What did you do to your CT70 today

Discussion in 'General' started by Tori, Jul 10, 2012.

  1. detdrbuzzard

    detdrbuzzard Active Member

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    Friday while out riding the mighty CT 70 started having a very hard time going into 4th gear so I grabbed the XL 70 motor out of my basement and transplanted it into the Mighty CT 70 frame, too bad I didn't notice the broken exhaust studs begore I bolted the motor in
     
  2. racerx

    racerx Administrator
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    Ruh-roh(!)
     
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  3. detdrbuzzard

    detdrbuzzard Active Member

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    seeing that it has to be opened up to fix the trans I guess i'll order a big bore kit for it too
     
  4. kirrbby

    kirrbby Well-Known Member

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    vintagehondaminitrails.com has tooling to drill out the broken studs. I think the price is pretty reasonable.
     
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  5. red69

    red69 Well-Known Member

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    Never miss an opportunity to get bigger!:devilish:
     
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  6. racerx

    racerx Administrator
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    I'd start by looking under the outer clutch cover. This could be something as simple as a loose shift star.

    If you do end up splitting the cases, plan on replacing the shift forks. And, consider the possibility of adding a stroker crank; that's easy to do and not a whole lot of bucks. I do realize that this may be opening a can of worms. There's nothing wrong with adding a 52mm/88cc bore-up, it'll be a nice little bit of extra zing and can be simple as just the bore-up kit...or as extensive as building a 108cc stroker tune. The difference is in the amount of usable power. You'd be able to easily keep pace with city, suburban & rural traffic with a longer arm swinging that piston...50mph sustained no problemo, and enough added torque to really swing the needle on the seat-of-the-pants dyno. It's far easier to go through the planning process, even if you ultimately decide to keep things basic and simple...than it is to wish you'd taken things further, after the fact. Once that motor is buttoned-up & running well, you won't want to go back in. Think of this as "measure twice, buy once" applied to engine building/tuning.
     
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  7. detdrbuzzard

    detdrbuzzard Active Member

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    i'm heading to Belleville to have one of the ford mechanics I work with extract them for me, he has a nice shop setup in his barn
     
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  8. cjpayne

    cjpayne Well-Known Member

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    Free is always nice.lol
     
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  9. airblazer

    airblazer Active Member

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    Is stepping up to 108cc as simple as combining this stroker crank and this 88cc big bore kit, for example? I haven't purchased an 88cc kit yet as whenever I'm free at home I'm trying to get my Z50 rideable. But since my CT70 is in 1000 pieces in a storage bin in my garage, now is a great time to learn what I can do once I get back to it (I have to replace/bore up my cylinder anyway). I'm guessing since you mentioned it's opening a can of worms that maybe the stock carb, clutch, oil pump, etc., are among the list of needed upgrades to accomodate this kind of a build...
     
  10. racerx

    racerx Administrator
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    That's basically it. Stock stroke + 52mm bore = 88cc. 52mm bore + 51mm stroke = 108cc. TBparts is pretty good with their product descriptions & support.

    As for the support upgrades...

    First off, a high-volume oil pump is a good idea with any displacement increase, even a basic bore-up. If you're doing a rebuild...and building a larger-displacement tune is not very different than a rebuild...a new oil pump is cheap insurance. Using a high-volume replacement is about the same money and the only additional work is enlarging the top end metering orifice, a 5-minute job...if you work slowly. Additional oil flow aids cooling.

    Next up, now that the motor can make a lot more grunt, the clutch needs to be more robust...to control it. Heavy-duty clutch springs + a new clutch pack (plates & discs) are the minimum. However, HD springs...at least for the manual clutch...have gotten tougher to find. For manual, I'd either use the Takegawa 3-discs clutch, it's a lot of value for the money. For a semi-auto, HD springs are readily available..however...TBparts semi-auto clutch is nice upgrade, all-new parts. They also offer a full manual flavor, too. If you're building a high-revving tune, TBparts also offers a billet clutch basket for either.

    Cam selection depends on which head you're running. With a 6v/plain bearing head, there aren't many choices...it's basically stock, "fast road" and race. Since bigger displacement makes any given cam profile "act smaller" I'd go for a more aggressive bumpstick, and opt for "HD" valve springs. (They're not really a lot stiffer, but have wider coil spacing to prevent binding with higher valve lfit.) That way, a cam-swap is easy, if you change your mind later.

    Overheating is always a concern, one you have road-going power and sustained cruising, at speed, becomes possible. A dipstick oil thermometer is an inexpensive way of monitoring temps. Once you have enough power to sustain 50mph+, it's likely you'll need an auxiliary oil cooler.

    Lastly, since horsepower equals airflow...and vice-versa...you'll need a bigger carb to allow deeper inhalation and a free-flowing exhaust to let those ponies exhale. A Mikuni VM20 carb is a known good choice, along with a rotated intake and open-element air filter. There are a number of exhausts from which to choose.

    This might sound like a lot of changes. In a way it is...but...it's not complicated. The only additional parts are an oil cooler kit and dipstick thermometer and it could be argued that the thermometer is just a part substitution. The rest, in reality, little more than using different parts. Most are items that would be replaced as part of a stock rebuild.
     
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  11. airblazer

    airblazer Active Member

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    Thanks for the info Bob @racerx Can you tell me more about enlarging the top end metering orifice? Is this a modification to the case?
     
  12. racerx

    racerx Administrator
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    The TB kit includes a 2mm drill...or at least it used to. Every kit should have instructions. So at most you might have to source a drill. I have a dedicated pin vise, with the right size drill; takes about 2 minutes to run it through the metering orifice. Beyond that, it's just cleaning...which is easy, especially with the cases split.
     
  13. detdrbuzzard

    detdrbuzzard Active Member

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    got the exhaust studs removed on the XL 70 motor. with new studs installed I got the exhaust installed also and fired it up 20200628_172121.jpg
     
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  14. cjpayne

    cjpayne Well-Known Member

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    Does it have the 1dn 3up pattern? I had an SL70 when I was a kid and thats the shift pattern I remember.
     
  15. detdrbuzzard

    detdrbuzzard Active Member

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    I think it does, I hope it does cause it would stop the confusion when I hop on one of the bigger bikes
     
  16. Rob Dodds

    Rob Dodds New Member

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    I’ve been fabricating PVC parts into fork covers for K3 CT70. In progress. Used my Unimat to modify a 1” pipe and 1” coupling into a top fork cover. Still needs final adjustments. Will photo finished product
     

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  17. detdrbuzzard

    detdrbuzzard Active Member

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    today I put the frame cradle on played with the carb some and adjusted the clutch then took it on its first ride with the XL motor, one down three up trans too 20200629_192340.jpg 20200629_193453.jpg 20200629_210802.jpg
     
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  18. detdrbuzzard

    detdrbuzzard Active Member

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    took a short ride yesterday and went to the mailbox but kept the speed limited to 30mph. stopped on the way for a pic with heavy equip 20200630_190021.jpg 20200630_190357.jpg ment
     
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