dogman dan
1 PW
The key to preventing spinout of front hub axles is three key items. Tourque arms are a good idea, but getting these two things right is even more important.
1. Selecting an appropriate fork, made of steel.
2. Getting the nut tight.
3. Getting the fit of the washers correct, so the nut stays tight.
Even though a fork may be steel, some are too light to be very strong. A great number of forks designed for quick release hubs have had the dropouts shaved down to the bare minimum of metal to save weight. Such forks may not have the extra strength needed to handle the forces of a hub motor, even a 500 watt one. You want forks with lots of extra metal. Often these forks are found on cheaper bikes, and new forks can be bought for expensive bikes that are strong. Forks intended for bmx bikes tend to be strong for mounting footpegs on the front wheel. Surly also makes a good strong fork. On the cheaper mountain bikes, the suspension forks may have steel lower tubes and dropouts. With these steel suspension forks clearance for the motor may be very tight. 9c motors may be the best choice for these narrow forks.
The bike I'm fitting this fork to is similar to some I've seen in bike shops, Trek, Giant, etc that sell in the $250-$350 price range. Still sorta low end, they still have a steel bottom end on the suspension fork, or maybe even non suspension. The forks have the smaller cup or lawyer lips designed for QR. These bikes are often chosen for motors because they have steel forks, and are a bit better quality than the $160 mongoose or pacific at wallmart. The pix show a mongoose bike I found at the flea, that had steel suspension forks that were a better quality than found on wallbikes. 60mm travel instead of 40, and much thicker stronger tubes with a welded on dropout. The rest of the bike is nice too, with good components and 100 mm travel rear suspension. $20 at the flea,
This shows the dropouts from a set of steel suspension forks on a mongoose bike, and how the cup for the QR hub looks. These "lawyer lips" are the problem when fitting a hub motor since the motor washers are bigger. Looking at the dropout in the background, you can see how the cup is stamped into the dropout. The cup is perfectly fitted to the quick release hub so if the hub gets loose the wheel won't fall out.
This shows the way a motor hub washer fits the dropout. Hub motors have a larger axle with flat sides so the nuts and washers are larger than normal. Even if your bike has bolt on wheels, you may still have this problem. Look close at the gap between the washer and the bottom of the cup. This is the critical area that causes spinout. As you ride, the washer slowly bends, deforming into the cup. Eventually this causes enough space to loosen the nut. Just a bit of loosening greatly reduces the ammount of force it takes to allow the axle to spinout. When using an aluminum alloy fork, tightening the nut with this gap there can result in a hairline crack, that causes the wheel to fall off later. Do not use alloy forks!
The old school way to fix this is with a lockwasher, from a large bolt. This doesn't work with the tab on a tourqe washer, and the washer is still just slightly too big for this set of dropuouts. With just a bit of grinding to make the washer smaller, this would work with a tourqe arm just fine. Another approach could be to grind the tourqe washer smaller, but that would weaken it a lot.
The solution for this is a special C washer sold by Ebikes.ca . But being cheap and in a hurry, I cut the lockwasher into a C washer, and pinched it tighter so it fit into the cup.View attachment 2
This shows the hub installed. If you look very close, you can see the c washer completely fills the space so the tourqe washer does not contact the fork and all the forces of the tightend nut are on the bottom of the cup. The washer is now supported so it can't deform into the space and let the nut get loose. If you have a tourqe arm, substitute it for the tourque washer. You also see in this picture that the hub doesn't fit between the forks. One nice thing about the cheap steel forks is that you can bend them to create the needed clearance. In this case, a good hard pinch with vise grips gave me the extra 1/8" I needed.
That covers getting the fit right, which should prevent the nut from loosening. In my experience, usually not getting a flat for at least 1000 miles, I have not had the nuts get loose on a properly fitted hub.
As you tighten the nuts, look very closely for any sign that the axle wants to spit out of the dropout. This is a big red flag that something doesn't fit right and spreading forces are being put on the forks. At first the forces push the axle out, later they just bend the dropouts into a V shape.
Sometimes the axle won't quite fit into the dropouts. Filing away paint is OK. Filing off the metal is not. A better approach is to shave the flats of the axle, but again, not a lot. If it really really won't fit, Get new forks. Sometimes a fork has a flat dropout, but has little tabs on the tips to keep a loose wheel on the bike. Bending the tabs down may work, or file them off. Just don't weaken the dropout!
Now to the question of how tight? You want it tight, but I have stripped out an axle using too big a wrench. What I do now is use a small crescent wrench with a handle about 6" long. Tighten the nuts snug, but not tight. Then start making them tighter, a little bit at a time. Get them fairly tight. Then spend a half hour or more wiring the bike, or having a beer. Then after any tiny bit of metal deformation has happened to the washers, tighten pretty hard with the short wrench. I have not had a loose nut, or a stripped axle since I started this procedure. The time I stripped an axle, I was using a long wrench and all my strength.
If the hub is not fresh out of the box, like you are fixing a flat, you can tighten the nuts all the way in one go. The washers are already settled into the dropouts and won't need the half hour.
1. Selecting an appropriate fork, made of steel.
2. Getting the nut tight.
3. Getting the fit of the washers correct, so the nut stays tight.
Even though a fork may be steel, some are too light to be very strong. A great number of forks designed for quick release hubs have had the dropouts shaved down to the bare minimum of metal to save weight. Such forks may not have the extra strength needed to handle the forces of a hub motor, even a 500 watt one. You want forks with lots of extra metal. Often these forks are found on cheaper bikes, and new forks can be bought for expensive bikes that are strong. Forks intended for bmx bikes tend to be strong for mounting footpegs on the front wheel. Surly also makes a good strong fork. On the cheaper mountain bikes, the suspension forks may have steel lower tubes and dropouts. With these steel suspension forks clearance for the motor may be very tight. 9c motors may be the best choice for these narrow forks.
The bike I'm fitting this fork to is similar to some I've seen in bike shops, Trek, Giant, etc that sell in the $250-$350 price range. Still sorta low end, they still have a steel bottom end on the suspension fork, or maybe even non suspension. The forks have the smaller cup or lawyer lips designed for QR. These bikes are often chosen for motors because they have steel forks, and are a bit better quality than the $160 mongoose or pacific at wallmart. The pix show a mongoose bike I found at the flea, that had steel suspension forks that were a better quality than found on wallbikes. 60mm travel instead of 40, and much thicker stronger tubes with a welded on dropout. The rest of the bike is nice too, with good components and 100 mm travel rear suspension. $20 at the flea,
This shows the dropouts from a set of steel suspension forks on a mongoose bike, and how the cup for the QR hub looks. These "lawyer lips" are the problem when fitting a hub motor since the motor washers are bigger. Looking at the dropout in the background, you can see how the cup is stamped into the dropout. The cup is perfectly fitted to the quick release hub so if the hub gets loose the wheel won't fall out.
This shows the way a motor hub washer fits the dropout. Hub motors have a larger axle with flat sides so the nuts and washers are larger than normal. Even if your bike has bolt on wheels, you may still have this problem. Look close at the gap between the washer and the bottom of the cup. This is the critical area that causes spinout. As you ride, the washer slowly bends, deforming into the cup. Eventually this causes enough space to loosen the nut. Just a bit of loosening greatly reduces the ammount of force it takes to allow the axle to spinout. When using an aluminum alloy fork, tightening the nut with this gap there can result in a hairline crack, that causes the wheel to fall off later. Do not use alloy forks!
The old school way to fix this is with a lockwasher, from a large bolt. This doesn't work with the tab on a tourqe washer, and the washer is still just slightly too big for this set of dropuouts. With just a bit of grinding to make the washer smaller, this would work with a tourqe arm just fine. Another approach could be to grind the tourqe washer smaller, but that would weaken it a lot.
The solution for this is a special C washer sold by Ebikes.ca . But being cheap and in a hurry, I cut the lockwasher into a C washer, and pinched it tighter so it fit into the cup.View attachment 2
This shows the hub installed. If you look very close, you can see the c washer completely fills the space so the tourqe washer does not contact the fork and all the forces of the tightend nut are on the bottom of the cup. The washer is now supported so it can't deform into the space and let the nut get loose. If you have a tourqe arm, substitute it for the tourque washer. You also see in this picture that the hub doesn't fit between the forks. One nice thing about the cheap steel forks is that you can bend them to create the needed clearance. In this case, a good hard pinch with vise grips gave me the extra 1/8" I needed.
That covers getting the fit right, which should prevent the nut from loosening. In my experience, usually not getting a flat for at least 1000 miles, I have not had the nuts get loose on a properly fitted hub.
As you tighten the nuts, look very closely for any sign that the axle wants to spit out of the dropout. This is a big red flag that something doesn't fit right and spreading forces are being put on the forks. At first the forces push the axle out, later they just bend the dropouts into a V shape.
Sometimes the axle won't quite fit into the dropouts. Filing away paint is OK. Filing off the metal is not. A better approach is to shave the flats of the axle, but again, not a lot. If it really really won't fit, Get new forks. Sometimes a fork has a flat dropout, but has little tabs on the tips to keep a loose wheel on the bike. Bending the tabs down may work, or file them off. Just don't weaken the dropout!
Now to the question of how tight? You want it tight, but I have stripped out an axle using too big a wrench. What I do now is use a small crescent wrench with a handle about 6" long. Tighten the nuts snug, but not tight. Then start making them tighter, a little bit at a time. Get them fairly tight. Then spend a half hour or more wiring the bike, or having a beer. Then after any tiny bit of metal deformation has happened to the washers, tighten pretty hard with the short wrench. I have not had a loose nut, or a stripped axle since I started this procedure. The time I stripped an axle, I was using a long wrench and all my strength.
If the hub is not fresh out of the box, like you are fixing a flat, you can tighten the nuts all the way in one go. The washers are already settled into the dropouts and won't need the half hour.
. Next step is to braze weld the washer into place, you don't want to arc weld as this leaves rough edges and doesn't get the proper penetration and fusion; you want to braze weld as this is like soldering copper plumbing but with higher heat and stronger solder ie bronze. You will need a oxy/mapp setup at least for the required amount of heat. Next use a dremmel to cut the 'C' in the dropout to match the fork.
Don't do that! You don't want to be removing metal from the dropout as this weakens and compromizes it!