I'm toying with the idea of making my own push-rods from solid 10mm ally rod, taken down to 9.7mm at the bottom and threaded for 1/8" BSPP hex blanking caps for adjuster use, with stud and bearing grade Loctite keeping it all in place, then drill and tap these 1/4" BSC for the iron barrel tappet adjusters. The tops could be drilled and tapped 6mm if the AVL tappet adjuster ball ends aren't too big to fit the AVL rockers. 1/8" BSPP is a fairly fine thread.
A.
I haven't checked the forum for a couple months I guess. Interesting, I just modded my pushrods today, maybe something not unlike what you're outlining here. They had seemed a weak link to me especially being so far wound out, despite my having put spacers over the threads 'twixt the locknut and pushrod to help strengthen that rather spindly thread on the (late CI, metric) adjuster cup, one of which was already bent slightly (it was a second-hand piece I'd put in "temporarily"). As noted earlier, I still had a lot of valvetrain noise of uncertain origin, and it's been seriously irritating my tinnitus. Today that was solved, maybe partly as a function of having both my adjusters actually straight.
Other possible noise source: A few weeks ago had the timing cover off and observed that cam gear backlash was not consistent from one point of rotation to another (yes, had the pushrods out, so fully unloaded). When I'd set them correctly at their point of tightest interference, then at other points the gears meshed loose enough to likely be causing some of my rattle. Wasn't sure if this was due to wear (they were a used set of CI cams I'd just been experimenting with), or (more likely) poor machining on RE's part. The new OE ones I put in today are still not perfect in this regard (so it probably is the machining more than wear), but they seem better than those I had in there. I've still got more backlash on one side of the gear than the other, but not too bad.
Also noted that even when pushrods are set to zero clearance cold, they become really loose when hot. I mean, REALLY loose. Which means the cylinder/head are expanding a lot more than the pushrods, despite both being aluminum. This seems a curious thing that I guess can only be indicative of temperature differences amongst components. Short of fitting a CI cylinder block or finding a pushrod material with a much higher coefficient of thermal expansion (not likely), the quest for a quiet AVL might end here, I thought.
Anyway, what I ultimately did was found a set of old CI pushrods with the 1/4-28 adjuster threads, these are substantially beefier than the M6's on late CI's / AVL's. So I figured that would largely eliminate the possibility of bending. Only trouble being that CI pushrods are hollow and without fabricating a bushing (not a lathe owner at present), the ID is too large to provide the needed press-fit for the little spherical steel nib from the AVL pushrod's top end. And I think there were problems on the early AVL's with pushrods bending - I'm going to guess in the hollow design being carried over from the CI's. Other problem is that the ID of the CI adjuster assembly, where it press-fits onto the machined OD of the pushrod, is larger. So no press-fit available there, either.
So here's what I did: Removed the complete adjuster from the old-model CI pushrod. Removed the steel nib from the AVL pushrod top-end. Inverted the AVL pushrod. Drilled out the threaded (originally bottom) end of the pushrod sufficient to provide the press-fit for the nib, and pressed it in. On the other (originally top) end, I drilled out the original nib-hole to 1/4" to allow clearance for the new, larger adjuster threads, then pressed the complete adjuster assembly on that end. Depending on the particular pushrod's OD, it may or may not press-fit directly - my original pushrods were a perfect OD for it. If the pushrods' OD is too large (like my RE replacements), the OD can be turned down slightly (mount rod in hand drill and use flat-file/emery cloth) to provide the proper press-fit.
So basically I've got upside-down solid aluminum AVL push-rods with AVL top nibs and the beefy old-model 1/4-28 adjuster cups. In my case I also shortened my pushrods by a few mm's to allow for enough adjustment, but that's mainly because my cylinder was shortened by 2.5mm. This would not be necessary for everyone.
As outlined earlier, I had installed the larger-diameter CI tappets at the time of my last rebuild, and now with the stronger adjusters, I'm feeling much confident about valvetrain reliability now. Besides tappet feet sometimes breaking off, the AVL's were known (here in India at least) to "throw" the pushrods, meaning they'd sometimes fall out of the fairly shallow little sockets in the OE AVL tappets.
Only possible downside in all this is that everything's now a LOT heavier than stock. I've got CI tappets which are a LOT heavier than the AVL's. I've got solid AVL pushrods which are a LOT heavier than the hollow CI's. And I've got the old-version CI adjuster assemblies which are a LOT heavier than the AVL's tiny bits. If I were building something with the idea of high-revs, I'd turn down / eliminate whatever I could on the adjusters to lose some weight there, or else drill/tap the original AVL hardware, which is a lot smaller/lighter, to accept the 1/4-28 cups. And I'd probably go with the tubular pushrods, too, all in the interest of avoiding valve-float. For my intended rpm range, I don't expect problems.
Bike's been running really great, really strong, about as much power as I feel I would ever need with local roads in view, extremely responsive and certainly pulls a fair bit harder than a stock AVL, that across the entire rev range. I've still not really revved it near redline (whatever that is), mainly because I actually don't need to in order to move along briskly, also because I've got this extra power working on a stock crank and don't really want to push the limits till I've at least got some good use out of the bike. I figure a year from now I might be in the mood to pull it all apart again... and if so will do the crankpin and bearing up better.
For now, might change the oil and then am hoping to just ride it for some months with minimal fiddling. If my warmup and short ride home this evening were any indication, it's quieter than it has ever been, quieter even than some of the hydraulic-lifter UCE's I hear running around. Probably going to take it out to Lahaul/Spiti valleys with some riding buddies in a couple weeks. Only a measly little 13,500ft pass between here and there (I'm sure the bike has been above 18,000 more than once before I owned it), lol.
-Eric