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Misc: Everything Else Standard Comet Special



Cyborg

Well Known and Active Website User
VOC Member
#81
Could you imagine being a parent and having to endure that with a straight face! I'd have blood dripping down my chin from biting my tongue so hard.
 
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chankly bore

Well Known and Active Website User
VOC Member
#83
I'm assuming it will get drowned out when the rest of the percussion section starts up. Sort of like the 3rd graders playing the 1812 overture.
I recommend the Portsmouth Sinfonia version; the 1712 Overture by P.D.Q. Bach runs a close second! On a more topical note Laurie Binns tried a riveted fibre disc on the large idler and I seem to remember someone lining the timing cover in lead sheet as well.
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
#84
....... Laurie Binns tried a riveted fibre disc on the large idler and I seem to remember someone lining the timing cover in lead sheet as well.
There must be something in the air. I was spinning my large idler the other day and noticed the "ringing". Many years ago I had an Ariel Square Four. The two crankshafts were coupled together by two gears that were maybe 5 or 6 inches in diameter. Each gear had an annulus of fibre fixed on to damp out the "ringing".
 

vibrac

Well Known and Active Website User
VOC Member
#85
On the subject of idlers let me make an observation
I bet if someone had just made the alloy idler he would sell hundreds to aspiring Vincent owners who would all swear by the quieter running and less inertia.
My premise is that they got a bad reputation because they were done to death in the spares desert of the late 60's and early 70's when many cheap bikes were run down, poorly lubricated ,ran on two piece supports that gave way and they were past their run life
Perhaps a new alloy idler properly set up would last and give advantages for a good five years of use - not that I have one but its a item for discussion.
 

greg brillus

Well Known and Active Website User
VOC Member
#86
I've never had any bad noises from the timing chest, except if the meshing of any two gears were too tight. Weren't the alloy gears good for about 40 thousand miles before they start shedding their teeth. A new one would last most riders for ever now.
 

chankly bore

Well Known and Active Website User
VOC Member
#89
On the subject of idlers let me make an observation
I bet if someone had just made the alloy idler he would sell hundreds to aspiring Vincent owners who would all swear by the quieter running and less inertia.
My premise is that they got a bad reputation because they were done to death in the spares desert of the late 60's and early 70's when many cheap bikes were run down, poorly lubricated ,ran on two piece supports that gave way and they were past their run life
Perhaps a new alloy idler properly set up would last and give advantages for a good five years of use - not that I have one but its a item for discussion.
I've never had any bad noises from the timing chest, except if the meshing of any two gears were too tight. Weren't the alloy gears good for about 40 thousand miles before they start shedding their teeth. A new one would last most riders for ever now.
My Comet was a "70's" bike and I agree entirely with you blokes. When I finally got down to getting the thing running properly I discovered a piston crown welded in situ, a home-made big-end, a Polson sand-cast piston and two alloy idlers with precarious dentition. In fact, the only bike that made more whirring noises than the Comet was a brand-new MV Agusta that passed me in Elizabeth Street one Saturday morning! How long did Tony Rose's idler gear last?
 
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Cyborg

Well Known and Active Website User
VOC Member
#90
When I heard the ringing in the Comet it was when I was setting up the backlash. That notchy feeling caused by the magnets in the Alton made the ringing amazingly loud. I did look up at the wall and wonder about the alloy and bronze gears hanging there, but the fear of a VOC fatwa made me stay with the steel.
 

Bill Thomas

Well Known and Active Website User
VOC Member
#91
Anybody who has had to clean out those bits of Alloy Idler, Which get every where, What a Mess !,
I don't think they would want to do it again. Cheers Bill.
 

oexing

Well Known and Active Website User
VOC Member
#92
The post-war BMWs had alu helical cam gears till 1969 that were matched to each engine case in paired sets for minimum backlash, cases were marked for easy ordering of spares, like "-2" or "+3" according to machining tolerances in the cases. Horex post-war had helical alu cam gears as well, there were never dramatic failures with them, just slow wear with high mileage. I think the straight cut gears on Vincent engines will not do acceptable mileages when having alu instead of steel. You would have to fabricate helical types for better operation.
Ford V 6 from late sixties till late eighties had helical tufnol cam gears but these had really decent sizes compared to the tiny gear module in our bikes.

Vic
BMW alu cam gear top, behind disc breather, oil pump bottom :
P1030218.JPG

Horex 400 alu cam gear, home made experimental camshaft :
P1020327.JPG
 

Oldhaven

Well Known and Active Website User
VOC Member
#93
Today I am fitting the Newby clutch and belt and ran into something I should have anticipated, but never having dealt with Comet primaries before I missed it. I can't recall anyone else mentioning it here for their own conversions, as it is pretty obvious. I guess I have to machine the outer cover for the belt, removing at least part of the shrouding inside web for the 30mm belt run. There must not be a problem with a single row chain that runs entirely in the inner cover. As a matter of fact, due to the position of the casting hole in the inner primary I used for the bottom gearbox mount, I am going to have to take just a bit off the inner right at the top near a bolt hole as the clutch is higher and the belt runs pretty close to it. I hate to take more than I need to and this will make a stock part non original, but I am pretty sure it will never go back on a stock Burman gearbox Comet. I will be removing at least the areas marked in the photos. Is that about right?

Ron
IMG_1155.jpg IMG_1156.jpg
 

timetraveller

Well Known and Active Website User
VOC Member
#94
It might not be applicable but it might help to look back at what DavidD did with his belt drive. He made a much deeper GRP cover and the bike races with that so ground clearance is not a problem.
 

Oldhaven

Well Known and Active Website User
VOC Member
#95
Thanks TT, but I've gone too far down the path of using the stock inner primary cover for gearbox mounting purposes so the stock outer cover for my street only project is my best plan, plus I just spent a couple of days removing scratches and corrosion from its previous race career and polishing it so it looks presentable right now. I'm mostly just interested in how others have used the belts with a standard Comet outer cover.

Ron
 

chankly bore

Well Known and Active Website User
VOC Member
#96
I found I needed to relieve one of the chaincase cover screw bosses at about the 6 o'clock area, as the Newby belt was just hitting there. I fabricated a cover from three struts of 3/4" x 1/8" steel strip and some shaped and riveted alloy sheet. I used the standard BAP gearbox, as I don't mind telegraphing the engine room when I need to change gears.
 

davidd

Well Known and Active Website User
VOC Member
#97
Ron,

Carleton did this conversion and ran his Newby inside a stock cover. I doubt he has a photo, but a call to him might boost your confidence. I think I have mentioned this here, but it would probably be unsearchable. My memory was that he told me he had to cut the shroud. He did not mention it being too near the bolt hole, but he was running an Albion box. The difference may just be that your box is mounted a bit higher, so the clutch is closer to the top of the primary inner.

Frankly, it looks fine to me. I would mill that off. The belt should be tight to the drum up there and not flapping around.

MidOhio99.jpg

You can't see too much here, but you can spot the belt in the empty cap hole. We shared a garage in the pits at the 1999 Mid Ohio race. That is the 1-7/16" carb he was running at the time.

David
 

Oldhaven

Well Known and Active Website User
VOC Member
#98
I am not sure I can reach him by phone, but I'll email him about it. That's an interesting picture. Looks like a Norton points housing with an experimental coil setup. It must have been easier to prepare a machine then.

We are a bit constrained for location when these gearbox conversions are done if we choose the center of the casting hole behind the regular lower gearbox mount hole. If I had known what I do now I would have filled the casting hole and made the lower mount a bit off center and lower so it was closer to the correct location that the Burman uses and centered in the hole in the inner case. I didn't know the Commando mainshaft to lower mount distance at the time. Well, I am pretty sure no one will be tearing up what I am making and putting a regular Comet together anytime soon.
 

davidd

Well Known and Active Website User
VOC Member
#99
We both ran Mistral units with Rita ignition. Carleton did some funky Dyna coil set up that seemed to work but drove the Dynojet computers crazy.

I would not have told you to pay attention to the mainshaft height because I normally use a flat plate and then mount my cover last, wherever it comes out. I am reasonably careful to start with the same holes as stock.
DSCN2457.jpg
When the box was mounted it ended up here:
DSCN2528.jpg
This is the correct distance from the engine mainshaft.
DSCN2546.jpg
The clutch goes on.
DSCN2605.jpg
I split the differences on the up and down, for and aft and drill the three mounting holes.

David
 

vibrac

Well Known and Active Website User
VOC Member
I have done it both ways on the flash I carved away the clutch shroud and part of the periferal casting (Albion box) but on my egli comet (Norton box) I used a plate and spaced out the primary cover with a 1" strip I will post a photo never done one with a burman box and belt drive
Choice was mainly driven by what I had in the way of parts
 


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