Strange Frame
- Thread starter olChris
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Olchris
Hi,Greetings from Sydney,
Have following this thread with interest,the best bloke here (Laurie Aldterton) wants the engine/gearbox/swingarm /rearwheel all bolted in with nothing else on the frame,before he starts the straightening of any frame.
So I hope it all goes well for you.
If you need a battery carrier I have one surplus to requirements.
Brett
Hi,Greetings from Sydney,
Have following this thread with interest,the best bloke here (Laurie Aldterton) wants the engine/gearbox/swingarm /rearwheel all bolted in with nothing else on the frame,before he starts the straightening of any frame.
So I hope it all goes well for you.
If you need a battery carrier I have one surplus to requirements.
Brett
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Rosey said:
I can understand that Brett.. There is a lot of flex in the frame without being "ridgidlly" secured... I have never done a bike frame before so im certainly got SFA experience with them. But i know now, that they have virtually no resistance with the method i used and are obviously not meant to be "stressed" sideways... When observing the frame from the side the frame strength is considerably more in the fore and aft direction (from impact damage)... And is basically a pipe "cradling" a motor and gearbox.. (i visualise two tribesman each at ends of a long timber pole carrying their prey) Same principle Low COGravity..
IMO after some thought........Having engine and rigidity fixed when straightening would not allow for dimentional checking of all mounting points.. So maybe when engine, cradle,g/box is removed the frame for whatever reason it will flex/spring and refittment of mechanicals may be difficult. ??????????
Thank for the offer of the battery tray..
Edit,, unless you can/want to stress relieve the frame with heat......... Which is another debate..
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Check out this while your there , jpn-750-commando-t14854-30.html in for a penny , in for a pound .
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olChris said:
Hi olChris,
The checking method you've used and advocated by Gripper, is not accurate enough, as Gripper well knows judging by the weaving problems he's reported on the NOC forum. Although he wont admit it's the frame, more like too much weight on the front, too much weight on the rear, baggy clothing, rider induced and the last excuse was chain pull. He's fitted rod-end head steady, adjustable iso's, steering damper and Lansdowne fork dampers and still the bike weaves.....in a straight line. That he's experiencing problems with a new, unused frame indicates they weren't accurate enough when they left the factory.
Bending the steering head would appear to have improved things, but you need to check it on a surface table as per "Worlds Straightest Commando". Getting the steering axis square to the iso mountings is the first step. You also need to check that the swingarm spindle is square in two planes to the steering axis also. This is essential, if out, then as the rear suspension moves the rear wheel centre line will move in relation to the frame centre line plane and cause handling problems similar to worn swingarm bearings.
You need to find a friendly machine shop with a surface table. I doubt if a shop with a straightening jig will be accurate enough, ask them what tolerances they work to, even though they wont beat the surface table for accuracy. I'll guarantee if you assemble as is you'll have handling problems, ask Gripper.
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Today i thought i would fit the cradle including swingarm, g/box and motor to assure me the frame is plum and does not required any excessive force to fit, so far so good.
This is being done to check the swing arm axis and symentry to the head tube.........
Fitted the new RGM Iso bushes to rear, no problem then proceed to do same for front......... Thats a lotta extra rubber to squeeze in a hole by hand..
. So here in is the question is that correct ???. as i cant be sure the ISo bracket is ridgydigge for the 72, did they manufacture iso support brackets with different tube size????
EDIT .. ave since found this....... fit-rgm-iso-rubbers-t14240-15.html?hilit=rgm%20front%20iso ... So common problem.........
Today i thought i would fit the cradle including swingarm, g/box and motor to assure me the frame is plum and does not required any excessive force to fit, so far so good.
This is being done to check the swing arm axis and symentry to the head tube.........
Fitted the new RGM Iso bushes to rear, no problem then proceed to do same for front......... Thats a lotta extra rubber to squeeze in a hole by hand..
. So here in is the question is that correct ???. as i cant be sure the ISo bracket is ridgydigge for the 72, did they manufacture iso support brackets with different tube size????
EDIT .. ave since found this....... fit-rgm-iso-rubbers-t14240-15.html?hilit=rgm%20front%20iso ... So common problem.........
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...Al-otment said:
Within a few Thou !!!!!!!!! Is that on a hot day or cold day??
Considering the engine, gbox, rear swing arm are all mounted on "rubber" of dubious heritage, the presumtion that maintaining front and rear wheel alignment "within a few thou's" at any given moment of the day is .......... difficult/maybe impossible ........ Not to mention maintaining alignment under vigorous riding conditions...
We are talking "a few thousandths" as you say within this discussion, not a few millimeters... I will get this frame and appendages to within 0.5 millimeter (cos i can still read that on a tape).. So far its within that, tho havn't checked swingarm yet.... dealing with front ISO atm......
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olChris said:
Chris,
For your wheels give Budgie a call at Spoked Wheel Services in Bayswater. There is not much about wheel building that he does not know. Will build wheels to whatever you want. Also Murray at Cyclecraft is a wealth of Knowledge and happy to pass it along. Very talented, does custom work all the time or straight up rebuilds.
Tim
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olChris said:
Dosen't matter if it's cold or hot as the whole assembly will be subject to the same temperature so you get uniform expansion. A 40 deg C change in temp will have next to no effect on steel anyway. The rubber only allows movement in the vertical plane which has no effect on rear wheel to frame centre line alignment. All frames will flex in use dependent on loads but starting off with a misaligned assembly guarantees problems. You've misunderstood, I didn't state wheel alignment to within a few thou, I was referring to alignment of axes.
As I said before, you want the swingarm axis square in two planes to the steering head axis. On the surface table it's not too difficult to get alignment to within 0.001". 0.020" is way too much and will cause problems. Misalignment between the above axes is multiplied at the rear wheel, where you'll get varying degrees of misalignment between rear wheel centre line and frame centre line plane as the suspension moves.
Have it your own way, you'll be able to have endless discussions with Gripper as to why your bikes wobble down the motorway and round the corners. Have a read of http://vintagenet.us/phantom/wsc.html" and tell me where the author's gone wrong.
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I've read that article multiple times and keep coming back to the issue of manufacturing tolerances and whether they really can effect handling. The reason is that most people don't have access to the equipment used to straighten the frame like they did. Can we all get perfection? Is it necessary?
Some measurements can be made and it's prudent to do them when rebuilding a bike to insure that frame is not damaged, but beyond that what can we really do?
The comments on "The Bare Minimum" make sense and then insuring that the iso's are in good shape (new) along with an aftermarket head steady (Dave Taylor) and proper adjustment seems to be the best approach.
I will be doing new iso's and head steady on my MKIII over the winter, and plan to do as much measurement as I can so maybe my opinon will change once I get into it.
Some measurements can be made and it's prudent to do them when rebuilding a bike to insure that frame is not damaged, but beyond that what can we really do?
The comments on "The Bare Minimum" make sense and then insuring that the iso's are in good shape (new) along with an aftermarket head steady (Dave Taylor) and proper adjustment seems to be the best approach.
I will be doing new iso's and head steady on my MKIII over the winter, and plan to do as much measurement as I can so maybe my opinon will change once I get into it.
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dennisgb said:
With the swing arm axis square (at right angles) to the steering head axis in two planes (plan and front view if you like) at 90 deg to each other then as the swingarm pivots, the rear wheel, viewed from the rear, will move in a vertical plane parallel to the frame centre line plane. The alignment will remain constant as it moves up and down.
When the axes are not square then as the swingarm pivots the degree of alignment changes because the rear wheel is not moving in a vertical plane but an arc, viewed from the rear. Therefore rear wheel to frame centre line alignment is constantly changing as the suspension absorbs bumps and the swing arm moves up and down. This is what causes the weaves on Commando's and any bike where these axes are not square. Commando's are more sensitive to this misalignment than other bikes because of the isolastic assembly but it is NOT the iso's which cause the problem - it's the relationship between the steering and swing arm axis.
I don't know what Norton manufacturing tolerances were, regarding the chassis, but whatever they were they weren't adequate. What I do know is after I'd squared front and rear iso brackets to the steering axis, followed by the swingarm axis and then marked a frame centre line reference on the swingarm, the rear wheel centre line was nearly 1/4" off the frame centre line. I ended up moving the whole iso assembly - engine, gearbox, cradle, front iso etc - approx 1/4" across to the right side of the bike (timing side) to achieve rear wheel centre line to frame centre line alignment. The rear wheel now sits central to the frame seat loop, also there's now clearance between the chainguard and drive side Koni shock.
In this case 'perfection' is 90 degrees and is only necessary if you don't want your bike weaving and wobbling on the straight and around corners.
dennisgb said:
The iso's only effect handling if the clearances are too big. All the rubbers do is absorb engine vibrations - they have no affect on handling whatsoever.
Prior to alignment front and rear iso mounts were out of parallel to each other in front and plan views. Obviously neither were square to the steering head axis. Prior to alignment the bike would get out of control through bends when hitting bumps. Post alignment there are no problems. I'm not making this up. All Commando's should handle without problems, but the frames need to be checked and precisely aligned.
Only chassis mods on my bike is an iso head steady and fork top bush and damper tube mod. Getting your bikes frame aligned is essential if you want it to handle. The popular chassis mods e.g Dave Taylor head steady, are addressing the symptoms not the cause.
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Al-otment,
You make very good points. So essentially all the mods and new iso's are good but if the frame is off it makes no difference. I will try to figure out a way to do the measurements, but in the article they machined the surfaces to get them true. This requires a pretty large mill that can handle the frame. Most of us do not have access to this equipment...so what do we do?
I'm curious about you moving the engine 1/4". What is the relationship to this measurement and the built in offset in the swing arm and rear wheel that is well documented?
Dennis
You make very good points. So essentially all the mods and new iso's are good but if the frame is off it makes no difference. I will try to figure out a way to do the measurements, but in the article they machined the surfaces to get them true. This requires a pretty large mill that can handle the frame. Most of us do not have access to this equipment...so what do we do?
I'm curious about you moving the engine 1/4". What is the relationship to this measurement and the built in offset in the swing arm and rear wheel that is well documented?
Dennis
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dennisgb said:
Dennis,
Find yourself a sympathetic machine shop with an engineer who understands the problem and a surface table. After reading "WSC" I spent a while trying to figure out an alternative method and concluded there isn't one. You need fixed horizontal and vertical datum. So I bought the necessary tools inc. a granite surface table. I don't use a mill to re-cut the holes - I've worked out another method.
dennisgb said:
I didn't measure any relationships between offsets, don't worry about them. The frame centre line was established as per "WSC". I only ended up moving the whole assembly across (inc. swingarm and rear wheel assembly) as I figured it was too much to pull the rim across by adjusting the spokes. Due to Norton's manufacturing methods I reckon no two frames are the same and you have to do what is required per frame. Unfortunately there are no definitive dimensions - you just need to do what is necessary to achieve square axes and centre line alignment.
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Al-otment,
I do have a number of people who have the right equipment, but set-up could be complicated. The question is how much to spend. I do plan to put a mill in my shop but not anything big enough to handle the Norton. Maybe when I tear into it I will figure out that a little bigger machine could be of value...but those are slippery slopes...things seem to get bigger and better and start to break the bank.
Have you ever wondered how they fabricated the frames at Norton in the first place? You have to believe they had fixtures during welding that placed the parts in the right place...maybe they took them out of the fixtures and they changed shape...but if that was the case they should have been checked and fixed...maybe the specs were just to wide and they didn't know it.
I do have a number of people who have the right equipment, but set-up could be complicated. The question is how much to spend. I do plan to put a mill in my shop but not anything big enough to handle the Norton. Maybe when I tear into it I will figure out that a little bigger machine could be of value...but those are slippery slopes...things seem to get bigger and better and start to break the bank.
Have you ever wondered how they fabricated the frames at Norton in the first place? You have to believe they had fixtures during welding that placed the parts in the right place...maybe they took them out of the fixtures and they changed shape...but if that was the case they should have been checked and fixed...maybe the specs were just to wide and they didn't know it.
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Thanks L.A.B,
I find the historical stuff very interesting. The methods and sources. Find myself running all over the web trying to find info on the how's and why's.
Technically the methods represented the times and the history of development. Mistakes that were made, were really not mistakes at all, but more of how things were done and in some cases had always been done which is part of the problem. We can look at it from knowledge that really wasn't available or the norm back then. We find ourselves trying to correct it all after the fact, but it still helps to understand.
Dennis
I find the historical stuff very interesting. The methods and sources. Find myself running all over the web trying to find info on the how's and why's.
Technically the methods represented the times and the history of development. Mistakes that were made, were really not mistakes at all, but more of how things were done and in some cases had always been done which is part of the problem. We can look at it from knowledge that really wasn't available or the norm back then. We find ourselves trying to correct it all after the fact, but it still helps to understand.
Dennis
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The LUGs for the ISO bolts , if you throw meter or four foot STRAIGTH ! steel rods through them . will show squarness laterally & vetically ,
Should be dead parrallel viewed head on . Measure between ends & do check for squareness in plan and laterally . The laser & or string line
and a BIG builders square being handy here .
Like I said , easyest datum is from rear cross brace , as its least likely to have been deranged , so a good base to establish datums to measure from ,
frame inverted ( on bench ? )
THE PROBLEM is its NOT " rubber Mounted " . Its mounted in vertically displaceble locators . THESE have to be Dead Square * parrallel etc , so as to
Not Bind , grind and jam . thus the alignment here is paramount . Laterally there should be EQUAL clearance Each Side at the Front , with the rear just
locked ( overshimmed ) . If the faces arnt parrallel , the things wedge the gap - so is all to cack .
Setting it all up parrallel is a start to getting the Iso's doing what theyre designed to - HOLD THE DRIVE TRAIN IN ALIGNMENT . Theres a thing .
Something a bit fancyer for a top steady stops longitudeinal rotation and jamming , or as suggested - a Iso under the cradle is likely better .
Iso Bolt Holes should align for free installation of bolts , unimpeded and unforced . The rubber supports the drive train in the longitudeinal / vertical
plane ONLY . the thrust washers control lateral location . I prefer 0.0025 to 0.0045 Max . More induceing wander , on irregular surfaces .
Idealy Id keep it under 0.004. at 0.002 it starts to bind . Locked up theyre bone shakers & likely frame breakers .
if you can bludge a wideline featherbed , its a easy install & well worthwhile . Un Isoed . rebalaced flywheel .
Should be dead parrallel viewed head on . Measure between ends & do check for squareness in plan and laterally . The laser & or string line
and a BIG builders square being handy here .
Like I said , easyest datum is from rear cross brace , as its least likely to have been deranged , so a good base to establish datums to measure from ,
frame inverted ( on bench ? )
THE PROBLEM is its NOT " rubber Mounted " . Its mounted in vertically displaceble locators . THESE have to be Dead Square * parrallel etc , so as to
Not Bind , grind and jam . thus the alignment here is paramount . Laterally there should be EQUAL clearance Each Side at the Front , with the rear just
locked ( overshimmed ) . If the faces arnt parrallel , the things wedge the gap - so is all to cack .
Setting it all up parrallel is a start to getting the Iso's doing what theyre designed to - HOLD THE DRIVE TRAIN IN ALIGNMENT . Theres a thing .
Something a bit fancyer for a top steady stops longitudeinal rotation and jamming , or as suggested - a Iso under the cradle is likely better .
Iso Bolt Holes should align for free installation of bolts , unimpeded and unforced . The rubber supports the drive train in the longitudeinal / vertical
plane ONLY . the thrust washers control lateral location . I prefer 0.0025 to 0.0045 Max . More induceing wander , on irregular surfaces .
Idealy Id keep it under 0.004. at 0.002 it starts to bind . Locked up theyre bone shakers & likely frame breakers .
if you can bludge a wideline featherbed , its a easy install & well worthwhile . Un Isoed . rebalaced flywheel .
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Wow, arent them RGM front Iso's a PITA to fit.. Nevertheless is a nice firm front support.. Eventually once fitted to engine and frame all bolts were a "Hand" fit.. minimal efffort was required to fit engine and transmission, although untentioned at this point..
Once bolted losely i checked the swing arm for alingment to my datum point and found it to be within 2 mm thu is full arc movement, so was happy with that .. Then checked its horizontal (90Deg) to head tube/datum point.. bugger tis up to 4mm out ... Meaning one side of the trailing arm on the swing arm is 4 mm higher/lower that the other...
So it need to be removed and assessed in its own right for squareness... By eye it looks good, so hoping the misalignment is in the spindle bushing.?? .
I asked the question elsewhere about removing the spindle shaft.. It seem frozen in there, all retainers removed but and wont budge (yet) any advice??
Once bolted losely i checked the swing arm for alingment to my datum point and found it to be within 2 mm thu is full arc movement, so was happy with that .. Then checked its horizontal (90Deg) to head tube/datum point..
bugger tis up to 4mm out ... Meaning one side of the trailing arm on the swing arm is 4 mm higher/lower that the other...So it need to be removed and assessed in its own right for squareness... By eye it looks good, so hoping the misalignment is in the spindle bushing.??
. I asked the question elsewhere about removing the spindle shaft.. It seem frozen in there, all retainers removed but and wont budge (yet) any advice??
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