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Hi guys, I'm in the process of getting the RB carb/head done so it is time to see if it's a stock or aftermarket piston. I was told when I got bought the bike that it had been rebuilt so I was hoping it was a wiseco piston. Scraped the carbon off the crown and there was a b stamped into it. I look in the exhaust port and see those beautiful machined marks of a forged piston! I did a compression test before I pulled the head and it was 130lbs so I'm a happy camper!
Now my question, I can move the piston with my fingers. With the piston at tdc, I can turn it in the bore, just a bit, but still it moves around. Is that normal?

jjavaman wrote: Now my question, I can move the piston with my fingers. With the piston at tdc, I can turn it in the bore, just a bit, but still it moves around. Is that normal?

You mean you can move it clockwise/counter-clockwise inside the cylinder? How much does it move?

That's right, it moves maybe a 1/16 " clockwise/counterclockwise.

jjavaman wrote:That's right, it moves maybe a 1/16 " clockwise/counterclockwise.

hmmm I'm watching this one for accurate information

If it moves that much, I'd be real curious about the condition of the wrist pin bearing. Is there clunking or any up and down clearance at the piston when you rock the flywheel back and forth?

A new piston kit and wrist bearing is pretty cheap. Especially after you've already removed the head, etc. Replacing the piston is also an opportunity to clean the power valves.

jjavaman wrote: Scraped the carbon off the crown and there was a b stamped into it. I look in the exhaust port and see those beautiful machined marks of a forged piston!

Was there anything else stamped on the top of the piston? Wiseco's usually have several letters/numbers on the top.

Something doesn't seem right. Since you have the down time, I would pull the cylinder and inspect things further.

Ya,I'm going to pull the cylinder and clean the kips so I'll look a little closer at the piston then. Don't you love winter down time.

Hi can someone tell me if this is a forged piston? By looking at some previous posts I'm thinking it is because of the machining marks.https://imageshack.us/my/images https://imageshack.us/i/eys6RaYJj

jjavaman wrote:Hi can someone tell me if this is a forged piston? By looking at some previous posts I'm thinking it is because of the machining marks.https://imageshack.us/my/images https://imageshack.us/i/eys6RaYJj

What is on the top of the piston? It should have Wiseco's P/N.

https://imageshack.com/i/exkFtWrVj All it has in the top of the piston is a B and a arrow. Hope this helps.

If that is all it has on the top then it isn't a Wiseco.

Now with the cylinder off, what is loose that causes the piston to rotate?

My 'assumed' stock 220 piston looked like that on top except it had a "C" instead of the "B."
I meant to find it last night and look at the side.

Well I've decided that it's a stock piston,reading the manual it talks about the piston having a A or a B on the top and mine does. There is a lot of slop in the wrist pin,back and forth movement so I'm going to order me a wiseco.

You'll want a top end kit, or get the gasket set and wrist pin separately. Piston kit does not usually come with wrist pin bearing.

If that excess clearance is due to an oversize bore in the connecting rod, a new wrist pin and roller bearing assembly won't solve the problem. I would suggest you remove the piston from the rod, and check the clearance with just the wrist pin and roller bearing assembly. If that bore is worn oversize, a new rod is probably the best solution.