Stock (dual) seat - Corbin mounting

robs ss · May 1, 2020

I am in the process of mounting a stock seat to my interstate. Currently has Corbin Gunfighter. As many of you will know, Matt (cNw) draws the line at fitting dual seats but there will be times when I would like to ride 2-up. I will have it upholstered with rear hump after getting the base to fit.
I have most of the Corbin mounting hardware - I like the idea of "turn the key - remove" and "push down - on"
I was wondering if anyone else had gone down this path and has some advice (nice advice!)
The bike is an Interstate - but that's not really important to a custom fit.

Fast Eddie · May 1, 2020

Dual seat is big. Two people are heavy. Stock seat base is thin steel and a pillion on the rear of it is going to put a lot of leverage on the central single fixing point. I think one of the reasons a Corbin is heavy is the base is so thick, to give it strength.

robs ss · May 2, 2020

Fast Eddie said:
Dual seat is big. Two people are heavy. Stock seat base is thin steel and a pillion on the rear of it is going to put a lot of leverage on the central single fixing point. I think one of the reasons a Corbin is heavy is the base is so thick, to give it strength.

Yep - I am putting extra support rubbers on the base for this very reason

oldbeezer · May 2, 2020

I am not sure it applies to your particular bike, but aren't the rear loops on the Commando prone to bending.

o0norton0o · May 2, 2020

To make a long story short,... my bike was originally a roadster. I only use non-ethanol fuel in my bike and gas stations which serve non-ethanol fuel are few and far between. So, I transformed my commando into an interstate for the extra fuel capacity.

That slow transformation, started with the interstate tank first. I cut down the old original roadster seat as a temporary saddle until I decided on the permanant choice. The cut down seat which is about the same size as a corbin, didn't really balance well visually with the larger tank. I see this with a lot of bikes of all kinds where the proportions don't look good to the eye.

Here's my commando with it's original roadster tank and seat. The seat and tank have a well balanced look together.

Here's my commando in transition with the short seat and interstate tank... The seat looks small and out of balance with the size of the tank.

Here's the same seat photoshopped to look longer so I could get an idea of what looks best with the interstate tank.

I didn't think there was any question that the big tank needed a longer seat to balance the look of the bike. Here's the seat I ended up using.

Certainly, everyone has their own visual preferences, and some other people disregard the idea that visual balance even matters. I think it matters a bit, but I can also say that I faced compromises visually when it came to my fairing. It would look better if it was lower along with lower handlebars, but I just don't want to ride in that low handlebar position, so I struck a compromise...

robs ss · May 9, 2020

Well, I made a start on the seat base:

removed the "ears" that fix to the shock mounts.
replaced the six standard rubbers with Corbin ones.
added 4 extra ones - with red tape, specifically:
2 on the frame spine - same as Corbin extras,
and 2 either side of the Corbin spike mounting brace - I feel these will be the most important as the stock base is flimsier than the Corbin one, as Fast Eddie has pointed out in #2 above.
Cut a preliminary hole for the Corbin spike to poke through.
Taped up the curve that I will modify the rear of the base to - similar(ish) the the rear of the Corbin Gunfighter.

After a bit of judicious panel beating the base rests evenly on all rubbers.
One good point, I note, is that the 4 (stock) rubber positions rest on the mudguard (fender) instead of the frame loop. This would mean any load here is shared between the loop (weak point - as Oldbeezer mentioned above - #4) and the mudguard mounting behind the oil tank & battery box - a good idea, I think.
What I am heading for (I think) is similar to the Gunfighter but with 8" extra seat room and the rear hump 3" shorter (7" instead of 10"). The hump will limit how far back the passenger can sit, therefore reducing the potential load on the loop.
Photos below - comments welcome.
Cheers
Rob

robs ss · May 9, 2020

I'm also toying with the idea of tig welding small wire "hooks" all over the upper surface of the base then smearing a thick(ish) layer of fibre reinforced epoxy resin over it to improve the strength of the base - hopefully reducing the load on the rear loop and improving the overall strength of the seat.
Anyone done something similar?
Cheers

Fast Eddie · May 9, 2020

I think that strengthening the base with some glass fibre is a good idea. Not sure if welding on ‘hooks’ is overkill or not? But blasting the base to give it a good key would be wise me thinks.

its interesting to see what your doing, if I could be bothered I’d actually do the opposite, I wish my Corbin mounted on the stock shock bolts !

Interbak · May 10, 2020

I like where you’re heading with this Rob, but I’d skip the rear hump. There are several long humped seats available, and personally I think they look really odd, and are just wasted space.

robs ss · May 10, 2020

Interbak said:
I like where you’re heading with this Rob, but I’d skip the rear hump. There are several long humped seats available, and personally I think they look really odd, and are just wasted space.

Thanks Interbak
Personally I like a hump on the back (no pun intended)
Probably goes back to my admiration of the Works Nortons - I finished the styling of my M50/ES2 after that look (see below)
I'm not after quite that racer look but something near it.

Interbak · May 10, 2020

Totally different look. The Manx style seat goes perfectly on a featherbed, I have a similar one on my Atlas Cafe racer. I‘m referring to a long humped seat on an Interstate, or even a Roadster. The Corbin works well, but a humped dual seat just looks wrong to me.

robs ss · May 10, 2020

Interbak said:
Totally different look. The Manx style seat goes perfectly on a featherbed, I have a similar one on my Atlas Cafe racer. I‘m referring to a long humped seat on an Interstate, or even a Roadster. The Corbin works well, but a humped dual seat just looks wrong to me.

Sorry - I didn't mean it would look like that seat - just that I like the look (and functionality) of a rear hump.

I have done a scaled sketch of the existing Gunfighter set and what I think is achievable with a modified "stock" pan.
The rear view shows how the Corbin seat wraps around the mudguard which I'm sure can be done when rounding and re-profiling the back of the stock pan. I like that look rather than the flat base at the rear of the stock seat.

swooshdave · May 10, 2020

What about keeping it simple and getting something like this.

https://texavina.com/norton-commando-interstate-750-850-solo-cafe-racer-seat-sku-s4154/

Richard Tool · May 10, 2020

Hi robs ss - it looks like a very well thought out plan . I think the idea of reinforcing the base is a good idea - I would try West System epoxy and I don’t think welding on hooks is needed or even benificial. The bond between the epoxy and seat base should be continuous. As Fast Eddie noted the seat base should be taken down to bare metal and the surface roughed up in some fashion to give it some “ tooth “ for the material to bond to. I would recommend woven fiberglass cloth rather than mat and do multiple laminates - the more thickness the greater the strength. Experiment on scrap first - the pieces you cut off from rounding off the rear would be ideal as it is obviously the same material .

robs ss · May 11, 2020

Thanks blokes
I hadn't seen those Swoosh, but it hasn't changed my resolve to "do my own thing".
Good advice Richard - a may well omit the hooks. I may also finish the resin reinforcement with a top layer of carbon-fibre cloth (for rigidity)

Interbak · May 11, 2020

Hey Rob, I like your design, it flows well. A buddy of mine took a Corbin and rather than chopping off the nose, he moved the mounting tabs forward, and modified the base to fit around the fender, to work with the Interstate tank. It looked great, but moved the seating position quite a bit to the rear. He’s tall, so it worked for him. The type Swoosh posted is what I had in visioned you were talking about, don’t care for it.

swooshdave · May 11, 2020

Interbak said:
Hey Rob, I like your design, it flows well. A buddy of mine took a Corbin and rather than chopping off the nose, he moved the mounting tabs forward, and modified the base to fit around the fender, to work with the Interstate tank. It looked great, but moved the seating position quite a bit to the rear. He’s tall, so it worked for him. The type Swoosh posted is what I had in visioned you were talking about, don’t care for it.

Have you seen that seat on a bike? They look rather sharp.

Interbak · May 11, 2020

i’ve seen them in pictures, not in person, still not a fan. Personal preferences.

robs ss · Sep 29, 2020

Well, things have progressed a little in this difficult environment - and I have a couple of questions for you (at the end):

I have trimmed the rear of the base to to a curve similar to the Corbin Gunfighter.
I have some 1.2mm mild steel sheet to overlay the "vertical" part around the periphery of the base (and a friendly neighbour to TIG it for me). This should give the seat maker a robust flange to attach the cover to.
I have fabricated a box and tube to allow the Corbin latch and cable to fit into the stock steel pan.
Most of the Corbin lock/latch parts are here - the rest will be soon (hopefully)!
I have 10m of 4" wide carbon fibre cloth. Still working on resin selection (see below)
A seat maker (Brisbane - 550km south) has agreed with my plan and will custom make the seat after I have finished the pan.

My questions to you are:

It seems the best plan is to use an epoxy primer onto the bare steel then use epoxy resin for the carbon fibre layers (3?). I've been advised that polyester resin does not like or take to primers so would need to be applied to bare steel (I'm nervous of rust occurring here!) Any knowledge gratefully accepted.
A bloke from one of the local marine workshops, and supplier of resins, has told me quite emphatically that carbon fibre laid over steel will cause "galvanic reaction" (his words) and eat away the steel. He says this will occur through resins and primers. I am quite dubious but also somewhat concerned about this possibility. Has any of you ever heard of this? Is it "fake news" (to quote he of the $100,000 hair)?

I look forward to help here.
Cheers
Rob