A misunderstanding not a gearing question

Discussion in 'General' started by Deoodles, Sep 27, 2018.

  1. Deoodles

    Deoodles Active Member

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    No need Kirrbby. I hate to tell you my plans but it’s whats best for me. I am going to disassemble my 108 for this build. It has the TB race head on it that’s why I’m trying to get the piston figured out. I didn’t know TB 117 was 54mm so that makes understanding the post easier. Getting this narrowed down. Thanks
     
  2. Deoodles

    Deoodles Active Member

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    Good pictures. I have the same dome on the 108 right now. My first 108 attempt had the piston slightly above the deck and once warmed up it made contact. Changing to the TB piston fixed it.
     
  3. kirrbby

    kirrbby Well-Known Member

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    Oh no. I certainly understand your logic. Not everyone needs a bunch of motors on the shelf, lol.
    Did you notice the date on that thread I linked..? And I still have that engine...in a box, lolol. Bout 10 miles on it.

    If you needed a motor on the shelf, YOU would know it.
     
  4. Deoodles

    Deoodles Active Member

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    Not entirely true let’s not forget I’ve got the CHP 88 completely rebuilt trans and all in the K-3 that hasn’t moved for over a year
     
  5. racerx

    racerx Administrator
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    Understandable, if you were after something other than your stated goal. For the long-distance/high-mileage road tourer/cruiser you're after, with a broad torque and usable power across the band...and 60mph+ taking a lower seat priority, the V2 or the original Takegawa +r of which it's a copy, would be the antithesis of what you want. Why? First off, check piston fitment. I'm pretty certain that a piston that will work with one of these race heads will also work with the TB head you already have. Second, any power increases are going to come at higher rpm, likely sacrificing some low-midrange torque. Third, I don't completely trust aftermarket roller rockers...too many unexplained failures, including one that bit fatcaaat. An OEM roller rocker setup, fine, Honda builds durable road machines and has a hard-earned, longstanding, reputation at stake...plus a slightly larger (cough, cough:rolleyes:) R&D budget. That's a lot of additional bucks to spend on improvements that don't fit your goal and uncertain longevity.

    If you can't find a piston that'll work with your TB head, or have one modified to fit, then IMO you'd be better off spending less dough on a lightly modified & rebuilt K0-era CT70 head...that you know will get along with a known piston. That should still give you 60-65mph power, in addition to the added low/midrange grunt you're after. For that matter, a 52x54 setup should give you most of the torque boost...and open the door to a number of 52mm pistons, which are more common than 54mm.
     
  6. kirrbby

    kirrbby Well-Known Member

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    So you wouldn't consider the V2 head for a cruiser/stomper? More for a high revving tune?
    I was considering it as a good substitute for the 4valve Modernworks head that I had on my dax. Im pretty sure that has roller rockers too.
    I thought...bigger head, (ports and valves) allow more air thru the engine, in and out.
    More air=good.
    Not always?
    (Aside from the questionable reputation of the V2 head)
     
  7. Deoodles

    Deoodles Active Member

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    66B6A750-8810-4518-AAC9-A5726EBEBF9D.png Here’s what it looks like. Suggestions?


    FYI. Tb responded to my combustion chamber volume question.

    “We lost that data in a computer crash and have not had time to get it back yet. We only have that info on the KLX parts at this time.”
     
    #47 Deoodles, Oct 3, 2018
    Last edited: Oct 3, 2018
  8. racerx

    racerx Administrator
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    First off, I am not knocking the V2 head. It had its growing pains, as did the Takegawa version that it copied. There was a learning curve, which included real-world experience that always seems to be the final stage. TB products deliver a lot of bang for the bucks. Some early adopters of the +R head learned the hard way: there are mechanical limits and being the first kid on the block to have the latest & greatest toy can have its downside. Q/C issues got resolved, as you'd expect with a reputable outfit. But there's still no magic. These are sold as "race" parts for a reason.

    Yes, airflow = horsepower potential = mph. And there's the overwhelming crowd favorite, the price tag. The rhetorical question remains "is that all there is to this...one-and-done...they all lived happily ever after?" Horsepower is an indirect value, a mathematical manipulation based on torque...the only directly measured value of engine output. There are two basic ways to make a given hp number: the size of the "bang" per firing stroke and the number of "bangs" per minute. For example, compare a 6.5hp CL70 motor to an industrial engine (Briggs & Stratton, Tecumseh) of that era making the same rated hp... 72cc displacement vs ~300cc. By the numbers, 6.5hp @ 10Krpm is ~3lb-ft; that same hp @3600rpm more like 11lb-ft.

    This is already more longwinded than I'd like. Suffice it to say that increased airflow, from the same displacement, means increased rpm. The engine remains the same size (displacement) air pump, it's only been tuned to work more efficiently more times per minute. Since usable powerband is rarely more than 5-6Krpm wide, something's gotta give, in this scenario it's the low end. For the sake of brevity, I'll refer you back to your own thread, where the high revs are not strictly to your liking. What's your impression of that bike vs. your black cruiser?

    Cutting to the chase, ~120cc is enough to make 70-75mph power levels...but at what cost? As speed increases, the required power curve gets logarithmically steeper. Consider that 60mph requires nearly 60% more hp than 50mph...now, extrapolate that out to 70-75mph. You're talking about 2-2.5hp per cubic inch...far more "race" than daily driver. Just dialing-back the tune to a realistically usable level (~10mph) takes a tremendous amount of mechanical stress(es) off the engine, gives a nice fat-n-flat power curve, and you'd still have enough power to easily exceed the posted speed limit on anything but a limited-access freeway.
     
  9. racerx

    racerx Administrator
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    Couldn't read your parts list on a small screen. IDK, sounds to me like someone doesn't want to answer your question...a little surprising and a lot disappointing. Of course, this is something you could check yourself, once the head is off the engine; it'll just be kinda cumbersome (for a one-time thing) and messy.

    IDK about using cylinder spacers. That could cause other problems. I'm thinking in terms of timing chain tension and cam timing. With the top end gasket overkill I see, you should be able to just take your pick of head gaskets. Best, wild-assed, guess is that the thick, composition-type will pair best with the high-compression (pop-up) piston. If you go with the flat top, then the shim type gasket may be the better choice...gotta know the head chamber volume and whether piston-to-valve clearance is adequate.

    For a road bike, ~12:1 CR would make me nervous. It's not like fuel quality has been wonderful and it's unlikely to improve. It's gotten to the point where 92/93 octane is as good as it (reliably) gets and that's been largely replaced by 91. E85 has the octane but is wildly impractical for these bikes. Between susceptible fuel system parts (fuel lines, petcock packing, bowl gasket, tank filler gasket),increased consumption rate (figure ~40%) and spotty availability, it'd be a pain in the arse.
     
  10. Deoodles

    Deoodles Active Member

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    I was not educated on what compression ratio does to rideability I just thought higher is better. Are you saying shoot for the 12 to 13 mm compression chamber and not worry about what the ratio is?
     
  11. racerx

    racerx Administrator
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    Compression ratio has a direct impact on octane requirement. The higher the peak pressure inside the combustion chamber, the higher the octane requirement. There's quite a bit of differing opinion as to the effect of bore diameter as well. Back in the carbureted, pre-electronic engine management days, it was generally accepted that 93 octane would "tolerate" up to ~9.5:1 CR in automotive V8s. That is grossly oversimplified, there's a lot more variables than just static CR. I only included bore diameter because it seems relevant, imho. The flame front can only travel so fast; a smaller bore & combustion chamber means that it has less distance to cover. Thus, while I've seen charts that (ostensibly) claim a <54mm bore makes it possible to get away with up to ~12:1 on 87 octane, I wouldn't bet an engine on that claim...without further information. But then, I'm old-school...emphasis on "old". Between engineering knowledge that didn't exist circa 1970 and sophisticated EFI technology, we're seeing car engines with compression ratios that would have required Sunoco 260...back when it was ~100 octane and had as much lead as a shotgun shell...that are perfectly happy on 2018 goat pis...I mean pump gas.

    Once you know the open volume at BDC & TDC, it's basic math. 120cc volume, at BDC, 12cc chamber volume at TDC...120/12 = 10:1 static CR.

    Apply that math to the dratv 54x54 "kit" and you can figure out what the open volume is, at TDC, using displacement and static CR number. And, yes, piston dome, head gasket thickness, and deck height (where the piston sits, relative to the top of the cylinder...which can be altered with cylinder spacers) can all make a difference. So, assuming a nominal 12.5:1 CR with the pop-up piston, it's a helluva lot easier to calculate the difference, if a flat top piston were substituted and you know chamber volume of the head itself. Measuring piston dome displacement is way more involved...a little too involved, imho
     
  12. OLD CT

    OLD CT Well-Known Member

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    I have spoke to Ray on the phone and filled him in on all the details of my 54x54mm 124cc ''known good'' combo.
    BTW, the Webike clutch kit is part# 02-01-0217
     
  13. Deoodles

    Deoodles Active Member

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    Thanks Pat. Please check that number. Search brings up no result
     
  14. Deoodles

    Deoodles Active Member

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    Gathering parts some needed and some wanted. I purchased a clutch kit with a primary reduction of 3.722. What does this mean?
     
  15. kirrbby

    kirrbby Well-Known Member

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    67÷18=3.722
    Same primary gears as a CT70 H, but different than a 83 atc70.
     
    Deoodles likes this.
  16. racerx

    racerx Administrator
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    Yep, all that's needed is a little math to calculate the optimal sprocket combo...as a good starting point. When you're going for every last little bit of efficiency, there's no substitute for real-world testing, i.e. 'get on that pony and ride'. Nothing will tell you what it wants, with greater precision, than saddle time.
     
  17. Deoodles

    Deoodles Active Member

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    I started to organize this upgrade. Kitaco clutch kit, oil thermometer dip stick and a D style exhaust from Webikes. All on the way. Still need to get the hard parts for the motor. I pulled the motor out of the frame today. Think I found my oil leak. Either the left forward foot peg bolt hole or from the case screw to the hole. Has to be a crack. I got this case from eBay and it was probably like this when I got them. Im not about to repair a non numbered ATC70 case so now I’m shopping for a decent left side matching case for this build or a new set from something. Any years better than others.

    Edit. I see TRX cases were recommended In an earlier post. I’m going to have to wait for a decent set.
     
    #57 Deoodles, Oct 13, 2018
    Last edited: Oct 13, 2018
  18. racerx

    racerx Administrator
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    What you're after are GB4 (or later) cases. In real world, practical, terms that just means needle tranny bearings and configured to accept the 12V/CDI alternator assembly without mods...IOW..."12v cases".

    Probably not that tough to have the break welded. I've done this with breaks at the ends of blind holes at the kickstarter shaft, rear chainguard mount as well as footrest bosses. The only ones that are a big deal involve the kickstart shaft; precision machining is required. That said, guess what...I'd do what you're intending and source an intact case half. It's just less hassle, unless the SN matters to you.

    Just thinking aloud here, you may have an easier time sourcing used `90-vintage engine, or lower end. Any 49 or 72cc horizontal of that vintage will be the same, for your purposes...i.e. mechanically. That might also give you the option of just swapping-out the tranny, head & electrical stuffs to build your new engine...and use the rest (the "leftovers") to build into a 3-speed/semi-automatic 108, that could be sold, offsetting a nice chunk of the cost...not to mention putting a decent 108 into the hands of a fellow enthusiast. Then again, I could be wrong...:whistle:
     
  19. kirrbby

    kirrbby Well-Known Member

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  20. Deoodles

    Deoodles Active Member

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    Wondering out loud. Where is that motor!!!! :whistle:
     

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