Anyone have a source for big t8f/8mm freewheel sprockets?

GoldenMotor.com
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dchevygod

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May 23, 2014
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I've seen them but can't locate anything available or in stock. I have 11:54 as my current primary reduction, My dilemma is that my secondary drive sprocket is too small "24t" and the chain is dropping on pot holes catching and it destroyed a decent Alivio derailleur among other things on my last ride. 35 mph and that noise scared the crap out of me. I was lucky that the spokes didn't try and eat the chain/derailleur throwing me off. :-||

So after that short rant. Im going to up size the secondary sprocket substantially but I need to maintain my current motor reduction or real close to it. So the 72+ tooth t8f sprocket for a freewheel is where im falling short. If anyone has a line on where they could be purchased that would be awesome!
 
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dchevygod

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May 23, 2014
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Colorado springs
I found a 74t on aliexpress that will need modified. Im hoping 5-7 will chime in here since I know he has run a 460 with a 5:1 thru t8f on a shift kit.

Now I wonder if i should get the 34t or 40t for the pedal chain? Im upsizing from 54 to 74 on the secondary sprocket so the 2nd primary is 24t now and i think 30 is to small of a jump and 40 may be too big ill get the 34 tooth and see how it feels if im still not able to pull hills or flats like i want Ive got the 13tooth pinion to try and can get the 40t 2nd primary if 1-2-3 shifts are too low geared.

My ultimate goal is to have a bike that can wheelie in 1st and do 50 in 8th while maintaining a reliable pedal drivetrain so if and when I break it again I can pedal home. The chain jump on the 24t was proving to be a big hurdle so ill change the setup and see where else there may be a weak point.
 
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5-7HEAVEN

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Aug 2, 2008
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5-7HEAVEN here. Sad to see that the 10t and72t sprockets are unavailable. That's what I'm running, along with a 24t chainring sprocket and 11-34 8-speed cassette. First gear is off-road hillclimbing ability. 51:1 in first gear, 16.5:1 in 8th gear. That's SUPER-low gearing. Yes, my chain drops near the bottom bracket too.

Luckily, I trimmed the excess bolts and used five locknuts. When my chain dropped before, it'd jam on the extended bolts and destroy the chain. This last time, there was no damage. Afterwards, I installed an SBP Jump Stop. I hope that stops the chain from falling.

Try to make your gear ratio as low as possible, if you want to wheelstand. From your information, if you have an 11t/54t gear set, your primary ratio is 24.545:1. If you have an 11-34 cassette, your chain ring gear set of 34/24 is 1.42:1. First gear is 34.77:1 and 8th gear is 11.25:1. Changing to 11t/74t lowers first gear to 47.65:1/15.42:1 8th gear. That's an awesome low gear. However, if you use a 30t, first gear raises to 38.12:1/12.33:1 8th gear.

With the 34t chain ring, your first gear changes to 33.64/10.88:1 8th gear. With a 40t chain ring, first gear is now 28.59:1/9.25:1 8th gear. Throw in the 13t and 40t into the mix, and you'll have a super DOG. First gear will be 24.19:1/7.83:1 8th gear.
All your efforts will make your bike very disappointing. First, install the 74t sprocket and SBP Jump stop. Just run that.

With 11t/54t gears, your 7th(13.3:1) and 8th speeds are basically useless. With 11t/74t/30 gears, 7th(14.58:1) and 8th speeds are useless. With 11t/74t/34t, 5th(16.82:1), 6th(14.84:1), 7th(12.86:1)and 8th speeds are useless. With 13t/74t/40t, 4th(14.23:1), 5th(12.1:1)6th(10.67:1), 7th(9.25:1) and 8th speeds are useless.
 
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5-7HEAVEN

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Aug 2, 2008
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BTW, even with a 24t chain ring and 11t/72t primaries, I can easily pedal home.

To further prevent chain jump, ya might want to do what Necromancer recommended. Bolt a larger chain ring sprocket inboard of the 24t as a chain jump stop.
 
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dchevygod

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May 23, 2014
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Colorado springs
Thanks 5-7. Ok so that issue with the chain dropping. I have the front derailleur as a jump stop otherwise it would fall towards the frame all the time. On big bumps it jumps the other way and it hadn't grabbed or destroyed anything till last ride at 35mph in 4th hit a pot hole dropped the chain and carnage insued. The chain is trashed the derailleur is broken in two places and bent to **** as well as the 23t is pretty much fubar. I guess a larger sprocket next to the 23 may be my best bet to keep the chain in line. I wanted to modify the derailleur more so it is better suited as a jump stop. It will need narrowed and welded in place. This may be my best option.
 
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5-7HEAVEN

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Aug 2, 2008
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Years ago, a friend and I rode our mb's to Sandy Beach, a 20-mile round trip. I had my Scooterguy-mounted 460, and Rick had a 460 w/Staton chain drive. On the return leg thru Waikiki, I broke a spring in my clutch, which jammed between the shoe and the clutch drum. LOL, it was reminiscent of the time I broke my clutch on my '66 Mustang in 1970(Fortunately, its starter was able to get the car rolling, then start the engine). Anyway, I got home with my bike by jacking the rear tire off the ground, starting the engine, then quickly rolling the bike off the stand and hopping on. I could also pedal the bike, but rolling starts were more fun. I had a 10t/72t/30t/11-34 cassette on my bike, back then.

On another time, the bicycle chain dropped, broke at the bottom bracket, then destroyed the rear derailleur. I put the spare chain directly onto 4th gear, then pedaled and motored my 460-powered mb home at speed.

I was hunting online for 72t sprockets. There were none available, but I did find that 74t you mentioned. You'll have to drill 5 mounting holes, but no biggie.
 
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dchevygod

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May 23, 2014
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Colorado springs
And make the center hole 54mm but its well within my ability. The 74t will get my ratio better but i wish a 10 tooth could be found and run a 30t to help with chain suck.
 
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dchevygod

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May 23, 2014
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Colorado springs
Or just bite the bullet get a sturmey 5spd IGH up the 2nd primary to a 40 tooth and finish reduction with a large input gear on the IGH. Add a spring loaded chain idler, Beef up the chain/sprockets and see how that feels.
 
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5-7HEAVEN

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Aug 2, 2008
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You'll be fine with just adding the 74t.

Funny you should mention Sturmey-Archer. I'm building up an NOS Diamondback cantilever frame. I was lucky to find a new SA 8-speed hub with disc brake, laced into a wheel, $95 shipped, minus cable, shifter and miscellaneous items. The frame was built for a 7-speed freewheel, so the rear is 135mm OLD. The hub slipped right in; it has a 25t sprocket.

Like you, I'm center-mounting my engine (Tanaka 47R). Like you, I realized the 5:1 gearbox makes the engine WIDE. So just for kicks, I'm doing WITHOUT the gearbox, using the standard bell and facing the drive sprocket to the left-side. Instead of running a jackshaft, I'm driving the power through the bottom bracket. So my 72t is on the left-side, chained to a 6t on the clutch bell. On the right side is my 24t sprocket, which chains up to the 25t on the Sturmey hub. First gear is 40.63:1. Eighth speed is unusable at 12.5:1, but 7th speed is 16.25 and 6th gear is pulling at 18.53:1.

I bought two 5" stainless steel discs, 18 gauge thick. If my chain jumps again, I'm gonna sandwich the 24t chainring with these SS plates. The 24t is only 4inches in diameter. There's no way it'll jump a 5.25" disc if the chain is tight.

Unsure how well running power through the bottom brackett will perform. I've never heard it done before, WHILE KEEPING THE PEDALS. I got all the sprockets and adaptors, left-hand freewheels,etc. All I gotta do now is have left-hand threads machined onto the left-side pedal arm. Also need tor groove the bottom bracket-left side- for a keyway. My right-side has the groove.
 
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dchevygod

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May 23, 2014
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Colorado springs
I understand your concept but how are your pedals going to stay in sync? Using the bb cartridge will work fine if you can find a way to keep the crank arms 180° out from each other. Maybe a pedal arm jackshaft? That would only spin when the pedals turn, not under engine power. 4 equal toothed sprockets and a jack shaft could overcome the "crazy pedals" no freewheels needed
 
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5-7HEAVEN

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Aug 2, 2008
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Yes I know I may never synchronize the pedals. For me, the pedaling is not important. I think I can live with it.

But I do intend to isolate and freewheel the pedal arms from the main shaft. If not, the pedals would literally break my legs, once the engine fired up, lol.

Check this out. If these guys can live for unsynchronized pedaling at heavy expense, I'll try my way for kicks, lol.

http://www.powercranks.com/OrderPowerCranks.html

I'm off to try my new Jump Stop. Let me know how the Chain Spy works. I'll probably buy one soon.
 
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5-7HEAVEN

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Aug 2, 2008
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Lol, now you've got a LOT of choices.

Today, I rode my bike using the new Jump Stop. I hadn't ridden it in years. Last week, it broke down 5 times in a half-mile. This time, I rode farther without breakdowns. No chain jump, no major carb trouble.dnut

I'm inclined to try the $26.25 Ultim8-Origin-8 one.
 
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