N15CS rear mudguard & support

I’m looking for some guidance on sorting through my N15CS rear mudguard mounting. The other threads on this have been very helpful but don’t address a few points:

What are the PN’s for the support tube (032256) mounting hardware? I can’t find the two bolts in the parts book (not the upper shock mounting bolts) in any of the related sections.

The parts book identifies a mudguard-support spacer, nut & bolt: 031590, 000004 & 000370. Where is this hardware used? And what are the dimensions of the 000370 bolt?

Thank you! I’m building a period desert bike with the goal of competing next April.

Chris

Chris Johnson said:

I’m looking for some guidance on sorting through my N15CS rear mudguard mounting. The other threads on this have been very helpful but don’t address a few points:

What are the PN’s for the support tube (032256) mounting hardware? I can’t find the two bolts in the parts book (not the upper shock mounting bolts) in any of the related sections.

The parts book identifies a mudguard-support spacer, nut & bolt: 031590, 000004 & 000370. Where is this hardware used? And what are the dimensions of the 000370 bolt?

Thank you! I’m building a period desert bike with the goal of competing next April.

Chris

Click to expand...

Please check your messages. Mark

It's all becoming foggy, but maybe some of those fasteners you listed are for the bottom support? Mine doesn't have a center one. If help is still needed after Mark's input, I can do some measurements of bolts/nuts/washers, just no crossover brace info.

Yes, there are some gaps in the parts list and by "support bridge" they mean the support tube's rear end.

The mudguard-support tube (or loop) was fixed by the two upper shock bolts 016359, 1 off bolt 000370 (5/16" x 26tpi x 1-3/4"), 1 off bolt bolt 000371 (5/16" x 26tpi x 2"), 4 off washer 000011, 2 off nut 000004 (5/16") and 2 off spacers (**).
At the rear the mudguard was fixed to the loop by 2 off bolt 012565 (2BA x 1/2"), 2 off 000039 small washer, 2 off 000190 spring washer, and 2 off 000080 nut.

You may want to put a spring washer 000192 under nut 000004. Length of bolts allow it.

** There is a spacer between flanges of each subframe rail, probably 031590, to prevent the frame member from being crushed. Unfortunately I haven't been able to verify length of this spacer. Baxter Cycle has them but no length is stated.
On my frame they are retained inside - I may be able to pry them out.

2BA is feeble for fixing the mudguard. UNF 3/16" or M5 is better suited.

I hope this helps.

- Knut

Revised 11/10/2025

Thank you guys for your input! That last bit really clears it up for me. Ill be mounting an alloy guard and will probably open up those 2BA mounting holes to 1/4”.

Chris

We want pictures. By 'we' I mean 'me'.

Not much to show yet…
-Finalizing the valves & seats with a few improvements in there. Will flow this head & a stock head to see if I made it any better.
-JS1/Axtell cam with BSA followers are fit. I’m in the process of weight matching the rotating parts before balance.
-Frame is coated, waiting on a bucket of hardware to come back from cad plating, one shock hanging loosely in place. I’ll be purchasing Excel flanged rims for it today.

Chris

Whoa, nice, beyond my pay grade.

Looking at that seat, where's it from? I bought a seat from Baxter's for my N15 (no piping on cover) and I sink right through it to the pan. It is very difficult to find good firm seat foam. I'm well over 200 lbs, but I never sink through any other seats. I wrote to RK Leighton about the issue, not knowing if that seat from Baxter's is from them, as it wasn't mentioned. They seem highly regarded, so after describing it and being assured it is firm, I bought a seat cover/foam kit and it's exactly the same, it's like it's memory foam. So the seat really was from them. Just wasted $220 on the exact same thing I already have.

This is a Leighton seat & foam over the original pan. I still need to figure out how to attach the cover, I seem to remember the scraps of the original were riveted…

Good to know about the foam. We might be about the same size and now is the time to address a too soft condition.

Chris

Chris Johnson said:

This is a Leighton seat & foam over the original pan. I still need to figure out how to attach the cover, I seem to remember the scraps of the original were riveted…

Good to know about the foam. We might be about the same size and now is the time to address a too soft condition.

Chris

Click to expand...

Contact cement, apply to the pan and the inside of the cover, let it dry till tacky (normal way, it's on the can's instructions) and it will bond just fine. That's how the seat I got was secured. Once it's on, it's set; there's no adjustment!

My 'remedy' was to glue a thin (maybe 1/2") yoga pad on the seat base. That was after I bought some 'high density' foam that I thought was firm enough (it wasn't, another waste of money), and tried to shape a replacement. I swear, it's the absolute worst, most frustrating thing about the N15. The yoga pad works, I don't get a sore butt now, but it's just not right. My 45 year old Suzuki and other bikes are just fine. And stretching the seat cover just a little more has started to separate the stitching.

So now I have a replacement cover, stitching is good on it, since it is new, but has the same thin stretchy (garbage, IMO) material, some memory foam that I'll sink through just like before, and no way to turn on this issue. I'm so bummed! I have spent many hours looking for good foam, researching foam types and ratings to no end, but no luck online. So I went to a store and threw more money away, it seemed OK but I just can't carve weird seat shapes. I think the best bet is to go to a boatyard upholsterer but where I live, they won't spit at you for less than $500 and I am not wealthy.

gpzkat said:

I bought a seat from Baxter's for my N15 (no piping on cover) and I sink right through it to the pan. It is very difficult to find good firm seat foam. They seem highly regarded, so after describing it and being assured it is firm, I bought a seat cover/foam kit and it's exactly the same, it's like it's memory foam.

Click to expand...

Hi Tom, can you post a picture of the foam that Leighton supplied, please? I bought a few foam & cover kits from Leighton for my Commando projects which look the part, although not tested on the road as yet. Foam density (I use this term for rate of elastic modulus) appears to be higher than the original foam.

The off-white foam Leighton supplied appears to have been produced in Germany. It's of similar density to the foam used in my F800 seat, which is comfy enough for a street bike. Seats are not comparable though. Being an off-road bike, the G/N15CS seat will need a progressive stiffness rate foam. Mixing two foams of different density (stiffness), the overall stiffness will actually decline. For instance, if one layer has stiffness k1 and the second layer stiffness k2 = 2*k1, assuming a linear force-displacement characteristic, the overall stiffness will be 2/3*k1 only. That's not intuitive.

Which density has the yoga mat of your experiment? Maybe you should try gluing several layers of this mat to reach the desired height. Note that some foams are not weather proof.

- Knut

Hi Knut

Here is the seat and the cover, which is a thin and stretchy material. I can squeeze the foam as shown, close to its maximum compression. The density seems uniform.

The mat is pretty dense, I don't know the number. I thought of using thicker, garden knee pad, which is about 1 1/4" and nice & firm. I think it would make a great base for me, but I would have to do surgery on the seat.

Apologies for the side-turn on this post but maybe it's useful info.

Tom and Chris,

The density is insufficient. You should be looking at cross-linked PE (XLPE) which has a density of 9 PCF (about 1400 N/m3). Some special grades for racing application go even higher. One company offering this quality is https://www.kickstarter.de/sitzbankbau_1

In the US, you may call Foam Factory. They highest grade they stock is 8 PCF, maybe they can supply 9 PCF on application.

Mexican Evacolors (www.evacolors.com) produces XLPE foam of 9 PCF density. You need to look for a stockist.

- Knut

Thanks Knut. I read up a lot on foam, down the rabbit hole. Problem is, I can't shape stuff; I just don't have the coordination or patience, and always screw things up royally. Leighton says they can send a replacement, but it may not be any better, not sure. I sent them the pic, we are going back/forth. They are a reputable company and have many satisfied customers. Except it's way too squishy.

Maybe I'm an outlier, but I always preferred firm seats in my vehicles. For example in the old days, I loved my '84 VW GTI seats; they were a revelation compared to the 'sink in' of American cars. Boat cushions are really good, and there are a lot of shops near me, just way too expensive, many $ hundreds.

The most comfortable seat I have ever sat on is my son's little toy, a '79 ATC110 that he got for pocket change. The seller knew a marine upholsterer and had it done. Wow, it's just superb. My 2013 KTM 450 EXC seat is way too firm, even for me. My big GS1100E had a slightly too-firm seat when new (as I recall riding 1100 miles in one day back in 83), but time has been good to it, and it's a big comfy bench now.

I like posting pics so here's the ATC

Tom,
Leighton's shaped seat foam appears to be almost flat. If you pre-assemble a foam pack of desired density and trace the outer shape of Leighton's seat foam onto it, I don't believe a boatyard upholsterer will charge you much just to do the cutting (it should be accomplished in few minutes). Luckily I have such a company nearby and I know the owner. I will have a go at it in the new year.


- Knut

That's good advice, thanks for the input. I expect an Email tomorrow, the son or perhaps grandson of the founder said he's wlling to send replacement foam, but he wasn't sure it would correct the problem. If I can get some specs on what other foam they may have, that may be the ticket. I should think they are experts and have various materials available.

Oh, and back to the OP Chris - do you have a build thread? These old warhorses are so cool; it's great to have another restoration being done - big props. I just got back from a great ride through the canyons on mine, but the right side exhaust collar let loose. I've been riding it for about 1K miles with no issues, and fell asleep on checking them, as I thought I'd solved it during the break-in period. Thanks to info on this forum, I had much better (but evidently not perfect) luck using Suzuki exhaust gaskets, which are the same as my other two '83 GS1100Es, coincidentally. Time to safety wire them, I'm out of Suzuki ones for now, so I'll use the Andover ones and wire it up, as I'm riding tomorrow. Here's my bike, I absolutely love it, it isn't a scorcher but runs beautifully.

Just to come full circle on my initial question - last night I actually held the oil tank in place and the parts manual organization finally clicked in my head & made sense… not at all intuitive but I understand now.

Regarding the 5/16” forward mounting bolts for the rear mudguard support:
-The right side hardware is listed with the oil tank parts and calls out bolt 000371.
-The left side hardware is grouped in with the rear mudguard parts and calls for bolt 000370.

I’ll probably start a build thread. This forum has been pretty helpful in answering a lot of my questions via old threads.

Thanks again, guys!
Chris

Chris Johnson said:

Regarding the 5/16” forward mounting bolts for the rear mudguard support:
-The right side hardware is listed with the oil tank parts and calls out bolt 000371.
-The left side hardware is grouped in with the rear mudguard parts and calls for bolt 000370.

Click to expand...

Very good find! I have updated my post above, including bolt dimensions.

- Knut

gpzkat said:

That's good advice, thanks for the input. I expect an Email tomorrow, the son or perhaps grandson of the founder said he's wlling to send replacement foam, but he wasn't sure it would correct the problem. If I can get some specs on what other foam they may have, that may be the ticket. I should think they are experts and have various materials available.

Oh, and back to the OP Chris - do you have a build thread? These old warhorses are so cool; it's great to have another restoration being done - big props. I just got back from a great ride through the canyons on mine, but the right side exhaust collar let loose. I've been riding it for about 1K miles with no issues, and fell asleep on checking them, as I thought I'd solved it during the break-in period. Thanks to info on this forum, I had much better (but evidently not perfect) luck using Suzuki exhaust gaskets, which are the same as my other two '83 GS1100Es, coincidentally. Time to safety wire them, I'm out of Suzuki ones for now, so I'll use the Andover ones and wire it up, as I'm riding tomorrow. Here's my bike, I absolutely love it, it isn't a scorcher but runs beautifully.

Click to expand...

Nice bike, but the seat is an eyesore.
Try to make it more flowing, more in line with the fuel tank:


OP:
if you plan to carry luggage, it is better to strenghten the rear loop:

No luggage on this one but I’m glad you brought this up. After seeing photos of several other’s standard mudguard support, I realize mine is odd. Now that I look at it more closely, it doesn’t quite look like an OEM quality part even though I was fooled by it previously. Mine has a flag shaped forward mounting tab and the fit to the frame is too irregular with all the interacting surfaces. I guess I’m on the hunt for a proper rear support now.

Chris