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Post by ltsride on Mar 22, 2011 12:26:39 GMT -5
OK so here is the deal, i got a new 90cc from PFS, installed it and it ran good. i put maybe 20-30 miles on it over the last month (still too cold to ride much). well i had planed a 54mm bbk and a 45mm stroker crank when i got the 90cc so i went an got the parts from autotech355. i tore the 90cc apart and installed the stroker crank and bbk. every thing went together pretty easy. checked the squish and it looked good (.086 inch i think) and leak-down test was good. so i got the engine back in and it fired right up an sounded great. i started with a 100 main jet just to be safe and it was way rich so after about 5 minutes just on the stand idling with small burps of the throttle the garage was so full of smoke i couldn't breathe even with the door open so i shut the engine off and dropped to a 95mj started it back up and it was allot better but, and this is the part that gets me but it was noisier than hell, like the piston was hitting the head or like the crank was hitting the case or something. when i gave it some throttle it smoothed out. a friend listened to it an said the crank was bent or the bearings were bad or i did something wrong. so i pulled everything apart again an looked for any signs of the crank hitting the case or the piston hitting the head or even the con rod hitting the cylinder base but i could find no signs of any contact. then i measured the old crank and the new one, there both the same diameter (counter weights) an the stroker is just a hair skinner across the weights. then i set the crank up in a set of v-blocks an it looked good. then i checked the bearings an there good an tight an spin smoothly.so i put everything back together with an extra base gasket (squish now .106in) got it started again an it sounded fine, it idled for a min or 2 an stalled so i started it back up and there it is again (clackity clack) not as bad though so i said the heck with it, adjusted the carb and took it for a good spin (40 miles). it sounds good and runs great with lots of power, no vibrations or weird noise. it's just at low rpm >2400 it sounds like the engines gona come apart but raise the rpm <2500 an it smooths out an sounds fine. please some one help me out (what should i do)
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Post by 90GTVert on Mar 22, 2011 17:50:50 GMT -5
Are you 100% sure it's the engine? One of my scoots has something up with the variator and it will make a clackity clack noise till I get the RPM up above 2000RPM.
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Post by ltsride on Mar 22, 2011 18:54:58 GMT -5
no it's not the vari, that was my first thought though, the sound is louder on that side so i took the vari off and started it again and still noisy. i am thinking of pulling the crank from the left side to seat it against the bearing and doing the same to the right side. when i installed the crank i heated up the bearing race in the case with a heat gun and dropped the bearing in on both halfs. then i let everything cool down for a while. then i heated up the left side bearing and slid the crank in but left it just off the bearing 1/16 or so to try an keep it centered in the case. then i heated up the right side bearing & case and slid that over the crank and tried to tighten the case down before it cooled off to much. i think the right side is a 1/16 or so off the bearing also. maybe pulling the crank so that it seats against the bearings on both sides will like peload it somehow i just don't want bend the crank.
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Post by ltsride on Mar 23, 2011 8:14:18 GMT -5
how is it that you guys install your cranks? i got a hold of a couple of repair manuals online and they show the bearing installed in the right case half then it says to install the bearings on the crank (i assume the left bearing on the crank) then it say to decide the length between the webings and to pull the crank into the left case half, the the other manual says to install the crank into the left case and seat the crank to the bearing then install the right case half by pulling it onto the crank till the case halfs meet. well we just got another 4" of snow so i'm in no big hurry.
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Post by 90GTVert on Mar 23, 2011 9:17:14 GMT -5
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Post by 190mech on Mar 23, 2011 11:24:41 GMT -5
The 54mm piston skirt may be hitting the case on the down stroke,usually on the exhaust side..
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Post by ltsride on Mar 23, 2011 13:44:21 GMT -5
thanks 190mech i will look into that, didn't realy think of that. it's weird how it goes away at higher revs
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Post by ltsride on Mar 28, 2011 11:15:43 GMT -5
well i had the cv cover off and the vari off and thought what else could be making such a racket after i pulled it all apart again and nothing was hitting any thing, so i pulled the starter stuff out and put the vari on with the cover and kick started it**holly crap no friggen noise. well i started looking at the starter clutch and it looked fine, gave it a little shake an oops them little cylinders and the springs came out. i put it back together after washing all the parts and gave it a light coat of 3 in 1 oil. i put all that back to gether (cvt, starter gaers, & clutch) and it runs like a dream.
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Post by 90GTVert on Mar 28, 2011 11:55:07 GMT -5
Good to hear it was nothing serious. Thanks for updating us.
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