polini seize, porting, rebuild pt 1 and EPIC TORQUE

25Jan10

this weekend we (bandits and tbs) stayed at a rad cabin in the appalachian mountains. a few miles into the 30 mile ride i was coming to the top of a long hill when my motor started getting noisy. polini’s are loud kits and i’ve heard some weird noises out of mine with nothing wrong, so i kept pushing up the hill. then the noise started getting louder. just as i was about to back off…ZINK, ERRRRRRRRR…shit. i pulled the head and pleasantly found a tiny bit of aluminum transfered, no gouging and good compression. so i started it back up and that devil noise was immediately there, coming from my bottom end. i didn’t want to risk the kit, so i decided against trying to run it back. i got back last night and tore into to try and figure out the issue.
thankfully none of the seize spots put any gouges or scuffs in the nikasil and the piston is ship shape.
ZINK!
ZINK!
ZINK!
ZINK!
clutch bell has seen some REVVIN
REVVIN

i haven’t gotten the clutch or flywheel off yet, so i haven’t ruled anything out. the dmp unstuffed crank (what i initially thought it was) has a little side to side play, but nothing front to back and both roller bearings look great. still need to do some investigating to find out what caused this.

i haven’t taken this bottom end apart since i put it together 3k miles ago, and this was pretty good timing because i was going to rebuild it before racing anyway. the metra 80 i bought from vic came with a brand new treats aluminum stuffed crank. that’ll be going in it plus a fresh set of bearings and seals. i’m also going to switch cdi boxes from the all in one treats box to 77 which has a separate cdi box and coil. i’ve heard rumors the 77 box allows for slightly higher revs, we’ll find out.

while the cylinder was off i did some more (i took the intake back 2.5mm when i built it) porting work to it. i started with taking the intake ports, manifold side, back another 2.5mm.
polini porting
polini porting
polini porting
all the work is done without touching the cylinder wall. it’s super easy porting that can increase your intake flow. i’m also going to be widening my exhaust and modding the stock 2 petal reedcage for more flow. that, some experimental puch clutch mods and possibly an 18 mikuni will have this motor race ready.

BONUS ENTERTAINMENT. when i broke down nate pushed me all the way back to our cabin with his fa50, this was capped off by pulling my maxi and i up a hill i made it only halfway up earlier that day with a 40mph running start.

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7 Responses to “polini seize, porting, rebuild pt 1 and EPIC TORQUE”

  1. If your moped rallies look more like tractor pulls…
    you might be a Bandit.

  2. 3 cuperzacko

    how did it seize? (well soft seize). Looks fine, go big with the exhaust, and get a 4 petal.

    • 4 gabeb

      that’s what i’m confused by. i was convinced at the time it was the bottom end because the noise that got loud right before it seized was super loud when i started it back up. but i haven’t found anything wrong in the bottom end so far. i guess the noise could have been the ring sticking weird, not sure yet. did you ever get a measurement on your exhaust? i’m curious where it’s at. sticking with the 2 petal for now. i want to keep pushing to see what it’s capable of.

  3. 5 tweeder

    classic bing seize! šŸ˜‰

    get a god damn 4-petal and a real carburetor.

    • 6 gabeb

      sigh…unfortunately for my ego, i’m pretty sure you’re right. i was planning on switching to the 18 mikuni i had on my derbi, maybe i’ll start looking for a 4 petal on the cheap.

  4. 7 Nate Bandit

    Fuck the 4 petal! Do it with your flats and 15mm, or forever miss out on ridding the unicorn.


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