MOPED ARMY

They are not too bad to rebuild. I’ve always got the case apart with a rubber mallet and you just need a bearing puller for the bearings. And a flywheel puller as well. Just keep everything organized and you should be fine.

Upon further inspection my piston seems to have a “U” stamped in the top, any ideas of what this means? I was hoping for STD, but it may be. About to mic it.

And it get 39.97-39.98 or so

It seems smooth as glass in that bore. (edited)

I took some more measurements... see photos

I took these measurements from both sides with identical results. I’m not sure that head gasket specs like this help but it sure doesn’t hurt to know what your working with.

I’ve got a collection of precision measuring instruments. One is for extremely thin thickness measurements. May have fun with that one here.

Got the head cleaned up today, may blast it with the carb bodies(soda). Either way it’s got about 2 lbs less carbon on it now.

The pistons up next and I may just paint that head with some high heat or powder coat and be done. Anyone ever powder a head?

Think about exactly what is happening in the cylinder .

The old rings have conformed / formed to the cylinder and in the process have worn the wall clean/smooth . That cylinder is likely no longer the cross hatched round as it was at manufacture . New rings are perfectly round . Without a decent crosshatch , how will those new rings ever form to the cylinder and provide good compression ?

New rings in an old untouched bore is a fantastic recipe for massive blow by .

I prefer a bar hone , as they tend to hold straight rather than following any deformity .

Check with your local auto parts store . They might have one to 'loan' you .

Check You tube for a quick tutorial on usage .

Mind you it was riding this way.

I use this flex hone on qt50 and other cylinders. Is it the best thing to use? I don't know but it has worked fine for me in putting a decent crosshatch on the cylinder walls. It just takes 20 seconds maybe and run the drill in both directions. A new piston and rings are so cheap, I would just go that route. Of course, measure your ring gap and adjust as necessary or run the ring expander under the 2nd ring if your gap is too far from the minimum spec.

And of course, you need to thoroughly clean the cylinder and ports after honing it. New rings require cylinder honing. You've got a bit of wear inside your cylinder and it looks like that piston has soft seized several times - both indications would strongly suggest that a cylinder honing is mandatory. Not sure why some pw50 guy with experience would say otherwise. I guess I could speculate - he was probably assuming that you didn't have easy access to a hone but who knows what he was assuming, right?

I've seen qt's running with similar and worse piston/rings/cylinders but since you've got it apart, it only makes sense to replace what you can.

Alright so I’m all set up to hone, set my mind on an inexpensive 40mm replacement piston. I do have two rotating lowered engines.

The one that I’ve really set my mind to using has a bit of a clunk to it at the low part of its stroke, but that could be due to having a shaft attached, the other doesn’t.

I think I may get one full top end and see how that does. I am short a top end set up on one motor.

I’ll be ready for next week to get here. Should have something running

I really wanted this to be my (split the cases and totally redo it, from the ground up" motor. but I may be forced to use it. I think its just fine but i am going to explore more.

$300 plus with Treats today.... MLM stock plus pipe, gaskets, seals, other stuff I can’t think of.

FZ/FT60 top end kit from EBay. New foot peg bracket, some other exciting stuff. Roysenen reeds.

Bigger jets.

Stock piston just in case.

Let’s see what this thing can do!!!

Powder coated says Monday he’s done!!

I can’t wait to start putting things together.

I’ve got a second frame waiting to go! (edited)

You got it. There will be videos.

Return the yt60 knockoff top end. That will only fail miserably. Get the malossi kit or get Yamaha oem yt60 top end.

Dang.... I was hoping to hone, chamfer and get by with it. Bummer