crank pin hole

So... can anyone tell me, if you want to increase the crankpin size of your crank to 22mm.... what size hole is required in the crank webs...i had some other crank wheels (suzuki)enlarged to accept a 22mm crankpin but wow how loose where they. .. crank still in cupboard unusable in the present condition. i would think that there must be a calculation required or a chart to refer too

Get a Zeus book

Nigel,
       A little context; John Rennick of Epimetheus fame has a 1600cc nitrous breathing 125hp Vincent engine. The crankpin of the EN36 crank has a .006" interference fit with the crank-discs, and .005" with the mainshafts.
Now I recon with your more modest 25, or so, hp Bantam running a 22mm pin, you need around .002"/ .0025" interference fit with the discs. My w/c engine`s crank runs a .002" interference fit and it has never moved.
The picture is of my currently moribund air-cooled engine project, What I do is bore each disc for the mainshafts, then bolt the two together with a hollow sleeve and a length of studding. The crankpin holes, are bored as one, this ensures all bores are parallel and coaxial, job done.

Hope this is what you need, Trevor

Trevor, thanks for info... spent most this morning googling zuse and couldnt understand how a cat in a hat would be of any help... ( no offence ment dan but:lol!: )

oh, by the way, those crank cases dont look standard but then again looks like rules are only a guidance

it has tables to tell you how much you should leave in the hole or on the shaft depending if you want a an interference transition or clearance fit, and according to the dia it will say the amount needed, simples ! I have a Zeus book , but its a- cold out side and b- I don't think I could just go and find it with out going through ton of boxes in the garage since I've moved ! but I would make it 0.002 max tight, warm it up and you can fit it by hand, don't hit it or press it, if you need that then the crank wheel is too cold , zeus book I think also has co-efficient's of linear expansion too

Zeus table of fits, straight out of my metric copy, not too much here about the rough and tumble of Bantam crankpin fits though

Trevor

Thanks Dan and Trevor.. once opened up to the required size do you have to reheat treat ?

k6 -n6 fit, roughly 15-26 microns in the upper limits of those fits, heat treat? whats it made of? was it heat treated before? ,as it'll most likely get hot frequently i'd guess its not too much of a problem heating it up, an oven is ideal (gas mk8 ! 200c)a blow torch would be bad if too localised and fierce

Dave, my precision engineer mate made 22mm crankpins for 186cc D7 flywheels, in EN36 I think. Bored holes, lapped to 3 thou fit.
Takes a few tons to press, but stiff as a .......... !
Shortened same pins for TZ250 rod for short stroke 125 too.
He makes them over size, then ground for clearance.

morning everybody..,  

found some crank wheels with 22mm crank pin... only the shafts need correcting.. maybe

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