seat mount w/ hoska tank

jimstravlin · Post by **jimstravlin** » Wed Jun 20, 2012 8:27 am

i just purchased an 8.5 gallon Hoska tank for my R69S. i got the tank mounted and purchased the seat extension piece from HH gastanks to get the Denfeld solo seat out from under the tank and moved back and now sits about 2.5 to 3 inches from the rear of the tank. The seat bottoms on the rear fender when i hit bumps. i am only about 180 lbs and seem to need more support beyond the standard silent block that comes with the Denfeld solo seat. does anyone have a solution to this problem? has anyone encountered this problem before? Thanks.... jim

schrader7032 · Post by **schrader7032** » Wed Jun 20, 2012 8:47 am

There are some adjustments to the fulcrum point on the silent block. IIRC moving this point further aft will stiffen the silent block somewhat.

jimstravlin · Post by **jimstravlin** » Wed Jun 20, 2012 9:00 am

when the block is forward all the way the suspension is a bit stiffer but, the seat rail that the seat mounts to will hit the tank at the tank tunnel...

schrader7032 · Post by **schrader7032** » Wed Jun 20, 2012 9:30 am

Hmmm...from a mechanical standpoint, the closer the silent block gets to the pivot under the tank, the more vertical force it has to carry. If the rider were 200 lbs and the silent block could be put directly underneath the rider, the silent block supports 200 lbs. If the silent block is moved much farther forward to the pivot, the silent block has to support the weight of 200 lbs times the ratio of the total length of the seat rail divided by the distance from the pivot point to the silent block. If the silent block is midway in the length of the seat rail, the total load at the silent block doubles to 400 lbs.

jimstravlin · Post by **jimstravlin** » Wed Jun 20, 2012 10:08 am

Kurt....at this point the block is in the middle and that seems the best point for the most support. although the ride is comfy the seat still bottoms. i have thought about shortening the seat rail, which would shorten the fulcrum.that is a lot of fairly exacting work but may be the only answer. i know i am not the only person with a /2 and hoska tank. i am also not the heaviest guy to mount the denfeld seat with this tank configuration so i am appealing to all of you with more experience than me. thanks.... jim

schrader7032 · Post by **schrader7032** » Wed Jun 20, 2012 11:09 am

Jim -

Good point...I have no experience with these types of setups...just thinking about the mechanics involved. Back to lurk mode!

Bill7593 · Post by **Bill7593** » Wed Jun 20, 2012 12:45 pm

It seems like your options are limited here. You could raise the seat hieght with a spacer on the frame under the seat mount, but you'd probably need too much for that to be pratical. You could stiffen the seat suspension with fabricated helper springs or add a rubber stop to the fender where the seat hits it. The only other approach that comes to mind is switching seats. You probably don't want a bench seat or we wouldn't be having this conversation in the first place. Perhaps you could switch to a solo seat that is suspended by the horizontal coil spring, Piaggio I think. There might be more adjustment in that seat.

Bill

bmwmyplace · Post by **bmwmyplace** » Thu Jun 21, 2012 5:49 am

Jim I have been thinking about this myself of late , I have never heard of these extentions being available ... what about a pic? I was thinking in order to obtain the same spring rate using the same rubber block , the block would also need to be placed rearward by the same amount as the extention piece surely?....This I guess would require fabricating appropriate brackets to suit .....and I think my solution is the use a Pagusa seat of an Adler it has a Tee bar that is simiar but has provision for a centeral coil spring . hmm I should go down to the shop and refresh my memory cheers peter

schrader7032 · Post by **schrader7032** » Thu Jun 21, 2012 6:52 am

Pictures about mid way on this page:

http://www.beemergarage.com/Tanks10.html

It looks like they have not changed the location of the silent block.

jimstravlin · Post by **jimstravlin** » Fri Jun 22, 2012 9:30 am

sorry to take so long getting back. yes, pix are in order. the conversion on the beemer garage site is exactly the same part i purchased from HH gas tanks. the piece is well made and fits perfectly as well as working as explained. Joe at HHgastanks told me that the seat may bottom from a heavy person, but thought my weight of about 180 would not cause it to do so. i do like the idea of the double silent block, i have thought about that but i think it will be a fabrication problem. good winter work. right now i have 3 R69 restorations in progress.
thanks for the comments and will get back with pix.... jim

Vintage BMW Motorcycle Owners

seat mount w/ hoska tank

seat mount w/ hoska tank

There are some adjustments to

tried that

Hmmm...from a mechanical

right

Jim - Good point...I have no

Seat with Hoske tank

Jim I have been thinking

Pictures about mid way on

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