Post by: riffraff on July 05, 2012, 07:15:56 AM
http://rpmmfg.com/BigBoreStrokerCR640.aspx
Post by: factoryX on July 05, 2012, 09:36:21 AM
Post by: Jeram on July 05, 2012, 11:13:22 AM
the cylinders are actually made by these guys who cast alot of big-big bore cylinders for various bikes
http://www.cpindinc.com/
Post by: Stusmoke on July 05, 2012, 01:09:56 PM
That much horsepower isn't usable on a motocross track thats for sure, but enduro might be a different deal entirely. A 7 speed WR tranny powered by that 640 engine would be a real touring machine. And of course a four stroke eater
Post by: SachsGS on July 05, 2012, 02:43:16 PM
Post by: factoryX on July 05, 2012, 05:06:40 PM
Post by: Jeram on July 06, 2012, 02:05:27 AM
that, hill climbing, sand duning and maybe flat track and perhaps road racing would be the only real uses
Post by: nom de guerre on July 06, 2012, 02:30:49 AM
Post by: Stusmoke on July 06, 2012, 02:43:34 AM
Must be fun kickstarting one of those things.
I was thinking the same thing haha. My 250 can be difficult but a 640? I think an electric start is in order
Post by: cnrcpla on July 06, 2012, 02:54:54 AM
Post by: Jeram on July 06, 2012, 03:18:39 AM
That is a big piston for road racing IMO Jeram, when ATK tried the 685 in SM, it just didn't rev and work all that well. I would love to hill climb it though!!! I rode a Maico 620 and it was fast for sure...
this cylinder is no slouch in a straight line, regardless of piston size.
10 second quarter miles puts 600cc sportsbikes to shame
Post by: Stusmoke on July 06, 2012, 03:33:04 AM
That is a big piston for road racing IMO Jeram, when ATK tried the 685 in SM, it just didn't rev and work all that well. I would love to hill climb it though!!! I rode a Maico 620 and it was fast for sure...
this cylinder is no slouch in a straight line, regardless of piston size.
10 second quarter miles puts 600cc sportsbikes to shame
HAH! Destroyed... Thats damned awesome. four joke sports bikes... ppfft
Post by: bearorso on July 06, 2012, 12:31:53 PM
By just being a bit 'blind', and not looking for the cheaper options, when comparing the cost of an OEM crank assembly, RPMs stroker crank is not that pricey, with our dollars exchange rate - so, I can 'fool' myself into thinking it's a reasonable expense.
Not to have a fire breather - indeed, my goal is to make my 500 even more of a big pussycat - grunty, and smoother revving. In my riding, I don't get near high revs (and I mean high revs for a 500 - not anything else) I'd adjust ports only to achieve that, and, hopefully will have sourced a wide ratio gearbox to put in, whilst doing the rebuild.
Case machining / reinforcement, is no problem. I could probably do a stroker myself / in combination with local specialists, but RPM have a good rep, (though I'm a bit
?? about the Prox Rod kit used) and the projected price is not too bad - my time is valuable, to me, and sometimes, I'd rather use it to make money.
Post by: Jeram on July 06, 2012, 03:57:20 PM
low ports, longer pipe, alter the head, etc.
Should be able to turn it into 500cc of stump pulling tractor torque.
be extra stroke will help even more-so!