With Robb Nortier's designed rear frame gauge and a straight edge, it is quite simple to check the frame alignment. This one was about 1/4" out. I was surprised how easy it was to bend the rear frame section with the use of my bench vice and a big bar. Ron

email (option): ronpier@talk21.com

It took me quite a few restoration jobs before I realized that checking out frame alignment could be a good idea. Makes quite a difference when a bike has front and rear wheels in one line.

Henk

email (option): ahum@quicknet.nl

If they're so easy to twist, doesn't the first pothole put them back out again ?

Is it a question of low-tensile tubing ?

I did wonder that myself Rik. However, these M20 frames are immensely heavy. Does make you wonder how they twist?

Ron

email (option): ronpier@talk21.com

Probably sidecars and loose fasteners. I'd hope that they're resistant to twisting when bolted up solid. Is it something that you find on various makes, Ron ?

My Norton frame was straight although the forks had taken a knock and had quite a twist but it didn't need straight edges to see that.

I ran a sidecar on my ZM20 rigid for a few years when throwing the outfit into a right turning you could hear the rear chain go out of line and feel the rear frame flex, when I eventually stripped bike for a total rebuild the frame was perfectly inline.I think these frames are damaged when they are stripped of all other parts and thrown around.I had one shot blasted a few years back and when I went to pick it up found the guy had bent the rear section out of shape...Dave

So far, the only other bent frames I've had were my Ariel W/NG and my mates WD/CO and the tank tube on my WD/L. I've never checked my every day WM20 so I ride it in obliviousness. Ron

email (option): ronpier@talk21.com

I hope you tried it with the box section pole around 180 degrees in case it was that that was bent

email (option): horror@blueyonder.co.uk

ron is that a worn hole in the cross piece

email (option): roger.beck@node6.com

Teaching Granny Dave? Yes I put the channel both sides and also turned it through 90 degrees several times to check any warp in it.
I have re-enacted this shot to show how easy it was to tweak the frame with a big crow bar in an upward direction. It's all a bit guesswork and I overdid it on the first go, so had to go back in the other direction. Just about spot on now till the first pot hole maybe Ron

PS Roger, I think the bit you are referring too, is just where I have sanded some paint off the top cross piece.

email (option): ronpier@talk21.com

Sorry Grandma
On my 16H frame there was no use in taking any measurements as there's no engine cradle. The tubes were all over the place and could be "altered" very easiy. But when the engine and rear wheel went in it pulled it into shape. Everything seemed to fit with very little clearance each side, so I guess it's in line

email (option): horror@blueyonder.co.uk

Hi Ron
how did you determine which side was out

email (option): markbrob1@hotmail.com

In all honesty Dave. When you're bumping up some country lane and the arse end is leaping about. You are not thinking "I'm very glad my frame is dead straight" You are just happy that the back wheel is sort of following the front wheel

Ron

email (option): ronpier@talk21.com

Hi All
The back wheel never followed the front when I had an M20! But that was cos it was trying to pull a double adult sidecar around. But seriously it was scary, the outfit had a mind of its own.

Yes, if it was a Fireblade you might have a problem with the frame out a bit, but I think you'll get away with it on a rigid side valve

email (option): horror@blueyonder.co.uk

Sorry Mark I missed your post. The tool that is bolted where the wheel spindle goes has a centre line scribed on it. With a straight edge clamped at the front down tube and saddle tube as in my first picture, you measure to the scribed line. Repeat on the opposite side. If the frame is straight, the measurements should be the same. Otherwise trial and error tweaking till it's correct. Ron

email (option): ronpier@talk21.com

I had 3 M20s all at the same time a while back and they all handled quite differently due to variations in the wear of the forks and probably, frame alignment...My 'main' M20 has always had fairly 'neutral' handling..The other two had a tendency to go better into a corner in one direction than the other but you soon got used to it...
A frequent 'giveaway' for a bent frame is apparent when fitting the back wheel...If the frame has to be tweeked to get the wheel in, or conversely, it is too wide and is pulled in by tightening the wheel nuts it's more than likely bent...Ian

email (option): ian@wright52.plus.com

Just one thing here, I noticed that axle gauge has a "centre line" in the wheel spindle gap, I'm under the impression the rear forks aren't supposed to be an even distance from a centre line on these frames ... does that gauge go only one way round to take that into account ?




Another thing I've noticed when straightening these frames, the rear sections often got bent with a wheel in place, that often means the axle plates may have got bent slightly at the same time, so its important after straightening to then fix the wheel in & check alignment again after tightening it as bent axle plates will easily pull the rear section back out of line.

Yes Fred. The gauge has a nick out one side to clear the snail cam pimple. Ron

email (option): ronpier@talk21.com

I see, I read the thread & was concerned that it may be assumed by some that the fork ends were equal,
....as mentioned in a previous thread, later front girder forks also have been incorrectly straightened to be equal which causes problems.
But it would still be possible to have a cut out for the snail cam & be marked central rather that offset so just wondered if it followed the same offset as the drawing.

I never checked my frame. Just made sure the front wheel was right in the middle of the front fork legs and that the rear rim was in line with the front rim.
I can drive my m20 without holding the handlebars, so it should be OK.

I like using string lines & spirit level, I hang a plumline in front of the headstock to not be leaning to one side or other then check engine plates are all vertical, then check the front & rear wheels are exactly vertical then finally check wheels are inline with each other & inline with engine/gearbox plates & headstock by using string lines.

Well Micheal. The dilemma is that the front wheel should not be in the middle of the forks. As discussed in a previous thread. The forks are splayed out on the left to accommodate the speedo drive.
Hopefully Robb Nortier will not mind me posting his drawing of the rear guage here. Ron

email (option): ronpier@talk21.com

email (option): viaconsu [at] planet [dot] nl

Ron, I shouldn't have doubted the gauges design should I :D

Hans, middle of the tyre needs to be inline with the top mudguard mount & top rail grease nipple, then its neither here nor there if they have a splayed left leg or not.
The wheel & headstock inline with each other is what your aiming at, BSA pulled the left leg out to fit a speedo drive.

my father towed a 1930s hillman minx convertable with his sunbeam lion 9 with sidecar fitted up a steep hill do you think he should have check the frame alignment afterwards( and i scrapped the bike in the late sixties boo hoo)

email (option): roger.beck@node6.com

My 'modern' bike is a Commando. In comparison with those, any bike that doesn't have a rubber hinge in the middle steers well !

Hans if your front wheel offset measurements comply with those in the standards book and you have the correct cone spacer on the brake plate side and with the speedo and those two thick washers and nut on the opposite side. Your wheel should be nearer the right fork leg than the left. It's taken me a while to get my head round it, but this will put the wheel in the middle of the frame. Ron

email (option): ronpier@talk21.com