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

craig

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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?
 
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Martyn Goodwin

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Non-VOC Member
I would suggest that alignment with the spring box mounts is not that critical. What is critical is alignment of the wheel axle with the front main (lower) pivot. How does that look on you RFM?
 

litnman

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VOC Member
Check out this older thread:
 

Bill Thomas

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VOC Member
I did one once and used a known good one as a guide, Lucky I had one off a Bike !,
I found it more easy to undo and remove the 2 rear bolts and pop the top frame tubes away
from the lower tubes, As they are located on dowels,
And bent them cold, Good Luck.
 

Herman-Handlebars

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Non-VOC Member
I would suggest making a jig with adjustment points at the axles end. This would help with checking alignment and measuring. Then if you deside to reposition for example one rear axle plate, it can be held correctly during brazing.
This is something I may well be doing myself, as the cycle parts I am using are in poor condition and I suspect have been crashed unfortunately.
 

craig

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VOC Member
Is there a Vincent specialist to send this first posted RFM, and have it repaired by someone who has the proper tools and is experienced with this?
USA? Canada? UK? France? Germany?

So pulled a spare RFM out and set it up on the lift to compare crude dimensions with the RFM previously posted.
I leveled the rear wheel with a bubble level, vertically across open rear brake drum, both sides.

Measuring 12" out from center, both sides, I get about a 3mm drop to left side.

The first RFM measures about 12mm drop to left side.

RFMSpare3mm.jpg


This poor photography, probably sloppy set up, poor camera use, but you get idea.

This picture shows the "spare" RFM, not my original posted problem.
Both series C RFM.

I would have to pick a backdrop sheet with vertical lines, duh.
Thanks
Craig
 
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greg brillus

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VOC Member
Craig, the only real tool you need per-say, is a descent press.........this is so you can "Hold firm" the forward end of the frame and then use brute strength to twist the other using lengths of bar, tubes whatever it takes........I have straightened many bent Girdraulic fork blades, and sometimes it takes 3 people to do this, especially if they are twisted.........Because the rear frame is triangulated, it is very strong, the tubes are the only weakness, so they will shift if you can exert enough force, whilst keeping the other end firm. Good luck with it all...........Cheers......... Greg.
 

Magnetoman

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VOC Member
You might find the tools and techniques I used to straighten and align a BSA frame useful for what you have to do, starting with the following post:

 

craig

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VOC Member
I would like to send this RFM to a shop that has the fixtures/tooling/parts and does this Vincent RFM repair on a regular basis.
Has anyone had this bent RFM repair done?
There have got to be dozens of bent UFM/RFM out in the world, my guess.

20201129_BentRFM11.jpg
 
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