Topic: Who was trying "other" pistons in a CB750F rebuild?

[Terry in Australia]

Okey Dokey, I meant to post some pics of the Action Fours pistons yesterday, but after spending 5 hours replacing the rear brake caliper on my 'Wang, then riding 150 miles to bed the pads in, it was too dark to go hunting for them. Anyway, here they are now:











Cheers, Terry.

[HondaMan]

Hey...I have a set that looks just like those!

[MiGhost]

And as promised. Specs for the stock KZ650 pistons.

KZ650 76-82
Bore x Stroke: 62 X 54 mm
13001-1002 PISTON,STD
PISTON DIA.: 62.0mm tapers >61.5mm at rings (Note the taper just above the pin in the first pic above.)
PISTON PIN  C to DOME: 31.50mm
PISTON PIN  C to DECK: 24.50mm
OVERALL HEIGHT: 58.25
DECK to SKIRT BOTTOM: 51.25mm
DOME HEIGHT: 7mm
PIN LENGTH: 52.25mm

Note: 58mm dia. dome offset to intake. 4.0mm flat shoulder at exhaust. 

Note: No longer available stock, but 0.50mm & 1.00mm overbore available through IMD Piston Co. in the UK.
http://stores.ebay.com/IMD-Pistons/_i.html?_nkw=kz650&submit=Search&_sid=1028788763

Note: 64mm big bore available through Wiseco.

From '80 KZ650F1 service manual:
Cylinder bores:
Std dia:   61.995-62.003mm
Wear limit:   62.100mm
Piston/bore clearance: 0.032-0.055mm (0.0013-0.0022in)

Connnecting rod:
Big end journal OD:
Unmarked:   34.984-34.994mm (1.3773-1.3777in)
Marked '1':   34.995-35.000mm (1.3778-1.3780in)
Wear Limit:   34.97mm (1.3768in)
BE ID:
Unmarked:   38.000-38.008mm (1.4961-1.4964in)   
Marked '1':   38.009-38.016mm (1.4964-1.4967in)
Wear Limit:   35.94mm (1.4150in)
Journal clearance: 0.034-0.076mm (0.0013-0.0030in)
Wear Limit:   0.11mm (0.0043in)

Small End:
Gudgeon pin OD: 14.994-14.998mm (wear limit: 14.96mm)
Piston boss Dia: 15.004-15.009mm (wear limit: 15.07mm)
Small end bush dia: 15.003-15.014mm (wear limit 15.05mm)
Piston boss to gudgeon pin clearance: 0.006-0.015mm (0.0002-0.0006in)
Gudgeon pin to small end bush clearance: 0.005-0.020mm (0.0002-0.0008in)

[HondaMan]

Some success!
The machine shop who does my tricky work for me has agreed to make a tool in their lathe that will let us cut back the top shoulder of these pistons by 1.0mm. This should make fine +0.50mm oversize pistons for the K7-8 engines (and the F0-1 as well). I'm taking the rest of the set to them tomorrow.