I've not seen any mention in the forum of the connecting rod center-center length.  Carrillo doesn't list a rod with dimensions for the 650 and neither does the OEM service manual, so I'm wondering if someone has measured one while they had an engine apart.

Generally, the longer the rod (compared to the stroke) the better, but a long-rod 650 could be a VERY tall engine.    

thanks,
Michael

I have a friend who understands balancing with balance shafts, but I'm not up on the details of what to do when modifying weights of the different parts.  He's written freeware for analyzing a basic single cylinder (no extra shafts), but balance shafts seem to add a fair bit of complexity.

John Ulrich's "Road Racing World and Motorcycle Technology" magazine has very useful spec sheets on road tests.  They adopted my suggestion to add rod c-c length to the specs so that people could see the rod/stroke ratios.  It is interesting to see what different manufacturers do, and how it might vary for different applications (street vs MX vs roadrace).

I road raced a Yamaha TT500-engined bike for 6 years in the late 70s/early 80s.  The Yamaha has a fairly short rod ratio.  I recall being told that Mert Lawill was involved in a TT500 short tracker project and that it wasn't putting out the expected power until he suggested they put in a longer rod.  The person who built several of my race engines would put long rods into 4T trials bike engines as he said it made them smoother at the very low RPM they usually used in a section.  I was going to build a TY400 Yamaha vintage trials bike for the AHRMA Modern Classic class using a short stroke/long rod SR400 crank in a TT500 engine (another project that didn't get very far).  He also built some short stroke/long rod Yamahas for racing.  

I talked with a former American Federation of Motorcycles (AFM - a California race club started in the 1950s that I raced with for decades) #1 plate holder who had a lot of success with big-displacement Yamaha FZR400-based engines.  He told me he'd built one with 3:1 rod ratio and it was a big improvement, and he'd have been happy to go even longer on the rods but there was no way to squeeze them in.

I got a long rod/high-pin piston kit from a racer who specialized in the BSA unit single 500cc, mostly for dirt track, and he claimed it made a big difference.  Other people who used them confirmed his claims

Your nominal 166mm figure gives a rounded off 1.76:1 rod/stroke ratio which is better than I expected.  An additional 4mm for a zero deck would be 1.81:1.  Unfortunately, the longer the stroke, the less impact a couple of mm of extra length makes.  I haven't had a chance to measure a piston to see how much the pin could be raised in one.

A TT500 is 1.72:1, a unit single BSA 500 is 1.69:1, Yamaha R6 2.05:1, some GSXR600s at 2.6:1 (some variance with different model years on the modern sport bikes), but 2:1 is often mentioned as a target for a good rod ratio for high performance.

Adding 22mm to the rod on a 650 would be a chore, but interesting.  What my friend did on the long rod engines is he increased the rod lengths based on cam chain pitch to make it where he didn't have to add a 1/2 link into the chain.    

I suspect that for reasonable street use the 650 is in the "not bad but could be better" range since it is RPM limited by the stroke.  6500 RPM is about where it hits 4000 ft/min mean piston speed and while I've seen mention of people going to 7500 RPM (4626 ft/min) and a bit higher, those speeds sound chancy to me with an OEM rod designed for a low horsepower engine.  I had a Carrillo rod in my 500 Yamaha with an 84mm stroke and I still tried to keep the red line below 8000 RPM which was 4400 ft/minute as I saw other Yamaha 500 racers with blown engines from revving them to the max.  That little bit of extra power didn't make any difference in my lap times because I was the limiting factor, not the bike.  

Thanks for the rod info, and all the other stuff you've shared (and I've been busy copying off for study).

cheers,
Michael

I've already got one of those paperweights from my Honda 216 vintage racer, though it was due to a pattern valve breaking where the stem and head were joined.

FinnHammer, I've enjoyed reading your build thread, you are doing some nice work!

Thanks for that video, the presenter does a good job of explaining the situation.

In "Tuning for Speed" Phil Irving gives a formula for calculating piston loads, and I ran some Savage numbers through my spreadsheet.

stock rod, Wiseco piston, 6500 RPM:
2864.04 lbf load      TDC      1.766:1 rod ratio
1600.10 lbf load      BDC      
           
long rod:
2790.09 lbf load      TDC      2:1 rod ratio
1674.05 lbf load      BDC      

That tracks the video with the longer rod reducing both the load at TDC and also the variance between the TDC and BDC loads.

Piston pin offset can also make some difference in things like sideloads at midstroke.

But as far as the rod, I think the Savage will be one of those "it is what it is" situations.

I've seen some vintage pistons with thick rings that were widely spaced, so fixing that can help to make space to raise the pin in the piston.  Also, race pistons will try and bring the top ring closer to the deck to reduce the top ring volume as the gasses above the ring aren't helping the compression ratio or doing much work, but if that is pushed too far the top ring will be exposed to too much heat and fail.

Here's a handy calculator for pistons:
https://www.wiseco.com/compression-calculator/

I'm going to play with the ports.  I have an Audie Technologies FlowQuik that I will have to drag out of hiding.  I've pulled molds from the ports but I should put those photos into a different thread.

Here's some information on the new Ducati 659cc Superquadro single for comparison:

https://www.cycleworld.com/motorcycle-news/ducati-new-superquadro-660-single-...

659cc Ducati Superquadro 77.5hp @ 9750 RPM, or 85hp @ 9500 RPM with exhaust changes, 116m x 62.4mm, 46.8 and 38.2mm valves.  110mm rods for 1.81:1 rod ratio (which Cameron considers "shortish") where Ducati twins are usually in the 2-2.2:1 range.

Putting the Ducati numbers into Irving's formula @ 9750RPM and keeping the same piston weight (though I'd expect the larger Ducati piston to be heavier) gives

TDC      4279.47 lbf
BDC      2388.26 lbf

At 6500 RPM to match the Savage calculation:
TDC      1901.98
BDC      1061.45

A short stroke helps too!  But if a person wanted a short stroke high revving single, they probably wouldn't have purchased a Savage.

cheers,
Michael

For the price of one of the new Ducatis you could have 5-10 Savages.  

It seems like you could handle the job of cutting the steering head free (or mostly free) and welding it back on after steepening the rake angle.  That was not an unknown modification on TT500 Yamahas, especially if being used for dirt track.

Dave,
Your description of the steering is good, I lacked the vocabulary to phrase it so well, but it does indeed "flop" into the corner. That is a spot on description.
It feels, to some extent, like the top half of the wheel is too heavy, and I am in the process of building a lighter wheel with a 1.85" h-profile alluminium rim, it will be fitted with a 3.6 " TT100 dunlop tire, for the period look. Not the Savage period, but my period which was in the early seventies. Rear tire will come next, with 18" h- section allu rim and a 4.1" wide TT100 tire. That big balloon in the rear can not be beneficial for cornering, and skinny tires are beautifull. Back in the day, this tire selection would support much larger bikes than the Savage. Longer rear shocks will follow by then.
I also intend to lower the front, by using the modified lower yoke as the top one.Visually this slants  the cylinder slightly forward which I like. I don't quit undertand what you mean about the spacers..

I think I have to back out of any further discussion about the front fork, for the moment,  because I am unfamiliar with the nomenclature used, and I have not found a proper cross section drawing of the fork, so that I might visualise how it actually functions.
Dave, Michael, for now, thanks for your input, I will return to this subject when I have gotten myself a better understanding of the innards of the fork.

Possibly read this thread from start to end:
https://suzukisavage.com/cgi-bin/YaBB.pl?num=1421689358