Is this right?

[qr4life]

I recently put up a thread about having noise at TDC and someone suggested that I take the motor apart and see if I could find what was making the noise and I found this. If you click on the link to the videos you will see what I am talking about. Brand new everything, stock bore. I don't currently own a caliper to check the actual size of the piston. Is the piston suppose to move that much?

 

[yamaha28]

The second video is normal, dunno about the first video though. Might want to check that bore with micrometer.

Why did you replace the piston?

 

[qr4life]

It was time for a rebuild. I rebuilt everything on the motor.

 

[yamaha28]

It was time for a rebuild. I rebuilt everything on the motor.

For what reason though? Low compression, underpowered, or just because you wanted a fresh motor?

 

[EZRider76]

Think I remember reading some where that is ok....but maybe not because of clearance specs from the rings to the cylinder wall. You definitely should invest in some calipers and measure the cylinder ID and the Rings OD, then subtract the OD from the ID, divide by two and see if that final number falls within the spec clearnace tolerance range.

 

[sicivicdude]

The second video is normal, dunno about the first video though. Might want to check that bore with micrometer.

Why did you replace the piston?

X2

The second video is normal, the piston does not control the side to side thrust of the assembly like Suzuki LT's (8-| at wrist pin thrust washers!) but that piston to cylinder clearance appears quite excessive...

The piston is actually NOT a perfect cylindrical piece of aluminum. It's actually tapered slightly so that the top is smaller than the bottom. The bottom spends all its time in the relatively cool incoming intake stream while the crown spends most of its time in the relatively hot combustion chamber area. So in order to keep both ends happy, they make the bottom a clearanced fit (.002" for wiseco's) and taper the piston. That's why a cold engine has a "wobbly" piston in it. The first few seconds that crown heats up and expands to fit the cylinder better.

However, yours seems to have a lot more than normal"wobbliness" to it. You need to measure the current bore size and current piston size. I have seen a piston that was smaller than the stated size (It was a wiseco too!) but I attributed it to shipping damage.

 

[blasterdemon7]

Did they bore with or without the piston in hand?

 

[Larry's Shee]

So who decided on the piston size? In the first vid, are the rings on the piston? Can't think of many reasons I would ever put a new piston in an old, worn out hole.

 

[qr4life]

I rebuilt the motor becuase it was time for a rebuild. Before I aquired the motor, it had never been rebuilt. I purchased a brand new OEM cylinder, stock bore. I then had KOR port and rework the head. He also rebuilt the bottom end for me. And yes Larry there are rings on the piston and I did not put a brand new piston in an old hole. Everything on the motor is brand new, now Im wondering if it is possible that somehow I received the wrong size piston.

 

[scotj77]

that is a brand new cylinder with a brand new weisco 66m piston it shouldn't be that loose. don't run it. did ken take a look at the piston and cylinder together. he woulda noticed that.

 

[scotj77]

main thing now is to get that topend measured properly. then figure out who to go after for some free replacement parts.

 

[Larry's Shee]

What's the number on top of piston?