Can you help me ID a piston?

[courier11sec]

Here is a piston out of my new to me big bore motor for the 750 project:
Need to know if it's an 850 piston or a wiseco big bore piston?



Thanks again for your knowledge.

[Nessism]

Yoshimura?

[Tarbash 27]

Yoshimura?

definately

[courier11sec]

I see! So I wonder where one might find a set of rings for this unit?

[first timer]

100% yosh piston no mistake. Take a look at this thread to get some ideas where to start looking for piston rings, good luck.

http://www.thegsresources.com/_forum/showthread.php?t=134498

Maybe you can use wiseco rings?

Please let me know what you find I would like to have a second set of rings for my motor.

[courier11sec]

You know, I've got to say that this forum is fantastic for getting help with any GS related questions. This evening alone I have made two threads asking for knowledge and advice and immediately gotten all I hoped for and more.
Thanks a lot guys...

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I wonder what compression ratio these are meant to produce? Sure is a high dome...

[Old Colt]

Most all of the ring companies can supply to a dimension.
Bore dia, groove width and grove depth are the key numbers.

[49er]

I wonder what compression ratio these are meant to produce? Sure is a high dome...

Yoshi racing ratios for the GS1000's were quoted at 11.5-1. To get that they were using the stock bore (70mm from memory). Not sure what thickness the head gasket was nor the bore diameters of that gasket. You need to know this to calculate the ratio. If those are GS1000 pistons, the gudgeon height will be different to the 750/850 ones.

[Big Jay]

Those are old pistons and probably use ring far thicker than anything available. What is the bore size?

Jay

[courier11sec]

My buddy mic'ed it, I don't remember what he came up with for bore size, but bore and stroke got him to 849.5cc