> Graham Motzing Wrote:
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>
>
> i mean, really, a lot of the people posting on here with 10's of 1000's
>
> i think you could keep the stock crank in it, yeah the RPMs are bad for
> them but most of the damage is from increased load and heat from a kit.
> The 50cc puch kits are barely more power than stock so a clean stock
> crank should last just about forever.
No that’s a fallacy, It is the rpm that’s mostly the problem,
Cranks do not last forever just because you’re running a 50cc kit not a 70cc kit unless you run stock rpm for some puch cranks don’t even have needle bearings at the bottom big end bearing and have only teeny tiny little oil grooves in con rod at big end so very little lube gets in to big end or to the sides of the big end of the Conrod unlike the small end of the rod because it has a oil hole,
This crank (which was low mi and in great shape to begin with) got the big end of con rod side friction welded to the crank lobes when upped the RPM to around 9,000 rpm but still running the stock 50cc cylinder, It ran good full synthetic motor oil and a heavy 50 to 1 mix more like a 45 to 1 mix,
I’ve had several puch stock crank lock ups when I upped the rpm and for me it was always the big end of the rod and always same thing: Rod was friction welded to the side of the lobes something like this:
Reed type kits/cylinders take a bigger jet and have a more gas oil in air mixture into the crankcase and you may be able to get a bit more RPM out of them if you want to try before they lock up but regular piston port kits run a smaller/leaner jet so there’s less gas in the air mix and less getting to the sides of the crank so rpms need to be kept down