Datsun Roadster Forum-311s.org

Peter, did Dave ask you to sign a waiver as to the viability of your keyway? Jim, can you give some insight as to the U20 rotating stress/shear, versus an R16? In other words, in layman's terms, how much rotational stress/shear might be on the little bit of keyway, in each engine application? The upper chain does have a bit of weight in a U20.
And doesn't Dave rebuild engines professionally, and some, like Peter's, with enormous power? Would a "professional engine builder" let a customer make such a choice?
Again, aren't you really just driving the camshaft, etc? Pat

The clamp force of the roadster 5th gear doesn’t seem to work so well. I personally would never trust relying on nothing but clamp force on a large rotating assembly.

Good point Mike. I would have to agree.


"Jim, can you give some insight as to the U20 rotating stress/shear, versus an R16? In other words, in layman's terms, how much rotational stress/shear might be on the little bit of keyway, in each engine application? The upper chain does have a bit of weight in a U20."

Sure Pat, but it's pretty complicated....

"just driving the camshaft?" no, there is far more load than you might realize and it's not static, meaning that it is varying at every point in rotation..the crank sprocket is accelerating (and decelerating) the cam and masses of all the parts, it has the variable geared load from the oil pump (substantial) and dist, a little for the fuel pump, you are accelerating the pushrods and lifters up, and they are pushing the cam(rotationally) on the downstroke, and of course you are accelerating the rockers and compressing the valve springs and accelerating the valves and valve hardware. And then add to that friction EVERY where you look. Yes, that is a substantial amount of friction and work.

The more radical the cam lift and springs, and harder the engine is pushed, the higher all the acceleration forces.

As for differences between U and R, that's even more complicated. Complex is an understatement. yes, there is more mass with the U20 valvetrain, The chains themselves require relatively minimal forces since they roll so easily, and of course there is the flywheel effect of the rotational sprockets (wanting to stay rotating at the same speed), but there is more hardware. Lots of engines actually fail on deceleration because when you let off the gas, lots of the forces reverse almost instantaneously and that reversal shock/impulse is significant.

Either way, Nissan chose basically the same 5mm crank key for both the U & the R, so their engineers obviously thought the 5mm key was both necessary and sufficient for both engines. They could have simply indexed it with a thin sheet metal key, yes?

Would a "professional engine builder" let a customer make such a choice? I don't know if Peter made the choice or not, doesn't really matter, but yes all "professional engine builders" have customers make "less than optimal" choices frequently: tired used parts, cheap parts, "I can't afford to turn the crank", can we just use it as is, new rocker arms?,does it really need new valves? new guides?, 250$ to balance it? does it really need a valve job? can we do it cheaper? so yes..

I think we have flogged this topic to death- as long as the lower timing gear stays put, all will be well. If it rotates (ever) its all over no matter who built it or what the motor cost.

I believe the (much) better approach is to correctly add the keyway no matter who does the work, so that would be my recommendation to anyone. The cost is a relatively small part of a well done stroker project.

Thanks jim, I appreciate your insight, but still have to ask the questions. Pat