tear down, overhaul, rebuild. Ningbo GTX chinarelli.

[repherence2]

did some tinkering on SlowPed.

playing with the JAD Scorpion-style pipe to see how it fits up to the bike with the 94cc engine.

the owner of Qwik Fix Garage works with me now, so i told him about this pipe that i hacked up hand he told me to check out the guys at Exhaust Systems Hawaii to see if they can weld up the pipe in the configuration that i need it to be for it to mount up to the minarelli block because it is originally a street race pipe from the Philippines for the DIO, not the minarelli/JOG.

[repherence2]

in the process of getting ready to change out the crank seal on the stator side, i decided to remove the bore. in the process, i found that my cooling fan was destroyed.

the head and bore cleaned up pretty well. the bore still looks good, can see some of the original cross hatch hone marks in the bore. can tell that this thing got HOT. the wrist pin has all kinds of colors now. i ran it Hard all this time, and who knows how long the fan was broke. all i can say is that Motul 710 is some good stuff. it never did soft seize and the way the wrist pin looks, this thing went beyond 400* F. now that i have seen what i have seen, i don't feel bad about spending $27 a quart on it (i like to buy local to support the local small businesses, especially the local scooter/moped shops).








i think i might just pull this motor out for now and do some maintenance on it. i lost one of the piston circlips last night so this this is block is useless for now. i have another block that has a Ruima Jog90 spline/taper crank with 10mm wrist pin conrod. that block is set up with a ported Motoforce Mid Race bore. i raised the main exhaust port to 20mm from the top and the auxiliary ports to 21mm, as far as degrees...i have no clue, only ballpark idea (i copied a Polini Evo2 water cooled bore kit that i have). that block has a NCY small rotor ignition and i have a Yasuni C21 for it. i also have the stock engine from when i bought SlowPed. so, it's just a matter of direction of fiddling. i think i should make an attempt at firing up that 70cc Motoforce/Yasuni engine. that should be a fun thing to tune (sarc) . part of me fells like i been farting around with this 90cc sport stuff for too long. "Sport" in the sense that i have been limited by the exhausts that are readily available for me to use, YMS V8. that pretty much limits my big block ventures to Street/Sport level. so, maybe it is time for a slight modification/maintenance period for this engine for now. i think it is time to play around with the 70cc "race" stuff now.

as for the Taida 54mm bore, i cleaned up the head, scrapped off the carbon and cleaned it with light grit sand paper to remove the carbon. cleaned the head of the piston with some wet sanding with light grit sand paper. cleaned up the piston ring grooves. sanded of the carbon/coking on the rings. sanded the exhaust port to remove the carbon build up. surprisingly the bore is still good. like i mentioned earlier, you can still see the factory honing marks. the rings are probably shot. one looks to be about 0.015" gap and the other looks to be 0.020". i could be totally wrong, but until i get a feeler gauge to verify it, i will go with .015 and .020 gap. i ran a file across the exhaust flange of the bore to flatten it. i still got more cleaning to do on the exhaust port to get rid of the carbon. i think i will try to "polish" the port this time around. i am probably going to re-port the exhaust port. right now, the window is like a side ward "O". i am thinking about making it more of a flat roof like the Corsa or the MHR replica (for Dio). i hacked the flange and a stub portion of the headder from a YMS V8 pipe. the stub sockets perfectly into the JAD pipe, but the transition is questionable. i am not an exhaust expert but for mock up purposes, it works for now as far as adapting the large port Dio JAD pipe to mount up to the small port of the Miarelli. so Bakaracer from another forum says the Corsa lives at 9,700-11,000 depending on the pipe. 190mech told me the JAD pipe is tuned for 11,000. so, copying the Corsa timings and window is an easy way to keep it simple. ...or the other route is playing with the stock 49cc engine with the plastic heat shield V8 exhaust. no matter which way, it's an adventure in tuning. Good Times in the Irie Lab!

[808ministroke]

sounds like my kinda problems. . .
the best kine to have.
I would definitely venture into the 70 race realm especially s8nce u already got the perfect pipe #Uall$

[repherence2]

changed out my crank seals on both sides. flywheel side had more oil than i expected. it thought that seal was good when i installed it. the variator side did not have as much oil but i know i rolled the lip of the seal upon installation. so i swapped out Polini seals for Athena crank seals.

existing Polini seal on stator/flywheel side.




did some minor maintenance. cleaned the CVT. cleaned the bore, piston, and head. in the process, i found my flywheel puller after over a year! replaced the existing rear brake cable with a new one. had to reposition the arm on the brake cam. had to change the pilot jet to get it to run now that the seals are changed out.

[190mech]

Need to find a real squish type head instead of that 'waffle' Yamaha type head,your motor will thank you for it!Keep that exhaust port roof radius!!Frits Overmars has a drawing of the ideal race single port configuration , will post it tomorrow as I'm on a road trip now,,

[repherence2]

Oct 8, 2022 18:13:29 GMT -5 190mech said:

Need to find a real squish type head instead of that 'waffle' Yamaha type head,your motor will thank you for it!Keep that exhaust port roof radius!!Frits Overmars has a drawing of the ideal race single port configuration , will post it tomorrow as I'm on a road trip now,,

thanks 190mech for your input i appreciate your wisdom!   you know me, i am a make-anykine kind of person.  although what i do is always within reason, i do some reasearch, not full-on research, and then i make my guesstimate.  i appreciate your wisdom, knowledge, and guidance that you give to me.

i was thinking the same thing about the 'waffle' head.  when i had it all apart and i was cleaning the head, i thought about a squish band  head as well.  i could not figure out where to get a 54mm squish band head for this minarelli.  i was also thinking about buying a 'Dio' 54mm aftermarket squish band head from one of the local moped shops and then massaging the bolt holes to allow it to fit the minarelli bore stud bolt circle diameter.  i'm pretty sure compression is very low with this 'waffle' head and head gasket installed.  i was actually thinking about taping sand paper to the piston and lapping in a squish band o the head, and then lapping down the head sealing surface to increase the compression.  the piston goes into the head about 2 mm before the piston actually contacts the waffle.  that leads me to believe that squish and compression must suck on this Taida bore kit.  but that's plenty work and i was not ready to commit to that. 

this Taida 54mm kit seems like an 'economy' bore kit replacement that is aluminum/nicasil.  considering i already raised the exhaust port at least 2mm when i ported it years ago.  the 'waffle' head is actually the Taida head that came with this 54mm bore kit.  i am pretty sure it is not a "performance" kit but rather a replacement 'economy' bore kit, but at least it comes with porting potential out of the box.

i did not re-port the exhaust and it remains the same shape as the in the pictures.  all i did was clean the carbon deposits out of the port and lil' bit polish with sand paper. 

but yes, Squish Band head is in the works, or at least the thought of a squish band head has started.  so, the Moped-Shop-Quest will be searching for a 54mm 'Dio' head with squish band to see if i can make it work on this Taida bore.  i also dug up an NCY 47mm squish band head that i modified into a drill guide and tap guide for me to drill and tap the block to install helicoil thread inserts for the bore studs.  for now i am using it as a visual tool to see if i can take a 47mm NCY squish band head and adapt it to the 54mm bore.  i know i have an unmolested  NCY head in one of my moped parts bins, i just need to go search for it. 

[190mech]

Here is Frits Overmars exhaust port drawing;

[808ministroke]

Oct 9, 2022 19:13:43 GMT -5 190mech said:

Here is Frits Overmars exhaust port drawing;

I've looked at those 2 examples for a while and tried to say for exactly what the whole difference was between the 2 between the 2 from all that I can gather the one that the person prefers on the left side as a more gradual taper on the top of the port while the 1 that is not optimal has a more square taper that's shorter or maybe just more square it's hard to tell because there's only 2 measurements given

[repherence2]

so to recap what i did since Friday and into the weekend,

my main intentions was to change out the crank seals because i know that had damaged one of them upon installation a while ago. i was rushing at that time and i pinched/rolled one of the lips on the Polini crank seals. i did not have a way of pulling it back out so i just sent it in and hoped for the best.

i removed the head and bore. in the process of removing the shrouds, i found that my jog90 cooling fan was destroyed. i cleaned up the head, piston, and exhaust port, removing all of the carbon. cleaned up the rings and the lands, got rid of the coking. this engine got HOT. wrist pin looks hardened / heat treated.

found a replacement circlip to replace the one that i lost upon removal. reinstalled the all the existing parts. same rings,same wrist pin, same wrist pin bearing. Chance 'um. they still looked good visually and the fit up of the pin, bearing, and piston was tight and snug.

replaced the cooling fan with another jog90 fan.

replaced the existing break cable, it showed signs of stretching and needed to be replaced.

changed the pilot jet from a 42 to a 45. readjusted the idle screw and air mix screw.

changed oil in the gearbox.

installed new spark plug.

changed out the rear brake shoes because i damaged the existing set trying to install the wheel in the dark of night, persuading the wheel on with a hammer, not realizing the the lip of the drum was snagging on the brake shoe.

over all, SlowPed runs good. there is a noticeable difference in acceleration and carb tune now that the crank seals are good. i took it on a shakedown run on Saturday around the neighborhood in Kailua. terrorized the locals of my town with some mid day BRAAP BRAAP BRAAP. there were times when it would stumble and run a lil' shitty but i think it was because the bike sat for a while, it rained a few days, and some water got into the fuel tank from the gas cap. ripped it around town at WOT to clear out most of the fuel in the tank.

Sunday: since the SlowPed was running so well on the initial shake down run after i got it reassembled on Saturday, i decided to take SlowPed on a longer shakedown run. i also thought there was going to be a moped-cruise yesterday so i went on the hunt. initial run from Kailua to Waimanalo to Sandy Beach to Waikiki to Downtown Honolulu and then back home to Kailua in the reverse route. no moped-cuise . but that's okay, i was having too much fun rippin' it. i filled the tank up twice and added 2 ounces of 10% r/c nitro to each full tank. at over $5 a gallon, yesterday's shakedown run costed me more than $12. add to that the Motul 710 and the r/c nitro that was consumed and the total cost is probably near $15 for the 2 hours.

no breakdowns. no pushing. so far, so good. it runs way better than it did with the last set of compromised crank seals. there is a small portion in the low-throttle area where there is a small dead spot. i am pretty sure that it is my needle setting on the carb. i was too lazy to tune the needle yesterday.

right now, it has the YMS V8 pipe that rattles, but it runs okay.

since today is a holiday, i am thinking about taking out on a shakedown run to Jurassic Park and out to the North Shore or to the Shrimp-shacks in Kahuku. i will probably swap out the belts before i make the run. it has a Mitsuboshi 792 x 16.6 right now. i want to try a 788 belt to see if there is a difference in top speed performance.

[repherence2]

i just got back from a shakedown run from Kailua out to the Shrimp-shacks in Kahuku (kahuku high school football team is no.1 in hawaii and no.58 in the nation). the odometer was at 8699 when i left the gas station in Kailua after topping off with 1.1 gallons and 3 ounces of 10% rc nitro. topped off 0.5 gallons again before the shrimp farms in Kahuku. turned around after the shrimp farms and ripped it back home. the final reading on the odometer is 8758.

before i left the house, i changed the belt from a 792 x 16.6 to a 788 belt. there was a noticeable difference in the way the the bike got up to speed. it could do 50+ MPH full up. did some long WOT runs, full tuck, and i got the needle to the blue high beam indicator on the speedo cluster. top speed is definitely faster with the 788 belt.

i also changed the carb needle clip position before i left the house. for the longest time, it was at 1 above the bottom or 2/5. i changed it to the middle clip position (3/5) before i left the house. it made a difference and it greatly minimized the dead spot at 1/8-1/4 throttle.

so, the end results:

1. i made it home and did not have to push the bike.

2. i ran 59 Kilometers in the course of almost 3 hours.

3. i did multiple WOT, full throttle, and full tuck runs. 60+ MPH, good enuff, especially on a 35 MPH coastal highway that has one lane for each direction.

4. i topped off a total of 1.6 gallons of gas. i think i have about 1/2 tank left.


**Bonus** i told my Girlfriend that SlowPed just did a round trip from Kailua out to the shrimp farms and back (almost 60km) in just under 3 hours of cruise/run time. she nodded her head to acknowledge an accomplishment, "Not bad considering that it was not running and in pieces 2 days ago," she said.


so now that this minor overhaul of SlowPed has been shaken down, i am going to play around and modify a cylinder head from a 47.6 mm Motoforce mid-race kit so that i can use it on the Taida 54 mm bore kit.

the next evolution to this 94cc engine is to install a squish band head and get the JAD pipe mocked up and welded up run on this Minarelli.

[repherence2]

i power lapped a 54mm squish band into a 47.6mm Motoforce mid-race head. i chucked up a spark plug in the drill. screwed the head onto the spark plug. u applied strips of 3M Safety-Walk non-skid tape to a HOCA 54mm piston. using the drill to spin/turn the cylinder head via the spark plug, wet sanded the head with the piston (with Safety-Walk non-skid applied to the face of the piston) pressing the piston against the head. now it has an 11 mm squish band.

[repherence2]

finished up the modified Motoforce cylinder head.





one head is a 47mm NCY squish band head that i modified into a drill and tap guide for me to convert one of my blocks from M7 studs to 1/4-20UNC bolts. now it has thin 1/4-20 stainless steel Keenserts installed in the block.

the other head is the modified Motoforce 47mm head. both heads were identical to each other. the new squish band is 11mm wide. i used a 54mm HOCA piston as the lapping tool, applied Safety-Walk non-skid tape to the piston and spun the head with a drill via the spark plug.

[repherence2]

Oct 8, 2022 18:13:29 GMT -5 190mech said:

Need to find a real squish type head instead of that 'waffle' Yamaha type head,your motor will thank you for it!

i just installed the squish band head.

oh what a difference in performance.  it is noticeable.  i pulls harder and has a lot more oomph now.

[repherence2]

this morning, it went for a rip on SlowPed. for some time now (weeks...months) i have been watching a crack on the throttle tube getting bigger and bigger as time goes by.

so today, i decided to do some preventive repairs on the throttle tube so that i does not break on me while i am riding far away from home. that would be some Broke Dick Action.



decided to use Cyanoacrylate and some Baking Soda. taped the inside of the tube with masking tape to function as a backing strip for the powdered baking soda and glue until it cured/dried. once filled in, i peeled away the masking tape from the inside of the throttle tube.



end result. hard to see from the sh!tty picture, but it is filled in. i am going to reinstall it and take it on a shake down run today to see how the repair holds up to Torsion forces from twisting the throttle.

[repherence2]

ideas and works from the Irie Lab...

hacked the flange off of my corroded YMS V8 pipe. (heat wrap + water + salty air = DISASTER!)

while probin' out, i found out that the V8 flange/header can socket into the JAD flange/header.







internally, it is Not a nice transition, but we will see how it goes. as far as a "solution" it seems like it will work out. i'm not building a Hyper Race machine and i am just trying to keep it simple.

now that SlowPed had a squish band head installed on the 54mm bore, i can only imagine what it will be like when this JAD pipe is finally welded up and installed on the minarelli. i have been stuck in the 9k rpm realm for a long time with these YMS V8 pipes. it will be a different realm when this thing revs up to 11k. ...but still plenty work to do, but one day, when it is done, should be some fun.