practical frame straightening

Has anyone successfully straightened the frame on their Commando ?

I'm not looking for the world's straightest Commando, but I would like my bike to be a little straighter. Obviously the frames can be adjusted. I think the upset occured when I dropped the bike on the right side. Now the isolastics don't have the same clearance on the top and the bottom.

In particular, how did/would you hold the steering head/backbone to move the down tubes ?

Thanks

Greg

Greg a crooked Commando only matters if assembly-fitting a hassle or impossible after its un-sprung disassembled. It does about nothing to the handling as front forks adjust to keep tires in same direction, even if not inline with each other. Just lever and bash and push pull as needed so iso mounts fit ok and check swing arm is horizontal even spindle to axle. Bend cold to work harden more stable.
Bars thru holes and straight edges and string lengths help guide ya.
Fork stanchions need to be pretty straight, Check by rolling against each other. Machine shops can often correct back enough to work well.

I agree with Hobot, he knows his Commandos !!!

hobot only knows old abused Combats, peak of the BI golden age, not Commandos' full range of lessor versions. On top of being bent not being much a bother, being very sloppy swing arm to forks ain't much a bother either to fling one way or the other, just a twitch taking up slack, but all hell breaks loose quicker-sooner on held sweepers, so beware. I'm taking care on Ms Peel just to see if I can, but my factory Trixie got 6 ft breaker bar to get center stand to sit level, wood wedges and sludge hammer to get iso tabs to accept engine/cradle and a good smacking of the under spine tube so headsteady will go back on w/o 3/8" offset and spacers. She rode as nice hands off as any bike and handles like any ordinary Commando going silent and sure after 2000ish rpm. I had machine shop mostly straighten the stanchions the 1st deer killing strike bent up.

If I were going to straighten a frame...not saying I would but IF I would do something like the following...

Find a length of steel pipe that fits well inside the neck tube. I would take a piece of 2 X 12 long enough for the frame to sit on upside down.
I would bore a hole in it to socket the steel pipe into. I would then lay the frame upside down and screw blocking on both sides of the back bone to help hold it in place. Then putting the steel pipe through the neck and pinning it into the hole would give me one lever, then by inserting a second lever between the down tubes and anchoring it at the backbone or edge of the plank I would put some twisting pressure on to move the tubes in the direction I wanted. My guess is it would take less pressure than imagined. If you got carried away you would have to worry about twisting the neck, but I don't see too many ways of getting ahold of it without using that as a purchase.

This is just one variation of possibilities...

You could always try laying the bike down on the opposite side.

Russ

Ugh what a task to handle and nail down frame you describe. But some way to hold frame when applying bending force will be needed. A second big helper helps.
Would help to know what is bent of course. I'd think clamping frame bottom tubes down on big sheet of plywood you can stand on would hold it to bend on.
First thing I'd do is get frame to sit vertical on the bottom tubes. Next I'd get the front/rear iso plates/tabs separated to accept the isolastics opened up to running clearance. Some bashing/bending care to get iso mating surfaces close to parallel. 3rd I'd put tube in stem and tweak that to align with vertical frame. Lastly I'd put engine in to see how head steady fits and either bash on spine brace tube or lever through the iso frame mounts to re-angle whole power unit to fit at top as well as bottom. Swing arm is vulnerable to bend on crashes too.

BTW what have you found to indicate a tweaked frame?

I thinkk that the frame is tweeked because the clearance measurements on the isolatics vary from top to bottom. If I set 0.010" on the top of the right front mount, it is tight on the bottom. I opened up the fronts so I had 0.008-0.010" at the bottom. I removed all the shims from both sides of the rear mount to get 0.003-0.004". Vibration hangs aound until about 3000 - 3500 rpm and the mirrors never clear up.

Looking at the frame, the down tubes are much lighter than the steering head/backbone/rear plate assmebly, so pinning it down like a bug and levering on the down tubes seems like a more controllable method than bashing away at it (sorry Steve). Checking to see that the pivots and mounts are parallel with rods seems like a good way to go.

Greg

gjr said:

I thinkk that the frame is tweeked because the clearance measurements on the isolatics vary from top to bottom. If I set 0.010" on the top of the right front mount, it is tight on the bottom. I opened up the fronts so I had 0.008-0.010" at the bottom. I removed all the shims from both sides of the rear mount to get 0.003-0.004". Vibration hangs aound until about 3000 - 3500 rpm and the mirrors never clear up.

Looking at the frame, the down tubes are much lighter than the steering head/backbone/rear plate assmebly, so pinning it down like a bug and levering on the down tubes seems like a more controllable method than bashing away at it (sorry Steve). Checking to see that the pivots and mounts are parallel with rods seems like a good way to go.

Greg

Click to expand...

FWIW it is done regularly on steel bicycles with success so it might work....there are some good (bicycle)web pages on checking alignment with string, straightening, etc that might help

Smoothness is Commandoness, period end of story throw in the ole towel wrap it up, otherwise not a real Commando, just another vibrator ordinary cycle.

Greg, me steve is learning along with ya. I just dealt with too tight a fit of front iso in frame to even get it in with wedges beat hard to spread. I found the front tabs were a few 1000ths wider at bottom than top. I put in all thread rod to spread hard against the top of tabs while beating in careful with drift on bottom/rear of tabs. This gained a bit more parallel fit but not perfect. In the end I had to have machined off in 2 separate trial/errors .03" off RH of front mount for .06" total and then still needed wedges to ease in with wood block and easy sledge hammering.

Trixie was initially found with front tabs spread apart ~,09" beyond manuals spacing, sheeze. She is spread apart up there a bit more yet, but should work a treat. This Combat went silent about 2200 prior with adjustable iso's set nearly as close as manual lists. Her head steady was in great bind - under tube skewed over ~3/8", even with rubber 1/4" spacers on opposite mount sides. Only vibe detectable over 2200 was a buzz sense on intervals of strong side way head winds
or holding some turns that moved top of engine to compress steady to transmit.
Trixie is non-rodded, I rode her twice into hinged handling early on to know what to never-ever do again, so just sane ordinary turns I'm taking above.

As to the stem leaning, as you say its robust fixed to the spine so guess what gave in and should give again to bring er mostly upright, the down tubes. You don't know yet if that's even an issue, likely not. Trixie's T-bone deer strike bent forks easy visible and slammed apart my L knee on cylinder to bend the under spine tube, but the steering stem stayed aligned fine and so did the yokes. She rode hands off as good as any non tri linked Commando, slow to over the ton afterwards - but having to assemble with helper and terrific brute force. This time around I'm fixing her enough a single dumb mechanic can assemble with ordinary size tools and force.

I did decide to try what worked a treat in Ms Peel, I ground a 45' bevel on the front big doughnuts to narrow rim ~1/2 width, Hope is sooner stillness and no intervals of buzz from horizontal vibrations in side ways binds.

To tie frame down hard upright I'd use 2x4's across the tubes screwed/bolted at ends. But hey after I had Peel rear loop pinned and welded back on it still was droopy, so only way to move it was lifting frame over head and coming down harder and harder on carpet on cement. Not exactly a good example to follow I guess.

I've cut / drilled through various spots in frame and its un-settling to see how thin wall it is. Commandos are thoroughbred design is so many ways but the isolastic chassis/power unit tops the list to me.

If I wasn't in the mood to tear the bike down to bare frame and check everything I would find a large adjustable wrench with parallel jaws, adjust the gap to fit the tab and give it a tweak in the direction needed to bring it 90 degrees the the iso bolt. It would bother me not knowing if my frame was tweaked, but tearing it down just for this is a pretty big job too. I am sure there are a lot of readers who will disagree with this idea but the steel is pretty soft and pretty resiliant. If later you tear the bike down you could undo it. I mean after all it sounds like we are talking thousandths of an inch here. Just something to ponder.

Russ

UGH in mine flat jaws would not have helped close the top of tabs while spreading the bottom welded side. The tabs are rather stiff and likely only the half above the hole would give any. Fortunately the way the isolastic mounts made, as long as it fits between tabs close the iso assembly itself provided flat parallel surfaces for slick motion.

Hobot - I gotta disagree. Straight and square matters. Yeah the steering head will compensate somewhat but evil will be lurking.

Strip the seat and tank off, use some tie downs from the rafters to hold the bike vertical with weight on the wheels and isolastics, get it dead plumb, then check wheel alignment with string strung between four jack stands, two on each side.

For what its worth, when all is said and done to get near percect wheel alignment try a couple of 6 foot fluorenscent bulbs on each side of the tires.

Im going back to drinkin.

cheers

The frame man...Scramento, CA....$400.00 for frame, SW & engine plates...
Philippe

Yes I have succesfully straightened a saggy rear frame loop by doing the opposite move that caused it ,using upward strength and a helper to hold solid the bike ! More serious was the sidestand lug rail tube thing , lug was fine , just the tube had moved in from P.O. kicking it on the sidestand. Used a 5 - ton hydraulick jack angled up to the backbone area above air filter area as it seemed strongest. Fitted pieces of wood that would not slip out with the pressures at both frame ends involved , also to spread out the load. A few ratchets later lower sidestand area was happy to be back where it should be , no heat was involved and all measured up good. Had to try something or toss the frame. The quotes I got to do this were prohibative , and then one frame shop suggested just doing the opposite energy that caused it and that was the eureka moment for me. He also said "no heat" . O.K.

Similar problem to gjr with adjusting front isolastic? This is how it looks with the bolt coming through - needs levering and hammering to get it through the left tab then the iso gap is different top/bottom, front/back. Maybe caused by kicking it on sidestand, as Torontonian says?



Bike won't steer hands off, dives to the left. Though this could maybe be bent yokes/forks or swingarm?

The rear frame loop used to be bent down so I hauled it back more or less straight using an 8 foot length of timber and angle iron across as a fulcrum. But I'm not sure it isn't a bit twisted still.

The frame man, Sacramento sounds good but a bit far away. Anybody know of anywhere in the UK (North) for Commando frame straightening?

Until every like sagged skewed donuts to tire size, worn profile and proper air balance its hard to tell what it doing what to veer off to the L. About all bikes do more or less even my pure rigid straight tires inline SV650. Crown of road matters too. Can try the short cut methods, if no joy you know what's next or just put up with it.

Oh yeah I've tried all the rear wheel alignment methods. Discovered the rear wheel is off set ~3/8" to DS. After a few flats away from home I discovered that just getting same finger space at front of swing arm works a treat. Chain tension has to be fudged with aligning of course.

mcns said:

For what its worth, when all is said and done to get near percect wheel alignment try a couple of 6 foot fluorenscent bulbs on each side of the tires.

Im going back to drinkin.

cheers

Click to expand...

Yeah, and 8 ft steel studs work well too.

xbacksideslider said:

mcns said:

For what its worth, when all is said and done to get near percect wheel alignment try a couple of 6 foot fluorenscent bulbs on each side of the tires.

Im going back to drinkin.

cheers

Click to expand...

Yeah, and 8 ft steel studs work well too.

Click to expand...

As long as you all are thinking about alignment, what do you think about this idea for finding the centerline of the frame ?:

A line through the center of the steering head and a line along the spine define a plane that is the centerline of the frame. A laser level should be able to draw the plane. The front and rear isolastic mounting points should be perpendicular to that plane. A straight rod through the iso mounts and a square on the rod to see if the mounts are perpendicular to the plane.

Easier or better ways ?

Greg

Yes, use brute force till assembles w/o strain and rides fine hands off with a bit of body english to compensate for the about universal drift up road crown center.
Set rear tire for about equal space in swing arm V. The closer you measure a Cdo the more you find. Search worlds straightest Commando for N'th degree of indexing but it didn't do a thing for improving handling over any other easy to assemble Commando. Most annoying thing of a crooked Commando is it tends to buzz from slight horizontal vibrations, not the vibes that hurt in vertical major orbital.