts. A point to note at this stage is that a gearbox will always want to move backwards when the motorbike is rolling along, even if most people might assume the opposite to be the case. Given the inevitable wear and slack in decades-old parts, it is always good policy to ensure that a pre-unit gearbox is "pushed forwards" when finally adjusted, thereby taking up any slack in, for instance, the mounting lugs, in which the axial mounting studs might be a tad loose sixty years on. In this case, your main 'player' is that front adjuster: if your final adjustment is done on the front, the gearbox will be prevented from creeping backwards as you unleash the horses.

Indeed. With, say, pre-unit BSAs and Triumphs, the drill is to set the tension by pushing the gearbox forwards with the adjuster(s) (My old '61 Bonnie had twin adjusters) so that the latter hold it under tension against the pull from the rear chain. The adjuster physically pushes the gearbox or, rather, the upper mounting stud forwards. In other words, you adjust the chain up tight and then slacken it slowly until you arrive at the correct slack. The adjuster, mounting stud and gearbox are now in the right position to obviate rearward creep under motive power.

The same effect is achieved on a Comet by pushing the gearbox forwards with the front adjuster. The pull from the rear chain will put the front adjuster under tension against the lower mounting stud. The rear adjuster simply acts as a steady and would not be able to counter any pull from the rear chain. Being bass-ackwards or upside-down, you see, it's, um, a bit different. The good news for Charlie is that even if he ends up howling at the moon after a dozen failed tries, once he gets it right, it shan't go out of adjustment for ages! :D

PK
 

Prosper Keating

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Parts diagram with one of the adjusters in question visible. They bear on each side of F48/6. The timing or righthand side nuts on F48/6 and FT33 are slackened off prior to adjustment.
 

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Ian Savage

VOC Vice President
VOC Member
Primary Adjustment

One more thing to watch is if the adjuster bolts in the gearbox are original they are cycle thread, i.e. fine pitch, and will strip in the blink of spanner!

Make sure the top and bottom cross bolts are slack (Prosper ment to say F48/7as and F48/6;)) and the rear adjuster bolt is backed out before touching the front.

Does this sound like ‘been there – done that’ !!
Ian
 
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minivin

Well Known and Active Forum User
VOC Member
We always taught that when adjusting any bikes chain tension, the middle of the chain should flex approx 1.5 inches whilst on the centrestand so when the rider is on the bike and the weight of the rider is on the bike the chain will move approx half an inch

mick

Frame geometry et cetera has a major affect whether compression of the suspension results in slackening or tightening of the chain et cetera. I'm sticking with the Service Managers recommendations :D
 

alscomet

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VOC Member
comet chain tension

Make sure you adjust the chain tension whilst the bike is on both tyres not on its stand. al
 

Pharquarx

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Non-VOC Member
I have spent the last couple of weekends taking the bike apart, bolt by bolt, all except the engine and the transmission, to clean, inspect, understand and reassemble. Just a note to thank "all you all" (correct plural for "you all") for your input on this item for your comprehensive input on how to do this correctly and properly. I understand and, it clears up some of the questions that I had while disassembling the bike, such as what is this bolt for, etc. What a wonderful machine, love the design and engineering that went into it, so glad that I started this fascination and interest with motorcycles with a Vincent.
 

deejay499

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VOC Member
Hello. Chain adjusters. Two methods for replacing and getting true.

1.With the rear wheel rearmost, screw in adjusters until the end is flush with the frame and keep equal amount of turns until they reach the clicking position. (presuming both adjusters are identical)

2. I personally uses a string line around the front wheel and to both sides of the rear wheel, taking into account the difference in tyre sizes, gets the rear wheel exactly right, usually just touching the string on both sides.
Guaranteed to be straight.

Good luck with the Comet, a great little bike. DJ
 

Duke2211

New Forum User
Non-VOC Member
Hullo chaps - I am looking for simple info on primary chain tension on a 51 comet with an Alton starter kit fitted - not that it should make any difference. I have an 89 Harley sportster and its quotes a certain tension value.

Cheers, Duke
 
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