• Welcome to the forum 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, Online Forum 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 forum website.

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

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

Comet Chain Adjuster - Adjustment Criteria

Pharquarx

Well Known and Active Forum 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
 

bmetcalf

Well Known and Active Forum Website User
VOC Member
Take the usual precaution to have the axle parallel to the gearbox shaft. Twin owner here, so no info in Comet chain slack.
 

minivin

Well Known and Active Forum 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 Forum 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 Forum 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 Forum 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 Forum 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 Forum 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 Forum 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 Forum 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
 
Warning! This thread is more than 14yrs ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Top