more tank comparison info- primarily 550 Seca and 650 Seca

I posted this in a different forum a couple weeks ago, but thought I'd put it here, too, for anyone else interested in some more tank info. We all know about the 750 Maxim tank being a direct replacement for the 650 maxim tank.

Back on the old site, I submitted a forum on swapping 650rj(non-turbo) tanks with a 650 maxim tank. I'll see if I can dredge that up later, and try to combine everything into one bigger post when I get a chance:

Here's some info that I put together after someone asked about a possible 550 Seca/650 Seca (non-turbo) swap. Since I had one of each sitting right next to each other, I decided to swap them around and see what would happen.


I couldn't resist the opportunity to swap parts around on two bikes already sitting side by side , so here is a side-by-side and swapping-tanks comparison:

650rj tank on a 550r

650rj tank is slightly shorter in length, by about 1/4 inch at rear oval mounting hole. However, if the tank is pulled back just that tiny bit it will bolt into place. Doing that though, pulls the front hooks about 1/4" back, which leaves a slightly "loose" fit at the front.

The petcock just clears the valve cover but with enough clearance to not be an issue.

The bottom rear of the tank does interfere with the seat pan's lower front corners but they could be trimmed back and re-shaped a bit to allow the seat token and close again.

The front of the seat is too long, too, but if it is cut back and re-shaped and re-curved I could be made to fit nicely.

All that would cosmetic changes, and readily do-able.
The only "major" issue will be that the bottom of the cramped edge of the tank touches the top ends of the airbox. Once the tank is bolted down there will be pressure in the airbox. If the airbox is heated and softened, the two "channels" could be formed. I guess the tank could be trimmed, but I think that may weaken the seams and I wouldn't recommend that.

550r tank on the 650rj

The 550r tank is about1/4" too long, PLUS the front mounting grommets are just a little bit too wide for the tank to slide on.

When the grommets were removed the tank almost fits right in place.

However, the lower front edges of the tank interfered with the horns. If those are lowered or relocated, that issue will be easily resolved.

The rear of the tank tunnel interferes with the frame but if the tank rear is raised about an inch or so, it clears the frame. If some makes a riser/spacer to mount the tank just that little bit higher its right in line above the regular rear mount

The issues to really address would be --what to do about the tank grommets on the 650r, and the rear mount. Hereare the solutions....

Two things must be done for the front:

1. The big ring on the mount needs to be moved in toward the backbone about 1/4" on each mount to allow the rubber grommets to fit in the slightly narrower tunnel of the tank.

2. Use the grommets from the 550r, as they are slightly less tall AND the have a little bit smaller diameter that the 650rj grommets.

For the rear of the tank--make spacer to mount the end of the tank about an inch or so higher above the original mount.

Long and short of it:

Either tank can fit on either bike with either seat mods and airbox mods to put a 650r tank on a 550r; or, minor alteration to the front tank mounts on the 650r, relocate the horns, and add a riser for the rear mount will allow the 550r tank to fit on the 650r.

Dave fox

 

Dave, go back and re-read your post. NO WAY is the 650R tank "shorter in length" than the 550R tank. The 650 tank is easily a good 3" longer than the 550 tank. (I have both in the garage right now too.)

The MOUNTING POINTS might be as described; as the rear mount on the 650 tank is well up the tunnel from the rear, whereas the 550's rear mount is on a tab projecting clear of the rear of the tank.

But then again, I can't see why anyone would want to put a 650 Seca tank on a 550 Seca. Or vice-versa, for that matter. Most of the adaptive uses I've seen of the 550 Seca tank have been for 650 Maxims or other cafe/bobber projects.

 

I didn't say one tank is longer than the other ..... I said one is too short to reach the rear mount, and the other overshoots the mount when the tanks are swapped to the opposite frames.

I took that information directly from the two bikes as the sat right next to each other WITH THE TANKS SWAPPED. That way I could do a direct comparison of what would fit/not fit.

The whole thing was simply the result of another listmember asking if there is another tank to fit his bike ( one of those two Seca's, and another member replied that the other Seca tank looked sort of similar.

So I figured since I had them right here, I'd pull and swap tanks and see what happens.

I'm don't care whether someone would or would not want to do that particular swap, but the info is now available..... Kind of like the info that's out there for people who want to put a Harley tank on their bike....

The fact is that the 650 Seca tank does have greater capacity, so there may be someone who WOULD want to do the mod.

Dave

 

For the 4 litre extra capacity and because it suits the single seat I will be using far better than the 550 tank, even if I wasn't using the single seat I'd still be looking at using it for the extra capacity