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Frame repair.
Posted: Wed Feb 28, 2018 7:25 pm
by SteveD
I scored a car load of parts recently. The frame was part of it. The seller said he was unable to guarantee it's straightness before the deal was struck.
The ruler is at the lower edge of the right headstock gusset. The deflection can be seen as the reflection of the ruler diverges.
The R upper edge & the left upper & lower edges are straight.
The frame is from a 1981 R100RS. It came with a matching number engine, clutch, gearbox, subframe, swingarm & shaft,wheels, carbs and a few smaller miscellaneous bits & pieces.
If a bike shop or insurance assessor was assessing this under the rules here in Victoria I believe it'd be written off.
Re: Frame repair.
Posted: Wed Feb 28, 2018 11:26 pm
by Beemerboff
Is there a specialist frame straightener in Melbourne? If there is they should be able to tell you PDQ.
Were there any papers with the bike?
Depending on the state, insurance total write off's might be listed with the rego authorities, as much to prevent rebirthing as for safety reasons.
They are in the convict settlement further round the coast
Motorcycle frames are usually made from cold drawn steel tube, so if you straighten them using heat from a oxy torch the resultant frame will be somewhere between 25/40% less rigid.
Whether this makes them unsafe is a mater for a qualified engineer, but few back yard, er, engineers, seem to bother much.
Re: Frame repair.
Posted: Wed Feb 28, 2018 11:42 pm
by robert
" if you straighten them using heat from a oxy torch the resultant frame will be somewhere between 25/40% less rigid."
Where did this information come from?
Re: Frame repair.
Posted: Thu Mar 01, 2018 5:22 am
by Beemerboff
Motorcycle Engineering , by P.E. Irving.
Published in softback by Clymer Publications in 1973 at the reasonable price of $5-and probably available today on Amazon for $600- Or $20- on Ebay.
Information on cold worked products, or anything else for that matter, is not hard to find Google, although there will always be a variety of differing opinions.
Not everyone will agree with PEI, who also wrote under the nom de plume of Slide Rule.
And designed Vincents in his spare time.
Or was it the other way round?
Re: Frame repair.
Posted: Thu Mar 01, 2018 6:17 am
by SteveD
Google shows a couple of possible straighteners but I don't really want to spend anything on it.
It was from a deceased estate in Tassie, not much info forthcoming.
There was other stuff in the deal,the frame was added.Attached to it is a subframe and the swingarm & shaft and they look fine.
Re: Frame repair.
Posted: Thu Mar 01, 2018 9:11 am
by Wobbly
We straighten classic bike frames at the shop where I work. You cannot tell anything by looking at the exterior of the frame and I urge you to stop doing so. Headpost issues are best measured by placing a long bar down through the headpost and allowing the bar to center on the bearing area using cones. The bar we use is 6 feet long and will extend to the level of the lower motor mount. (Thought I had photos, but I can't find them this AM.) Then you simply measure horizontally from the bar's lower tip to the motor mount.
Our bar is maybe 1-3/8 dia, so if we measure any misalignment we simply pull on the bar. If pulling won't work we have hydraulic and mechanical jacks we can put in place. We try to do as much of this without heat as we can, but sometimes it just can't be avoided. Rarely do we need to get things cherry red before things start moving.
Of course this is all on really rare motorcycles. Gold Stars, Norton Manx, Square Fours, and the like.
However, in your particular case, let me tell you that I'd be considering a substitute frame. BMW frames are plentiful. The tools to swap the number tags are a lot less costly than bars and jacks. And the scale of work is much more within the grasp of a home-based shop. And too... the tools you would need to buy (Dremel grinders, number stamps, files) would be tools you'd be more likely to use again and again on a weekly basis.
Just my 2 cents.
Re: Frame repair.
Posted: Thu Mar 01, 2018 7:48 pm
by Beemerboff
i think Steve already knows the law in his home state of Victoria, and that is that no repairs whatsoever are permitted to damaged motorcycle frames, no matter what the are constructed from and how they are constructed.
Presumably this is because the authorities have been advised by suitably qualified and experienced engineers that it cannot always be done safely.
Particularly if the are carried out with people with no formal training or qualifications.
And it might realistic to expect that the qualifications required are more than the possession of a six feet length of bar and a jack, which it appears is all that you consider is needed.
FWIW a bronze welded Manx Norton frame is quite different to a brazed lug Ariel Square Four and requires a completely different repair technique - Phil's book will explain it all if you get a copy, but on brazed lug frames you unbraze the lugs and insert new tubes.
And if there is any frame which shouldn't be repaired it is probably a Manx one which is bronze welded from stiff, brittle thin wall Reynolds 531 tubing, whose cold worked yield strength of 45 tons is reduced to 25 tons in a fully annealed condition and proportionally along the way.
And backyard brazing which overheats the steel might permit excessive inter-crystallne penetration which will reduce the strength even further, to dangerous levels.
Re: Frame repair.
Posted: Fri Mar 02, 2018 7:01 am
by SteveD
Thanks Wobbly & Beemerboff. The compliance plate has been removed so I'd say it's unregisterable now. I knew it wasn't guaranteed as straight, it was added because I bought the other stuff. I won't be spending any further money on it. About 10-11 years back the laws here changed. Frame straighteners went out of business overnight, including Bob Martins old business which was considered the best place to go. Frame straighteners do still exist however I have no idea what they do.maybe just racing bikes?
In the back of my mind I had hoped I might construct a bike from the bits I bought and stuff I already have. As it is, the shed is getting crowded so best not to proceed until I sort that.
Grant and me missed a $500 intact but not running 81 RT two days ago. Too slow on the phone 
It had a full staintune exhaust on it! That's $2200 to buy new these days.
Re: Frame repair.
Posted: Fri Mar 02, 2018 8:02 am
by Bill Smith
After my crash in 2003, I bought my R100RS back from the insurer and sent the frame to a shop on California that had BMW frame jigs. They straightened the steering head and bike still tracks true at 302K miles. All that said, a tweaked frame isn't the end, in my experience.
Re: Frame repair.
Posted: Sun Mar 04, 2018 8:13 pm
by Wobbly
Beemerboff wrote: ↑Thu Mar 01, 2018 7:48 pm
i think Steve already knows the law in his home state of Victoria, and that is that no repairs whatsoever are permitted to damaged motorcycle frames, no matter what the are constructed from and how they are constructed.
Presumably this is because the authorities have been advised by suitably qualified and experienced engineers that it cannot always be done safely.
Particularly if the are carried out with people with no formal training or qualifications.
And it might realistic to expect that the qualifications required are more than the possession of a six feet length of bar and a jack, which it appears is all that you consider is needed.
FWIW a bronze welded Manx Norton frame is quite different to a brazed lug Ariel Square Four and requires a completely different repair technique - Phil's book will explain it all if you get a copy, but on brazed lug frames you unbraze the lugs and insert new tubes.
And if there is any frame which shouldn't be repaired it is probably a Manx one which is bronze welded from stiff, brittle thin wall Reynolds 531 tubing, whose cold worked yield strength of 45 tons is reduced to 25 tons in a fully annealed condition and proportionally along the way.
And backyard brazing which overheats the steel might permit excessive inter-crystallne penetration which will reduce the strength even further, to dangerous levels.
Thanks, but I am a degreed mechanical engineer and the BMW frame is no Manx wonder frame. In no way did I mean to infer that this is a simple job, only that with great patience and care, miracles can be achieved.
All the best.