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Engine Piston Options 10 months 4 hours ago #31456

  • Kawboy
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I'm sure I posted info on pistons in the last year but I can't seem to find it. So.......I'm always toying with thoughts and I had heard that-

1. KZ650 pistons could be used

2. That somewhere and I think it was someone in Africa did a 66mm big bore

I bought a KZ650 piston from EBay and sized it up and it's so close to the KZ1300 piston it would be a clone except for the fact that its available in a second oversize  63mm as an option piston for the KZ650's.

Then for giggles I found a set of KZ750 pistons listed on EBay for $9.95 shipping and I couldn't resist. It sizes up just like the other pistons from the KZ1300 and the KZ650 at it comes in at 66mm for the stock pistons.

I have to mention that there are 2 KZ750's. One is a 2 cylinder which I believe is the KZ750-G and the other is the 4 cylinder KZ750-E. The 66mm pistons are from the KZ750-E

Now all I need is access to a milling machine. Punch out the cylinder liners and bore the block for custom sleeves from someplace like L.A. Sleeve in California. Oh could I have fun !!!!66mm bore would bring you to 1457 cc's Yippee KI Ya. 


piston on the left  KZ750-E , piston in the middle KZ1300, piston on the right KZ650 

  
Left piston KZ750-E, center piston KZ1300, right piston KZ650 63mm piston
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Engine Piston Options 9 months 4 weeks ago #31466

  • biltonjim
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Very interesting.  I’ve often wondered, though, how does the fitment of such oversized pistons affect the balance of the crank/rods/piston assembly, assuming (as seems likely) larger pistons are heavier?  Would the engine vibrate noticeably?  

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Engine Piston Options 9 months 4 weeks ago #31468

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Very interesting.  I’ve often wondered, though, how does the fitment of such oversized pistons affect the balance of the crank/rods/piston assembly, assuming (as seems likely) larger pistons are heavier?  Would the engine vibrate noticeably?  
Well, you're not wrong. Weight is a consideration. I weighed the KZ650 first oversize pistons ( the piston in the pic 63mm) against the stock KZ1300 pistons and they were only 5 grams heavier. I haven't had a chance to weigh the KZ750-E pistons yet and I will when I get a chance. I suspect they will be slightly heavier than the other 2 but not significant.

for me, doing the restoration rebuild of my bike is a test of my ability and where I can take it. It's an engineering challenge and get me into things that get me thinking outside of the box. Going to 66mm pistons requires machining the cylinder block to accept custom cylinder sleeves. then once assembled, do a combustion chamber volume and calculate out the compression ratio and either adjust the cylinder height or machine the top of the pistons to get the compression ratio somewhere close to the stock ratio.
Engine blueprinting is something I haven't done since the 80's and I really enjoyed doing it. Weight balancing a set of connecting rods, weight balancing pistons, having the crankshaft balanced for a new rotating mass and reciprocating mass- all very interesting to me. 

First things first. Finish that damned 3 season room, then back to the KZ.
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Engine Piston Options 9 months 4 weeks ago #31469

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How is the house renovation coming along, Kawboy?

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Engine Piston Options 9 months 4 weeks ago #31471

  • dcarver220b
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Heat. How you gonna shed extra heat with marginal cooling system?

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Engine Piston Options 9 months 4 weeks ago #31475

  • Kawboy
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Being Canadian, we don't ride around in Easy Bake Oven temperatures. Anything above 85F is A/C weather . We also have had an influx of what we call Municipal speed cameras. Some have fixed positions, some are mobile. They issue tickets for anything over the speed limit i.e. no grace. Plus they added an additional 30% to the amount due and called it a "Victim Fine Surcharge" supposedly to be paid out to victims involved in accidents with people who didn't have vehicle insurance. I got one of these tickets for going 8 Km/hr ( 5 Mph) over the limit and it cost me $72.

I've already modified the rad fan to a 7 blade fan from a ZRX1200 and it pushes a lot more air than the stock fan
 
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