Piaggio Zip Air cooled 50cc (Are cranks balanced when bought)??

dont worry about it. this isnt balancing anyway, its truing.... balancing involves removing and placing weight/material to the crank, truing means making it straight/turn concentricly
never ever ever had to do this to a new crank, and if an old crank came out of true it was time for a new conrod ether way...

 

if you have to ask, just dont do it.. it IS fairly basic, but its not simple. the bearings are friction fit so the bearings are fitted to a heated case then the crank fitted to a heated bearing. really, you wanna see someone do one first hand, or practice a few times on a junker, as it can literally jam solid to the point you need bash it apart with a hammer. thus the need for re truing. pull thee ngine out, strip it down to a crank in a case then take it to a reputable motocross shop for a rebuild. shouldnt be more than 30 to 60 quid depending on the cheek factor of the guy doing the work. nocks alot of the expense off a crank fitting and you have almost done it all yourself.

 

it will be balanced out of the box dw.... it literally wont go in the engine and spin if its not balanced, its a tight ass fit requiring heat and skill when there dead centre straight, ive only ever seen any kind of runout on the variator side, but then its the entire shaft thats bent, so the crank was scrap anyway. honestly your worrying about how fragile a seriously strong/well pressed together part is. it takes over 50 ton to put a crank together you wont bend one dropping it (dont drop it) ive thrown them and not really bent them, just conrod (temper temper)

crank run in? no such thing, if its fitted right, has the correct endfloat and spins nice and free befor installing the seals, its as good as run in. theres nothing that needs to break in. the cylinder is diff.. if its an ali kit, measure and ajust ring end gap (should know what this is if your fitting a crank and kit) and then just hot cycle the engine a few times.. then a light ride, then a short hard ride, an its prettymuch run in, just dont pin it for 3 mile at a time for a few days or so. if its an iron kit, set ring end again, but set it a little bit wider than usually would, these swell more and kits these days are only going down in quality. i have regular hot siezes with new pistons first running in, that then run for thousands of miles.. just a bit tight on the ring end is all. so ye, ring end, plenty oil when building, good few hot cycles (as in, let the bike idle till uits warm, then cool compleatly) then a gental SHORT ride, like, round the block a few times at really low throttle, let it cool, take it for a clear out (so round the block a few times but have a few 3 second full throttle blasts) you want to use ALL: of the throttle but vary it as much as possible, but not try and hit top speed everywhere for a good few hundread miles, with iron kits you literally FEEL when they free up, its like riding down the road and the bike all of a sudden just feekls more powerfull/easier to rev/happier... from this point you can just pin the fuck out of it, its iron, if it siezes you can just cop a new piston.


running in is a personal thing, air on caution if unsure, but tbh ive done this for 2 decades, i treat bikes like shit when i know i can, and i personally ride 8 miles up and over a massive hill from sea level daily, i dont have the option to gently run bikes in, this is why they have a tendancy to hot sieze/i run a little more ring end gap now to accomidate, i get through rings fast, but i use the cheapest quality piston kits i can find so an entire piston kit is less than malossi ring set... so i dont mind if i only get a few thousand out of a piston. im up to 2500 on the one im running at the min, had a hot sieze first ride, and one last night, so ima pull the oil pump, run it premix and see if it go's again, if so, oil pump back in and new piston... had a look the other day and it was clean as a whistle, daily at 60/70 for 8 miles full throttle almost the whole way, with a massive hill.... its an enigne, they can break so easily, but once there right they really can be strong as fuck/deal with alot of abuse. 6 odd siezes and the new crank i put in is straight as an arrow still

there will always be a difference with a bike you play on, and a bike you have to use!