Topic: Need help identifying pistons

[PeWe]

Dynoman recommend 0.0025” (0.0635mm) for their 1000cc pistons, forged JE 71.25mm.
My old 836 did not smoke with cast pistons and 0.2mm clearance.
That cylinder need CycleX 65.5 mm pistons (849cc).

[754]

Man I can't afford to stick a new set of pistons, but then I won't go dragracing the week I put them in..
 But.. someone always has so they plan for it.

[754]

 I got some pistons out if a 78 F model.
 These pistons have a high crown, about 5 mm higher than edge of piston .they are marked 410.
The rods are marked s59 and S50.
 I thought 77/78 had flat tops due to smaller chamber size.. what do I have here ?

[smacd11]

Looks like 77-78 750F used 410 pistons.  Found this on ebay:

https://www.ebay.ca/itm/Honda-CB750F-Piston-2nd-OS-50mm-1977-78-13103-410-003-NOS-OEM-NEW/152446644431?hash=item237e8730cf:g:5v4AAOSwr~lYrkDP&vxp=mtr

[cbr954]

They are F pistons.  The F had larger combustion chamber then the K's.  The few I have measured have been 5 to 6 cc larger then the K

[smacd11]

I found a post somewhere that said the 77-8 F's (410) had 28cc combustion chamber, the K0-6 (300) were 22cc, and the K7-8/F1 (392) were 24cc.

[cbr954]

Thats about what I found for volumes but they do vary quite a bit from the factory.

[754]

Son of you used the F pistons in an earlier K, you should get a nice boost in compression, I suspect rings may be pricey.

[Medyo Bastos]

I use to run ‘em in k’s back in my youth


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