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I have my engine apart for a check/refresh and I know that the crank in my bike has had some work before, but also that it was at some point fitted w a Yamaha rod that wasn't superlight.. My scales now show approx 5,1kg for the crank assembly w the rod
1) Does anybody know or wanna share a crank weight with rod that they think work well for race use?
2) Was this Yamaha rod swap a normal modification and doen anyone know what rod they might have used?

Eldert or Nigel will have the answer if they happen to check in.




Colin

a picure or dimensions of the rod would help to identify the rod .

i used 135.5 mm long Yamaha rods in widecase Ducati engines but that was because nothing else was available

Eldert

Thanks I will get a picc tommorrow. Did the weight sound reasonable to You?

crankshaft weight sound OK to me . as long as the balance factor is within specs i would leave it like that

nothing wrong with a heavy crankshaft and a external flywheel . it wil make your crankcase last longer .

Eldert

Glad to hear the weight is ok. The Yamaha rod is 130mm long, but there is a whole heap of different Yamaha rods thats 130mm length it seems. Couldnt find much in the way of nmbrs either. Only marked 005 on one side and R and some markings on the other side.
Not really important what it is either, but would be nice to know..

Hello Bendik
That isn't a Yamaha rod, it's a Husaberg conrod, which would explain the 130mm length. They are good rods, but probably not ideal for a W/C 250/350 as it's a bit short. There is a 125mm rod as well and I used them a lot years ago in N/C's when nothing else was available. However they are now fairly obsolete as an original part now and were expensive last time I enquired. It was only the rod that was useable in the N/C. KTM uses that length rod, but I think they use a larger bearing.

Regards Nigel

Thanks for the reply, this is a NC engine, sand it came w a packing plate underneath the cylinder

They should have used the 125mm version, in principle the longer rod should work better, but I would be concerned about the engagement of the bevel gear coupling faces. Is it a N/C 350? the engagement is already short as original. I will email you with any balance info if you need it, the N/C flywheels are on the overly light side, so no need to be concerned there.

Regards Nigel

Hi Nigel

Its a NC250 Mach 1 based bike. When You say the coupling faces, You mean the area I have circled in red on the photo?

And You wre dead right on the Vic camp rev counter drive, thanks