Went to rechamber my head and found disappointment

[blaster214]

Well guys I am going to throw my head on the lathe tomorrow. Took it off and while I was there I figured I'd see what the bore was at. Went to wipe some carbon build up off the top off the piston and got a tink tink sound as I did.

So with th piston at tdc at the crown it had .020 of clearance. Have a sneaky suspicion it's time for a new top end.
I'll be taking the jug off today and measuring everything to see where I'm at.

Wierd though I haven't heard any piston slap. Something has happened before though cause the squish band looks like someone jabbed it with a flat head a bunch of times. The cylinder looks good no scoring.

Funny though the po told me it had a new top end.


Question. The top of the piston has 22.66a on it. I can only assume that is a std size. Is that a factory yamaha piston. Dont recall any others being marked like that.either way I'll know more once I get the jug off and measure everything.

Thinking maybe the po got yhe wrong size piston for the jug.

 

[Awk08]

wrong size piston for the jug

There is only one way to get the correct piston to cylinder clearance ...... bore/hone the cylinder to that exact pistons suggested clearance.
you cannot buy the correct piston for the hole, the hole must be made to fit the exact piston used

had you checked the compression ?

 

[blaster214]

Yea I have to take the jug off when I get home and measure it and the piston and see where I'm at.

Yea I checked compression when I bought it like 6 months ago. Po told me it had a new top end so I checked and it was 132.

It has been running great and starts on the first kick. Just seems like way to much slop. Idk what it is right now cause I took the head off to rechamber it not expecting to find the piston having so much play.

Either way I'll find out today after work.

Curious as to what those numbers on the piston are. Its 22.66a. I'm assuming that's a std bore size piston but I'll measure it when I get the jug off

 

[blaster214]

And just to be clear I wasn't trying to say I was gonna order a piston for the bore size. Just guessing at what has been done previously. Thanks for the heads up though awk.

At this point I cant do anything until I get home. At least it wont be boiling hot outside while I'm taking it apart lol

 

[blaster214]

So I measured the piston and cylinder
It is as follows.
The piston measures 67.70 at the skirt. The crown measures 67.55.

The cylinder is 67.77 and 67.78 at the top.

The cylinder at the bottom is 67.79 and 67.80

The two cylinder numbers are measured for roundness. Its within .01 mm. So the cylinder looks fine and the piston looks fine. The piston has the following numbers.

On the intake side 22.66a and in the middle mo 68.00. Anyone know what piston this might be.

From what I've measured everything looks good. Tell me if I missed something.

Edit. I think the clearance is more towards the high side but still within tolerance

 

[blaster214]

Got the head done today. The chamber is right around 20cc. Chamber is 1.545 in diameter. Squish band diameter is 2.647. Squish band was cut at 11 degrees. Gotaa get it on and check squish and compression

 

[blaster214]

So I forgot the solder I couldn't measure the squish band. I'll get it measured tomorrow

 

[Slydog]

Looks like it's time to sleeve that cylinder. 68mm is basically max bore.

 

[blaster214]

What do you think about the measurements.
Diameter is 67.80 at the biggest measurement.

How about this piston
https://www.amazon.com/dp/B07CLJ1BDY/?tag=jyj356j5-20

Says it 67.92. And my cylinder isn't out of round or scored up. I could have the cylinder matched to that piston and be good right.

I realize that I'm out of bores at 68 but that should give me enough room to get one more top end out of this cylinder correct.

If the shop takes it to 67.98 that would leave me with .006 piston to cylinder gap. In the meantime I could save up some money for another cylinder or have this one sleeved when the time comes.

 

[Slydog]

You should be ok. Run it by your machinist that is doing the work. They will want to take their own measurements first

 

[blaster214]

Just talked to Ken. He said said to take it to 68.25.

It's close to last bore anyway just gotta get a piston now. Bummer is I just called the shop I trust and 6 weeks out. Might be calling ken back and ship it to him. Guess I'm not gonna port this cylinder since I'm only getting one more out of it

 

[Slydog]

6 weeks! If that's a local place they must be busy. That sucks.

 

[blaster214]

Yea its local but I stopped by today and talked to them they said if I bring it in next week they can probably have it done the following week cause it's a single cylinder there jamm packed with v8s right now. So at least ot wont take that long