Doing a 701 for a mate at the moment, new crank, pistons seals etc etc. The sleves have been bored to match the larger wsm pistons and every thing is as per usual apart from a couple of things. 1: The new piston pins have sideways movment when the circlips are in like the pin is to short by about 3mm (im guessing). The last engine I used wisco pistons and I dont remember that problem. My book says there shouldnt be any movment... but im not to sure whats normal. 2: is there a minium piston to head clearence spec any where? The head and top of the cases have both been skimmed, Dont think it looks like much but with out a head gasket the pistons hit the head so I know there closer than the head gasket thickness. Havnt measured it but it must be under 2mm? 2.5: Ive already spoken to Aquanob end about this but with the longer piston pin needle roller bearing (aparently there are two) I shouldnt be using the washers. To me this is weird as the roller bearing will be sliding all over the place rubbing on the inside of the piston? Maybe im thinking about it too much...
1 - that clearance in the ends of the pins is normal and is in every jetski engine I have worked on. 2 - About 64 thou is the minimum squish. Measure it by sticking a bit of solder down the spark plug hole and push it right out to the edge of the bore, then turn the engine over by hand to squash the solder. measure in several different places. The best place to measure is in line with the crank as the piston cant tilt as much in that direction. 2.5 - Don't use washers 3 - Ride it like you stole it
1. as dazza sez. 2. measure squish as dazza sez, or make an educated guess by taking gasket thickness (approx 1mm) , below deck height of piston (approx 0.5mm), step in the head before angle begins (approx 0-1mm depending on head / if its been skimmed) 2.5. There are 2 or 3 types of these needle rollers. yamaha 650/ kawi 750 style , these are 25mm wide and have no room for washers (so not required) then there is the yamaha 701 ones which are 23 - 24mm depending on brand , these are intended to be used with the 1mm thrust washers on each side. but alot of people dont use these as they are prone to failure. so typically they are used without washers , or use the wider yam650/ kawi750 ones so there is a little less sideways play.
