New Zongshen RX3 (ZS250GY-3) Dual Sport

[jimjr21]

Making a stroker crank is easy. Just go to a smaller crank pin diameter. However that is also a way to make it less reliable.
I will be looking for a reliable way to make a stroker crank. However it needs to be 3+mm or no go as power gain would be minimal for an expensive assembly.

[oldqwerty]

Originally Posted by jimjr21

Making a stroker crank is easy. Just go to a smaller crank pin diameter. However that is also a way to make it less reliable.
I will be looking for a reliable way to make a stroker crank. However it needs to be 3+mm or no go as power gain would be minimal for an expensive assembly.

I had an old guy who would press out the pin, weld up the holes, grind the welds smooth, redrill the holes, then press the assembly back together for $500. Unfortunately, he passed away last summer. I have to find a new machinist because I'm not that good.

[pete]

Originally Posted by jimjr21

Making a stroker crank is easy. Just go to a smaller crank pin diameter. However that is also a way to make it less reliable.
I will be looking for a reliable way to make a stroker crank. However it needs to be 3+mm or no go as power gain would be minimal for an expensive assembly.

How dose going to a smaller crank pin diameter increass the stroke ?
Stoke is the centre line of the crank pin & main journal X2
the Dia of either has no bearing on the stoke..
to increass the stroke you have to move the centre line of them
ferther apart...

[jimjr21]

Originally Posted by pete

How dose going to a smaller crank pin diameter increass the stroke ?
Stoke is the centre line of the crank pin & main journal X2
the Dia of either has no bearing on the stoke..
to increass the stroke you have to move the centre line of them
ferther apart...

There are clearances from crankshaft and rod assembly to the surrounding case. These clearances have to be maintained.
So if you have a 24mm crank pin stock and switch to a 22mm pin. Keep the thickness of rod the same and the outside location of the pin the same the center line of the crank pin will move to a 2mm larger circle. Presto +2mm stroke.
Now clearances to head must be maintained. So you need a -1mm rod length center to center. But the real clearance issue happens at BDC where now the piston is 2mm further towards the crank and case. This is why sometimes you see spacer plates put into stroker kits to clearance piston to crank issues. But then you run into cam timing and cam chain length issues. Other ways around it are pistons with different pin heights to compensate with using a crank and rod setup that has pin in higher location than stock.

[pete]

Originally Posted by jimjr21

There are clearances from crankshaft and rod assembly to the surrounding case. These clearances have to be maintained.
So if you have a 24mm crank pin stock and switch to a 22mm pin. Keep the thickness of rod the same and the outside location of the pin the same the center line of the crank pin will move to a 2mm larger circle. Presto +2mm stroke.
Now clearances to head must be maintained. So you need a -1mm rod length center to center. But the real clearance issue happens at BDC where now the piston is 2mm further towards the crank and case. This is why sometimes you see spacer plates put into stroker kits to clearance piston to crank issues. But then you run into cam timing and cam chain length issues. Other ways around it are pistons with different pin heights to compensate with using a crank and rod setup that has pin in higher location than stock.

So you are increassing the distance between main & big end centres... Correct?
A bit more involved than a "smaller Dia crank pin" that was stated in the earlyer post..

Not hard to sorce con rod blanks to machine what ever length rod you require..

I have built complete cranks for Jawa / Westlake & GM speedway motors

[jimjr21]

Originally Posted by pete

So you are increassing the distance between main & big end centres... Correct?
A bit more involved than a "smaller Dia crank pin" that was stated in the earlyer post..

Not hard to sorce con rod blanks to machine what ever length rod you require..

I have built complete cranks for Jawa / Westlake & GM speedway motors

Yes a bit more involved.
Been kicking around ideas with other engine builders and we tend to not include the technical details of each possibility as we are familiar with them. I responded here with that mindset.

Anyways I can not wait to be testing my prototypes in a few weeks.

And maybe I will build an all out power engine and test to failure. See how far I can push parts.

[Huck369]

Got my Hand Guard mounted, installed a set of 1 1/2" risers on the handlebars and this cured the dash interference but will still interfere with anything plugged into the lighter port at full turn...

[woodlandsprite]

Originally Posted by Huck369

Got my Hand Guard mounted, installed a set of 1 1/2" risers on the handlebars and this cured the dash interference but will still interfere with anything plugged into the lighter port at full turn...

Is installing a set or risers as straight forward as unbolting the handlebars, inserting the risers and rebolting the handlebars? Any adjustments needed to cables?

(just for reference, yes I'm a complete newb to working on a motorcycle and no, I still don't have my bike yet)

[Weldangrind]

Originally Posted by jimjr21

And maybe I will build an all out power engine and test to failure. See how far I can push parts.

Please set up the tripod and video camera!