Misc: Everything Else Standard Comet Special

Bill Thomas

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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

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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

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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

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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

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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

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Non-VOC Member
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

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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

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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

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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

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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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