300/440/550 pistons and crank questions

[On the fly NY]

Noob here..hello to all...1987 JS 550 teardown and rebuild, crank seals are shot, bearings are freewheeling nicely...

question #1, is there supposed to be any space between the middle spacer and the 2 bearings on the crank between the connecting rods?

question #2, looking at new pistons and I am seeing sizes in the plus .25mm to .75mm, even +1 mm...so my question is do the cylinders need to be bored out for anything larger than the std 75mm pistons....sorry if this sounds like a silly question.

Thank you

 

[WFO Speedracer]

Std pistons are 75mm so add whatever dimension your cylinder is bored to , lets say it is now 75.75 mm and it needs to be bored again , you would need 76mm pistons or 1.00mm O/S .

Your best bet is to take it to the machine shop and let them tell you what size pistons you need , as far as the first question goes I am not following you on that one.

 

[On the fly NY]

thanks for your response SR...this is my 3rd time posting back to you here, last 2 just disappeared or were deleted ....want to reach out to administrator for some help but the "contact us" button doesn't seem to be active, so no help there....am hoping this post sticks around unless I am doing something wrong here on my end, which is quite possible

thanks for your input on the pistons, mine measure 75mm so I ordered accordingly.

as for the crankshaft, I was asking about the black striped between the 2 orange striped bearings in the middle but I have that figured out now

 

[blackkstar]

Definitely take it to a machine shop. You want to go up in size as little as possible because you can only bore a cylinder so many times before you have to get a new sleeve. But sometimes it's damaged so much you have to go up more than one size (i.e. 75mm stock to 76mm). Sometimes the sleeve breaks and you have to put a new sleeve in even if you could bore it out further if there was not a crack. You also don't want to run more than one cylinder way more out of whack than the others, i.e. one at 75mm and one at 76.5mm.

You don't want to fight the game of guessing because you will end up with pistons you can't use. Usually it cost $15 to $20 to ship back a piston to return it and if it's a $100 piston returning it ends up being a waste of money, but if it's too small you'll probably never use it anytime soon, the only time you'd need a smaller piston is if you had to resleeved. And I don't know the situation with 550 sleeves, I know kaw 750s are cast sleeves so you either have to put a sleeve in a sleeve or you cut the old one out (instead of using a press) and put in a heavy duty one (LA Sleeve sells them).

 

[WFO Speedracer]

Definitely take it to a machine shop. You want to go up in size as little as possible because you can only bore a cylinder so many times before you have to get a new sleeve. But sometimes it's damaged so much you have to go up more than one size (i.e. 75mm stock to 76mm). Sometimes the sleeve breaks and you have to put a new sleeve in even if you could bore it out further if there was not a crack. You also don't want to run more than one cylinder way more out of whack than the others, i.e. one at 75mm and one at 76.5mm.

You don't want to fight the game of guessing because you will end up with pistons you can't use. Usually it cost $15 to $20 to ship back a piston to return it and if it's a $100 piston returning it ends up being a waste of money, but if it's too small you'll probably never use it anytime soon, the only time you'd need a smaller piston is if you had to resleeved. And I don't know the situation with 550 sleeves, I know kaw 750s are cast sleeves so you either have to put a sleeve in a sleeve or you cut the old one out (instead of using a press) and put in a heavy duty one (LA Sleeve sells them).

On an 87 model 550 you won't be putting in a new sleeve , the whole cylinder is cast iron, you get another cylinder.