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Unchain My Bike... Or So I Thought...


BusyLittleShop

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Unchain my bike... or so I thought...

Hans Renold is credited with inventing roller chain in 1880... but
here we are 127 years later and bikes are still laboring under a
steely... heavy... clanky... messy... chain... Mercy me chains are a
pain... belts spell relief... and so my belt drive conversion starts
with an engineering drawing...

gallery_3131_51_26197.jpg

Gates Poly Chain comes in 3 belt sizes... 14mm pitch is what HD
employs on their cruisers... 8mm is what I used on the VF500
Belt-0-Ceptor... 11mm is the little known in between belt but only
comes in lengths of 155T and 172T... I need 166T to make it work on
Mr.RC45...

gallery_3131_51_3294.jpg

I started with a Buell 11mm pitch sprockets and belt... a 30T up
front and 70T out back... they were machined them to fit Mr.RC45...
so far so good

 

Buell's steel 30T 11mm spocket installed on the RC45 primary shaft...

gallery_3131_51_45790.jpg

Buell's aluminum 72T 11mm sprocket installed on the RC45 axle...

gallery_3131_51_18651.jpg

 
Ideally I needed 628mm between centers as evident with Mr.RC45's 17T
43T 110 links of chain prove to show...

gallery_3131_51_100085.jpg

But when I added the Buell 30T 72T 155T setup it measured 561mm
between centers... 67mm too short...

gallery_3131_51_84588.jpg


Next I ordered a 172 tooth belt from BMW but with the Buell sprockets
the BMW belt was 664mm between centers... 36mm too long...

gallery_3131_51_60739.jpg

 

Maybe if I machine my own 76T sprocket so I started with a 20lb block
of 7075 T6 Aluminum...

gallery_3131_51_62149.jpg


After the teeth were cut by RCD Engineering the block was down to 10
lbs at this stage...

gallery_3131_51_496.jpg


After milling the spokes using only hand eye coordination it was down
to 1 lb 13 oz...

gallery_3131_51_52808.jpg


Now with the Buell 30T sprocket 172T BMW belt and 76T home made
sprocket the distance between centers was 651mm... 23mm too long...
because of the single sided swing arm I limited to 20mm adjustment so
I knew it would be close... how close??? less than 3mm or .118
thousands of an inch separates success from failure...

gallery_3131_51_80322.jpg


I have failed to unchain Mr.RC45... not that I didn't come close... I
came within 3mm of enjoying a light weight... maintenance free...
snatch free... lubeless belt drive system... it all came down to
finding the right number of teeth in a 11mm pitch belt... and so with
only 2 bikes in the world that employ the 11mm pitch belt (2003 Buell
and the 2007 BMW 800) I have to wait for a 3rd bike to employ the
little known 11mm pitch Poly Chain Belt...

So in conclusion after $1000 dollars in parts and a custom 7075 T6
aluminum sprocket consuming over 30 days worth of machining... I have
NO joy to report... in fact I'm devastated and sad... not to mention
Gates Rubber wants $65K for the mold of a custom 166T 11mm pitch
belt...

Mock up
gallery_3131_51_84342.jpg

 

 

 

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Guest black06vfr
Man that's alot of money for nothing. But you do have some pretty parts there, maybe use them as home decorations?

It' hard to believe that there isn't something else out there that would work. This might sound dumb, but what about an automotive timing belt from a single overhead cam engine?

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Woooah BLS, you are a man on a mission. Such a shame, you were real close. Emmm, but isn't that (realtively) a lot of dough to be throwing around wantonly??

Now you've gone and done it, one can cheat and use your figures to analyse. Just thinking aloud here, but... by adding 4 teeth you've shortened the distance between centres by 13 mm. So, that roughly translates to shortening the distance 'tween centres by 3.25 mm per tooth. In hindsight we now know you needed to shorten that by at least 3 mm more, to be within the 20 mm tolerance you mention (although I take it the more the better), so in rough theory you need one more tooth. Hmmmm

If we suppose that the ratio between the increase in radius and the number of teeth is constant or a direct relationship, (something tells me it isn't quite, because of the angular math due to the belt), but supposing it were, you would only need one (1) more tooth, or a 77-T sprocket. But like I said, that's too rough so, one could overshoot to be sure and increase it to two (2) more teeth. So that would be a 78-T sprocket instead. In terms of reducing that distance, more teeth is better, buuuuut..... not so for your gearing...

I don't know in real terms how that would affect the power output at the wheel, (compared to stock) that is beyond me... but you've already gone up 4 teeth on the original idea of the Buell rear sprocket which, if you chose the Buell one for a reason... means you're getting well away from that reasoning if you go up a whole 6 teeth...

OK, computing some more math into it to double check things, I'm fairly certain that you would need just 2 more teeth. It comes down to the error margin....

If I calculate the circumference (and thus the radius) of the sprocket based on the distance between teeth of 0.433 (this is rough math) I get a discrepancy of 1.8 mm from your 13 mm difference between centres (prolly due to the angular math the belt supposes, which I did not apply). In other words only 11.2 mm, which would imply 2.8 mm per tooth. which as I said is not quite enough, so you factor in good old down on the farm common sense and go up 2 Teeth!!!

:idea3: :goofy:

Got a money back guarantee on that sprocket??? :goofy: :goofy:

Any math graduates or professors confirm??? I know my calculations are missing a couple of minor factors but I reckon they're negligible enough... jeez, if you're going to cut out your spokes by eye!!! :goofy: :goofy:

Then again, HS' idea might save you money and it's such a small difference it just might work... talk to Toro1... he rigged up a tensioner on his blower. I reckon it'll be cheaper, but you've also got to calculate the specs for fabbing that and find a suitable mounting point and means... unless Toro1's fits already (that would be too much to ask) ... maybe one (1) more tooth AND a tensioner... to save face on the power at the wheel issue...

Do I make sense??

Good luck, we're all anxious to see it work :goofy: :goofy: :goofy:

(I'm gunna regret posting this...)

Edited by Auspañol
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Man Larry, as close as you are to having this thing licked, you really should take a long hard look at buell's tensioners. I think it, or something very similar, would work to take up the little bit of slack.

By the way, that machined rear sprocket looks HAWT!

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Guest vfrrider

Larry,

OK, critical distance is sprocket to sprocket on the RC45? Is this critical distance the same on RC45, RC30, VFR750, VFR800?

Or a tensioner?

Just an idea.

Larry

VFRrider

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to 1 lb 13 oz...

gallery_3131_51_52808.jpg

m pitch belt...

I really respect custom machine work.

I grew up and worked in a prototype machine shop, my dad owned it. Custom one off, or small run, stuff for the fledging space program made out of aluminum, magnesium and titanium. My job was to fly cut on a mill the exotic materials down to size. I never developed the skill those great machinists had on the lathes that worked for my dad. The reason why; when I turned 16 yrs old, old enough for a real job, I left his shop and became a lifeguard. The girls were better look’n than the machinist and the girls did not wear much :thumbsup: I regret that decision now, sort of :idea3:

Your work is stunning :thumbsup:

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Isn't a tensioner required if the swingarm pivot and countershaft sprockets aren't on the same axis, anyway? With any kind of power, it seems like you couldn't allow much variation in belt tension due to swingarm movement. I suppose you might get away with it if the countershaft sprocket is quite close to the swingarm pivot, and in line with the swingarm near the center of travel. Even with my Hawk GT, when I added a longer rear shock, I also added a chain roller under swingarm pivot to help with the changes in chain tension due to the relatively higher pivot location. If your drawing is accurate, it'd be really easy to determine the change in distance between the sprockets through the range of travel by just drawing an arc. Have you done that?

Weren't there some early reports of belt problems with the new Buell 1125? What was that about? Wider belt needed?

:idea3: You could just buy a Buell. Better bike, anyway. :P

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aww that sprocket you brought to bubbas didnt work? Have you considered a belt tensioner?

Hiya HS... yep they are the same sprocket I brought to Bubbas

last year in July and it don't work...

I already thought about rollers... but the BMW belt is

kind of rubbery whereas the Buell belt is more plastic... the

different being you can run a roller against Buell belt but not

against the BMW belt without taking the life out of it... besides I

don't think I have the room on Mr.RC45 dense packaging...

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I really wanted to go down this route when I had a VFR so have followed every posting on this topic.

Bummer man that it didn't work out as you hoped.

Is it impossible to add a small tensioner running on the lower slack side of the BMW belt on the INSIDE of the belt? Obviously it will have to be a toothed pulley. Your observation that the BMW belt is soft would not apply to the inner toothed side since that is intended to run over pulleys. There would be very little wrap around the tensioner pulley since you are already so close to the allowable range. It would, as Fallzboater, & other, say compensate for the changing center distance as the wheel moves.

The 30 + 76 combination gives a ratio of 2.533 which is very close to the original 2.529 that the standard 17 + 43 gives so it really would be great if you could make it work.

I admire your manual milling work tremendously.

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Guys, look at the pics. Belt might not clear the swingarm under tension. sad.gif

The Buell sprocket (3rd photo) seems to come real close to the swingarm!! So I'm not sure if you've placed the custom-made one to check, but with 4 more teeth it must be getting close to touching... unless the photo is deceiving...

Edited by Auspañol
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Guys, look at the pics. Belt might not clear the swingarm under tension. sad.gif

The Buell sprocket (3rd photo) seems to come real close to the swingarm!! So I'm not sure if you've placed the custom-made one to check, but with 4 more teeth it must be getting close to touching... unless the photo is deceiving...

Hopefully Larry is trying to obtain his required measurement with the axle & hub oriented as far forward as possible... in the case that the belt doesn't stretch, he'll have the shortest wheelbase possible.

That'll allow him to gain a couple mm by moving the eccentric...

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From working on my supercharger project and designing Harley open primary belt drives, I know how difficult this process is. My question is this -- how did you figure out the ideal center distance for the 30T/76T combo? Tensioning is so key with these drives, and after talking to Gates engineers several times, I know that they almost never recommend fixed center distances.

The pitch length of the 172T belt is 74.488" and the pitch length of your 30T/76T combo with a center distance of 25.630" (651mm) is 74.605", thus you must be preloading the belt a certain amount. Gates has special formulas for computing the tension -- did you use these in determining the center distance?

The part that bugs me about the belt drive is the varying tension in the belt as the suspension moves up and down. I'm guessing most manufacturers that do this set the tension to be ideal when an 1xx-lb. rider is on the bike, and any time the suspension moves, it varies slightly from this ideal figure. I also believe that Buell uses a spring loaded belt tensioner on their bikes, located on the slack side of the belt (which can be seen here, and the patent is here). I know Gates does not recommend using outside idlers on ribbed surface Poly Chain belts, so I'm not sure how Harley gets away with this one. They also do not recommend using spring loaded tensioners.

Anyway, here is the actual PolyChain manual. Pertinent engineering data begins on page 40. If you have not yet contacted Gates, I suggest you do. It's a pain to get a hold of their engineers, but once you do, they know their stuff (I can personally recommend Jack Timmerman).

Best of luck, as you don't need to give up hope yet. :thumbsup:

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Emmm, but isn't that (realtively) a lot of dough to be throwing around wantonly??

Auspanol...... emmmmm, you are married right? so you should know all about wantonly..... :P

BLS,

you got the cash to blow, blow it.

the last jacket you will wear has no pockets......

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From working on my supercharger project and designing Harley open primary belt drives, I know how difficult this process is. My question is this -- how did you figure out the ideal center distance for the 30T/76T combo?

Anyway, here is the actual PolyChain manual. Pertinent engineering data begins on page 40. If you have not yet contacted Gates, I suggest you do. It's a pain to get a hold of their engineers, but once you do, they know their stuff (I can personally recommend Jack Timmerman).

Best of luck, as you don't need to give up hope yet. :thumbsup:

Thanks for the questions Toro...

I stretched them out and measured the centers of the 110 links of

chain and the 17/43 sprocket on the milling table... then I stretch

and tensioned the belts and measured their centers... I also produce a

full scale engineering drawing as a second opinion... it would be nice if

Honda would release the engineering drawings to the RC45...

I've been working with Gate's Engineers since 1989 with my first belt

drive project... thanks but I have the engineering manuals and Mr.

Timmerman name sounds familiar...

I have yet to see any problem... however complicated... which when you

think about it all the time... did not become solved... in short I never give up...

I've even worked out a solution to run belts and change over all

gearing... if I change the gear on the crank and the gear on the

clutch that would afford overall gear ratio change without upsetting

ride height or belt tension... trick no???

BeltCloseUp.jpg

gallery_3131_51_14630.jpg

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Is there a problem with simply adding a roller idler pulley, or is this a preference to try to not run one.............. +1.gif

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