7 Speed Cassette Spacer on 8 Speed Hub

[stemwinder]

I'm installing a 7 speed cassette on an 8 speed hub on a Bafang G310 motor. I have the 4.5 mm spacer but I'm thinking it might make more sense to put a gear there rather than have a hole. I'm sure I have an old shimano 7 speed cassette that came off an FH-HG20 hub packed away somewhere. Do they come apart. Would you just stack up anything that totals 4.5 mm or would the gear stack up differently and require a different thickness. Or does this make no sense.

 

[motomech]

Except possibly a flat washer between the end of the spline and the inside of the drop-out, you don't need any kind of spacer to install the 7-gear cassette. Swapping cassettes doesn't mean they have to be exactly the same width.
I'm assuming the 7-speed has a 13T sm. gear. Do yourself a favor since you have it apart. spend a little and get a cluster w/ an 11 T sm. gear that will help w/ your pedal gearing for cruise. It doesn't have to be high-end, most people don 't shift much w/ a motor anyhow.

 

[E-HP]

I'd ride it as is for a couple of months. By then you will have shed your old non-ebike habits (e.g. downshifting when you come to an intersection, etc.) and formed some new ebike riding habits. You may or may not be shifting much (with the smaller geared hub, you may still shift a bit), but you'll know more about what range of gears you'll mostly be using.

 

[stemwinder]

Thanks all for your replies
First my knowledge when I posted was that I've put 7 speed cassettes on 7 hubs and I've put 8 speed cassettes on 8-9-10 hubs but I've never put a 7 speed cassette on an 8-9-10 speed hub. I'm only going by Sheldon who says that a 4.5 spacer is needed to put a 7 speed cassette on an 8-9-10 speed hub.
My shop is not lit to well right now because most of my good T5s are in my plant room. And no there is not any pot.
So this is the deal I put on the 6 gears of the cassette and the last gear sits on the shoulder like it should. There is what appears to be in the bad light a 4.5 mm gap between the top most gear of the 6 gears and the built in spacer on the last gear that sits on the shoulder.

 

[stemwinder]

In the day light everything stacked up the on the 8-9-10 speed hub with 4.5 mm spacer exactly the same as the cassette itself did on a 7 speed hub. Except for the rivets on the back of the cassette interfering with the spacer, I have to file a groove in the spacer or find a correct spacer with the groove in it. No problem. So yes a spacer is needed.

So I'm back to my original question does it make sense to replace the spacer with a dummy gear and some spacers. The reason I ask is I have on several occasions knocked the chain off the sprocket into the spokes or that plastic thingy. I thinking the gear would reduce the chance of the chain ending up wedged against the can.

 

[amberwolf]

How was the chain knocked off?

If it happened during shifting, then you need to adjust the derailer limit screws so they can't go past the sprockets you intend to use.

If it happened from bumpy roads, etc, then you need to adjust the derailer tension screw so the slack is better taken up, or even remove some of the links so that you still have enough for maximum necessary chain wrap on the largest front and rear gears, but not enough to have bouncy slack in smaller gears. If that can't be done, you may need a derailer with higher capacity for reeling in the loose chain.

If you don't know how to do the above things, http://sheldonbrown.com has almost all the bicycle maintenance info you might ever want.

 

[stemwinder]

by amberwolf » Apr 25 2020 12:48am

How was the chain knocked off?

Both times I hit something once an alder stump hidden in the grass and once I clipped a very visible rock.