Required distance between freewheel and dropout question.

[e-beach]

On a standard mountain bike, is there a required distance between the smallest gear on the freewheel and the frame/dropout that is next to it. The reason I ask is that the yescomusa rear hub motors seem to need crush washers for spacer adaptations that don't come with the kit. Without a modified spacer custom fitted by the purchaser the frame/dropout and the freewheel come in contact like this...

So my question is this: On a mountain bike, when the chain has been shifted to the smallest gear on the freewheel, is there a required space needed between the chain and the frame/dropout or is a millimeter or two fine just as long as the chain isn't rubbing on the frame?

Any and all thoughts would be helpful.

Thanks

 

[wesnewell]

There just has to be enough so the chain doesn't touch. When I used my 7 spd freewheel, it required either 2 or 3 washers on the inside to get clearance. You must have at least one or you may crush the spacer when tightening the axle nut. This will apply to any hub motor with a freewheel.

 

[d8veh]

The drop-out on that bike is not vertical. If you tighten the wheel nut, it should pull it parallel to the face of the washer and you might see your clearance appear.

 

[e-beach]

The drop-out on that bike is not vertical. If you tighten the wheel nut, it should pull it parallel to the face of the washer and you might see your clearance appear.

I actually straightened it after I took the picture but the clearance never appeared.
But once I put a modified lock washer as a spacer of about 11/64 in width (4.2mm) between the inner axle sleeve and the inside of the dropout,I had enough clearance to make it work. :lol:

But the question remains how little clearance is too little.

 

[wesnewell]

If it never touches, it doesn't mater if it an inch or .001 of an inch.

 

[Chalo]

To elaborate a bit on what Wes said, It's only important that the freewheel and chain not make contact during normal running or normal shifting. They can be very close, just as they are on modern 10-speed and 11-speed bike drivetrains. If you want to be able to use your top gear, you have to have enough space to clear the chain too, and to shift it in and out of the gap. (Throw another washer underneath the head of your luggage rack mounting bolt to keep it from sticking out.)

If this were an ordinary bike axle, the fix would be to remove the locknut on that side, add a spacer (a small diameter washer), and replace the locknut. You might or might not want to reduce the spacing on the left side of the wheel by a similar amount. Then tighten all the spokes on the right side of the wheel (re-dish the wheel) to pull the rim to the center of the new wider (or offset) axle stack.

With a hub motor, you need to get one or even two of the spacer washers designed to widen the axle stack (SpaceWasher14 at the ebikes.ca store), and just slip it on, no locknut. You have to make sure the washer stays on the inside of the frame dropout every time you mount the wheel. And of course you have to re-dish the wheel.

You could also tackle the problem by switching to a narrower six-speed or five-speed freewheel, and changing to a matching shifter if you are using index shifting. That would save you having to re-dish, and would leave more strength in the wheel since it would be more symmetrically tightened. Note that a normal bike shop will not have the special tool required to remove a freewheel from a hub motor, so you'll either have to go to an e-bike service place or you'll have to buy the tool yourself.

Chalo

 

[geeeyejo1]

Looks like I will find out this weekend - I picked up two different size lock washers at the hardware store by my job today - 4 of each (9/16 & 1/2) ID of hole is just about 14-15mm on both - thinking I will bend them with two pliers to open to avoid having to cut for the Hall sensor/power wire side - place over the wires then bend back. The two washers stacked together are just about 6mm thick. Best part was 8 washers only cost $2 total - a far cry from $4 a piece for custom ebike washers!
Will let you know how it works!

 

[wesnewell]

The 1/2" is too small at 12.7mm. 9/16th is perfect at 14.2875mm.
http://mdmetric.com/tech/cvtcht.htm

 

[Chalo]

The 1/2" is too small at 12.7mm. 9/16th is perfect at 14.2875mm.
http://mdmetric.com/tech/cvtcht.htm

Washers are always bigger on the ID than their nominal size. How much bigger varies by what kind of washer. USS spec flat washers always seem to slip over the next larger inch sized fastener, e.g. a 1/2" USS washer slips over a 9/16" bolt, no problem.

In this case, the closest fit is best.

 

[geeeyejo1]

The 1/2" is too small at 12.7mm. 9/16th is perfect at 14.2875mm.
http://mdmetric.com/tech/cvtcht.htm

Washers are always bigger on the ID than their nominal size. How much bigger varies by what kind of washer. USS spec flat washers always seem to slip over the next larger inch sized fastener, e.g. a 1/2" USS washer slips over a 9/16" bolt, no problem.

In this case, the closest fit is best.

Agreed - I was originally going to go to Home Depot with the washer provided with the kit to match up the OD and ID size - I stopped at the local store by my job on impulse and had to "eyeball" so picked up both the 1/2" and 9/16" as they both looked very close - figured at only $0.25 a piece I wouldn't take a chance and got four of each!