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Hi there - I have a little 1966 Narrowcase (originally a Monza, but it's a bit of a bitsa after I did a bit of a restoration project some years back)



If I were to be honest I barely use it, but I'm pretty happy with it just sitting there and looking lovely, but something that I've encountered a few times seems to be a design flaw with the seat mounting. The seat is the type that slides into two prongs on the frame, then secured by a bolt on either side through the rear frame tabs and mudguard mounts.



The trouble is that the bolt slots in the seat tabs face forward, meaning that under acceleration, the seat (and rider!) is under stress to disengage. There have been occasions where I have thought I'd torqued those retaining bolts up pretty tight, but midway through a ride, the seat still slips out.



It feels to me like those retaining tabs on the seat are the wrong way around. If those slots in the seat tabs were rear facing, then the bolts would prevent the seat from moving, and the assembly would stay secure.

There is a different type of seat mounting that is used on some of the bikes that I think uses a through bolt on the front fixing (rather than two prongs), which I think would probably be more secure.

For my wee Monza though, I'm tempted to take the seat pan to a welder and make some modifications to help keep the seat secure, but before I do that, I'd reach out to see if there might be some pearls of wisdom out there..

Thanks,
Mike

If you have the rear slots facing the other way how will you be able to engage front prongs?
I have similar fixings on my 350 Road. I fit a penny washer both sides of the slotted bracket to give more area for grip. Works for me.

Vertical slots?

Personally I'm wondering how you got so much power out of that bitsa such that it's capable of dislodging the seat under acceleration! I'm coming to you for my next tuning project.

Ian

I also have that seat mounting arrangement on my widecase 350 (which can accelerate pretty briskly) and have never encountered this issue Mine is held on with two 6mm socket head screws with nylock nuts and penny washers (frankly not even massively tight).
Cheers,
George

George wrote:If you have the rear slots facing the other way how will you be able to engage front prongs?
I have similar fixings on my 350 Road. I fit a penny washer both sides of the slotted bracket to give more area for grip. Works for me.

Quite simple - fully withdraw the bolts before installation, slide the seat into place until the (rear facing) slot lines up with the frame and mudguard lugs then the bolts will lock the seat in place.

Vertical slots?

Yup - that would work also.

Personally I'm wondering how you got so much power out of that bitsa such that it's capable of dislodging the seat under acceleration! I'm coming to you for my next tuning project.

Haha - the power out of it is quite fearsome

For the moment, I think I'll probably leave it, and perhaps find some spring washers, then man-up and tighten it properly, but it really feels like those tabs should be rear facing (even just for safety).

Mike wrote:

George wrote:If you have the rear slots facing the other way how will you be able to engage front prongs?
I have similar fixings on my 350 Road. I fit a penny washer both sides of the slotted bracket to give more area for grip. Works for me.

Quite simple - fully withdraw the bolts before installation, slide the seat into place until the (rear facing) slot lines up with the frame and mudguard lugs then the bolts will lock the seat in place.

My 350 is widecase 1975 and has welded studs on frame not bolts that's why I asked.

George wrote:My 350 is widecase 1975 and has welded studs on frame not bolts that's why I asked.

Ah - interesting! - thanks for highlighting the difference, my one has just lugs on the frame, through which 6mm bolts can fit - I had no idea there were differences here. I think studs on the frame would be an improvement.

Mike wrote: <snip> I think studs on the frame would be an improvement.

I often wish Ducati had fitted them - or just some nuts - to my SCR.

Or indeed that I had, before I got the frame re-painted.

(Right PITA to get the nuts/bolts done up. No 'finger room' ... But once done, the seat don't move )

Aye Mike,

A bonnie wee beastie you have there, certainly needs to be aired!

As for the slidey seat syndrome, "Gee the nuts a proper tweaking!".

Same as George (blethermaskite), I have owned my '74 450 MKIII since '76 and never had a problem with a rearward sliding seat. It was a pain to twiddle all the bits for alignment, including the rear mudguard central mountings. Since fitting my own fibreglass rear mudguard replacement, with no central mounting loop, there is less to juggle. Fitting the OME mudguard central stays with studs would have been a pain trying to flex the mudguard between the studs. Everyone to their own.

Use M8 x 20mm stainless hex screws, with the hex to the inside (doesn't rub the tyre if using a wide profile), stainless "Penny washers" inside and out, with a nyloc nut, done up tight; 15ft/lbs, could go to 19ft/lbs, with a touch of copper grease, if you want to use a torque setting for these fasteners.

Hope to see the wee beastie out and about.

Good health, Bill