62t/61x bb 85.5mm

[Chad24384]

I was wondering if anyone had answers for me on what I got in my engine. I bought this engine that is a 61x with big bore sleeves, and a 62t bottom end. The engine was a "thrust" 771 build. Thrust won't answer my questions so here they go.... I called wiseco to see if I could get 86mm pistons since I have aluminum transfer on the walls and some taper wear. The piston part number for the 85.5mm pistons in the engine are 813m08550. Wiseco says they are Kawasaki pistons. The pin height is 0.0145 higher but ring height is way different than a Yamaha 85.5 or 86mm piston. Do you think I could go with the Yamaha pistons since it's based off of that, or is ring height that big of a deal? I understand pin height will increase or decrease compression. What would the effects be? Wiseco said to send the cylinder out and get it nikasil coated and use 85.5 Kawasaki pistons again, or re sleeve it... any help would be great. Thanks.

 

[Jr.]

What you are describing was commonly referred to as a " flat top motor". This is a 61x cyl, resleeved and decked to run Kawasaki flat top Pistons. Power output will be better than Yamaha domed style Pistons. You will not be able to buy piston off the shelf from Weisco without modifying them.
You can however call DASA and buy what you need. DASA part # WC-8600. Then bore and clearance your cyl accordingly. Also note, you will need the correct domes in your head to have proper squish shape and clearance.
I'm very surprised Thrust is not responding to you? Give him a chance

Ski ya, Paul

 

[Chad24384]

Thanks for the explanation that helps alot! The domes have been custom cut for the 85.5mm pistons, do you think that going to other pistons will effect my domes?

 

[Jr.]

You will need to see if the dome will accept the 86mm bore? That and if there is enough material left to protect the o-ring and ring land. What brand head does it have?

 

[Chad24384]

It has an ada girdled head.

 

[Jr.]

Good! The Ada flat top domes are made to take 86mm bore.
Pop a dome to verify, part number on dome should be YAK8628L15 for a 28cc dome
If this is the same? You should be good to go

 

[Chad24384]

Awesome thanks for the help and advise! I'll be sure to do that today.

 

[yamabro]

Those motors do produce great power over a stock big bore, like Paul said.
Similar to the RIVA dominator set up