frame straightness

well, at this point in time with you committed to the present frame, having spent the money trying professional straightening and then powder coating

^^^ if I were in your shoes at this time I would just put the bike together, assemble the forks, wheels, motor, tranny, etc

and then start and ride it......it may be just fine...yes many here will disagree with me and insist on frame perfection and how safety important it is, and i get that

but you just might be A ok with the final result, I am saying this because there are thousands of non perfect Commando frames running around right now

including my own, which the previous owner had brutally installed a huge foot rest across and front down tubes and mashed, distorted them badly
I mixed JB Weld and filled it in to round out and repaint (knowing the JB Weld did nothing at all to restore frame tube to original structure) and have proceeded to ride the past 23 years with absolutely no negative handling consequences - yes I know there are more serious potential problems than frame down tubes, but still

my point is right now you can either put it together and, I feel, discover that Commando frames are quite tolerant of imperfections OR junk it and buy another new and expensive frame

Check this out!

http://www.vintagenet.us/phantom/wsc.html

Success straightening thing out

Click to expand...

Maybe someone can help me through this article with respect to the rear wheel? At one point, he says:
Something you may want to do while the swing arm is off the bike is put some accurate wheel alignment marks on your fork ends. You can use a beam compass (or measure carefully) with one end set on an edge of the fitted spindle and scribe a mark on the fork end where it will be visible with the chain adjusters. Without changing dimensions, mark the opposite side as well. Repeat this in 1/8" increments along the length of useable fork end on both sides and make permanent punch marks. You will never again have to wonder if the wheel is straight when you adjust the final drive chain.

At another point he says:
Measure in from each side plate to determine where the center is, and mark the spot on the top of the swing arm. If your frame is not bent, this should be exactly on the center line of the motorcycle.

Maybe someone can offer up a drawing showing the steering head, the cradle, the SA mounting area and the SA adjuster plates with the "offset" grossly exaggerated, so I can picture this?

BUT a little later:
The swing arm is not symmetrical because the engine and cradle assembly is offset 1/4". If the wheel does not line up correctly, you will need to have the spokes adjusted to move the rim over.

I take the last quote to mean that what he calls the center of the SA (equidistant from the side plates) is not on the center line of the frame.
So if the SA is not symmetrical, how could we use it to mark the adjustment slots or use the center of the SA to determine the center of the frame where the wheel shd be centered?
And if we just used the marked center of the SA to pick out center of the wheel, how cd we see this?: Note that the edge of the tire will be noticeably closer to the swing arm on the right side

Put another way, just how is the SA not symmetrical?

FWIW - These bike frames/components were never "perfectly aligned." Mostly they were "barely aligned" with no subsequent issues at all. A few years back a gentleman here posted that when he worked for Norton, building Commandos, it was not unusual at the factory to jump up and down on a frame as necessary to get it "aligned" sufficiently for the appropriate components to fit.

So I guess I'm suggesting that if it's within "jumping up and down" specs, it's probably fine.

Put another way, just how is the SA not symmetrical?

Click to expand...

The SA is symmetrical at the front where it attaches to the rear iso cradle, then in order to cater for the chain on the left side the left side arm moves out further than the right so that at the end of the SA where the wheel axle is the left axle plate is further away from the centre line than the right axle plate.

Repeat this in 1/8" increments along the length of useable fork end on both sides and make permanent punch marks.

Click to expand...

This is a ref to the forward backwards movement of the axle when the chain is adjusted, nothing to do with side to side.

kommando said:

Put another way, just how is the SA not symmetrical?

Click to expand...

The SA is symmetrical at the front where it attaches to the rear iso cradle, then in order to cater for the chain on the left side the left side arm moves out further than the right so that at the end of the SA where the wheel axle is the left axle plate is further away from the centre line than the right axle plate.

Click to expand...

The cradle is offset to the left of the frame centre line (approx. 1/8" - 3/16") therefore, it follows that the centre of the front (pivot) end of the swinging arm must also be offset left of the frame centre line because it attaches to the cradle.
The rear S/A plates need be equidistant from the frame centre line and also be the same distance apart on the outer faces as the frame inner shock mounting plates otherwise one or both shocks would lean to the side, so the right plate has to be further from the pivot centre.

http://www.nortonownersclub.org/support ... el-offsets
"
Commando wheel offset - the definitive answer

I have the definitive answer as to what is offset, how much, and which way!

I set up a 1973 850 on the frame table and verified it was straight. I then put together a dummy engine and installed it with new isolastics, new washers, Hemmings adjusters, and a Norvil head steady. I put both adjusters on the left side, checked the swinging arm in my fixture and then installed it in the frame. I took all the play out of the adjusters and started measuring:-

The frame is symmetrical
The engine/gearbox cradle is offset 1/8" to the left.
The swinging arm is offset 1/8" to the right so the axle pads end up centred in the frame

I then installed the rear wheel:-

The spoke flanges are offset 1/8" to the left as mounted in the arm, so the rim is laced off 1/8" to the right to put the tyre in the centre
The centre of the rim is 3.3/8" from a straight edge laid across the brake drum (not the backing plate

With the stock Dunlop rim, if you sight across the rim on the brake drum side you will see about 1/16" of hub when it's in the right place. In my opinion, front and rear adjusters should be on the same side. Otherwise as things wear and you take up the slop you angle the engine and gearbox in the frame. Since the swinging arm mounts to the cradle, a little one way in the front and a bit the other way in the back and the rear wheel is out of line considerably. The chain will still line up but the wheels will not.

Vernon Fueston (----------------) on NOC-L 22nd. Nov 1997"

Frames that have been down the road can easily be parallelogramed to one side. the symptoms will be difficulty in fitting the front iso bolt without distorting the front iso rubber. If the bend in the two frame loops extends to the rear iso tabs, then the gearbox cradle and obviously the swinging arm will no longer be aligned in the vertical plane. Without talking about the offset in rear wheel and whole engine/ gearbox being off centre, a rear wheel that is out of alignment vertically, needs sorting before you waste any more time trying to align the rear wheel. These frames are weak but adequate provided you are aware of their shortcomings. I rode for 30+ years on a bent frame before the light came on. A company in Shropshire (Metal Malarkey) have made a Commando with a proper frame that looks similar to the original.

Thanks for all of the advice, so i figure i have a few options. Take the frame back to the repairer, just build the bike as is, or get a new frame. I think its possible i may end up doing all three in the order above, cheers.

Could be the cradle is bent, did you get the cradle checked by the guy who straightened the frame and SA.

morton said:

Thanks for all of the advice, so i figure i have a few options. Take the frame back to the repairer, just build the bike as is, or get a new frame. I think its possible i may end up doing all three in the order above, cheers.

Click to expand...

Actually, there is a fourth option before you do any of the above. Confirm your cradle is straight. You can use a square on it. Then make sure it is set to the left of center in the frame. Measure off the frame gussets where the Z-plates attach to the cradle. It should be about 3/16" inch closer to the left side. Do you have a stock head steady? Bolt it up and check alignment. Do you have an adjustable head steady? Do you know if it is set up properly? It is possible there is something not correctly installed and this offset is fugged up. I really think you need to confirm this before you do anything else. Of course without laying eyes on the bike or seeing photos it is possible none of us understand the situation.

Russ

I've written a response to this a few times, because I am obsessed with spatial geometry like this and a lot of other mechanical stuff too... The problem with a norton is that there are so many components that determin the alignment result that it's hard to talk about any of it, without including all of the factors. At the point were you talk about everything in a linear fashion, you loose any common sense feeling for the simplicity of any bike's alignment or misalignment,... as the case may be.

Simply put, the wheels of any bike should be in planar alignment so when each one of them moves in their suspension, they remain in the same plane (when the bike is verticle). This means that certain things must correlate. All the axles, (both wheels and swingarm pivot) should be level at the same time, which can be used to check for alignment. Both wheels should be plumb when the front wheel is pointing down the centerline of the bike and the rear wheel is plumb.... These are resulting measurments determined by the components working in combination.

The above measurements are the result of numerous complicated systems combining together, unlike a rigid framed bike where there's no isolastic tubes, cradle symmetry, or headsteady alignment to factor in to a final result. With a norton, your result could be alignment, but you could have complimentary misaligned components like twisted isolastic tubes in one direction and an offset in your swingarm that corrects the alignment somewhat in the opposite direction, so the final results that indicate good wheel alignment may not actually mean your components are all perfect... I think that's why the ken augustine method is pretty definitive. It measures each component rather than their combined result.

BUT, I wonder if checking how close the final resulting alignment, without knowing how good each component measures is good enough for a streetbike. Does it matter if the frame is twisted slightly and the swingarm is twisted oppositely to create nearly perfect alignment? would it show up as poor handling on a street bike? or not be noticed at all?? I wonder.. opinions??

I don't have any experience with other Commandos, and don't really know just how straight my own is, so cannot offer an opinion about how bad it can be without upset.
But I'm quite certain that the Ken Augustine piece (mostly written by Stevan Thomas in 1998) is just plain wrong when it says:
Measure in from each side plate to determine where the center is, and mark the spot on the top of the swing arm. If your frame is not bent, this should be exactly on the center line of the motorcycle.
Looks to me that if you marked this "center" mentioned above and then made another mark 1/8 or 3/16" to the right, the second mark is the center of the frame, the place that should show the center of the wheel, and the place from which you cd measure and mark the rear axle adjuster plates. That's what I'm gonna do now. Off again with the wheel, fender, swingarm, etc.!

Thanks, L.A.B., for posting the Vernon Fueston article, and your comments. Very helpful, as usual!

PS How do I keep my photos from showing up sideways? The ones one my computer that I dragged over are all right-side up...

Measuring in from the side plates (gussets) does give you the center of the frame, just not the center of the swingarm or cradle.

I agree those side plates (gussets) wd show the frame center.

His fuller statement is:
Now, accurately mark the true center of the swing arm. Install the cradle/swing arm assembly in the frame with the PTFE washer clearance set to zero. Measure in from each side plate to determine where the center is, and mark the spot on the top of the swing arm. If your frame is not bent, this should be exactly on the center line of the motorcycle.

I assumed he was referring to the side plate of the cradle, since the gussets are more than 12" away from the swingarm. Maybe having the frame exactly level, he then dropped a plumb bob from the middle of the gussets to mark the SA? That wd work, yes.

If what we are seeking is the center of the frame, then it seems to me one would need to measure from the gussets of the frame regardless of where the cradle is. If the frame is straight and the cradle is in the correct position then the center of the frame will NOT be the center of the cradle.

The gussets I am referring to are the ones where the Z-plates bolt. They are just outboard of the cradle.

The gussets I am referring to are the ones where the Z-plates bolt. They are just outboard of the cradle.

NOW I see which side plates we are talking about.
I hereby retract my earlier claim of incorrectness in the Augustine/Thomas article, and hang my head in ignorance. :roll:
Thanks for staying with me, rvich.

I am very interested in this thread since I just got a recently purchased '74 850 running. On my android the lines from the article being refered to show up very bright light yellow. Almost invisible. I can just make out what is written, but only at full magnification and only very slowly. Not even sure I got it right. Maybe it's a setting on my end, but don't know what that setting would be. Just black print with quotes would be great.

Joe Schlaberdowski said:

I am very interested in this thread since I just got a recently purchased '74 850 running. On my android the lines from the article being refered to show up very bright light yellow. Almost invisible. I can just make out what is written, but only at full magnification and only very slowly. Not even sure I got it right. Maybe it's a setting on my end, but don't know what that setting would be. Just black print with quotes would be great.

Click to expand...

For posts like Mr. Ricks, I have to hit the "Switch to full style" button on the bottom of the page to get my Android Chrome browser out of mobile mode. Then, I hit the "Switch to Mobile style" link at the center under the posts to get back after I am done.

Thanks Gortnipper. That worked.

Just to ask, were the wheels rebuilt? It might be possible that some of the issues with front to rear alignment is due to incorrect spoke tension (note, I didn't read the entire thread in detail, but just in case this is a relevant point!)

I established that my frame was bent (paralellogramed I call it) I installed the headstock bearings and a steel bar 25mm diameter with a sharp point turned on it. With the frame upright I fitted two 1/2" rods through the front and rear iso lugs. I fitted two collars on these rods exactly in the centre of the two lugs, measured with a vernier calliper. You need to drop the rear centre point down to about 4 inches below the rear rod. A 3ft steel rule lined up with the two centre points should also line up with the point on your steering head pointer. My original frame was about 5/16" out. I purchased a new old stock frame from a friend and repeated the test. The pointer lined up perfectly. On that basis I think the frames were accurately manufactured. I also think the swinging arm was accurately manufactured. The accuracy of your basic frame needs to be established first. Then and only then can you progress on to the accuracy of the bits that are fitted to it. Cradle, head steady, swinging arm, and wheels can each have their own inaccuracies. Over forty years of swapping isolastic fittings for more modern ones and having wheels rebuilt by people with no knowledge of Commando geometry I'm surprised there are not more "bent" Commandos about.