Correct 422 piston pins

[Kool_Biker]

In my spares chest, I have two types of piston pins.
External dimensions are identical and both will fit pistons and con-rods.
But their internal diameters are slightly different, and hence their weight; ~9 mm and 44 grams on the left, compared to ~10 mm and 37 grams on the right.
I guess, 7 extra grams of reciprocating weight up there is something, so could you please advise which one of the two types is the correct one for the 79 Z?

P1070343.jpg

Cheers, Aris

[daves79x]

Aris:
Sorry for taking so long to reply. Here's what I found: All the wristpins I found here were original CBX ones and they all measure 10MM ID and all weigh 38G. I can't find any like your 9MM ones. I'd try to find all the 10MM ones to use. I'll post my rod findings on the other thread.

Dave

[Kool_Biker]

Hmmm, thanks Dave, very interesting.

Looking back at my notes I now realise what's happened; although I ordered the correct wristpins, P/N 13111-422-000 from David Silver Spares in the UK, they sent me P/N 13111-425-000 which according to them, superseded the original P/N.

Although externally dimensionally identical, their 1mm small ID makes them each about 7gm heavier.

In my books, and please correct me if I am wrong:

(a) The two P/N should never be mixed and matched in the same crank; they would compromise the balance of the engine, and
(b) They should be avoided, if possible altogether, as an extra 42 gm (7gm X 6) of avoidable reciprocating weight up there at 9,000 RPM can't be great

A good example I think, of how many traps there are out there ...

Aris

[Don]

Maybe a machinist could bore 7 grams out of the center of them?

Don

[Kool_Biker]

Been through this Don, would be easy enough and great ...
But, they are toughened
Aris

[bobcat]

when i built my CB900F, i used CBX pistons (900f and cbx share the same bore ,64.5 mm ,but have dramatically different stroke).
i used 4th over CBX pistons, but the wrist pins had a taper bore from each end ,thickest in the center ! its been about 16 years
since i built this thing and i cant remember if i used "pre-superceded X pins or 900F pins . might be worth investigating !

my FIRST entry !thanks NILS for your help !
bobcat

[bobcat]

when i built my CB900F, i used CBX pistons (900f and cbx share the same bore ,64.5 mm ,but have dramatically different stroke).
i used 4th over CBX pistons, but the wrist pins had a taper bore from each end ,thickest in the center ! its been about 16 years
since i built this thing and i cant remember if i used "pre-superceded X pins or 900F pins . might be worth investigating !

my FIRST entry !thanks NILS for your help !
bobcat

the best lessons learned are the
"hard way"

[NobleHops]

Welcome Bob, glad to have you!

N.

[EMS]

when i built my CB900F, i used CBX pistons (900f and cbx share the same bore ,64.5 mm ,but have dramatically different stroke).
bobcat

Welcome, bobcat!

Question: Does the original CB900F piston have a different number of rings than the CBX piston?

[bobcat]

same number of rings ,but CBX pistons are shorter and lighter than 900f . they are also "domed" where the 900f pistons
are almost flat top !

bobcat