Ontic's 1981 R80G/S build-up thread

A bit of an expensive project isn't it !

front end update,

Finally, this morning, my 320mm rotor arrived from Germany so this afternoon I was able to begin figuring out an adapter bracket.
Now, I have read in quite a few places that with these forks there are problems when one attempts to fit a 320mm rotor on a 21 inch wheel.
As far as I could find out there was no stock part (ie caliper bracket) to do this, and I had also read of interference between the rotor and the wheel, with fabbing required and even grinding the back of the caliper?
anyway, what the hell, I wanted a big rotor so I thought I would give it a go.

What I ended up scoring on ebay (for very little) was a caliper bracket for a 21 inch rotor from a slightly later KTM that had USD forks yet still took the same brembo two pot caliper.
So, it would fit my caliper, but of course having a different bolt spacing it would not fit my fork lower properly. I had no idea what would be required to make it work, or if it would work, but it seemed worth a try.

Here is this later 320mm caliper bracket bolted up with the new rotor in place positioning the caliper in the best possible position... head scratching time.




Originally I was planning on measuring up and making from scratch some kind of relocator bracket to reposition the caliper and its bracket into a good position for the rotor. Then, considering how close to ideal position the caliper sat by using the lower hole in this bracket, and looking at my materials at hand, I thought of something else.

I happened to have also bought off ebay another of these same calipers but this time with a bracket for a much smaller rotor, suited again to a later KTM with USD forks- it had the same spacing for the mount to the forks.
I got the idea to use this second caliper bracket on top in what might be described as a rather inelegant solution...
something like this but with the end cut off and a new bolt hole for my upper fork mount


so, with the need for little more than a hacksaw, a grinder and some files and sand paper and drills I set to work.


Off with the end and then I had to do a fare bit of grinding and filing the underside to get it to fit snugly into the shape of the WP extreme fork lower (I did not want to muck around with the fork lower itself at all)

anyway,
after a few hours of fiddling and fettling I got it together in a solution that may not look all that great but is very solid (possibly stronger than stock) and really quite simple.
That top bolt is spaced/shimmed between the brackets with an odd collection of bits that I will probably be replaced with a one peice sleeve.




here you can sort of see the position of the pads on the rotor.
this is the lower end of the pads- as can be seen the pads go right to the edge of the rotor

the top edge of the pads I have swung in a bit further to spread the load a bit wider over the rotor. It does not seem posible to get this caliper (with or without the bracket) deep enough onto the rotor to use all of the intended braking surface. I doubt this will be a problem but welcome any comments about this.


This is really as deep as I could get them onto the rotor without modifying the caliper- and even this took a little bit of filing on the caliper bracket in the rotor slot to get the most out of it,
all hard to explain and I don't have good pictures to do it for me.
If anyone is interested in the specifics just ask,

finally the comparison
old verses newer


All up I am not sure if it is 'interesting' or just plain fugly!

Whatever the case it feels like I could belt it with a BFH and it wouldn't go anywhere.


Next is just waiting for the new triples... unless I get impatient and decide to try this out by modifying the current KTM triples to fit.

Nice work!

I need to get to work myself....

Mate , that looks great , an impressive rotor !!!
and I reckon you were very lucky with that bracket ... go buy a Lotto ticket !

Indeed! I wanna see some more unholy progress While we are waiting for the new Rdubb triples are you tempted to try to get the front end working with the KTM triples? I am.
Despite my impatience, it would be great to be able to compare the two different offsets.

In the meantime I suppose I should follow your lead and pull these forks apart. I want to shorten them to stock beemer length like you have done and just get to know their innards.

What I am really curious about is re-springing and re-valving these things- how to figure out what to do. I've been given a contact to do this work, but I would love to be able to figure it out so I can do it myself- no, not for the personal satisfaction, but for the money!

I look forward to some very detailed discussions and experiments with this (when the time comes) on your Unholly thread as we each start to work with these forks.

Thanks mate,
the ebay description said the 320mm caliper bracket cost the seller $350 from 'the powerparts catologue':eek1 Given the stupid prices of these things new, let alone what we pay for them if we buy them through the 'proper places' in Australia that wouldn't have surprised me. Googling the part number (58413014000) however, shows it can now be bought here online for $150, so the description was BS.
It came to me in it's original brembo box with the original literature- and only cost me $10.50, so I reckon it was still a good buy

Just for interest (if anyone interested in this sort of thing actually reads this)
Having googled this part number I have, I followed a few discussions and I think I may have found what might be the actual stock part that might have done the job (ie fitting a 320mm rotor and two pot brembo caliper to a set of WP extreme forks)
Part number 58313049000
As visable in this parts fiche
http://www.ktmworld.com/ktm_oem_parts_schematic.asp?schematicId=50576&itemNumber=58313049000
The main reason it might not work is (I believe) if the fork lower mount for the caliper bracket is different to the one I have (some of my reading indicated this might be the case?).


I'll keep an eye out for the 'real' part, if I can get one cheap, just to neaten things up a bit, but in the mean time my double bracket doodad will have to do. Maybe it will warm on me in the mean time

The caliper mount is effective, though inelegant: well done. With your spacer/slleve solution, is there any concern with lateral torque on on the long allen bolt under braking? I'm sure it's fine, I'm just trying to visualize and understand all of the mounting points.

Thanks for the comment,
and a very fair question, exactly the sort of critique I am looking for.
Honestly, I don't know and hadn't put much concern into that specifically (yet). I see what you mean though. I've just gone out to the shed again and tried to simulate as much braking load type forces as I can. The bracket assembly feels as solid as a rock. Literally. No matter which way I push, pull and tweak on it, as hard as I possibly can, I can't get it to move in the slightest detectable amount. Of course real braking load will be a much higher force than anything I can simulate with my two hands, so I am just going to have to keep an eye on it when road testing finally begins. I am also going to make a very well fitted sleeve for that bolt.
So yeah, my feeling is it will be perfectly fine, but thank you for raising that concern and I will keep an eye on it. This is all-seat of the pants stuff for me, so I could be very wrong.

The caliper itself on the top and bottom sort of floats on the caliper bracket on two rubber bushed pins that would probably experience similar 'lateral torque' as this allen bolt in question. There is actually a fair bit of play or wobble in the caliper on the bracket.
These are very heavy duty strong allen bolts as well. Beemer bits from my parts- not sure of original application.

Cheers,

P.S.
I spoke to Paul Rooney this afternoon about frame reinforcing and swing arm lengthening, amongst a bunch of other helpful details. Going to have to start a new piggy bank with his name on it

A good thought on the allen screw .It would be good to have a very good fit on the sleeves so all the load is all shear rather than a combination of shear and bending .How does that sound ?

Thanks mate, it sounds good, and is what I was thinking without putting the correct terms to it
I'll probably measure it all up precisely and get something turned up.
Cheers,

Note: I am not an engineer, but I have built a couple of bikes. Front end swaps, supermoto conversions, and a substantial application of baling wire and duct tape is fine but when braking is concerned, I often take the straight and narrow path.

A second look at your photos has me more convinced. If the lower mounting point has the bolt running through both brackets and the fork leg, it should take a good bit of the flexibility out of the system. As a precaution, I would get/make a sleeve for the upper bolt that with an ID that matches the bolt and an OD like that of the fork lug. This sleeve should then have enough clamping surface area between the brackets to reduce the amount of lateral force that the bolt is subjected to.

neither am I

Yes, the lower mounting point has the bolt running through both brackets and the fork leg. I just happened to have a wide selection of allen head bolts (bmw parts) that perfectly fit the thread on the brackets and the holes in the fork legs.
In the outer bracket holes I have drilled out the threaded holes and the new middle hole so that the bolts are a perfect snug fit.
The lower bolt threads into the inner bracket. The middle bolt threads into a beefy nylock nut on the back of the upper mounting point on the fork leg, that I will also threadlock (and that sticks out no further towards the rotor than the inner bracket does). The upper bolt again threads into the inner bracket. There is no, absolutly NO, flex in the system (at leas at 'human induced' loads).

I hope that makes sense.

Excellent. That was pretty much my plan and I think what Sibbo was intending as well. The current two piece sleeve (shimmed with an extra couple of washers) I have on the moment is actually a perfect ID fit for the bolt, but is a little narrow OD for my liking (and is just there for mocking up anyway so I could acurately position the whole thing and drill the middle hole). The upper threaded holes in the brackets that this bolt goes through has a slightly raised area (as you can see) kind of like a cast in washer... what I was intending to do is turn up a sleeve that matches this OD. I could actually take it a bit wider to match the fork lug OD but I would then want to shim it or recess the face of the sleeve so that it also made contact and fitted perfectly over/around this raised area - otherwise there would be less point in making it wider than this area.
Does that makes sense?

About the straight and narrow path.
Yeah, This solution simply arose from working with parts and materials I had at hand. I didn't actually plan on doing it this way, I just realised that I with what I had I could get it done.

Out of my spare brembo caliper and bracket parts I also got a little magnetic sender thing thing that threads into that spare hole above the lower bracket hole. I believe this must have been for a speedo? So, if my stock speedo ever packs it in again, I shouldn't be too hard at all to get a digital speedo set up.

Cheers,

An overdue update with not a lot to add, but a few questions if anyone is reading,
sorry for the ramble, its just my style,

Basically I am slowly building up the parts pile.
A growing pile in the US will probably be shipped over soon, and I am just about to put in the big motobins order.

About the motobins order-

I know I need to do the timing chain (realy noisy)- so I am getting the complete timing chain kit, and I figure I might as well grab new camshaft and crankshaft sprockets for while I am in there.
If I am changing the sprockets is there anything else I need?
Is it standard to re-use woodruff keys or is it just cheap?

About the motobins carb rebuild kits- are the original (slightly more expensive) nitrile kits recommended, or are the pattern 'hydrin' ones which are described as lasting longer recommended?

A new issue I just noticed is that when I shake my swingarm from the side there is a little bit of play in the swingarm- no it is not just play in the final drive (I have that too) the swingarm nuts are torqued up very tight- within the swing arm I am not sure where this play would be coming from..
New swing arm bearings? Will that solve it? Any thing else likely to be required?

I am getting the single seat that motobins sells, which is (in their words) a siebenrock seat. Interestingly motobins sells it a lot cheaper than siebenrock does (175 Pound verses 275 Euro), but siebenrock sells the luggage carrier cheaper than motobins...
Anyway, I'd prefer a black single seat, but motobins only has the red, and for a 100 quid cheaper not counting extra postage by using both suppliers I'll take the red one!


In the mean time I've bought an ac/dc tig welder with the plan to make my own panniers and rear racks and have been practising a lot on a lot of scrap aluminium and steel... more practice required.

Although I quite like the look of the stock G/SPD luggage carrier and rear rack it seems to me like there is probably a lot of doubled up unnecessary metal and complexity there- subframe, luggage carrier, rear rack, pannier frames bolting to rear rack- overly complicated IMO and for my intended use.
also while the luggage carrier looks particularly good to my eye- for space and weight distribution it seems to sit a little bit higher than it could or should? I don't like wasted space like that and I would prefer the load to sit as low as it can.
Anyway, I am going to make my own simple one piece luggage carrier/rear rack that sits as close as possible to the top of the rear fender (as in sitting low). I need to get the single seat in hand so that I can measure up and make everything fit properly. I am going to add a little to the subframe itself so that the rear of the pannier frames mounts to the subframe instead of to the rear rack.
This all sounds complicated- hopefully the final images will show simplicity and make sense!

I made a hell of a lot of work for myself shortening my exhaust,
its used to stick out quite far from the back of the fender, after a lot of cutting, tigging, grinding, cutting, tigging, etc, etc, now it sits in nice and neat (and finally airtight) and I am lot happier with it.
Because of the 'custom' headers, Y-piece and non-G/S staintune, and how they sit, I was able to bring in the stock left side pannier frame about 25mm- which is another 25mm wider that the left side pannier can be. Good news.

Cutting and re-welding the pannier frame lug made me realise what crappy potmetal these stock pannier frames are made from:eek1 I am also going to be adding a wrap around rear bar to join both pannier frames together.

I have also started mocking up some subframe reinforcements
right side


I have had to make two subtle bends here- one to get proper clearance around the Ohlins spring and another to get around back under the pannier frame- a bit hard to see how the slight bends are sitting but it looks OK in the flesh.

left side is going to be a lot tricker and bendier. Up and around the exhaust and then back in.


at the moment I am just mocking these up with mild steel. I am assuming I should try to get some chrome molly steel for the final version? Really?

I've tried googling but does anyone know what steel our frames/subframes are made of? They are cro-mo aren't they?

Although I am happy to tackle a custom luggage carrier (and anything else that bolts on... and off) I don't think I am going to trust my tig welding for the actual subframe and will take it into a friends metal fab shop where he has a 'tig artist' working for him.
When the time comes the frame itself is going to be sent up to Paul Rooney for one of his frame reinforcement jobs.

And that's about it for the moment.

Motobins order is going off as soon as I can finalise it,
Cheers,

Gawd you're a neat and tidy fella Ontic ! My pannier mounts on the ST are 12mm solid mild ,there not that much metal ,they're strong and I can weld them up at any farmers shed if I break them . That said , yours will be beautiful!

As to those swing arm and carb questions, they sound like a good reason to drop into Boxerworks .

The play on the monolever could be because the bearing has been turning on the "adjusting " pin and has worn it.

Motoren Israel has slightly oversize pins which get a better grip of the bearing, and they are cheaper than OEM from Motobins too.

OEM pins are a loose fit in the bearing so if you are going to reinforce the frame it makes sense to tighten up the bearing fit too.

The frame tubes look and work like mild steel to me, you shouldn't really need much better.

My old man used to make a few pannier frames, and he used a thick wall pressure pipe, which was a bit better alloy then stock mild steel and worked/ bent easily too. But that was 50 years ago.

The stuff they currently use for petrol lines in servos is similar and is good gear too, but I dont know if it comes small enough for you.

For the brake caliper mount couldn't you weld a tab to the inner mount on the same plane?

Can’t believe I only just found this! You’re doing the old girl proud, and I loved your mini ride report with the rum and fishing.

PM’d you with a couple of questions.

HI, I have been following your progress for a while now.In the past I have used hydralic seamless tube for various racks/frame rails etc.Comes in assorted diameters,bends and welds easily,strong, and is cheap as chips.All good things.I buy from a local hydralic shop.Would be obliged if you could PM me Paul Rooneys contact details.Ta

Sibbo mate,
my tig welding is currently terrible! As a tig welder, I make an average brazer!
I didn't make those pannier frames, I've just narrowed the left one a little. Cut the tab off, shorten the tube and weld the tab back on. It sounded simple until the potmetal pannier frame tube just kept curling back and blowing through- I ended up having to drill through the tab, insert a steel dowel, weld it in, slide the tube over the dowel, weld it all up and call it good. It is good now, and it is strong, but it aint no 'stack of dimes'.

With my AC tig theoretically I could do that, but I have no idea how that might affect the temper of this cast alloy caliper bracket? Honestly, after seeing this system of bracket rellocation I am not too worried about my solution- I think it should work just fine,

Thanks mate, PM replied, hopefully there will be a lot more progress on this thread soon.

PM replied, thanks for the Hydraulic tube tip- I'll check it out.

Thanks a lot, some good tips. I am going to go out to the shed now and see if I can get the swing arm off and actually understand what you are talking about (I've never pulled the swing arm off and don't know how it actually works inside there). I'll try to check the adjustment pin for wear.

Interesting to hear about the mild steel thing- I will try to make it into a friends metal fab workshop again tomorrow morning and see if I can source some better pipe/tube. He just gave me this last bit I am playing with currently and doesn't even know what it is. It has a seem. It bends well and quite easily and it welds very well. Assumed to be simple mild steel.
Maybe more later,

Cheers guys,

On the mild steel solid round versus tube thing .. the weight difference is an interesting calculation ...there's not much in it and as for braze ... if you have manganese bronze rods and tig , go for it .It's very strong and durable .Neat too and nice with tube if you go that way .( Old bicycle frames from the tip are a good tube source ).