Hi Everyone,

I have a question for all the gurus out there in NSR land.

Has anyone tried to stoke a standard 250 crank or had new webs made.

The reason I'm asking is that the standard 250 has a bore/stroke of 54 x 54.5 which is nicely balanced and gives a generous time angle area for the stroke. This gives it a decent mid-range but also a substantial top end. By bolting on a NSR150 barrel the bore x stroke becomes 59 x 54.5, which is great for mid-range not so for top end as there is proportionally less transfer port time angle area. Therefore to rebalance the ports you need to increase the stroke, modify the height of the ports and includes a base spacer, crank case work etc.

Has anyone manage to stroke the crank successfully to give a 59mm stroke for example?

Regards
Dave

Ok,no takers then.

I am looking at three options:

1. Grinding a 2mm offset in to the big end pins. This will give a stroke of 58.5mm
2. Having new crank webs made, with an extra 2mm diameter.
3. Do nothing.

Option 1

This will be the easiest method, but will require the pins to be re-nitrided to ensure the correct hardness for the big end needle bearings. Secondly it will require a 4mm spacer and a drop of the port heights. It will also require a grind of the crank cases to ensure there at least 1mm clearance. It will also require a new conrod with a length around 108mm between centres if I keep to a standard Honda piston..

Option 2

This will be the more expensive option. For machine time/cost, full circle crank webs will be the best choice. However, this will reduce the crankcase volume (not good). The new webs would probably be stronger than the resized crank pins. It will still require a spacer to raise the barrel and port height adjustment etc.

Option 3

The cheapest option. I have ridden a Tyga 300 and absolutely loved the mid-range pull, but wasn't happy with the sudden top end drop off. The engine has so much more potential. Gaz, who owned the bike said it was dyno'd at 79 bhp (GP Performance - Fuchs rolling road dyno). It definitely felt that strong compared to my 250, as it could easily keep up with the 600s coming out of the corners. It was the straights that was the problem, just ran out off puff! Gaz's bike had pretty much the full Tyga bling except he was running standard heads (both had rears fitted). I'm pretty certain the standard Tyga pipes are not optimised for the 300, as the pipe's volume was designed for the 250.

Regards
Dave

Option 4 Dave, buy yourself a Honda RS250 GP bike, the 600's wont get away from you on the straights then, i have one which i take to trackdays along with my MC21 with a few HRC bits bolted on, one's around 60bhp, and the others around 80bhp, but guess which one comes out the van most, yep the 60bhp one, more easier to ride and more fun, knowing youv'e just annoyed a load of 600's with only 60bhp.
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Proud Father of , 05 ktm 400exc supermoto 2018 honda crf rx supermoto

I've heard that tyga do sell a 300 specific pipe but I've never asked so not sure .
If you go ahead with stroking the crank , you will either waste a lot of money and time or build a decent motor .
I'd like to see the dyno run from that 300 so that I can visualise this running out of puff you talk about .
Good luck , cheers , neal
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NSR300

Davey email me for more info . Nealgreyplumba@hotmail.com