Topic: CB750: Wiseco 10.25:1 K811 (811cc) street kit question.

[Garage_guy_chris]

I Just had a fast question regarding an older Wiseco 10.25:1 K811 (811cc) Street kit.  I know a few hi-comp kits had 2 different pistons depending on the side the valves are offset too.  I just wanted to confirm this wiseco kit IS NOT one with 2 different pistons.

[Terry in Australia]

I've never seen a Wiseco 811 or 836 kit with 2 different pistons mate, usually the valve cutaways are radiused right or left of the centre point so they'll work in any cylinder. Cheers, Terry.

[Garage_guy_chris]

Thats what I was hoping because i found 3 pistons locally being sold individually and another one is on its way from the internets.  so i wanted to make sure it wasnt one of those odd kits with different pistons. Hopefully the 4th shows up and i will have a complete kit. Surprisingly there isnt much info on these wiseco 811 kits on the web.  When were they discontinued? I would guess late 80's early 90's? Thats my guess based on the dot matrix printed stickers on the boxes??

[PeWe]

Check these if you need 811 pistons. 811 or 812..difference? same stuff? 64mm?
http://www.ebay.co.uk/itm/NOS-NEW-OLD-STOCK-811-FORGED-PISTON-KIT-CB750-K-F-CB-750-includes-rings-and-pins-/111072401637?pt=Motorcycles_Parts_Accessories&hash=item19dc6e58e5

[HondaMan]

Check these if you need 811 pistons. 811 or 812..difference? same stuff? 64mm?
http://www.ebay.co.uk/itm/NOS-NEW-OLD-STOCK-811-FORGED-PISTON-KIT-CB750-K-F-CB-750-includes-rings-and-pins-/111072401637?pt=Motorcycles_Parts_Accessories&hash=item19dc6e58e5

Well, I'll be...one of my favorite "big bore" kits from the '80s. They preserve the same powerband feeling of the 750, while cranking the HP up almost as much as the 836 kits, and run a LOT cooler. I do wish the old Yosh cast pistons in the 64mm bore were still around. Those were my favorites of all for race bikes. You got full valve flow, 10,000 RPM all with stock rods.

[Garage_guy_chris]

By continuing to scroll down and read this thread. Please dont hate me as i had nothing to do with the incured damage as it occured pre-purchase, at the hand of the previous owner.. Believe me this was a huge kick in the nuts to find this, infact the nuts are still hurting.... 2 pistons are still good so maybe one day i will find 2 other good ones i have been looking for the last 4months or so but due to my lack of info on them hasnt turned anything up.

hey hondaman you mean these right?





On another note what is this kit? Its the same one i have seen on ebay an average of about 3 times a week for 6 months?!?
 

Check these if you need 811 pistons. 811 or 812..difference? same stuff? 64mm?
http://www.ebay.co.uk/itm/NOS-NEW-OLD-STOCK-811-FORGED-PISTON-KIT-CB750-K-F-CB-750-includes-rings-and-pins-/111072401637?pt=Motorcycles_Parts_Accessories&hash=item19dc6e58e5

[thirsty 1]

Bummer

[grcamna2]

Check these if you need 811 pistons. 811 or 812..difference? same stuff? 64mm?
http://www.ebay.co.uk/itm/NOS-NEW-OLD-STOCK-811-FORGED-PISTON-KIT-CB750-K-F-CB-750-includes-rings-and-pins-/111072401637?pt=Motorcycles_Parts_Accessories&hash=item19dc6e58e5

Well, I'll be...one of my favorite "big bore" kits from the '80s. They preserve the same powerband feeling of the 750, while cranking the HP up almost as much as the 836 kits, and run a LOT cooler. I do wish the old Yosh cast pistons in the 64mm bore were still around. Those were my favorites of all for race bikes. You got full valve flow, 10,000 RPM all with stock rods.

What about using CB350 twin pistons,are the domes compatible w/ the head squish area ?

[HondaMan]

By continuing to scroll down and read this thread. Please dont hate me as i had nothing to do with the incured damage as it occured pre-purchase, at the hand of the previous owner.. Believe me this was a huge kick in the nuts to find this, infact the nuts are still hurting.... 2 pistons are still good so maybe one day i will find 2 other good ones i have been looking for the last 4months or so but due to my lack of info on them hasnt turned anything up.

hey hondaman you mean these right?





On another note what is this kit? Its the same one i have seen on ebay an average of about 3 times a week for 6 months?!?
 

Check these if you need 811 pistons. 811 or 812..difference? same stuff? 64mm?
http://www.ebay.co.uk/itm/NOS-NEW-OLD-STOCK-811-FORGED-PISTON-KIT-CB750-K-F-CB-750-includes-rings-and-pins-/111072401637?pt=Motorcycles_Parts_Accessories&hash=item19dc6e58e5

Ouch! Those in the engine ARE the genuine Yosh kit: see the "POP Y" cast letters on the pistons? Those ARE my favorite ones! Now my nuts hurt, too...

The ones on eBay look a lot like (copies of?) the old Powroll 811 versions. Action Fours had some real similar ones, but they didn't have the characteristic "notch" on the crown for "front". They just had a dot. If you go with those eBay versions, be sure to add some clearance. The cast Pop Y pistons used .0015" clearance (if done right) while the forged ones use about 0.0022" instead. Sometimes, the Pop Y ones got installed (incorrectly) with the .0022" numbers, which results in (ow...) seized skirts on the front of the pistons...the clearance is then too much for the oil to pass the heat through the oil film to the bores, unless by chance someone actually used 20w40 or 20w50 racing grade oils. The oil has to carry that heat away: on forged pistons it doesn't even happen until the pistons heat up, and they heat slowly. they also cool slowly, so they are bigger than the holes after a short stop like refueling and a Coke on a hot day, making hot restarts sometimes tricky if the clearance is too tight. Whenever you go big bore, always go 20w50 oils.