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General Minitrail Talk
Modifications
Help piece together a stroker kit for my build
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<blockquote data-quote="69ST" data-source="post: 161850" data-attributes="member: 5"><p>Fatcaaat was a lot clearer on the piston & crank issue than I was. And that's the operative word here "was"...the DRP 52mm/4-speed type crank joined the NLA parts list about 2 years ago. That is part of what makes the trailbikes 51mm arm the go-to stroker crank. The 3-speed flavor is the biggie, for most.</p><p></p><p>FWIW, I'd convert to 12v/CDI while doing this build. You're married to the long-rod/12v compression height piston, regardless of which trailbikes crank you use. So, with the piston selection sorted out, the last choice becomes ignition type. It's 2017, 12v/CDI is not only a huge improvement over the old 6v/breaker point setup, it's also the norm. For a road bike, that you're going to ride, do you really want to be tied to 6v bulbs and ignition maintenance?</p><p></p><p>As for reliability, imho, 45mph sustained should be no problem. That's close to the level which Honda took the venerable 49cc-based motor, with the C90...which never made it to North America. The biggest differences, with the 108 tune, are the torque output (big increase) and top speed potential which should be close to 60mph. Going by the convenient 80/20 rule, that should give you solid, usable, road power into the low 50s. It's that 50+ range where the stresses reach the steep portion of the curve. Going from 50 to 60mph requires ~60% more hp. IOW, while the lower end will definitely be worked harder, you're not really talking about riding with the throttle held wide-open all the time. 40-50mph really isn't asking the motor to work a lot harder than the factory engineers felt was viable. </p><p></p><p>In terms of estimating service life between rebuilds, I'm not an engineer. Best I can offer is an educated guess, based indirect experience & observation. The common denominator is odometer mileage. While it's relatively unusual to see a CT70 with 5-digit mileage showing, over the years I've seen a surprising number of SL & CL70 models with ~15K on the odometers. Likewise with S90s (different engine but close to the same era, displacement and hp). I've seen CT70 engines that were all done by the 2K mile mark, others that were still healthy in the 6-9K range and a few (less than a handful) well into 5-digit mileage. How the motor is treated makes all the difference. Get the setup, break-in & tuning optimized and keep clean oil in it and you're likely to get a lot of happy miles. And be certain you're running the proper oil type...wet-clutch compatible and plenty of zinc, to protect the transmission.</p></blockquote><p></p>
[QUOTE="69ST, post: 161850, member: 5"] Fatcaaat was a lot clearer on the piston & crank issue than I was. And that's the operative word here "was"...the DRP 52mm/4-speed type crank joined the NLA parts list about 2 years ago. That is part of what makes the trailbikes 51mm arm the go-to stroker crank. The 3-speed flavor is the biggie, for most. FWIW, I'd convert to 12v/CDI while doing this build. You're married to the long-rod/12v compression height piston, regardless of which trailbikes crank you use. So, with the piston selection sorted out, the last choice becomes ignition type. It's 2017, 12v/CDI is not only a huge improvement over the old 6v/breaker point setup, it's also the norm. For a road bike, that you're going to ride, do you really want to be tied to 6v bulbs and ignition maintenance? As for reliability, imho, 45mph sustained should be no problem. That's close to the level which Honda took the venerable 49cc-based motor, with the C90...which never made it to North America. The biggest differences, with the 108 tune, are the torque output (big increase) and top speed potential which should be close to 60mph. Going by the convenient 80/20 rule, that should give you solid, usable, road power into the low 50s. It's that 50+ range where the stresses reach the steep portion of the curve. Going from 50 to 60mph requires ~60% more hp. IOW, while the lower end will definitely be worked harder, you're not really talking about riding with the throttle held wide-open all the time. 40-50mph really isn't asking the motor to work a lot harder than the factory engineers felt was viable. In terms of estimating service life between rebuilds, I'm not an engineer. Best I can offer is an educated guess, based indirect experience & observation. The common denominator is odometer mileage. While it's relatively unusual to see a CT70 with 5-digit mileage showing, over the years I've seen a surprising number of SL & CL70 models with ~15K on the odometers. Likewise with S90s (different engine but close to the same era, displacement and hp). I've seen CT70 engines that were all done by the 2K mile mark, others that were still healthy in the 6-9K range and a few (less than a handful) well into 5-digit mileage. How the motor is treated makes all the difference. Get the setup, break-in & tuning optimized and keep clean oil in it and you're likely to get a lot of happy miles. And be certain you're running the proper oil type...wet-clutch compatible and plenty of zinc, to protect the transmission. [/QUOTE]
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Help piece together a stroker kit for my build
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