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FT: Frame (Twin) Rear Frame Member alignment and repairs to achieve alignment

craig

Well Known and Active Website User
VOC Member
I have a RFM i am looking at to use in a future project and it appears to me to out of alignment in a horizontal plane.
Leveling the 2 rear axle slots and putting a 3ft rule thru the pivot bores seems to show misaligned horizontal.

Is there an established procedure for checking RFM and UFM alignment?
And options on repair of either?

I am not looking for pontification on the safety of repairing vintage bike parts please
Thank you
Craig

I am trying to best to fully understand the instructions for crash damage in Paul Richardson's book page 40.
I have edited this page 40 text for my clarity.
My"twist" appears to me to be 7.0mm/ft

Crash Damage
Slight lateral bending can sometimes be corrected by heating the tubes adjacent to the lugs and re-setting each fork end individually.
Mandrils inserted through the pivot bearing and the rear-axle slots should be parallel, and the maximum permissible twist is 3/32 in. (2.38 mm.) per foot of mandril.

The inner fork-end faces should be parallel, 8.3/8 in. (21.27 mm.) apart;
the right-hand face (purple) is 9/16 in. 04.28 mm.) outside the face of the pivot-bearing lug,
the left-hand side face is 1.1/4 in. (31.75 mm.) outside the left-hand face of the pivot bearing lug.

The apex lug (yellow) is central to the fork ends, and the ears of the seat-stay lugs should also be parallel.

mo22croprfm3-jpg.38946

Is there a how to article on replacing the fork ends on an RFM?
Can you unbraze a fork end by heating it and pulling it off?
Are there dimensional drawings of the RFM that can more accurately describe the dimensions?
Top view?
Side view?
Pictures of disassembled RFM?
Depth of bore, engagement joint of brazed joints?
Tubing dimensions? Suppliers of tubing?
 
Last edited:

oexing

Well Known and Active Website User
VOC Member
Thanks, Glen, just a few minutes ago I looked at what I got after a lot of bending - not sideways - and quite rightly there is substantial offset I did not notice. Or better say I left them as they were in this respect. Have not yet decided what rear hub I´ll come up so still scope for anything that might turn up to get sprockets aligned.

Vic
 

Bill Thomas

Well Known and Active Website User
VOC Member
I think I put the offset on here for one of our friends, Maybe "Oldhaven" ?,
I have one bad eye and looking at it on the piss, drove me nuts !,
Lucky I had another Frame in bits to compare,
As Davidd said , How did I now the spare one was right ??.
All my Bikes ride fine, I have road raced them all !.
With out taking the bolts out and poping the top tubes out,
I think it would be very hard to get it right ?.
 
Last edited:

oexing

Well Known and Active Website User
VOC Member
Hmm, I think I´ll have to deal with what I find when rear frame is set and no more bending planned - which I´d try to avoid at this stage. The sprockets have to be right foremost so possibly some mods on wheel bearings resp. spacers may be the consequence. To get the rims centralized you can do a lot of offset by spoke tensions - which would be the final job.

Vic
 

clevtrev

Well Known and Active Website User
VOC Member
I think Clev Trev, Who knows a LOT !!,
Said the twin rear chain does NOT line up spot on ??.
Talk to us Trev .
The rear sprocket is 3/16" outboard of the final drive sprocket. I won`t say they all are, but the 5 out of the 5 I measured were. Then you have to consider the ernormous number of things that could cause that.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Thanks Trev, I try to remember your tips.
I must admit I have never checked it myself, A lot of modern Bikes are always changing
Sprockets and chains, But I have not seen much wear on my Sprockets.
All The Best, Bill.
 

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