Is my swingarm bent? bike pulls to left.

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harleyhappy
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Bikes: 75 shovel bitsa

Is my swingarm bent? bike pulls to left.

#1

Post by harleyhappy »

Hello all

I have an OEM round swingarm in my shovel bitsa, with a 58-62 juice drum, bendix brake plate with aftermarket drum and timken style repop star hub, with the correct axle (I think its a slightly different diameter because of the timken bearings)

I've done 2000 miles since building the bike, and it pulls to the left when I let go of the handlebars, unless I sit quite far off the right hand side of the bike. I have tried riding on both sides of the crown of the road, and it pulls left regardless. The front wheel is exactly in the middle of the forks, I've changed the fork oil and springs, and tweaked the handlebars each direction with no effect. I've got the rear wheel lined up with the front (plank of wood, string, eyeballing) and have tried a few degrees in each direction also with no effect.

I've also re offset the back wheel 4 times now, to various specs I've found, most recently palmers 11/16 hub inset from rim, which does seem to line up best, but its still pulling to the left. When I've been taking the wheel in and out I've noticed that if the brake plate sleeve nut is tight its very hard to get the axle flats into the RH side of the swingarm, I have to loosen the big nut and pull the RH side of the axle up hard to get it to push into the axle slot, even without the weight of the wheel pulling it down (eg, wheel out)

Does this point to a twisted swingarm? I presume the axle should slide though with no resistance anywhere until the hex hits the RH outside of the swingarm? Given where the side car mounting hole is, is it most likely that the RH SA leg is bent up? or the LH twisted down? and would this cause the leftward drift? Also, if its bent, whats the best way to fix it? I have a shop press, but no oxy acetylene.

Sorry for the long post, but I'm stumped!
Little Stan
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Re: Is my swingarm bent? bike pulls to left.

#2

Post by Little Stan »

A few thoughts as I rode a swing arm pan/shovel for decades.

Is your frame straight? Neck square with motor mounts and swing arm pivot? Is the starting adjustment point for the axle adjusters square with the pivot? Swing arm bearings! Drive side takes a beating and I once dumped my bike making a left turn due to a loose swing arm and flat bearings.

You can check your wheel alignment by jacking both wheels free and then put a 8 foot neon light bulb against the sides of the tires.

On a final note: Even though I have a truing stand (always building wheels for others) I still use the front end on my old pan when I'm lacing and truing my own wheels. Old scooters had interchangeable wheel hubs and if your front end is short, straight, known to be good use it to check the wheel centers of both wheels.

Getting long here but I know a guy that bought a new shovel back in the day and it turned horribly one way but fine the other. Wouldn't do it if he had his lady on the back! Finally sold it to a friend who took it apart and discovered the right rear part of the frame section had never been welded!

Wishing it was still the AMF days when I was young......

-'lil stan
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Re: Is my swingarm bent? bike pulls to left.

#3

Post by RUBONE »

In the late '60s (around '68) H-D started offsetting the rear wheel to compensate for pull to one side. It was a result of too much weight on the left due to all the mass of the starter and primary parts on e-start bikes. I'll have to dig and see if I can find the shop dope on it. I was working for a dealership from the early '70s to '80 and laced a lot of wheels. That was one of the tricks to make them track correctly.
harleyhappy
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Re: Is my swingarm bent? bike pulls to left.

#4

Post by harleyhappy »

Thanks for the helpful responses, a fine welcome to the site.

Not 100% on frame, I have had it completely bare, cleaned it and eyed it up the best I could and it looked ok, but no jig to be sure, so still a question mark over that, just crossing my fingers!

Swing arm bearings are new, can you clarify "starting adjustment point for the axle adjusters square with the pivot?" please?

Cant really stretch to a 8ft bulb, I live in the sticks, and hard to safely bring home on a bike, but I did do the same test with a nice straight 8x2 plank, and all looked well.

My front end is a 6" over narrow glide, so no joy to be had there as a truing stand!

I've read about the offset wheel, and thats why I've trued it side to side a few times (with no joy) but my bikes a skinny 1960's style chopper, kick only, tiny battery, horse shoe oil tank, tin primary and belt drive, so the weight should be pretty even side to side.
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Re: Is my swingarm bent? bike pulls to left.

#5

Post by Excalibur »

Welcome to the forum.

I hope I can help with this issue because I battled with a bent swingarm and more. I made a blog outlining how I fixed it. Some of it may apply:
Swingarm straightening
This a direct link to the particular page dealing the subject. Scroll down to the last post from 2016

Straightening my swingarm improved the tracking but it still pulls slightly. Since then I noted the axle doesn't slide into place easily without a bit of effort so I plan to revisit this when I replace the tire in the weeks. So I believe the rear s/a casting/s are not true perpendicular to the rest of the swingarm.

Good luck, hope this helps.
kfelt
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Re: Is my swingarm bent? bike pulls to left.

#6

Post by kfelt »

Just don't let go of the bars!
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