Front end swap sizes

Discussion in 'Modifications' started by MobileAZN, Nov 21, 2018.

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  1. MobileAZN

    MobileAZN New Member

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    When planning out this build, as I didn't get much of anything to go on for a front end, I was going to put on the inverted fork set you see for the CT70 everywhere. Seems up there at $400 (that's with shipping). So I've started looking around, and realized there are a ton of options for front ends, but I don't have the dimensions of any front end parts to really go on. I don't have a top clamp, the fork I received do not match, so I am unsure if what I have of them really goes to this 1977 CT70.

    Can anyone give me the measurements I need to look for when looking at the center pole of the triple? Fork length I should look for? I am considering the 12" wheel swap if that matters much.

    These are what I've found on Amazon that I'm thinking may fit from what I can gather, but I could be wayyyy off.

    http://a.co/d/3QBvUe9

    http://a.co/d/eu6jPCS

    I know I'll still need to get a brake setup and a hub for disc and such. Any pointers would be great. Or is just buying the $400 setup the best route to go?
     
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  3. OLD CT

    OLD CT Well-Known Member

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    I never installed the inverted front. Buying that crap off amazon you posted would be a mistake. Good bearings alone would cost 45 dollars.
    If the price is too good to be true, it probably isn't. True, I prefer a stock 1977 front end. It would handle bumps just fine.
     
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  4. racerx

    racerx Administrator
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    For reasons of sheer practicality, I agree with OLD CT on this one. If $400 all-in seems expensive to you, best to stick with tried & true OEM K1-1979. Those can be rebuilt and oil-tuned to perform quite well, inexpensively. Suspension parts are rarely given the priority they should have. The bottom line is that real, high-quality, front end parts (fork legs, triple trees, brakes) cost real money, the size of the bike has no impact. For example, I've made my own billet disc brake hubs...$400 a pop, with slightly less than half that amount covering the billet aluminum, bearings, spacers & fasteners, the rest to the machinist - who charges very reasonable rates.

    As for assembling a custom/aftermarket front end on your own, it's deceptively complicated. The trees must have the right spacings, the steering stem has to fit the steering head bearings, the fork legs have to fit the trees and be of acceptable length (stock is 600mm, ~660mm is the practical limit), then there's the brake assembly (caliper, master cylinder, flex line, brake switch), caliper bracket, rotor, hub, axle and spacers, all of which must fit precisely. Sourcing a bunch of unknown, aftermarket, parts and expecting them to all fit..."plug & play"...like an engineered kit, is a guarantee for frustration. It only makes sense if you know what you're doing and have the wherewithal to modify/fab as needed. If you had that level of expertise, you'd not have posed those questions. That's not meant in any disrespectful way. The point is be forewarned. Marketing can and often does deviate wildly from reality. Note the complete absence of details...like critical dimensions...a HUGE red flag.
     
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  5. MobileAZN

    MobileAZN New Member

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    I don't think it's expensive, I just think it can be done for less. I'm in no hurry for anything. I have the time to do all of that. I've built plenty of other bikes.

    I posed those questions, because as stated, I don't have anything to go on. I don't have matching forks, fork parts, triples, any of that. The forks I do have aren't complete, aren't off the same bike years, and I'm not even sure go to this bike at all. As I have a lot of mismatched, incomplete parts, I'm not going to go original on this build. There isn't much to work with at all, and given the condition of the frame, many would have just left it for scrap.

    I asked for measurements. I posted links to other parts I have found that look like what that whole inverted front end setup looks like, trying to assemble it and source the parts for it to see if that complete front setup was worth it already assembled or not. The manuals don't exactly have all of the measurements.

    If I had a front end to go off of, I would have measured it all myself and fab'd what I needed to, but I don't. I do think it's pointless for me to have to go buy an OEM front end to get measurements from if it's already been done, and just doesn't have great documentation. Searching here doesn't yield much for measurements from others, just a lot of "buy OEM for a resto" or "do a complete front swap with the kit". There isn't much here from the pioneers who did do it.

    Thank you for the fork length at least. That gives me something that I didn't have before.
     
  6. MobileAZN

    MobileAZN New Member

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    https://phatmx.com/collections/hond...-inverted-disc-brake-front-end-pre-order-only
    https://tboltusa.com/store/ct70-upside-down-fork-kit-usa-only-p-440.html
    http://mytrailbuddystore.com/cncupsidedownforkanddiscbrakeaccembly.aspx
    https://ebay.us/yZj0AR
    https://ebay.us/zs8plH
    http://www.mx-performance.com/id123.html <-- Mid-page

    I forgot to add that for this particular setup, the inverted fork front end setup isn't a stretch to ask about measurements for parts and think that I can purchase these parts "off the shelf" and make them fit. The setups are all the same colors from quite a few people on the web. They all look exactly the same, and I doubt they are all the same person under different names/shops and I doubt they are sourcing them all from the same one guy making them in a shop in his backyard. It's probably all the same chinese parts. They are just putting them together and selling it as a completed kit and adding nothing custom to the final product.
     
    #5 MobileAZN, Nov 22, 2018
    Last edited: Nov 22, 2018
  7. scooter

    scooter Well-Known Member

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  8. racerx

    racerx Administrator
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    Width, as measured at the axle flanges, stock, is 150-155mm. That's going from memory. Aftermarket/custom I've seen them up to ~205mm, depending upon the wheel/hub/brake combo. A serious disc brake, with a ~220mm rotor needs considerably greater width to allow centering of the wheel. Tire OD is limited to ~20", even that limits clearance for suspension travel; stock is ~18.5". Whatever the fork excursion happens to be, you'll need that amount of clearance to avoid tire-to-fender contact under full compression. If you run a low-mount fender real estate gets super-tight, even with a ~19" tall tire. Stock suspension travel is ~3.25-3.50", going from memory. 4.5" of travel gets tight. Beyond 5" you'll likely need taller-than-stock fork legs. At ~6.00" of travel, excessive front end dive could be a problem.

    Keep in mind that things like tire removal, with a disc brake, as well as the rear end tire/suspension assembly must be considered as well. How much work are you willing to do to R&R the front wheel? Out back, you'll lose chain adjustment range once tire OD exceeds ~19". Front-to-rear ride height has to be kept in balance, especially with 60mph+ horsepower, or you could end up with a wheelie-happy machine. Extended length swingarms are available but, at +2CM, rear fender clearance becomes an issue, anything beyond that requires a custom fender mount setup. IMO, beyond +2CM the rear wheel looks like a foreign object being dragged behind the bike...OTOH, some folks like the look. As you move toward taller tires and longer-than-stock fork legs, longer rear shocks will be needed. Stock rear sock length is 330mm. With 19" tall tires you'll likely need 340mm shocks to keep the bike level. IDK if it's possible to go a whole lot taller than that, due to swingarm angulation and chain alignment. Best estimate, 350-360mm is pressing the absolute limits, without radical mods. And there's the cost factor. This stuff can add up quickly. I'm not averse to spending real money to get real suspension componentry. That said, $800+ for a pair of shocks is more than I'd care to spend...and that's on top of ~$3K worth of rolling chassis upgrades. Unless I've misunderstood, that's well beyond the scope of what you have planned.

    12-inch tires, of necessity, require shorter sidewalls. Since tires of this diameter don't have much mechanical advantage of typical fullsize bike tires, the sidewalls do a lot of work. They are major suspension components. Losing 1" of sidewall compliance + rim protection is not something I endorse. At best, you'll get a stiffer ride and plush ride quality, with control, is fiendishly difficult to realize with these bikes. If you live in an area where the roads are not really well maintained, rim damage is a real possibility. IMO, most of the guys who go with 12-inch rims do so for the aesthetics. That's legit, too, just go in knowing this beforehand.
     
  9. scooter

    scooter Well-Known Member

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  10. MobileAZN

    MobileAZN New Member

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    Thanks guys, that all helps a lot. It's been much more of a pain NOT having something to look at and measure than it is having a bad part that I can look at and replace. Not impossible, just a pain.
     
  11. racerx

    racerx Administrator
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    Engineering & machining a front end is a complicated, high-precision, process. Being off by a few thousandths of an inch can result in problems like bearings that won't seat or fork internals that wear out rapidly. Yes, one could view it as an ordeal. IMHO, it's more accurate to say that looks far simpler than it really is.
     

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