Crushing Aluminum

MysterySandwich · Jan 6, 2014

What's the general consensus when it comes to the strength of aluminum?

Will clamping some steel plates onto an aluminum frame bring up some problems? (Staton-inc FD on aluminum frame)

I'll be careful and not torque down the bolts too much, but what's the right amount? Would some rubber or some other kind of cushion help protect the aluminum frame? I know that that's really not a good idea when it comes to mounting 2 stroke engines in-frame...

rustycase · Jan 6, 2014

Yes, it will cause problems eventually, but if that's what you gotta do... well...

Use the largest possible bearing surface, and Not so it would encourage a direct break-off line.
I would use some quality gasket material sooner than rubber. Garlock?

The problem with aluminum is that it suffers from fatigue which leads to catastrophic failure. This was learned in a spectacular fashion in the aircraft industry.

Just my opinion... perhaps someone will have information of a long term success.

Good luck
rc

MotorBicycleRacing · Jan 6, 2014

MysterySandwich said:
What's the general consensus when it comes to the strength of aluminum?

Will clamping some steel plates onto an aluminum frame bring up some problems? (Staton-inc FD on aluminum frame.

It won't be a problem bolting that U bracket and plate to your frame.

Put thin pieces of rubber between the steel brackets and your frame and don't over tighten the bolts.

There is no comparison to putting rubber under a 2 stroke motor mounts.
Your friction drive motor channel is also secured by by 2 aluminum stays that go down to the axles.

Install a tire liner like Mr Tuffy and a thick thorn proof tire because the roller will drive any sharp objects into your back tire.
Carry a spare tube with you too because FDs get lots of rear wheel flats.

rogergendron1 · Jan 6, 2014

crushing aluminum.......

sounds like a new heavy metal rock band !!!!

but srly ..... u bolts are one of the best ways to mount a motor to a frame ! keep tightning it till you see the frame start to crush a tiny bit and thats how you know its tight enough !
i have a 35mph bike and the motor is held on by a u bolt in the rear with a plate going to the case bolts and a single 5/16ths through bolt, bolted through a steeel plate on the frames down tube and the motor boltas to that. have not had a single problem ever and the motor is as solid as a rock !

the bolt that goes through the frame in the front mount is has large washers bent in a curve to match the frames curve and its tightend so tight it crushes rthe frame slightly, this means the fram is crushed in just enough to want to push or spring back out and it keeps tention on the bolt to stay tight.

rustycase · Jan 6, 2014

lol

I never did consider the FD wheel driving thorns into a tire, with enthusiasm!
Tnx for that tip!
rc

MysterySandwich · Jan 6, 2014

Great, thanks guys!

So some nice gasket material in between the steel mounting plates and the aluminum frame. This Mr. Gasket 9615 should do the job well, yes?

I already regret buying a bike with 24" tires hah... hard to find some heavy duty inner tubes or compatible Mr.tuffy, contacted bikebuyers, hopefully they can help.

And as for torque'ing down the bolts until I see the frame crush slightly... is that really a good idea? makes me nervous!

MotorBicycleRacing · Jan 6, 2014

The Staton U clamp and plate are wide and just need a little cushioning so they don't rub on the seat stays.
A piece of thin inner tube is just fine for the job.

26" Tire liners are easy to cut to length for a 24" wheel with scissors.

MysterySandwich · Jan 8, 2014

Hey guys, thanks for all the good help!

Anyway, got my bike today and looks like there's a bigger

problem.

So the mount right behind the seat post... There's no room for all three bolts to bolt on, only for the middle one. I COULD move it up right behind the seat post and bolt the two on the side and not the middle, but then there'd be no room for the saddle.

See pics... : https://www.dropbox.com/sh/9e48n7ipqmddulz/Zp_1g3deJo
(disregard the first picture)

I'm not too excited about the idea of only mounting the middle (the steel plate would probably end up bending in) so the only thing I can think up of is getting some kind of extensions (see picture) but I don't know where I'd buy those...

OPEN TO ANY CREATIVITY!
:-||

Mike B · Jan 8, 2014

I tried to warn you...

I even showed how it goes on my bike.

You are going to have to fab up a custom bracket. It's gotta be strong too, that motor bracket takes the entire thrust from the engine driving the tire.

MotorBicycleRacing · Jan 8, 2014

Flip the bracket around and only use the center hole.

Then drill 2 more holes in the bracket on the inside of the seat stays.

Or you could notch the bracket in the middle removing the center hole
then re drill 2 outside holes higher up on the outside of the frame.

Then re drill the center hole below the notch.

Actually would be better to forget the middle hole and drill 2 more holes
on the inside of the frame so there would be 4 bolts, 2 on each side.

Of course you have to match the holes in the backing plate.

MysterySandwich · Jan 8, 2014

Mike B said:
I tried to warn you...

I even showed how it goes on my bike.

You are going to have to fab up a custom bracket. It's gotta be strong too, that motor bracket takes the entire thrust from the engine driving the tire.

Yeah I know :/

MotorBicycleRacing said:
Flip the bracket around and only use the center hole.

Then drill 2 more holes in the bracket on the inside of the seat stays.

Or you could notch the bracket in the middle removing the center hole
then re drill 2 outside holes higher up on the outside of the frame.

Then re drill the center hole below the notch.

Actually would be better to forget the middle hole and drill 2 more holes
on the inside of the frame so there would be 4 bolts, 2 on each side.

Of course you have to match the holes in the backing plate.

Hey thanks, those are some good ideas -- I'm not exactly sure what you mean by the third option.

But here are some crude drawings I did, is this what you meant by #1 & 2?
I like option #2 the best.

EDIT: Oay so I did some measurements and what not, #2 won't work, the steel in the middle will have to be grinded to the point where it is too thin, See pic

SO I think I'll have to go with #1 -- Will this be stable, even though there are no bolts holding on the outside of the seat stays?

MotorBicycleRacing · Jan 8, 2014

Mark the new holes on the actual bracket with felt tip and take pic
with it on the frame.

forget about the middle hole as there is nothing in the middle to clamp
around and it will only bend the U bracket and plate.

Put a hole on each side of the 2 seat stays in the U bracket so you are using 4 bolts to hold it on.
maybe you can use the 2 outside holes.

That is a large diameter strong aluminum tube to clamp to so no worries
about crushing it.

Mike B · Jan 8, 2014

That would be ideal. If you can get those outer bolts to clear the frame and drill 2 inner ones, you are golden.

Yeah, forget the center bolt.

You need to clamp from both sides of the stays or the bracket will move.

MysterySandwich · Jan 8, 2014

Okay So I actually already drilled the holes... See pics

Theres no room to drill holes on the outside of the seat stays.
Buuut.... We can combine the ideas -- What do you guys think about grinding off the middle/top hole to create leeway for the frame which would let me raise the ends a bit higher so I can drill holes on the Top left and right corners for 2 bolts? I'll just have 2 holes unused.

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Crushing Aluminum

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