Rod length to stroke ratio ?

What is his ratio in a standard 89mm stroke commando engine ? :

http://www.hondatuningmagazine.com/tech ... ewall.html

1.68 for the standard Commando engines, and 1.96 for the 750 short stroke.

Ken

Do you know what ratio Jim Scmidt's long rods give ?

Just posted this list on another thread.

Some rod/stroke ratios:

Stock Commando - 1.68
Stock Short Stroke 750 - 1.96
Short Stroke 750 with JS lightweight (6.400" c-c) rods - 2.02
JS lightweight kit for stock 89 mm stroke - 1.83
Maney 1007 cc kit with stock rods - 1.60
Maney 1007 cc kit with JS lightweight (6.400" c-c) rods - 1.75
Maney Ultra Short Stoke 750 (7r mm stroke) with stock rods - 1.99

Ken

Thanks for that - most useful.

acotrel said:

What is his ratio in a standard 89mm stroke commando engine ? :

http://www.hondatuningmagazine.com/tech ... ewall.html

Click to expand...

Dreamin of makin your Commando scream ???

Looking at those Honda car mills with 80mm - 90mm stroke dimensions, the good ol`Norton has the better dynamic reciprocating geometry ratio-wise.
My 2-stroke mills all run ~2:1 R/S ratios but I think thats due to ensuring cylinder port/timing dimensional factors mainly, although it doesn`t hurt rev-wise.
Newer 4-stroke mills run much shorter pistons, Aco - how does that Honda slug work out with deck height in a Norton?

Rohan, it is fast enough already. I would never describe a commando motor as screaming. My short stroke Triumph used to rev to 10,500. Sounded a lot different to my 850. It is about making it less likely to explode, and if it goes a bit harder, that is good but unnecessary. That silly commando motor really impresses me, but it makes me nervous when it spins up over 7,000rpm. I've fitted lighter pistons to motors in the past. In an 650 Triumph twin fitting BSA Gold Star pistons with reshaped crowns make a significant difference, even though they are only 30g lighter than standard. The acceleration is improved.
I find riding the Seeley effortless compared with my old Triumph, but it still takes a certain mindset to ride it really fast. What I find with it, is if I go to pass someone in the twisty bits,it has happened before I know it. If you think it, it has happened. I just hope nobody ever pulls a stupid while I'm coming up behind them. Historic racing is a bit dangerous that way. We sometimes see guys fall off when they are passed too quickly. It is worse than Allpowers C Grade ever was back in the early seventies. I still ride OK, but I know I have to watch myself.

'how does that Honda slug work out with deck height in a Norton?'

That was the main reason I didn't go there. I thought about making alloy barrels, and it is still an option, but shortening them is not as easy as with a triumph, and I couldn't get my mind straight about heli-coiling the threads for the studs to hold the head down. There is about 10mm in it, and you would have to machine off the four-valve stuff from the crown of the pistons. The crown is thick enough to have it poke up into the head if you machined the circumference in a four chuck lathe with offset to preserve the squish band. However they are Teflon coated with really skinny rings which would stop the flutter which robs a lot of engines of power output. I never thought of finding longer rods. The pistons are 73mm dia. so my 850 would have been downsized, and lose part of the squish band. It is not really the best answer for my motor, but it would be good to do it t o a 750.
It would be interesting to search the specs of Japanese bikes for a similar 79mm piston to use in an 850. The price is right, and everything about them is exciting.

Cheers Aco, could try a Wiseco catalogue? Those BMW 1000/4 superbikes run ~80mm bores...

Just one perspective here but when everything is said and done, instead of cobbing up a Honda or Suzuki piston you may as well go with a JSMotorsports package where you get the 1mm rings and can spray/bake the moly coatings on the skirts or you can pay out around $800 for JE pistons to make you four (4) pistons to your specification.

Is there some significant gain in mass reduction by going with making a Japanese MC piston work when compared to a JSMotorsport set up.

I have no commercial interest in JSMotorsports so no horse in this race.

I hope yoose guys realize that JIm S. is keeping his really light wt pistons to himself so a pity on Honda piston bench mark.

hobot said:

I hope yoose guys realize that JIm S. is keeping his really light wt pistons to himself so a pity on Honda piston bench mark.

Click to expand...

Explain this.

Jim has been known to drill holes in the skirts of pistons and do some hand lightening for his own use. Maybe that's what hobot is referring to. I think he is willing to take more risk with mods for his own use than for pistons he supplies to customers. Seems reasonable to me. The customers are certainly free to try taking more weight out on their own.

Jim also offers the pistons with the option of having JE machine the underside of the dome to match the contours of the valve notches. Not too difficult with CNC mills, but still a fairly expensive option for a small weight loss.

Ken

Yes as Ken stated Jim S runs his own current public offerings in Holey and Thinned trim condition enough to rise BF significantly, which likely helps his smooth sense in solid mount Featherbed test bed.

Got it.

So it is not a matter of negating JSMotorsports claims but only to mention that Jim lightens them even further for his own personal use.

I'll speculate here and say that for further weight reductions like holes in the skirts 1.) the cost to benefit for most buyers of JSMotorsports rod/piston package does not support having the piston manufacturer or some third part do the machining (diminishing returns) and/or 2.) the piston OEM will not do it.

Again, I don't have any horse in this race but think JSMotorsports offers a nice package for a lower reciprocating mass and more durable rod/piston package for those who need/want it.