Restoring & Modifying 1971 OIF TR120

[NM Bonny]

Updates:

Brakes: My friend, neighbor, and preferred machinist died last weekend (just 4 years my senior, from cancer). His young son and foreman will continue the business, but he's grieving and underwater trying to keep up, so I don't intend to bother him with my DIY front disc brake conversion project until he's got his feet under him.

So, I will press ahead with the remainder of the bike's refurbishments, and may be forced to run the OEM front brake by default for a time, anyway. I may install the longer actuating levers while inspecting the shoes and installing new bearings in the front hub. That'd be a fun interim experiment.

Suspension: I got the bushes, dust excluders, and new grease nipples in for the swing arm. So, whenever they send me the back-ordered bushing R&R tool, I will rebuild the swing arm and post some photos of the process.

Final drive: I went ahead and ordered a 47-tooth chainring, since the vendor said no problem sending it back if unused to swap for whatever else I may need (like a clutch or primary stuff). When it gets here, I'll determine the viability of modifying a 46-tooth chainring and post my findings with photos.

 

[atomsplitter]

Sad to hear about your machinist buddy. Look forward to seeing the upgrades progress. I recall upgrading the swingarm bushings and a solid axle on a 71 Yamaha XS 650 a number of years ago. The OEM bushes were plastic with a hollow axle fitted with a grease zirc, I found the upgrades on Mike's XS web site. I pressed the new bushes in with my bench vice with soft jaws. Huge improvement in handling performance.

 

[NM Bonny]

Sad to hear about your machinist buddy. Look forward to seeing the upgrades progress. I recall upgrading the swingarm bushings and a solid axle on a 71 Yamaha XS 650 a number of years ago. The OEM bushes were plastic with a hollow axle fitted with a grease zirc, I found the upgrades on Mike's XS web site. I pressed the new bushes in with my bench vice with soft jaws. Huge improvement in handling performance.

Thank you.

I owned the same Yamaha ($600 from the original owner in 1979), but thankfully never had to do the swingarm, as I was living in an apartment (two units from the sand in Ocean Beach, SD for $375 a month).

I could probably have used a socket and my arbor press to do the job, or borrowed the neighbor's (son's) lathe to roll my own tool, alter one of my existing bearing drivers, etc. But I aim to keep this bike until I kick no more (judging from my Dad, who just turned 93, it'll be a while), so I'll use it enough to pay for it.

And I like supporting the outfit who makes and sells them to folks who lack my abilities, Draganfly Motorcycles in the UK (even with shipping, you can sometimes get batches of parts for less than the domestic vendors). So, I went ahead and paid what I learned this morning is the new, arguably excessive price of the tool. Should be here shortly--and if I can recover my stride and the garage warms up a bit, hope to get back in the swing of things...

 

[NM Bonny]

Okay, here are a few photos of the result of overlaying the 47- and 46-tooth rings. As you can see, no problem re-drilling for the former's 5 holes; you'd just need to use button head Allen bolts in place of hex head bolts to affix the ring and still clear the chain links.

However, machining the inner bore would just break into the existing holes. I don't anticipate that'd be an issue with a heavy steel ring clamped to the rigid hub--but on the other hand, it'd be nicer if that were not the case.

Conclusion: EMGO could easily make up viable 46-tooth rings for the OIF bikes (the distance from central bore to bolt holes stays constant with the larger I.D. hole), and that would net a lot of sales IMHO. I've advised the vendor, and we'll see whether he thinks suggesting it to EMGO would interest them.

I could have my neighbor's shop make up a batch of these rings but it'd be expensive, and I'm retired. So, I'd have to get a substantial portion of the production run pre-ordered to be able to afford it. Perhaps someone who knows how could estimate the reduction in rpms with a 46-20 vs. 47-20 ratio--and assuming a 4.00-18 rear tire?

Ultimately, if I'm unsatisfied with the final gear ratio netted from my 47-20 combo, I'll re-drill and machine a 46-tooth ring and give it a try.

 

[NM Bonny]

In other developments, the neighbor's son and foreman has decided to maintain the machine shop, and is doing a run of new parts for the Creative Spridgets DIY intercooled supercharger conversion as we speak.

So, whenever the weather warms up a bit and I have time to R&R the headset bearings and races on this bike, I'll take the opportunity while the triple trees and forks are off the bike to go ahead and make a non-functional (acrylic or hardwood) prototype adapter for the Wilwood caliper to mate with the T140 sliders, Sporty aluminum hub, and 11.5" disc, per the earlier posts.

If the setup proves viable, as the preliminary mockup in the earlier posts suggests it should be (the margin of error is several thousandths, so I could be either wrong or right), I'll go ahead and have Zach make up a working prototype in 6061-T6 aluminum, order the Borrani rims, lace 'em up, and test the conversion out on a rip down the canyon to the Rio Grande.

Life is short. Why the heck not?

 

[grandpaul]

Sorry to hear of the loss of your machinist friend. We are the oldest generation for the most part...

Great project details, thanx.

 

[speedrattle]

rebel gears will make anything you want for anything you want. i had them do 37, 38, and 39-tooth sprockets for the 17-inch wheels on a T120 race bike.

not expensive, beautiful work, and quick.

but their website doesnt work for me

click on "reply" to see the images

 

[NM Bonny]

rebel gears will make anything you want for anything you want. i had them do 37, 38, and 39-tooth sprockets for the 17-inch wheels on a T120 race bike.

not expensive, beautiful work, and quick.

but their website doesnt work for me

click on "reply" to see the images

Wow, cool - thanks! I see they're made from 7075-T6, which is much harder than the 6061-T6 I call out for my CNC machined, non-wearing parts. What kind of wear are you getting out of the hard aluminum vs. steel OEM-style sprockets?

 

[NM Bonny]

Wow, cool - thanks! I see they're made from 7075-T6, which is much harder than the 6061-T6 I call out for my CNC machined, non-wearing parts. What kind of wear are you getting out of the hard aluminum vs. steel OEM-style sprockets?

Kevin,

No need to reply. I just talked to my machinist (the son and foreman, who's carrying on the business) while picking up some parts for Creative Spridgets, and he informed me that 7075 aluminum in T6 temper is essentially the same hardness as steel--just lighter. I'm excited about including a 46-tooth sprocket whenever I move up to 750cc.

Speaking of steel, he showed me a piece of Inconel, a nickel-chromium based superalloy called out by the engineer on the design for a new chip-making press, and it is unbelievably dense. The chunk in this photo is barely 1.5" square and weighs... yeah, nearly 3 lbs!

 

[NM Bonny]

Follow-up to post #144:

The OIF specialist vendor I spoke to is going to talk with Rebel Gears (thank you, Kevin) to see about making up a run of 46-tooth conical rear hub sprockets. I will keep you guys posted, as I told him I'd be among his first customers if they are viable and he invests in a run of them--and I suspect more than a few people following this thread might, too.

The prospect of '71-75 Bonnies being readily equipped with 20-46 gearing and an 11.5" lightweight DIY front disc brake conversion is very exciting. (At least I think it was '76 when the rear disc showed up...?)

 

[NM Bonny]

It was warm enough to where I felt like working in the garage, so I pulled the front end and R&R'd the headset races. They had felt pretty notchy and, as you can see, they were pitted a touch--and of course the grease was all dried out. But they're so cheap that it'd be ridiculous not to R&R them. That OEM tool is lovely for installing the races/spacers. With a big drift for removal, took me, like, 5 minutes to R&R the races. Didn't break a sweat...

Recorded some data for later comparison when the DIY front 11.5" front disc conversion is done:
- the built OEM steel front wheel w/axle, brake, and inflated K70 Dunlop is 31 lbs
- '71 OIF front end with steel triple clamps is 21.6 lbs... compared to 2000 Sporty front end with aluminum triple clamps (see photos) at 26.8 lbs--but with 39mm vs 35mm tubes

Of course, if the 'proof-of-concept' adapter I make up works, the new built wheel will have an aluminum rim, beefy aluminum Sporty hub shown earlier, and 11.5" stainless Performance Machine (Harley spec) rotor. It'll be interesting to see how the built wheel compares--though of course to be fair, I'd have to add the brake parts to the new setup's wheel weight. The fender is unsprung weight in both cases, so that's a wash. The L/H newer model slider is slightly heavier, due to the caliper mounting ear.

I toyed briefly with the notion of simply going with the Sporty front end, which would've saved the weight of the caliper adapter I'll be making up--likely less than 1 lb. of 6061-T6 aluminum. Other changes would've been: wheel base + 3/4"; tube spacing +5/16~3/8"; ride height unaffected, as the Sporty design allowed you to slide the triple clamps up and down the tubes as desired. Easy-peasy to make the handlebars and OEM '71 headlight mounts work. Similar style gauge mounts would've worked.

I would, however, have had to make up a new spindle to fit the smaller Triumph bearings (turning down the existing one would arguably have left too small a cross-section of steel near the top where the inside is drilled and tapped for the retainer bolt).

But I digress... last photos show the Bridgestone Battlax in 3.25/19. Looks like it will indeed fit inside the OEM fender fastener affair... just barely. Very likely, it will mean a fiddly fender installation routine or at worst fabricating some different retainer clips, maybe with button head screws, or whatever. But I think the meat will fit. The width of the beads is right about where it'll be when mounted in the 2.15" Borrani rim...

Anyway, I'll now make up a jig to hold the front end on the bench while I fit the later-model sliders, so I can fabricate the 'proof of concept' Wilwood caliper adapter prototype. Hope to get that done in the next several days.

I think I mentioned these brand new K70s will be available for, say, 50% of retail and shipping...? Never ridden, just rolled around the garage a bit--but no flat spots because the bike gets moved every couple of days...

 

[NM Bonny]

Okay, re-ordered the Wilwood 4-pot aluminum caliper. I'll (again) have 90 days to keep it before I have to ship it back if not sure it'll fit--but this time I hope to prove the concept as quickly as possible, and then have a working prototype machined from 6061-T6 before the end of the month. That'll depend on my machinist's production schedule, but he enjoys breaks from defense contractor work, so I'm pretty sure we should know if this DIY conversion will work pretty soon.

As regards the Performance Machine stainless, Harley-spec 11.5" rotor I've chosen (pictured earlier in the gross initial mock-up), Wilwood supplies their calipers with their claimed "industry-leading stainless steel rotor-compatible formulation." I haven't run a Wilwood caliper on a bike, but they've been around a very long time, so I expect their pad formulation to be top-notch.

Note: any 11.5" Harley-spec rotor will work with this setup, though. There is an amazing array of designs, but I just liked the dual 5-spoke version I chose, as the aesethic invokes the '70s as I remember them growing up (see pic here again).

On the Borrani aluminum rims (second pic), Buchanan's will lace them up for a C note, and I am reasonably sure that OEM Sporty centerline lacing will provide room for the hub between the Bonny's fork sliders, per the gross measurements taken earlier (they sell spoke kits for both the Bonny conical and Sporty hubs). But we'll see how the proof-of-concept mock-up goes. It's at least conceivable that either I'll have to dish the wheel slightly to the R/H side--in which case, I'd prefer to lace it up myself--or simply use a few thin shims to get clearance for the rotor, in which case I could ship them my hub and let them lace it up. We'll see...

 

[NM Bonny]

Okay, got the old sliders off--The oil was nasty dirty and based on what Rudy indicated, the viscosity was too high.

Also, immediately encountered a problem with the (otherwise great) reproduction of the OEM Triumph service tool sold by Steadfast, a vendor which I generally like. I don't think they manufacture the thing...

As you can see, the teeth were splayed out a bit and there was obviously no QC of the parts before being shipped to Steadfast. But it's as easy as two gentle taps with a ball peen hammer on the vise's anvil, then twisting the working end in some fine wet-dry sandpaper, followed by a couple of scuffs to break the edges of the teeth... and voila: works as it should.

However: the late-model sliders were manufactured at variance with each other--or there's some scuffing that raised irregularities inside the L/H slider, because while the R/H went on perfectly, very nice fit, the L/H threatened to inflict micro-scratches on the tubes, so I backed off. A little work with emory cloth just inside the bore didn't cut it.

I had to get a hone and crimp it into a piece of steel pipe from Home Depot, to clean corrosion out of the sliders for the '51 FL's similar DIY front disk brake conversion (penultimate pic). However, that's a 40mm hone. So, I'm hoping I can get a 35mm version to give these a quick whirl... Yes: Flex Hone (Brush Research) does make a 1-3/8" / 35mm one, part no. BC13824, so I'm good to go.

At any rate, grabbing one of the tubes in the bench vise's pipe teeth, padded by a welding glove, holds the front end sufficiently stiffly for the mock-up (last pic). So, assuming the caliper and hone get here around the same time, I should have the proof-of-concept caliper adapter made up fairly soon...

 

[Rocky]

Nice reports

 

[NM Bonny]

I used button head stainless screws on the '51 FL's DIY front disc brake conversion (1st pic), and will do the same here. Remaining pics show that it looks like 5/16-18 x 1" should do the trick here, even with a thin stainless washer. Plenty of room for the sometimes expansive heads on those things... I see that the PO of this used Sporty hub used blue loctite on the rotor fasteners.

It'll be interesting to see how much, if any unsprung weight we save with this setup; that stainless 11.5" rotor isn't light. I'll be relying on some weight savings from the aluminum rim. But no doubt both the increase in braking force and enhanced modulation will be worth it. Hope my initial gross measurements were right, and this setup will work.

If so, it'll be straightforward to replicate: just lace up (or have Buchanan's or another wheel smith lace up) an aluminum rim to a late-model Sporty hub, get a late-model disc slider, get a CNC-machined adapter from me, and bolt it together.

Note: if one wanted massively powerful dual discs, the brand new, aftermarket Sporty hubs (just google 1996-2003 front Sportster hub) often come two-sided. So, all you'd need is another L/H disc slider, and the caliper on that side goes ahead of the fork leg, as in this period-racer from the Isle of Man TT (last pic).

 

[NM Bonny]

Okee-dokee... got the hone in, cleaned up the bore of the L/H slider (yuck), deburred the bottom end of both stanchions a bit... and I'm excited to report that my earlier, gross 'measurements'--really, extrapolations with a significant degree of guess--were right on the money.

In short, this fairly critical stage of the initial design mock-up is a success! As you can see in the second photo, the only potential clearance issue is the button head Allen screws--but this is with the Sporty hub in the middle of its L/R travel on the 3/4" axle, and there's loads of room.

That said, the implication of that limitation is that if I need to move the hub away from centered--and toward the L/H slider--to make the adapter design work (which seems unlikely), then I'd have to get lower-clearance fasteners or countersink the rotor slightly. I don't want to have to resort to either thing for replicability and cost considerations, and based on this mock-up, I do not think I'll have to. That's also good because then lacing up the wheel involves no fancy measurements; you just lace it up centered--or have your wheel smith do that for you.

The third photo just reinforces how much room there is using the Sporty hub for this DIY 11.5" brake conversion: both between the rotor and slider, and between the slightly raised bosses (in an inboard direction) for the OEM caliper studs, there's loads of clearance.

Finally, as you can see in the first photo, this really should be a handsome conversion. As I've said, there are a bazillion Harley-spec rotors out there, so it's easy to find a design you like if not this double-five spoke version that strikes my fancy.

Note in that regard that there are both 'narrow' and 'wide' bedding band rotors, and this one is a narrow version, which I chose to more precisely match the pad area of the caliper I'm using. Of course, it doesn't matter if you have a wider than necessary bedding area; you just don't want your pads hanging off the edges. We will see if I miscalculated that factor when the caliper arrives, but I seem to recall that the pad was just a few thousandths narrower than the rotor's bedding area...

Therefore: I am moving forward to the next and final step in the initial design mock-up, and the Wilwood caliper should be here shortly to facilitate that. I think I figured out a way to make up the wooden mock-up adapter without fancy free-hand routing, and if so that'll make things a lot easier.

 

[NM Bonny]

A further note on this conversion, assuming I understood the data provided earlier, re: stanchions and sliders on OIF bikes:

I seem to recall that Rudie confirmed they all used essentially similar L/H disc brake sliders from '73 until the end of Meriden production (or at least until '83), with the chief difference being that the later sliders, like mine, have a groove for the seal-retainer circlip...?

I point this out because when conceiving this conversion, I had in mind owners of '71-72 OIF bikes. But I'm thinking that it should work as a 'big brake' upgrade on any Meriden bike from '71 to '83. Does that sound right?


A related point: Buchanan Spokes has kits for Harley Sporty hubs with shallow or deep drop-center aluminum rims (your choice), and indicates fitment for all 1973-2022 Sportsters. The hub photo they include is like mine, which I believe is for a '96-03 Sporty--but '03-'07 bikes have a very similar-looking, if not identical hub. The only exception on their website is the FLXR hub with staggered holes, which use a special kit--but same price (if you're buying a used or aftermarket new hub, you'll see many with the staggered holes).

However, the 11.5" rotor I'm using will only fit '96 and later Sporty hubs, if I'm correct. The below pics show a typical used example listed as fitting '96-'03 models, selling for $99 on eBay, with bearings installed (mine came with evidently serviceable bearings, but I'll likely replace them just to be safe, as it's easy). This one is like mine--single-sided, which I like aesthetically due to the smooth non-disc side, rather than the two-sided, dual-disc later versions.


At any rate, the caliper will arrive early next week, so I hope to have an answer on viability by next weekend. If I am successful in designing a stepped, once-piece adapter (which would require two-sided machining, so two setups), I just talked with my machinist, and he'll have no problem fitting me in to get a working prototype made up--though it may be early next month due to his production schedule.

But I've got plenty of fun stuff to do on this bike in the interim!

 

[Rudie]

I seem to recall that Rudie confirmed they all used essentially similar L/H disc brake sliders from '73 until the end of Meriden production (or at least until '83), with the chief difference being that the later sliders, like mine, have a groove for the seal-retainer circlip...?

Yes, same left hand slider from 73 'til the Meriden Co-op folded in 83; when Les Harris was licensed to resume production of the Bonneville in the late 1980's, he used Italian (Paioli?) forks.

thinking that it should work as a 'big brake' upgrade on any Meriden bike from '71 to '83. Does that sound right?

Possibly. 73 onwards disc brake fork legs are nearly an inch further apart than 69-73 drum brake legs, and there has been a kit to convert 73 onwards disc brake forks to 12" disc(s) around for many years, uses a spacer from the standard disc brake slider to move the standard caliper outwards by an inch.

 

[NM Bonny]

Yes, same left hand slider from 73 'til the Meriden Co-op folded in 83; when Les Harris was licensed to resume production of the Bonneville in the late 1980's, he used Italian (Paioli?) forks.


Possibly. 73 onwards disc brake fork legs are nearly an inch further apart than 69-73 drum brake legs, and there has been a kit to convert 73 onwards disc brake forks to 12" disc(s) around for many years, uses a spacer from the standard disc brake slider to move the standard caliper outwards by an inch.

Thanks for this, Rudie.

I'll make sure to note--if the part is viable and I were to offer it for sale--that it's designed for 71-72 triple clamps. If I were to offer it for the '73-on bikes, sounds like I'd need to include a simple ring spacer to go between the Sporty hub and the rotor. That spacer would be extremely cheap to make on the CNC lathe, which can feed stock, turn, drill, and part off automatically.

 

[NM Bonny]

As regards hub and rotor spacing, I neglected in post #156 to include this bird's eye view of how nicely the '96-'03 Sporty hub nestles in between the late-model Bonny sliders, using the narrower '71-'72 triple clamps. There's somewhere between 1/16" and 1/8" clearance on either side of the hub @ the sliders' inner faces while generating the space shown in the second two photos.

That may seem tight but it's plenty of room from the standpoint of the tolerances I can call out--and which my machinist can maintain--for the caliper adapter and axle spacers to center the hub.

Of course, if used with later model triple clamps, per Rudie's info re: wider stanchion spacing, there'd be even more clearance.

Also: I was mulling over the fender mounts as I fell asleep last night.

It occurred to me that in the event the OEM setup won't work--say, due to contact between the tire sidewalls and the steel cylindrical flanges that grab the rubber barrels on the fender stays--I could either make up more slender flanges that grip the stays without rubber barrels, or weld flanges to the stays.

In either such case, I'd place rubber O-rings between the flanges and the slider bosses to recoup the vibration isolation function of the OEM rubber barrels.