FT: Frame (Twin) Seat stay spacing

[milohiscox]

Hello
Sorry if this is a trivial question, but I'm restoring a series C Rapide and trying to improve my level of detail!

• The spacing between the seat stay damper brackets on my rear frame is exactly 9.0" centre to centre.
• The seat stays are vertical, so the spacing between the top ends is also 9.0" c-c.
• However, the spacing between the brackets on the seat base is only 8.5" c-c.
• It doesn't feel right just jamming them in, the dampers bind if I do.

What's wrong? Dodgy seat?
I'm considering giving the stays a bit of a bend in the vice.

Thanks for any advice.
Milo

 

[chankly bore]

I'd start by checking your rear frame for truth against "Richardson" page 36, (first edition). Have you confirmed your measurement with the wheel in and tightened up? If that measures up I would carefully take your seat apart and see that it has the necessary internal supports, including the "arch". I'd alter the seat, myself. It doesn't look original underneath, so I'd be suspicious of it. Was it originally on this bike? I would not bend the stays. "Know thy Beast" confirms that about 9" is the usual distance, so the seat is firming as the problem, I suppose.

 

[timetraveller]

Oh Dear! I've just been into the shed and made some measurements. One RFM with wheel tightened in is 8.75", Another RFM without wheel is 8.9" Distance centre to centre across the supports under the rear of a seat off the bike are 8.5". All worked when last used and did not give any trouble. So take your pick. I agree, do not bend the sear stays.

 

[Simon Dinsdale]

Just measured 4 RFM's. One from 1951 measured 8.9". The others from 1949, 1951 & 1952 all measured 9" and these are all on built up bikes.
The seats on all 4 bikes were 8.9" to 9" as well.
If you run these out of alignment the seat will still pivot etc but with sideload on the damper drums in the seat stays they will then cause friction and eventually wear. Extra friction here though also has another consequence:

On a series C you don't actually want any friction there at all and I run the seat stays with PTFE linings and adjust the damper knobs so there is no side play but they still pivot with no friction and a drop of loctite nutlock on the damper knob threads stops the knobs undoing. You don't want any mechanical friction interfering with the rear hydraulic damper as they will fight against each other and in my opinion the factory should have eliminated the friction damper when they introduced the hydraulic damper. I suspect when owners say the rear suspension is very hard on a series C that they have tightened up the seat stay damper knobs really tight to stop them undoing themselves and falling off.
Basically the seat stay damper is a left over from series B's of which most didn't have a rear hydraulic damper.

 

[vibrac]

I guess the seat is wrong PR1A/3 the frame is available from Vincent spares as a individual item

 

[Marcus Bowden]

Tim my handsome, you have the ability to remove the seat remove the under bracket bend it in the vice and refit surprised you even asked the question.

 

[chankly bore]

Yes, Marcus. But one needs to bend and/or re-drill the interior bracing to align with the "new" centres. Assuming the rear interior bracing is there, of course.

 

[milohiscox]

Thank you so much for the replies, wonderful to hear all these experienced views. Particular thanks to those who got their measuring tapes out.

The seat came with the bike, but the foam is pretty old and dry, so I think some seat modifications are in my future.

 

[milohiscox]

Love the PTFE idea on the dampers, found another thread on that.

 

[timetraveller]

Just measured a fully assembled road going Comet this morning. 9" across the support on the RFM and 8.6" across the seat brackets. I know the history of that bike and it must have been like that for 20 years or more.