Finn:

Glad you got the Kawasaki rear pulley machined and installed.

I agree with you - the lower rpm makes the Savage far more relaxed to cruise on.  I have never really noticed any noticeable loss of acceleration with it - it still gets up to speed quickly when you open the throttle.  I have noticed that in 5th gear the acceleration is reduced at speeds above 65mph - 5th gear has become a sort of "overdrive" gear and if I want to accelerate faster at speeds over 60mph - I need to drop down to 4th.  The only negative thing I have found is 30-35mph is a bit clumsy - 1st gear is too low of gearing and the the rpm is high.....2nd gear is a bit too tall and the rpm is a bit low.

It also lowered my highway cruising speed head temperature about 20 degrees farenheit.

You are in an elite group now - the only other people running this setup is Badwolf, you and me.

This setup works great on a light bike without saddle bags, windshield and an engine that has been modified to make more power.  It has made it easy to ride 70-75mph for extended distances on the highway when necessary. (I prefer the back roads - but sometimes you have to ride the highway to get to the good roads).

Well, to be honest I am probably a bit neurotic. (Understatement of the year!)

When I look at the conrod on the Savage, I can't help to notice: it is very skinny by all standards.
It is not thicker than my little finger, as if that is a measure of merit....

Anyway, I have been obsessed by a worry, that this conrod can break any moment, if I start to rev the engine to 8000rpm for any length of time.

Look at it: no engines designed to rev has such a skinny conrod.

Wow, that's a really good find!

But I also find 600 euros is a lot of money.I get a cramp in my paying muscle at 30 euros already.

I think you'd appreciate some feedback, so here I go...
if the Jawa is running at 11,000 rpm, there is four times as much force acting on it as when the engine is running at 5,500 (the force increases quadratically).

And suppose you're running at 8,000 rpm, you don't really need such a strong connecting rod. At 8,000 rpm, the pulling force is about 2.12 times greater, and I think our crankshaft can handle that.

I also think this heavier connecting rod disrupts the balance. And if you don't think that's a problem;
I would rather make the piston pin and the piston lighter and maybe drill some holes in the crankshaft to balance this again.

*You can machine the hollow piston pin on either side (make a bevel on it, because the end carries almost no force). And the piston can surely spare a gram or two here and there. And every gram at 8000 rpm weighs 4.2 kg due to the acceleration forces.

*You could also look for racing piston pins. They are thinner and made from high-alloy steels. https://www.llracing.eu/wrist-pins
*A needle bearing with more rollers would result in better dimensional stability of the big end.https://ikont.com/catalogs/general-product/5508_3_E_ALL.pdf
*You can also look for a connecting rod with a larger big end and then turn down the matching big end pin on both sides... And if you do that eccentrically, you have a larger stroke. (I don't know if the Savage's crankcase has room for that.)

I wonder if the DR 650 has a crankshaft with a stronger big end?
OEM 1216132E00

https://www.cmsnl.com/products/connecting-rod_1216132e00/

They are all ideas you have probably thought of yourself, but who knows.

That 37/35/37 setup is interesting but unfeasible given the cage required for the rollers; it would only have a wall thickness of half a millimeter. You really need a cage because the big-end bearing doesn't rotate continuously but moves back and forth, causing the rollers to be constantly forced against one another—which wouldn't work well. In any case, a cageless needle bearing is inherently less reliable, and for a big-end application, it would be extremely unreliable.

I would opt for the slightly shorter BSA connecting rod and compensate for the difference by machining the pin eccentrically. If done correctly, the piston-to-head clearance remains unchanged, and you gain a bit of displacement.
I hadn't yet considered the implications for the balance shaft, though; it would turn into a bit of a Frankenstein setup.
That’s why I’d ultimately choose the standard connecting rod. Of course, there’s always the option of having the original rod strength-tested; a company that certifies lifting straps and chains could easily help you out with that, provided you handle the preparation yourself.

Project better conrod is moving on.
Here is the crankshaft in CAD, and from here I can design a fixture to align and hold the parts together while I drive the crank together.

Strange that the left side with the flywheel and the generator is much beefier than the right drive side.

It is nice to handle these wonderfully well machined parts. Sad to think this is the past, and the future is battery driven.

I am sure I am missing something here.  If you grind the center of the crankpin undersize, how do you slip the new caged bearing over the pin?

If you are going to modify the crank assembly, have you considered going to a longer rod?  A longer rod will provide better mechanical advantage over the crank throw due to the improved angle of attack.  It will also reduce piston thrust and the associated frictional loss, and it will increase dwell at TDC.  Long rod engines make more power.  The stock cylinder will allow the use of a 3mm longer rod when combined with a stock piston.  It will bring the piston top right up to the cylinder deck at TDC.  So, with a 3mm longer rod and a stock piston you end up with higher compression, better mechanical advantage, reduced frictional losses, increased dwell at TDC.  All good stuff.

A modification like that is way beyond my capabilities.  Balancing the beast would require a technician with specialized skill and experience.  The balance shaft will make it a lot more complicated.  But the end result might be gratifying.

I see that both the LS and the old DR and the newer DR all use 37 x 47 x 25 rod bearings.  We already know that the piston pins on both the LS and the old DR are the same diameter.  It would be nice if one of those DR rods turned out to be about 3mm longer than the LS rod.  I suspect that's not the case since the DR is off road and the designers probably did all they could to keep engine height as low as reasonably achievable.

I would be more concerned over the balance than a rod failure.  Even if you manage to pull off the 35mm valve modification I don't think your con rod will be in jeopardy.

I've straightened out three of these cranks.  That's pretty easy.  Never had one that was twisted.  I suspect that would be a bit harder to correct.  Good luck, keep us in the loop.

Zevenenergie, taking that little moped from an 8K redline to 13K redline must have been fun.  Do you think it was choked off a bit with that 8mm carb?  That's like the size of a pencil.  I've got carbs that big on my model plane engines.  To run the engine up that high, did you have to switch to thinner piston rings?