The stock rods you guys are running im sure are not modified at all. I wonder if cryro treated polished rods can handle higher rpms
Bigger rod bolts are a must...
Even with 836 10.5:1 and daily 9500 rpm?
Back in the day...
I roadraced (briefly) a bastardization of parts: Yosh 2 ring slipper pistons, whatever size makes a true 750CC as that was the class limit, yosh head, stock size valves, RC big bump cam and springs, Weber carbs and a RD Racing Bol d'or replica pipe. Stock rods.
The 2nd oversize (0.5mm) makes it 749.5cc, I think? That was the Yosh kit of the days when I was in "production" racing, which could not exceed that 750cc limit.
Generally, what we noticed was this: if the compression (dynamic, for the most part) got past 10.25:1 at high RPM, the rods got into troubles. Often, the cams wound to 11k, which put it past the stock rods. BUT...the midget-car guys ran steady 12K RPM with stock rods, using the stock cams and modified pistons with (much) deeper valve pocket recesses and little welded-in ridges across the center of the piston top to both raise compression (to offset those deep pockets) and to control the overlap burn rate. I never saw a midget-car guy ever bend a stock rod. That led me to believe that it was the meeting of valves and pistons that were overloading the rods at real high RPM, except in the cases where guys had the Powroll 11:1 CR forged pistons (heavy!) and were just pounding them into the bottom of the stroke - they DID do some things to stock rods...!
I have often seen that bad things happen me often bring something very good in the end, better than before. It can sometimes take years to fully realise it.
My first set of 836 pistons, forged RC with good CR adapted for the head with opened chambers. Bad luck first year melting 2 of them. I replaced them with cast Action Fours that got lower CR with the head which I noticed when accelerating plus different and tamer sound.
I understand now that this was pure luck. I used the bike mostly on holidays with tours of 5000-6000kms in total during 3 weeks. Mostly high speed on Autobahn, Italian or French highways. I'm now convinced that the OEM rods did not fail due to the lower CR with Action Fours pistons with the heads opened chambers, more like the CB750 std CR.
(It must have been horrible to get a rod thru the case in high speed on a crowded highway or curved road in the Alps were speed was not low either. Overloaded bike with 2 persons + luggage)
The top speed however, did not suffer and the bike worked really well. I had no tachometer, top speed 210km/h with 17:48 gearing (about 8700rpms). I remember I often shifted to 4:th gear at 160km/h (100mph) which is about 9500rpms. see excel chart.
Using OEM rods + high rpms can be OK with lower CR, right? I have higher CR now and got need of better rods in my mind.
