Date: 29-11-21  Time: 05:27 am

Author Topic: Frame measurement after a crash  (Read 514 times)

MFD

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Frame measurement after a crash
« on: 30 October 2020, 09:39:37 pm »
Evening all,

I had an accident earlier this week - came around a left hander at (I guess) 40-50mph during some heavy rain and hit a layer of mud on the road, both wheels immediately let go and the bike dropped onto the left hand side and started to slide, then something upset it (I'm guessing it hit a cats eye), and it flipped over onto the right hand side, throwing me off to slide along the right hand gutter while the bike shot off ahead, bounced off the dirt verge and came to a halt back in the left hand lane.

Luckily there was noone coming the other way at that moment, so after a few seconds sliding down the road on my back I got back up without any serious injuries (just a few bruises seemingly), but the bike didn't get off so well. The left hand fork tube is *very* bent, the fairing got bent around sideways and several mounting tabs broken off, the instrument mounting bracket bent, left hand pillion footpeg and silencer bent into the frame until it popped off, both wing mirrors disintegrated (I only found the remains of one) and various other minor scuffs/breaks.

Right after the accident someone in a Tesco's delivery van stopped to help me up and make sure I was fine, then a builder with an empty trailer stopped and offered to take me home. People *can* be nice sometimes!

So here I am with a very broken Fazer in the garage now...

I've removed most of the bodywork, fuel tank, instruments, etc so I can get a good look at the frame and hopefully confirm all the geometry is still ok before starting repairs.

Can anyone advise particular things to check/measure on the frame, correct dimensions/tolerances or methods? Any help greatly appreciated as I've never done this before.

agricola

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Re: Frame measurement after a crash
« Reply #1 on: 31 October 2020, 10:47:19 am »
Sorry to hear that, but pleased you came out of it unscathed.


Before you consider any repair work, take into account the value of the bike immediately prior to the off, look at the damage that you currently know about and cost up the likely reapirs/replacements.


It may be more cost effective to replace the it and sell off what is salvageable from the bike


Good luck with it

Gnasher

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Re: Frame measurement after a crash
« Reply #2 on: 31 October 2020, 10:55:05 am »
Not really without a jig.  That said if the bike had no frontal or rear impact it's very unlikely the frame is bent or twisted, a careful visual inspection looking for impact damage, bent tubing and cracked paint around welds especially the headstock will confirm that.  Another easy way is to undo and loosen off all the engine bolts and remove them in turn if they all come out and back in without difficulty the frame isn't twisted.

The same will apply to all the the parts bolted to the frame, if they don't line up either the part it's self is bent or twisted or the frame is, it's most likely the former. :)
Later

MFD

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Re: Frame measurement after a crash
« Reply #3 on: 31 October 2020, 03:09:15 pm »
Thanks for your inputs so far. I like the bike and want to see it back on the road rather than broken for parts, if the frame is okay the only expensive bit will be new forks anyway; I think I can save the body parts.

The paint around the headstock tube welds is flaking off... as it was when I bought the bike. At the time I attributed it to rust, but I wonder if it had a crash before I bought it, especially considering one of the forks was (slightly) bent when I rebuilt them earlier in the year. Bodywork was immaculate at the time, so a crash seemed unlikely.

I've strung a line from the shaft that runs through the yokes and headstock bearings to a crossmember with a series of holes drilled through it under the seat. To the best of my ability to measure, at that crossmember and the two above the engine, the string is perfectly centered in the frame. I'm not too confident in my measurement where it passed over the fuel tank fixing hole at the front, which appeared to be ~2mm to the right, I'm not sure if that hole necessarily *should* be centered anyway.

I've not been able to find any good articles on frame geometry, but to my thinking, I've got these possible ways the frame could be distorted by a crash:

Lateral twisting
Lateral twisting of the frame, skewing the angle the steering will rotate around to the sides, moving the wheels out of line and also altering the tyres' contact patches. Will probably make it want to wander or prefer one direction, like when the rear wheel is misaligned.

Bending to the left/right
Sideways bending of the frame, without the above latteral twisting, moving the wheels out of line but not affecting the tyres' contact patches. I don't *think* this would impact the handling much, assuming the rear wheel alignment is adjusted to compensate?

Bending up/down
Bending up/down, or the frame being squashed shorter, moving the front wheel rearwards by reducing the steering rake angle. I think this would actually give it slightly sharper/sportier turning, but otherwise not impact the handling?

Obviously any distortion to the point that a weld is damaged is dangerous. I will do DPI testing of critical/stressed welds (i.e. the ones at the headstock tube).

I bought a digital inclinometer, intending to use it to rule out lateral twisting of the frame between the swingarm mounting uprights and the centerline of the yoke shaft, but I haven't come up with a way to get a reliable reading off of the latter yet.

Does my above thinking seem correct?

Thanks all

Gnasher

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Re: Frame measurement after a crash
« Reply #4 on: 31 October 2020, 03:29:17 pm »
As mentioned in my first post, there's no real way of accurately checking or measuring the frame without spec drawings/measurement and/or a jig.  I've put back together a good few hundred FZS over the years, most that didn't involve frontal or rear impact don't twist or bend and those that have have suffered severe side impact.  The methods I outlined are what I've used, basically the engine can't twist, without it being damaged or obvious signs of damage.  If the bolts are difficult to withdraw or require force to insert the frame is bent or twisted.     

Your flaking paint around the headstock and bent forks are indications of frontal impact and the frame could well be bent.  Just having good bodywork is not an indication there's been no frontal impact as all the bodywork and the firing frame can be replaced, that's said some stearlers who do insurance work repair the bent frame and pocket the new one.  So a check of your for damage wouldn't be a bad idea and the method above for the fame also applies to the firing frame everything should line up without effort.   
Later

MFD

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Re: Frame measurement after a crash
« Reply #5 on: 08 November 2020, 02:28:15 pm »
Finally spent some more time on it today...

Dye penetrant testing of the welds around the headstock hasn't revealed any obvious cracking.

I took the crash bars off, and they don't line up with the holes in the frame, but I don't think they fitted *perfectly* when they were new over 2 years ago, and I can still get them into position by hand using the bolts as guide pins. The upper hole on both bars is too high and the bottom front hole on the left hand side is too far forward, possibly suggesting the bars have been flattened out slightly by the crash... or they were always that wonky.

If anyone else has an FZS600 with Heed crash bars they don't mind taking off and doing a few measurements for me to compare against I'd be very grateful...