Anybody done it? Anybody know anybody who's done it? I know a 350 twin can make 90-100HP _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
Close _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
I would think it would be pretty difficult, and certianly cost prohibitive, to stroke a NSR250. _________________ james
Its not how fast you go...Its how you go fast.
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Mick, it looks like you were stroking it when you cut your fairing. _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
Depending on the stroke amount depends on what you do with teh cylinder.
If just a few mm stroke increase (like 3mm) you can get away with cylinder base spacers and relying on head gasket thickness to accept the now negative deck height.
To really get the best out of a stroke you could do with the NSR150sp cylinders too.... _________________ NSRless again...
Yes they can,......... but the nsr crank is not completly pressed together. The big end is only pressed on one side the other side is part of the the center crank throw. Plus Honda doesn't sell any parts for the crank. I've been talking with Glen from Falicon and he says no go. I said what about a billet crank( a billet tripple crank for a sled is $2500 ) he told me $15000-$20000. I said thanks but no thanks. I was thinking 4.5mm to square the bore back out ( 59mm bore 300 ) to about 320cc. _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
I dont think it is possible to use the offset bore cups approach, as seen on the TL125. If they are like the RGV they are scooped/hollowed out on the backside for lightness, and the big end pins are too close to the edge of the crank.
If the integral crank pins are solid you could always offset grind them down and use a rod with a smaller big end ID and bearing, but that only gives you about 1mm on teh throw, and a very difficult spacer to make up for the hole on the other side. The integral pins could also be offset built up with weld for another 1mm on the throw, giving 4mm on the stroke.
But its a lot of hassle and Im not sure about reliability...
I am working on chopping up an 54mm stroke RD250 crank to fit an RGV250 at 50.6mm - could the same Idea apply here? There are several KTM/japanese 200/220cc strokers around 57-60mm stroke? Might be hard work but possible not as hard as modifying teh stock crank. But where would the fun be if it were easy.... _________________ NSRless again...
As Vince says, welding up the pin and offset grinding is one choice. Just offset grinding could give us a 4mm~4.5mm stroke, but we'd be compromising strength by going down to a 22mm big end pin. Not a total disaster as this give us a good selection of MX rods to choose from, but whether they're up to handling the extra mojo is of course open to debate. Why did Honda see fit to use 25mm pin if a 22mm would have done the job.
Reducing the hole in the mating crankwheel is not too tricky. My mate has stroked many singles by welding and offset boring the big end pin hole. He makes a good job of it and has won many races.
Vince, I don't think the scoops are hollowed out but the big end pins are very close to the edge of the crank. I was thinking of offset grinding. My car engine builder does this all the time. He turned down my big end rod journals from 2.25" to 2" to allow a longer stroke longer rod and a bigger cam without interference. Matt, lets do some grinding Have you ever seen a crank let go at the big end without help from some piston debris. Not to say that it can't happen I've just never seen or heard of it happening. Plus I've got a great machineist who would be happy to whip up some titanium rods if we furnished some to copy This would add strength and reduce weight _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
AFAIK the main point when offset grinding is teh amount of overlap of the big and and crank journal - i.e. the diameters must overlap when viewed from one end.
I havent seen much stuff on dtnamic balancing so have no clue, but agaian Falicon say they can do it but I have no expereince of their services.
You might also need to make the crank groove bigger to clear the rod, so this could need some welding etc before machining.
sorry to say I've given up . other weays to pick up power much cheaper . As soon as I hit that lotto I'll find some billet cranks but untill then I'll be looking else where for power. _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
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This would add strength and reduce weight 
. other weays to pick up power much cheaper