Topic: Anyone else run Yoshimura Pistons in a 550?

[Justind97]

I'm putting my motor together for a dry run to check for clearances.

I haven't even bolted down the head and the pistons are hitting and pushing it up.

Barrels have been decked about .005".  Head the same. 

I have measured the height of the Pistons and they are about 8mm (5/16) taller than stocker from the wrist pin to the top of the dome.

Anyone else run these and know if I'm missing something here?

Thanks!!

[bwaller]

Where it's 8mm taller it shouldn't make contact. It's the compression shoulder height and that should be really close to stock. The problem with used heads & cylinders we don't know how much has been machined before we get them. Use an extra base gasket or two and with some solder or clay, see where it's hitting.

[FunJimmy]

A couple of picture goes a long way too.

[Justind97]

Pictures added to the original post

[FunJimmy]

Could you have 650 pistons?

Here are pics of my Yosh 550 slugs.
Just a little raised center section to bump CR.

[Justind97]

FunJimmy,  now you have me second guessing myself!

Pistons are 59.5mm,  but they don't say 550 like yours do.

They have YO2. And 301 below that

[FunJimmy]

FunJimmy,  now you have me second guessing myself!

Pistons are 59.5mm,  but they don't say 550 like yours do.

They have YO2. And 301 below that

Ya I saw that. 650 stock bore is 59.8mm.
I only raised the question because of the dome height.
Dynoman has 650 pistons with a similar dome

[turboguzzi]

as a rule of thumb, assuming gasket is about 1.2mm, then piston edge should be about level with block or +02.-03 max. so pack up some base gaskets to raise the block.
even then, i think your CR will be 15:1 or something! 500/550 have a small volume chamber in the head and hardly need much crown to get 12-13:1....

bolt everything up and measure combustion  chamber volume

650 have a much bigger chamber in the head, so that could explain.... if yours are a 650, then i'd say it's a no go or run methanol

[bwaller]

Justin, my answer sounds pretty stupid after you add pics. Like the others, I doubt those are meant for the 550. You could plop a 650 head on it, but unfortunately that puts you out of middleweight production, but you'd be ok for P3 light & middleweight. Carbs would fit but not sure about 550 exhaust on a 650 head.

Aren't those supposed to be Yosh pistons?

[Justind97]

Thanks TG.   I'll use another set of pistons I have.

Yes Brent, they are Yosh pistons. I didn't show it in the pictures.

[Bill/BentON Racing]

My Yosh pistons like FunJimmy's. Saw the pics , thought 16 to 1 lol. G' luck, Bill

[MRieck]

They are 550 pistons.....old ...but 550 pistons...was the base gasket installed and if so what thickness. The head and cylinder have minimal amounts off them.

[bwaller]

Cometic offers several thickness base gaskets. Used to be they have fibre in 0.015", 0.020, 0.039, 0.047, 0.060, 0.094, 0.125, & 0.188" thickness for the CB550. Plus Viton coated steel in 0.010, 0.014, & 0.020" that can be stacked too.

If they're 550 pistons then spacing the cylinder should work.

[turboguzzi]

They are 550 pistons.....old ...but 550 pistons...was the base gasket installed and if so what thickness. The head and cylinder have minimal amounts off them.

a bit surprised by your comment... this piston is off a  12:1 race motor, the top of the crown is 3mm above the edge.... but 8mm? seriously, maybe these are methanol pistons...

[bwaller]

He could measure the dome thickness and machine some off different parts of the dome, including the shoulder height