Frame Alignment Checking

[AshimotoK0]

Anyone reading my CB250RSA project resto will see that the bike has one fork stanchion quite badly distorted. I need to quiz the PO in the pub I go to to ask about the history but whatever, I need to check the frame alignment. MCID on here had put me onto an old school bike shop that does realignment but I would like to do some initial checks myself. I was thinking of clamping the frame to a solid bed with a long precision bar mounted through the swinging arm mount tube ( or a bar with cones on it) and adjust the frame position until it is clamped with the bar dead horizontal. (I have a digital inclinometer with dual lasers & accurate to 0.1 degree to set this up). Then mount another bar  with suitable adapters in the headstock tube and check that the bar is at 90 degrees to the horizontal bar in the swinging arm tube. If this measurement is out then worth the 200 mile trip to get it checked out/ realigned. Also been offered another frame with V5 but who is to know if it too is bent? Anyone on here done any DIY frame alignment measurements or can offer any further advice?
The PO (owned from new) did have a donor bike so there is a chance he swapped the stanchions from the donor. I think I will assume that the bottom yoke/ head bearings may be suspect, so I will replace.

[sye]

How about the straight edge method on the rear wheel? If that's not right then chances are the frame is twisted.

[Lobo]

Intriguing Ash, will be interested to know your findings; wondering what Hondas jig tolerances would have been back in the early 80s?

Your post does not mention verifying the castor angle in spec; nor checking any lateral offset of the headstock tube - both possibly affected by a front end collision?

Edit - I’ve now seen your post elsewhere wrt this checking, and suspect you’re well ahead of my observations! Forgive me.

[taysidedragon]

Ash, when checking the frame you might as well check the rear swingarm for alignment as well.

[AshimotoK0]

Sye ..  bike is totally stripped otherwise I would have tried the twin-string method 1st. Will also check out swinging arm of course. Wheels not a problem as got replacements anyway.

[Bryanj]

I once read an article that said if a fork tube took enough of a hit to bend then the frame was stressed and probably bent.
The 750 book used to have the measurements for frame checking but never seen it for other models.
You idea with swing arm bar and headstock pointer(long threaded car with cones instead of races) will work for 95% and will only fail if the forks have bent the frame straight back which rarely happens.
Long ago i did an insurance job on a cx500 which when finished i had to slide the forks through the yokes by 1 inch to get the bike to stand on centre stand with a wheel off the ground. Wheels were perfectly in line and handling perfect, there was heavy front damage including both tubes, bottom yoke, one slider and wheel which with cosmetics made the bike very close to a write off.

[Laverda Dave]

This is how the rat bike frame was checked at Hybrid motorcycles recently. Long bar with a pointer through the headstock. I had to fit the swing arm, rear shocks and slave crankcase prior to taking it to Hybrid. Frame was 100% in alignment, the first frame I have ever taken to be checked that was not out of alignment.

[AshimotoK0]

This is how the rat bike frame was checked at Hybrid motorcycles recently. Long bar with a pointer through the headstock. I had to fit the swing arm, rear shocks and slave crankcase prior to taking it to Hybrid. Frame was 100% in alignment, the first frame I have ever taken to be checked that was not out of alignment.

Dave .. can you explain how that works please. What reference do they do to the rear wheel and how do they align the rear wheel? without the front end fitted?

[andy120t]

I had my RD350LC checked after a crash years ago. The technique was the same - front end off but engine / swing arm and rear wheel etc in.

Would all dereference be taken from the back of the frame/ cranckcases....assuming they held it all square?

This isn't the company I used, but talks about the reference/alignment from swing arm pivot and headstock.

https://hbmotorcycles.co.uk/products-and-services/frame-alignment/

[AshimotoK0]

Question for Dave .. but not sent  by p.m./email  in case of interest to others.

I am making a jig and the front bit is a long length of perfectly straight 16mm ground bar I borrowed from work mounted in two conical collets that pass through the head bearings. Question though is how was the rear wheel centralised in the jig at the place that checked your 400F frame?  .. did they just use the scribed line markings on the swinging arm? Also, is it best to have the tyre off the rear wheel?

[Laverda Dave]

I'm not sure how he centralised the rear wheel Ash. However, he did phone me when he was doing it to ask if I had given him all the correct spacers. Although it was the rat bike frame I was having tested I fitted the rear wheel including the brake plate and sprocket from my other yellow 400/4 (the one in my avatar). I did this because the rat bike rear wheel has a wider rim (now cut off the hub as it was much too close to the inside of the swing arn). The tyre was on the wheel but this wasn't a problem.
The engine was bolted into the frame at the back, top and bottom and at the front on the upper engine mounts. There were no mounting bolts fitted in the lower front mounting as I didn't have any and he said it wasn't a problem as the engine was held in three other places. The engine I used consisted of an old pair of upper and lower crankcases, this was all he needed.
I know from the photos he sent me he was using spirit levels and an angle gauge. He did comment the head angle was quite steep but that was because the 400 was designed as an easy bike to ride.
This was the first frame I have had checked that didn't need tweaking despite it being in a front end prang.
I thought it may have been previously repaired but he said there were no signs whatsoever of any repairs as it was still original frame paint and no sign of any cracking or twisting.

[AshimotoK0]

Had an email from someone I greatly respect, suggesting that whilst the index marks on the sides of the swing arm were useful, the only accurate way to get the rear wheel aligned correctly is to set the distance from the centre of the swing arm pivot to the centre of the rear axle to be the same on both sides of the bike. So that's probably what I will do to start with .... it will also give me a good gauge of the accuracy of the markings on my particular swinging arm.

The swinging arm on this 250RS model  is evidently notorious for rotting out   ... but not on this one.. the PO worked in the paint shop at BAe Systems aircraft factory in Brough near me. I found he had coated some parts in a really thick layer of yellow chromate primer as used on aircraft. The black paint fell off with  'Paramose' 'proper' paint stripper but hardly touched the yellow primer.

[Bryanj]

I seem to remember the marks comment in the old handbooks, distance between marks is same each side but marks are not necessarily aligned side to side, i also remember that i never saw one that wasnt accurate, one of those just in case there is a rare one warnings