Hi Steve, As you think any bending at all is no good. The pushrod is made of a sturdy metal like tool steel. Very similar to what's called "drill rod" in USA. It's a tool steel they make drill bits & other tools out of. I've made a few push rods from drill rod. Hardened each end. I've made adjuster screws from drill rod as well. Both proved very durable like factory ones.
If you cannot straighten clutch rod, it will need new one. The rod must be quite straight. Between the bushing & the clutch end of main shaft the rod is unsupported in the hollow part for about 6-5/8". So it must be straight. The rod must be very free fitting in the main shaft without even a hint of binding.
How the push rod gets bent I don't know. I've purposely coil bound springs during testing & I can feel lever stop when coils are bound. I've had T140 where adjuster screw hits plug. If you are paying attention, you can feel the lever all of a sudden stop like somethings binding or is wrong. But if you keep squeezing, it might bend rod. I never kept squeezing.
Back to your rod, from factory only the ends of rod are hardened. Maybe about 1/2" or so with the tips that are really hard. The rest is just stiff steel. So you can usually straighten rod. It will have spring back for about 24-48 hrs. So after you have it perfect. Come back a few days later, it's not perfect again. So it may take a few attempts & a tad of overbending. Some aftermarket (pattern) rods are fully hardened end to end. Those may be much harder to straighten. BSA nut on Ebay was selling them. I don't see any advantage to fully hardened.
I've checked many rods for straightness & all have been very, very close to perfect rolling them on flat surface. I've never personally seen a bent clutch rod yet...
states rod is 7/32" (.2187"). I've measured several. They tend to be smaller diameter by about .002-.003" from factory. The length of rod is stated in manual
to be 11.812-11.822" About 11-13/16 in length. In my observation this is pretty much the case on original 650 rods.
However I've measured length of original T140 750 type rods & they have all been shorter by about .030" at 11.750" (11-3/4"). Yet... part # is the same.
I had a few bikes where rod or screw was problematic. A 1970 Tiger where rod wore a step in it about 4-7/16 from clutch end. Rod was replaced. New rod wore the same. Owner just lived with it.
My '73 Tiger did exact same thing!! Turns out this is caused by a burr in the bore of the main shaft where it necks down to the narrow on clutch end. The main shaft is hardened. I attempted to drill off burr, couldn't do it, shaft was too hard. I tried to crack it off driving hardened rod down bore. It was too strong to crack off. The burr could be plainly felt sticking a probe into the hole in main shaft & seen by shinning light into bore with shaft on bench. Indeed it was a burr. The burr narrowed rod by .016". The ID of the burr was a whisker larger than .218".
I observed this step & recorded wear. It was not wearing any further than it had in 11000 miles from new. I turned rod around. It started wearing decided new step in less than 100 miles. So I turned it back around while deciding on what is best way to proceed.
So I ended up making a custom rod that necked down at the burr such the step in rod always cleared burr. The ID of my main shaft at the left end was looser than normal. So I was able to use oversized rod 15/64" & neck it down at burr. Tapered the neck down transition smoothly to reduce the stress riser from the narrowed area. Turned the right end of rod down to .218" where it goes into bronze bushing. The left end of rod was 15/64 diam. for 3-3/4". Inspection of bronze bushing showed it was in perfect condition, even after 36000 miles. So that was not part of problems. This custom rod has worked very well & doesn't wear a step in it anymore. Been in bike a good 20000 miles now & still is.
As you may have guessed the factory rod on my bike was quite loose in clutch end of main shaft. 1/64+" wobble. Loose as a goose!! Yet... the custom rod which is a perfect fit gives no improvement in any way I can tell. I swapped old & custom rod a few times & extensively road tested. The wobble just didn't matter in real life. Truthfully, I could have just left the old rod in with the groove worn in it.
I've measured the bore in a handful of main shafts. It's all over the place, & can vary by .017".
The overall length of main shaft is about 11-1/8' long. The counter bore where bronze bushing goes is drilled about 6-7/8" deep, which means the narrower rod bore at clutch end is about 4-1/4 deep. The pressed in bronze bushing is about 3/8" long. Bore of bushing is supposedly clearance for rod. The bore of some of the new reproduction bushings I've been involved with is drilled too large. Even after pressing in new bushing bore feels worn out. Unless your bushing is really worn, new one might be worse...???
The factory rod adjustment screw is much longer than it needs to be. Pretty much all of the right foot T140 I've been involved with including my own, the screw hit the plug. A few actually wore hole though the plug & oil leaked out of slot. Owners said theirs is not hitting. But... removing plug it was. I've cut the screw shorter on slotted end & reslotted with hack saw.
To cut screw, take a donor 3/8-24 nut. Cut nut through to bore starting at a point of the hex. Deburr threads. Now screw adjuster screw into nut leaving the amount you want cut off exposed. Put nut in vise tightly such you can hacksaw screw tip off without screw spinning in nut. Deburr cut surface of screw. Put screw in nut with cut end sticking up the amount of depth of screwdriver slot you want. Again put nut tight in vise. This will allow easy cutting of slot without screw turning & there will be zero thread damage to screw threads. I have made these screw holder nuts for almost every size bolt/screw on bike. A safe & easy way to cut bolts & screws.
I've not seen many complaining of the plug wearing through on left foot shift bikes. Maybe factory modified casting of primary cover depth?
I wonder if the factory shortened clutch rod .030" in an attempt to gain more clearance? It wasn't enough. The 650 originally had thick seal on plug. They went to oring. The oring seemed fine on later 650. The 3 row chain crank case is a different casting. It's slightly wider than 650, but not quite wide enough??