I haven't heard anything more from Corbin about what they are going to do about the seat they made for me. I can only assume they don't think the issues I reported warrant any further action. Like I say, they stopped talking to me, and mentioned that I might have given them a bent bike to use.
I consider this a disappointment, to put it bluntly. If indeed, they made a seat molded to a bent bike, the mold isn't going to be right on any bike but mine. However, since I have 3 CB750F bikes, I can state with some confidence that the seat doesn't fit any of them properly.
The seat never actually fit well to the bike I gave them to use as a buck. And, when I put the seat on my other F bikes it was similar, but slightly worse.
I do like like the basic design, look, and appeal. But, fit was another issue.
They didn't use the original seat pan to locate hardware and attachment features, or use the original bumper engagement points that Honda made sure were the same among all models in the series.
First problem I noticed was that the cowl no longer "met" the grab bar, leaving a big gap between bumper and bar. This also effects how the cowl aligns with the tail light.
I also noticed that the right side of the seat was a bit higher than the right.
Closer inspection revealed the entire seat was shifted to the right about 1/4 inch. I found out why later, but this means both the seat hinge and the latch post are off center by this amount. You don't really notice this from 10-15 ft away. Just when you look closely.
I set about identifying and correcting these problems.
First I took off the hinge and latch post, and found the seat sits lower on the frame. Turns out that some of the bumpers aren't in contact with the frame using the original mount hardware. Not that this really matters as you will learn, later.
Even without the hinge and latch hardware, you still can't move the seat to the center as the rear most bumpers don't rest on the top of the frame arch, they contact the "sides" of the frame arch. I don't believe Honda worried about maintaining the dimensions at this point of the frame. So, to move the seat into correct frame center alignment, you must remove the frame arch bumpers from the seat. This must be done to get the back cowl bumpers to meet the grab rail, too.
I made a thinner frame bumper that met the frame in the center, at the top flat of the rear frame arch and placed it on the center of the seat, just as the stock Honda seat pan does.
But, the seat still won't center horizontally, because the Corbin seat pan now hits the the helmet holder hook on the right side.
So, I carved out the seat pan enough to allow the seat to center.
Next I saw that the mid seat frame bumpers were standing proud and acting like a fulcrum so either the front of the seat was up and the rear cowl bumpers made contact or vice versa. So, I removed the center bumpers and replaced them with thinner mock ups. (Neoprene rubber squares held on with two sided foam tape as I did for the rearmost seat pan bumper. These are just temporary to get the seat to fit right on the frame. I can work on something more permanent later, once I know the correct dimensions.)
Now the seat will fit onto all three of my CB750F frames, provided they don't have hinge or latch hardware. So, the next task is clear.
Using the stock hinge is out since it is positioned to make the seat too high and to the right of center, and Corbin used blind nuts mounted from the upholstery side (before the foam and upholstery were put on). To save the seat for actual use later I can't reposition the mount locations.
I decide to try making just the lower half of the hinge, so I can get the offset needed. Some metal work, and welding gets the seat mounted so the bumpers all make contact with the seat closed. But, you can't raise the seat without the upholstery seriously chafing on the left side of the seat. Why is this? Well the Corbin seat is wider and the bottom edge of the pan is lower than the stock seat for which the hinge hardware was made. This makes the arm length from pivot point longer and creates a wider arc of movement, thus the pan to shock interference. The easy "fix" for Corbin's fab shop, was to raise the seat, shift it to the right and "relieve" the bottom edge of the seat pan in the area of the shock mount so the covering will "give" as the seat is raised and the covering slides over it. (This discovery was rather disturbing for me.)
By this time, I was convinced that the Corbin seat pan really needed the mold revamp. And, I gave them a report (March 1) with my findings and plenty of photos to explain and illustrate the problems.
I continued to work on the seat hinge making and articulated hinge that would both raise the seat and allow it to pivot without scraping off the upholstery on the left upper shock mount. This was no small feat, actually, getting the dimensions and critical points to work with the very first hinge set made. But, it works as needed for this seat pan.
The latch was the last piece to fit. It, too, held the seat too high off the frame, out of contact with the load bumpers on the seat pan. The stock latch post has very large eyes in the mount to accept big rubber grommets and oval spacers. While the oval spacers did compensate for the offset mount position in the Corbin seat pan, the height was still wrong. Using no grommets or oval spacers I got the seat down fairly close, But I really need to grind out more of the seat pan for correct fit, or make a special latch post for the Corbin seat pan I have.
At this point I quit working on it and communicated my concerns again to Corbin to await their corrective approach. I withheld my report to the forum in hopes that correction would be identified without any embarrassment or negative reports to Corbin.
However, now I see they are accepting orders for the seats and I have no information that they are any different than the one made for me. I feel I must now warn prospective buyers about the fit problems I encountered.
My contact within Corbin is in marketing, and is the buffer between myself and whoever is actually responsible for the seat design/molds. I think they are all nice people there, and I had really hoped to make a final report in their favor. But, based on what I have seen so far, and the information shared by Corbin, I get the distinct impression that there is a "Not Invented Here" syndrome within the company, where outside input is rejected for any convenient reason. (I've actually encountered this before in my professional career, even within a company between departments.) Anyway, I cannot recommend the seat such as the one provided to me by Corbin. In fact, if I had actually purchased the seat, I would return it for a full refund.
My recommendation at this time, is that if you want a gunfighter seat design as shown by Corbin, you send them a stock Honda seat pan for the CB750F model and have them apply the foam and seat cover in that style. Then you will certainly have a very nice seat AND it will fit onto any CB750F using the stock hinge and latch Hardware. I've not found any fault with the foam and seat cover. But, the pan design is quite a different story.
Regards,
Lloyd
P.S. If you are interested in any specific pictures, I have plenty. I don't think it wise to post them all though.
