29 tooth front sprocket

I've found one in my box of bits, and am thinking of using this to reduce the loading through the gearbox.
There's a couple of other people using these, so I'm hoping that someone can tell me about the chain length. The previous owner, who obtained the sprocket, told me that he never managed to fit it because it needed a longer chain. Now that Andy does a duplex replacement chain, that problem is solvable. The standard chain is 92 pitches, so I thought that the new chain would be 3 pitches longer.I checked with Andy, and he tells me that the duplex cannot have an odd number of pitches, there being no cranked link available. This is available for a triplex though, oddly enough.

Question is, are people using a duplex with 94 pitches, or a cranked link in a triplex to give 95?

Cheers,
Steve.

Unless its a MK3 with fixed centres will the allowed movement in the gearbox allow you to go to 94 not 95.

You can check online if you can measure the min center distance

http://www.botlanta.org/converters/dale ... ocket.html

Thanks for the link there. It's a MkIIa, but the engine & gearbox are currently on the bench, so its a bit difficult to measure the minimum center distance.
Does anybody happen to have this info?

Cheers,
Steve.

Another route, using the link I posted get the calculated center distance for the std sprockets and links in chain, then using the same center distance and the new sprocket info then reverse calculate the new chain links. Adding 3 teeth to the small sprocket should not add 3 links to the chain as a max of 1.5 new teeth are in contact with the chain as the chain is in contact with less than 50% of the circumference of the small sprocket.

Steve, assuming you are putting a larger engine sprocket on the bike (you said you would need a longer primary chain), I don't understand how this "reduces the loading through the gearbox". Could you explain how the load is reduced? Seems to me that if you want to reduce the load on the gearbox, take it easy with the throttle in first, and shift earlier in the rpm range.

Stephen Hill

The higher primary gearing means less purchase on the mainshaft. Normally you would slightly reduce the secondary gearing to maintain the overall gearing. Because the gearbox internals are spinning faster, the loads are less on the mainshaft and between the gears. The other thing the Proddy racers used were dished engine primary and the gearbox secondary gear to put the external loads closer to the bearings - less leverage ? It is all stop-gap - the TTI box uses a 6mm larger diameter main shaft

Using the link provided by Kommando, a chain pitch of 0.375 and sprockets with 26 /57 teeth, this gives a center distance of 9.284400343910661 (!!)
Using a 29/57 combinaton, this gives a center distance of 9.03291732061645

Using a sensible figure, this is just over 0.25" difference.
Using 94 links, this gives a distance of approx 9.4"

I'm not sitting in the garage right now, but it _seems_ that both options look reasonable.
I think I will have to wait until the engine & gearbox have been reunited t ocheck this though.

Stephen Hill said:

Steve, assuming you are putting a larger engine sprocket on the bike (you said you would need a longer primary chain), I don't understand how this "reduces the loading through the gearbox". Could you explain how the load is reduced? Seems to me that if you want to reduce the load on the gearbox, take it easy with the throttle in first, and shift earlier in the rpm range.

Stephen Hill

Click to expand...

It reduces the load by spinning the gearbox faster, you reduce the size of the gearbox (counterhaft) sprocket if you want to maintain the same overall gearing.

I ran a 33 tooth engine sprocket with a Commando clutch on my Rickman Metisse in the '70s, works racers did something similar and then outriggers.

It is not really necessary on a road bike with a 4 speed, unless you are of a brutal nature, but belt drives tend to be used with a higher primary ratio. clearly there is a limit to sprocket size with an alterator, hence the 29 tooth.