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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.


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:

MartynG

Well Known and Active Website User
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

Well Known and Active Website User
VOC Member
Check out this older thread:
 

Bill Thomas

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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

Well Known and Active Website User
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
 

oexing

Well Known and Active Website User
VOC Member
I had to do same job on two rear frames a few weeks ago, Argentinian history as you can guess. My approach was to disengage the upper tubes from the doweled lower bigger tubes . You cannot possibly rectify the lot with all joints bolted up - and no good way to use brute force under a press. This would lead to curved funny shapes as you´d get bends where there were no before. Mostly snake like shapes then. So I got me the big welding torch after undoing the scews and levering the upper tubes out of dowel fits. So you put some big tube or monkey wrench on the rear end and heat at the suitable place to red and bend to your liking. You´d want to get axle of taper roller bearings parallel, resp. horizontal when viewed from behind, plus the wheel axle parallel as well. I made me two lengths of plastic disks to fit in the Timken bearing seats with central bore for pushing some straight stainless rod through to be placed on v-blocks or parallels on a table. So then you check the wheel axle slots for same heights left and right. Otherwise you´d have a rear wheel not vertical !! The shock absorber bores are not critical here, they may be allright after having all else in positions.
Once you got the lower big tubes correct with swing arm bearing bores horizontal and parallel on your table - plus rear forked ends parallel/same height too, you then look at the curved tubes on front and the upper tubes that have to engage the dowels again. For arriving there you have to think about where to go with the torch, either bending the curved tubes back when too short to reach the dowel. Or maybe just bending down or up when the loose ends are too high or low. Depends on what defect you got.
Anyway, with the torch you can feel the redhot tube to go where you want it, some lever force is certainly required but you get good control about what place has to give for the job to be done. A few hours will go for sure, but this depends on your standards of perfection then.
In case the forgings at the rear are f***d up a lot you could consider to have some welding done for perfect seating of nuts and spacers of the wheel axle components. Big washers are desirable, not original but an improvement, so you don´t squash faces again later.

Vic
P1080225.JPG
 

Bob

Active Website User
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.
Craig, I hope you can find some 'Twisted' people to sort this out, mind you that should be no problem after the current lockdowns!
 

Bill Thomas

Well Known and Active Website User
VOC Member
I spoke to Bob Culver some years ago, And asked Him if He had a Jig,
He said He didn't but would have a go and He would bend it cold,
So I thought I may as well have a go myself,
You have to be careful, The brazed end bits can break, But I was lucky,
I wonder if heat may upset the brazing, And that's why He does them cold.
 

oexing

Well Known and Active Website User
VOC Member
Temperature control for hot bending is no real problem, you see the red colour and keep some distance from brazed forgings. I would not want to bend cold, takes a lot of force and you rarely get kinks out of tubes at the right place. It is really a safe operation with a torch , unlike with a little help and hope from a press when you would be challenged how to place that unit under it to get the desired results. It is a very threedimensional shape so easier to hold it in a decent vice and apply heat for a one-man bending job. I did not clamp on castings for bending, only gripping the tubes and used some patience for having red heat for bending.

Vic
 

Bill Thomas

Well Known and Active Website User
VOC Member
I do remember Stan at MLG Motor cycles, Where I worked in the mid 6o s on BMW s,
Used heat on a proper jig, Chased the bends up and down for hours !.

The Vincent rear frame is a hard one to do, Because the tubes are meant to have a huge offset,
It's like they built the Bike and and thought S--t, The wheels don't line up :D .
Lets give it a bend here !.
 
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oexing

Well Known and Active Website User
VOC Member
Rear frames offset, really ? Looked pretty symmetrical to me. At least one can cope with spokes tensions but the sprockets have to be aligned for sure.

Vic
 

craig

Well Known and Active Website User
VOC Member
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

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?


RFMRearLugs2.jpg

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:

Glenliman

Well Known and Active Website User
VOC Member
Rear frames offset, really ? Looked pretty symmetrical to me. At least one can cope with spokes tensions but the sprockets have to be aligned for sure.

Vic
They are offset. I became aware of that fact when searching around for Egli frame drawings.
There is a very nicely drawn Egli swing arm drawing out there that is symmetrical. It will not work with a Vincent engine. For a standard type Egli which uses standard dimension head brackets, the swing arm needs to be built to the same offset as a standard Vincent RFM . A friend warned me about the symmetrical drawing, which was a good thing as I had it and was considering building from it before learning of the offset. He had spent a great deal of time building a beautiful swing arm to that drawing, only to chuck it in the scrap bin after discovering it would not work with the Vincent engine.

In the end I did something quite different (monoshock and 180 rear tire) and that required an even greater offset in both the head brackets and swing arm. None of the collection of Egli frame drawings that are readily available would suit my plans.
It was simple enough to make a full sized drawing based on what was needed.
Since then I've noticed that most motorcycles have some sort of offset in the swing arm.
It's like Bill says, the designers must design the swing arm last and just make the offset whatever it has to be in order to line everything up.
Come to think of it, that's what I did as well!

Glen
 
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