I never felt that I needed a BBSHD torque arm because my motor was tight up against the frame. But over time the toothed nut wore into the frame and started to let the weight of the motor move it up and down wearing the end of the BB shell. When I blew up the driveline and was waiting for parts I had the BB shell refaced ( Trek/ GF frames ar 73mm so no big deal if it's thinner). I ordered a couple of the thicker torque arms. Due to my 2 leg center stand folding to the left side I had to reverse the arm and attach it to the seat tube. First try clamping it interfered with the roller chain guide when I put the driveine back. So I ordered a 6mm nutsert installation kit and bolted it on with a 1/4" spacer to clear the roller guide bracket. The motor is still up against the frame but the weight is on the torque arm now. It ran about 3 years before the problem became apparent. The nutsert kit just has an Allen bolt running through it so I think the 6mm tool will do 5mm also with a smaller bolt and a couple washers. I probably could have done this w/o refacing the frame, but I sent it in for hub lube and sealed bearing headset also. The derailer hanger was bent too. Whether you want to make this part of the build or do it as a repair later my guess is at some point you will need one.
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I've got 8000mi on a BBSHD with no issues... haven't touched the motor mount nut since I pulled the motor to relube at about the 1000mi mark (~7000mi ago)
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I think whatever benefit the squishy tires bring is more than a little offset on how hard I pound the bike... just got around to truing the wheels (did it at about the 2-3000mi point due to my foot going into the spokes) and they were at least 7-8mm out in spots suggesting they've taken a pounding! =] -
I didn't do the first install myself. But 3 years it was probably done OK. Hard launches from traffic lights probably worked it loose. The torque arm IS nice and shiney! I needed to practice with the 6mm nutsert tool anyway for hanging a battery upside down on a Y frame project.
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Buying the socket instead of the $20 flat wrench solved all my issues. I wasn't having huge issues before but would eventually notice slight movement when I was just using the wrench.Comment
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They were out of the socket so I'm using the flat wrench. But if I had known that a knurled washer wash all that held a 160Nm motor in place I probably would have taken action sooner. It worked for 3 years so it's definitely not hopeless.I didn't have any tool for this until now, so it was as it came. if the washer can bite into the aluminum frame to hold the mptor, it can also chew it up to allow it to move around. Once that happens it doesn't work any more. It might have been more of an issue if my frame was 68mm BB to start with.My policy is if something fails upgrade it.Last edited by Retrorockit; 07-31-2022, 10:42 PM.
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I'm thinking that the major force here is not the motor at all. The torque on mine was up against the frame already, and the weight of the motor is not that great. The weight of the rider on the pedals is probably the major factor. So keeping the nut tightened may still be the major factor torque arm or not. I can see that as the washer teeth wear into the frame it could create slack and allow movement and wear. I suppose it will be 3 years before I find out if the torque arm is really better. I think the torquea arm won't wear into the frame and may stay tight due to that, and if it does loosen up won't allow movement. It probably doesn't resist the weight of the rider any better than the washer device.Comment
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OK I've got some miles on it, and the bike rides exactly the same. The damage repair to the BB shell resulted in about 3 exposed threads on the motor tube that weren't there before ( I got the thicker arm). I think if I put it back the way it was a 2nd repair would be quite a lot. I bought 2 of the arms, and now I own the Nutsert tool so going forward this will be plan A for me. I still don't own the socket. I just bang on the flat wrench with a mallet to snug it up (hit the handle not the other loop of the tool). -
I'm going to share some tips from doing the torque arrn to the seatpost mount.
1- it's easy to get the hole location started in the correct place by using a duplicating punch through the 6mm mounting hole. Even dill it to that size through the hole.
2- The drill bit will want to wander drilling out to 10mm for the 6mm nutsert. It's only touching the frame in 2 places and being pulled in opposite directions.It doesn't center itself in the pilot hole like it would on a flat surface. My motor wasn't against the frame itself but against some welded on cable guides. I had to grind them down some to make up for this..
3- Another option would be to drill through the frame all the way 6mmm and through bolt the arm. Cheaper than buying the Nutsert installer too.
4-On a thinner high alloy frame you might want to drill the far side hole big enough for a piece of tubing around the bolt from the back side so you don't crush the frame when you tighten the boltLast edited by Retrorockit; 08-06-2022, 07:43 AM.
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Last edited by mike paner; 01-28-2023, 06:44 AM.Comment
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They were out of stock on the socket when I was looking. Mine went 3 years w/o touching it before the motor loosened up, but it did require frame repair. So I'm used to not bothering with it. The torque arm puts me back in that place. Also it reminds me of the traction bars that used to hang under vintage Camaros. But that's a different problem..
Also the torque arm was about 1/3 the price of the socket.Last edited by Retrorockit; 01-28-2023, 07:12 AM.
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