6 speed to 7 speed conversion

Hi, I have an UM 36 going well since last November, up to about 300 miles now. Only issue is that the 14 tooth top gear ring on rear sprocket combined with 40T on chainring is not fast enough. It seems to be from the shimano "tourney" range, an MFTZ06 sprocket with 14/28 teeth. There seems to be no 6 speed alternative with shimano that goes lower on teeth. However there is a 7 speed MF HG50 11/34 (34 being a "megarange" up from 24 in second gear. ). I would obviously have to change to a 7 speed shifter, as well, but my question is whether the 7 speed will fit in between the frame mounting points,because I assume that a 7 speed freewheel must be wider than a 6 speed by one chain thickness. Can anyone advise if this is true? Is there a way for me to get a faster top gear?

thanks

Jonathan.

Hi Jonathon

The Tourney uses a freewheel of course, necessary on a rear motor bike like yours. The HG50 you mention is indeed a chainwidth wider and I doubt if there would be space for a seven speed freewheel on any rear motor bike.

All is not lost though, since Shimano do a 6 speed Megarange freewheel in their Cadet series, sprockets from 13 to 34 teeth, so that will give you some gain. Another good point is that it's only £9.99.

You'll need to change the rear mechanism though, since the sort of mechanism that comes with the 14 to 28 sets won't span the megarange sprocket. Something like the Shimano Acera Smart Cage mechanism will do the job, as it's megarange compatible.

Here's a supplier link for the Megarange freewheel.

And from the same supplier the Acera mechanism.

You could also make a small change to the chainwheel as well to get a bit more, say a 42 or 44 tooth.

.

Edited April 3, 200719 yr by flecc

6 or 7 speed freewhel

Hi, I have an UM 36 going well since last November, up to about 300 miles now. Only issue is that the 14 tooth top gear ring on rear sprocket combined with 40T on chainring is not fast enough. It seems to be from the shimano "tourney" range, an MFTZ06 sprocket with 14/28 teeth. There seems to be no 6 speed alternative with shimano that goes lower on teeth. However there is a 7 speed MF HG50 11/34 (34 being a "megarange" up from 24 in second gear. ). I would obviously have to change to a 7 speed shifter, as well, but my question is whether the 7 speed will fit in between the frame mounting points,because I assume that a 7 speed freewheel must be wider than a 6 speed by one chain thickness. Can anyone advise if this is true? Is there a way for me to get a faster top gear?

thanks

Jonathan.

If the 7 speed f/w is not as narrow as the 6: have you considered changing the chainwheel? Is yours an interchangeable chain ring? There are plenty of chainrings (like stronglight available for a tenner). You would only have to accept a higher bottom gear. 37 inches is a bit low anyway (if you have 26 inch wheels - even lower if you have smaller wheels) a 52 chain ring would give 52/14x36 = 96 top and 52/28x26 = 48 bottom.

Quite an improvement for a fit, healthy cyclist.

Peter

reply from Jonathan

Thanks for the really helpful replies as usual. Looks like best option would be the cadet, with possibly a larger chainring. The Chainring is unfortunately not replaceable. So would have to get new cranks and drill holes to re-mount pedelec sensor or "Convert" existing chain ring to replacelable, which is all surgery that I am not keen on.

13 teeth will put me at 17.23MPH with the pedal speed I had at 16MPH on 14 teeth, so a bit better. 11 teeth would be 20MPH, so would have been ideal. Maybe I will measure the gap with a view to the 7 speed solution, because the gap looks to be about 1 chain width. There is certainly plenty of extra length on the axle at the drive side, so if tight, I could put a spacer in. What do you think?

Jonathan.

Yes, no problem with a spacer Jonathon. Don't worry if you have to apply a touch of expansion to the frame, you won't harm it with a quarter or half an inch. Here I am in this photo demonstrating stretching out an alloy frame one and a half inches as a quick way to insert an inner tube:

http://users.tinyworld.co.uk/flecc/images/footmethodtubechange.jpg

Yes, the difference between the width of the HG50 freewheel version and the Cadet Megarange 6 is only 4 mm. You wouldn't need much of a spacer, maybe just a thick washer would be enough. The limitation on extra width is usually just the available spindle, but it seems yours is no problem.

.

Edited April 5, 200719 yr by flecc

Hi all , i've just fitted a 7 speed Megarange 34/11 cassette , a megarange derailleur , a 7 speed chain ( 2 of them , but one reduced in length to suit setup ) , a 7 speed gripshift .

I am having problems with the chain jumping on the 11 tooth gear now and then , it does seem like the chain isn't wrapped around the small sprocket enough , i have set the derailleur up following shimano instructions pdf i found on their site , when the chain is on the largest gear the derailleur long arm is vertical and the derailleur position stop contacts the frame notch .

If you have idea's how to fix the jumping be glad to hear them .

Will try to post some pictures .

atb

Wizard

what tends to happen when you fit a new chain and sprockets is that you find that the old chain and sprockets had more "give" due to wear and were therefore more forgiving to other tolerances being a little out. the most obvious of these external tolerances are the beraing in the hub and the gear changing cable. you can check for play in the hub by seeing if the rear wheel moves laterally - i.e. does it move side to side between the brake blocks. dont know of ny easy check of the gear cable ofther than fitting a fresh one and giving it a go.

of course, this is assuming that the no ammount of "normal" adjusting makes the gears work as desired.

Pictures loaded here Wizards Caravan Repair

atb

Wizard

The setup can vary according to the spring tension on different rear mechanism arm types Wizard. Shorten the chain a little so that when it's on the large megarange 34 tooth sprocket, the spindle of the bottom idler wheel of the rear mechanism is vertically in line with the front of the 34 tooth sprocket.

That will wrap the chain more around the 11 tooth sprocket and should stop the jumping. I use similar megarange freewheels on my two bikes and they are fine when set up as I've described. You can see the forward arm position on this photo of my Q bike:

http://users.tinyworld.co.uk/flecc/images/bothup.jpg

.

Thanks Flecc , i'll give it a go tomorrow and let you know how it goes .

atb

Wizard

Hi Jonathon

 

The Tourney uses a freewheel of course, necessary on a rear motor bike like yours. The HG50 you mention is indeed a chainwidth wider and I doubt if there would be space for a seven speed freewheel on any rear motor bike.

 

.

FYI Flecc, the Wisper has a 7-speed freewheel with rear hub. The wheel is significantly dished to accomodate, with the spokes on the freewheel side being near-vertical!

FYI Flecc, the Wisper has a 7-speed freewheel with rear hub. The wheel is significantly dished to accomodate, with the spokes on the freewheel side being near-vertical!

Thanks for the info Frank, I didn't realise they'd switched to a seven, as it used to be six. I hope their spindle survives!

That dishing is like I did on my Q bike conversion, Wisper again finding it necessary on their conversion from 6 to 7.

http://users.tinyworld.co.uk/flecc/images/wheeldish.jpg

Yes, that looks familiar!

7 gears was one of the changes when they moved from E to SE. Unfortunately they used the wrong megarange - its the 14-34, which is just a bit under-geared at the top end. I think they are going to put the 13-34 on the '2008' version of the SE. I have an 11-34 in my garage which I would put on if I didn't have to cut the motor wires to get at the freewheel!

Frank

I remember this from your previous posts Frank, and assumed 6 speed since Shimano don't list a 14 to 34 tooth 7 speed.

Shimano's HG50 that have is a much better option as we agreed, so if you decide to cut those wires, it would be best.

.

Hi Flecc , i tried what you suggested and the chain is still jumping over the gear , i took 2 links out of the chain , this brought the lower derailleur cog inline with the front of the large sprocket .

I then moved the derailleur round ( pivoted ) more to increase the amount of chain engagement on the small sprocket . This didn't work either , although i did only move it a small amount , maybe i need to move it round more , but i think the derailleur might start to clash with the large sprocket if i do this .

Any ideas what i can try next .

Thanks Wizard

Ps although the chain is forward more , when changing to the small sprocket the chain doesn't rise up like i expected it to .

Edited April 2, 200818 yr by Wizard9956

That's a bit baffling when I'm not able to see it. Is the chain definitely running in a straight line when on the centre sprocket of the set, so that it's not too out of line when on the small sprocket?

Is the chain 3/32"? You said seven speed I know.

Is there a tight chain link, such as at the join, stopping the chain turning smoothly around the sprocket?

Is there chain clearance from the frame all the time when the chain is running?

Finally, can you tell me which model rear mechanism you're using?

.

This is the chain i bought 7,8,14,18,21,24 SPEED BIKE BICYCLE DRIVE CHAIN NEW on eBay, also Chains Rings Bottom Brackets, Bike Parts, Cycling, Sporting Goods (end time 08-Mar-08 21:00:00 GMT)

I've checked for tight links , all ok .

Will post some pictures on the net in a mo showing the clearance .

This is the rear derailleur i bought SHIMANO SIS MEGARANGE REAR MECH DIRECT/BOLT ON FIT NEW on eBay, also Mechs Derailleurs, Bike Parts, Cycling, Sporting Goods (end time 09-Mar-08 21:45:00 GMT)

Thanks Wizard

Mmmm, I wouldn't use those parts. I'm not at all confident that's a genuine Shimano rear mechanism. They show four genuine Shimano ones above, but that one is marked SIS, and SIS is not a Shimano range but a type of system invented by Shimano. It might be a cheap range made by them for low cost bikes, but I don't know of it.

The chain doesn't look too clever either when enlarged, the stamped plates far from flat. Showing it as that mixture of cassette speeds and system speeds indicates someone selling who hasn't a clue on bike part naming. They should work of course, but if poor quality it won't help.

My own megaranges run with Shimano Acera rear mechanisms and SRAM standard 7/8 speed chain.

.

Edited April 2, 200818 yr by flecc

Thanks Flecc , looks like i need to spend some more money doh , when i can afford it i'll buy a Acera derailleur , i actually bought the sis one because i thought it was made to match the Megarange cassette .

I see what you mean about the chain stamped links , they look bowed when viewed from above .

atb

Wizard

Right, just seen your photos. The chain doesn't seem wrapped round enough when on the small sprocket, it should start running forward more horizontally underneath the sprocket, I think that's why it's jumping.

Have a look at this quick snap below of my filthy Q bike and you'll see the chain wraps forward more, and that's on a 13 tooth sprocket. On an 11 it would be even more forward.

The problem you have is the spring inside the frame mounting boss of the mechanism isn't rotating the arm forward strongly enough, so the chain is pulling the mechanism too vertical and running the chain late into the sprocket.

There should be a circlip on the centre bolt of that so that you can get at the spring, and you might find adjustment holes to tighten the spring rotation more. It's a very fiddly job though.

P.S, Just seen your reply, and as you'll see, you might still get away with those parts.

.

[ATTACH]246.vB[/ATTACH]

Edited April 2, 200818 yr by flecc

Found the circlip , i'll have a go at getting the spring to give more lift tomorrow , and report back .

Thanks Flecc

atb

Wizard

Hi Flecc , i took the derailleur apart today and moved the position of the spring on the upper pivot , i tried 3 different positions giving less spring tension , but although they all allowed the chain to wrap around the small sprocket better , each position caused the derailleur to clash when moving to the large sprocket ( 34 teeth ) . I'm going to have another look tomorrow and see if i can do anything else .

atb

Wizard