• Welcome to the website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Hon. Editor and Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this website.

    If you have previously registered to use this forum, you should log in now. CLICK HERE.

    If you have never registered to use this website before, please CLICK HERE.

Comet Chain Adjuster - Adjustment Criteria

Pharquarx

Well Known and Active Website User
Non-VOC Member
Good morning to all,

I am new to the Club and the Forums and located way West of Greenwich in Southern California. I recently imported a clean, pretty much all original 1950 Vincent Comet in operating condition from the UK and am absolutely thrilled. (I was denied everything on two wheels growing up and now that I am 60 and an orphan - I get to do this).

I have picked up much of the current and period guides, literature and manuals and, as is my habit, I take apart a little, clean and put back together. Take apart a little more the next time and put back together, etc. I am starting at the rear end of the bike and have two initial questions:

How do I know if I need to replace the drive chain? - I have seen the posting recommmending Sprocketsunlimited.com should it need replacement.

Secondly, what is the criteria I use to properly adjust the chain adjusters? - I have taken them off to clean them and now want to understand what that criteria is so I can do this right.

Looking forward to being a part of this.

Charlie
 

minivin

Well Known and Active Website User
VOC Member
Richardsons says:

"The rear chain should be renewed when stretch exceeds 2 per cent, which equals 1/4 in. per foot.

No details for comet specific slack, so I'd assume 3/4"
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Chain tension

Rather than remember what it is for every bike (the Sunbeam S7 is easy to remember) I remember only that when the chain is at its tightest, it needs 3/4" total up and down. That has the advantage of working for rigid bikes too.
I once went to visit John Surtees and among many other wonders, saw one of the Nortons that he had ridden. It had curiously extended rear shock nuts top and bottom on one side. I asked him what those were for, and he produced a strip of metal with two holes in it. When it slipped over the two extended nuts, the chain was at its tightest point. Hmmm. Genius is an infinite capacity for taking pains... (He used to warm up his Manx using a Primus and a saucepan. The Castrol R went into the saucepan, the saucepan went on to the Primus, and when it it was hot, the oil went into the Norton.)

Richardsons says:

"The rear chain should be renewed when stretch exceeds 2 per cent, which equals 1/4 in. per foot.

No details for comet specific slack, so I'd assume 3/4"
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Chain tension

Rather than remember what it is for every bike (the Sunbeam S7 is easiest to remember) I remember only that when the chain is at its tightest, it needs 3/4" total up and down. That has the advantage of working for rigid bikes too.
I once went to visit John Surtees and among many other wonders, saw one of the Nortons that he had ridden. It had curiously extended rear shock nuts top and bottom on one side. I asked him what those were for, and he produced a strip of metal with two holes in it. When it slipped over the two extended nuts, the chain was at its tightest point. Hmmm. Genius is an infinite capacity for taking pains... (He used to warm up his Manx using a Primus and a saucepan. The Castrol R went into the saucepan, the saucepan went on to the Primus, and when it it was hot, the oil went into the Norton.)

Richardsons says:

"The rear chain should be renewed when stretch exceeds 2 per cent, which equals 1/4 in. per foot.

No details for comet specific slack, so I'd assume 3/4"
 

Prosper Keating

Well Known and Active Website User
Non-VOC Member
Before you remove the rear chain, get another chain which can be attached to it and used to draw it off the gearbox drive sprocket, thereby leaving a chain in place: this makes replacement much easier.

Worn-out chains will feel very floppy when you have them off the motorbike. The standard formula, as mentioned here, dictates renewal when stretch equals 1/4" per foot or 6.5mm/30mm. Just lay the chain on the workbench beside a ruler, push the links together, and then pull them apart. A worn chain will also bow significantly sideways.

The same applies to the primary chain. Comet primary chains can live hard lives if the machine is used mainly for short trips around town because the ESA - the spring-loaded ramp cam shock absorber on the crankshaft - is more robust than, say, that found on BSAs and Triumphs and it can be as if the machine doesn't have one. Check the chain rollers for signs of cracking.

Sidenote on that score: have a good look at the tabs or 'ears' of your clutch friction plates. They take a lot of abuse because of this and I have known them to be ripped off new plates on a single long road trip, creating all sorts of hassle when trying to control the machine through towns! Remedy is to fit "big ear" plates with a basket to match or, as I shall be doing, a modern clutch mated to the chainwheel. I don't want to spook you or anything, as a new Comet rider. Just giving you a heads-up based on using a Comet pretty much as an everyday nail. :D

Chain adjustment: good points made here about chain tension. Get the Comet up on her rear stand and turn the rear wheel around, feeling the chain tension in the middle of the upper or lower run. There will be places where the chain is tighter than others. Always adjust a chain at its tightest spot. Ideally, you should have a friend sit on the bike but if you have no friends, then make allowances by increasing the 3/4" figure for the rear chain to and inch or just over, say 1 1/4". Better slightly too loose than too tight because a tight chain is no good for bearings and can even damage bearing housings in extreme cases. Remember that your hubs are made of alloy and that there is a reason why so many Vincent-HRD rear hubs are only useful as paperweights!

Likewise, find the tightest spot in the primary chain. The gearbox pivots on the upper mounting. The adjustment bolts run through the housing, with locknuts, and bear on the lower mounting. You'll need a good cranked wrench to slacken off the nuts (effected on the timing side) and, moreover, to tighten them up again. Just slacken off the nuts. No need for everything to be flopping about. Loosen off the adjusters' locknuts and the adjusters. Check chain tension. The requisite slack is 1/2" at the tightest spot. It will probably (hopefully!) be too loose.

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.

Now kick the engine over a few times. Recheck the chain tension and keep working until you get it right. Recheck the chain tension after doing up the gearbox mounting nuts dead tight as this can affect tension in some cases, depending on wear of components. Once you have adjusted the primary chain on any old pre-unit machine a few times, it becomes an easy enough task although it can be irritating. Then adjust up your rear chain and you're ready to rock and roll. Regarding lube in the primary chaincase, I tried all sorts of things but I am using simple two-stroke oil at the moment, with good results. Paris is not the best place for finding monogrades, fork oils are massively overpriced and the 20/50 stuff I use in the engine is a bit draggy in a Burman clutch, although my TR5 Trophy is happy on it.

Hope this helps. A well-sorted Comet can be a very fast machine. In fact, I would put it up there with Norton Inters in terms of long-legged fast touring. They were sneered at for a long time as "half a Vincent" but the postwar Comet is far closer to Irving's original vision than the veetwins. Not that I don't love 1000s. I have one. But get out there and enjoy your Comet. They're pretty damn good for British singles of the 1940s!

Prosper Keating
Paris
 
Last edited:

Len Matthews

Well Known and Active Website User
VOC Member
Lots of sound advice but if you are going to delve into the primary drive and clutch, take the opportunity to ensure the Clutch Centre nut is really tight and locked with the tab washer.
Several unlucky Comet owners have lost all drive when the Clutch Centre splines have stripped due to this nut being loose.
 

Pharquarx

Well Known and Active Website User
Non-VOC Member
Wow, this level of input and advice is absolutely incredible!!!! Much appreciation to all of you. It has finally become a rainy weekend here in SoCal, so no riding this weekend, a perfect time to delve into this. I really love this bike, it is perfect for me in terms of size, performance, matches my mechanical capability. I do plan on having and enjoying it for a long time and much of my enjoyment is working on it (I found this aspect to be the same with the restoration of my vintage 1956 VW). Thanks again to all of you.

Charlie
 
Last edited:

fgth130

Active Website User
VOC Member
Paul Richardson's book on the Vincents states 3/4" up and down movement is correct, the same figure as given in the Renold chain Co. brochure, and P.R's book also shows how to check for chain wear in Chapter VI. The book's available from the Spares Co.
Best of luck,
Frank
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Advanced chain adjustment technique...

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.

Before you remove the rear chain, get another chain which can be attached to it and used to draw it off the gearbox drive sprocket, thereby leaving a chain in place: this makes replacement much easier.

Worn-out chains will feel very floppy when you have them off the motorbike. The standard formula, as mentioned here, dictates renewal when stretch equals 1/4" per foot or 6.5mm/30mm. Just lay the chain on the workbench beside a ruler, push the links together, and then pull them apart. A worn chain will also bow significantly sideways.

The same applies to the primary chain. Comet primary chains can live hard lives if the machine is used mainly for short trips around town because the ESA - the spring-loaded ramp cam shock absorber on the crankshaft - is more robust than, say, that found on BSAs and Triumphs and it can be as if the machine doesn't have one. Check the chain rollers for signs of cracking.

Sidenote on that score: have a good look at the tabs or 'ears' of your clutch friction plates. They take a lot of abuse because of this and I have known them to be ripped off new plates on a single long road trip, creating all sorts of hassle when trying to control the machine through towns! Remedy is to fit "big ear" plates with a basket to match or, as I shall be doing, a modern clutch mated to the chainwheel. I don't want to spook you or anything, as a new Comet rider. Just giving you a heads-up based on using a Comet pretty much as an everyday nail. :D

Chain adjustment: good points made here about chain tension. Get the Comet up on her rear stand and turn the rear wheel around, feeling the chain tension in the middle of the upper or lower run. There will be places where the chain is tighter than others. Always adjust a chain at its tightest spot. Ideally, you should have a friend sit on the bike but if you have no friends, then make allowances by increasing the 3/4" figure for the rear chain to and inch or just over, say 1 1/4". Better slightly too loose than too tight because a tight chain is no good for bearings and can even damage bearing housings in extreme cases. Remember that your hubs are made of alloy and that there is a reason why so many Vincent-HRD rear hubs are only useful as paperweights!

Likewise, find the tightest spot in the primary chain. The gearbox pivots on the upper mounting. The adjustment bolts run through the housing, with locknuts, and bear on the lower mounting. You'll need a good cranked wrench to slacken off the nuts (effected on the timing side) and, moreover, to tighten them up again. Just slacken off the nuts. No need for everything to be flopping about. Loosen off the adjusters' locknuts and the adjusters. Check chain tension. The requisite slack is 1/2" at the tightest spot. It will probably (hopefully!) be too loose.

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.

Now kick the engine over a few times. Recheck the chain tension and keep working until you get it right. Recheck the chain tension after doing up the gearbox mounting nuts dead tight as this can affect tension in some cases, depending on wear of components. Once you have adjusted the primary chain on any old pre-unit machine a few times, it becomes an easy enough task although it can be irritating. Then adjust up your rear chain and you're ready to rock and roll. Regarding lube in the primary chaincase, I tried all sorts of things but I am using simple two-stroke oil at the moment, with good results. Paris is not the best place for finding monogrades, fork oils are massively overpriced and the 20/50 stuff I use in the engine is a bit draggy in a Burman clutch, although my TR5 Trophy is happy on it.

Hope this helps. A well-sorted Comet can be a very fast machine. In fact, I would put it up there with Norton Inters in terms of long-legged fast touring. They were sneered at for a long time as "half a Vincent" but the postwar Comet is far closer to Irving's original vision than the veetwins. Not that I don't love 1000s. I have one. But get out there and enjoy your Comet. They're pretty damn good for British singles of the 1940s!

Prosper Keating
Paris
 

Mickthevin

Well Known and Active Website User
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

Well Known and Active Website User
Non-VOC Member
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

Well Known and Active Website User
Non-VOC Member
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.
 

Attachments

  • Comet Tie Bracket.jpg
    Comet Tie Bracket.jpg
    99.8 KB · Views: 41

Ian Savage

Well Known and Active Website User
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
 
Last edited:

minivin

Well Known and Active Website 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
 

Pharquarx

Well Known and Active Website User
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

Well Known and Active Website User
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
 

Can't Find What You Need?

Buyer Beware: Fake or Real?

Top