After shedding the highly-modified RC Engineering stroker crank and rods, good replacement CB750F2 crankshaft and rods were installed in the same machined cases, which are to house the 73mm big bore top end. Getting the cases back together was pretty straightforward, but I didn’t mark the pistons properly, so when the F2 camshaft was installed, the valves hit the pistons. That required tearing the top end off again to reposition the pistons so the exhaust valve cutaways were facing towards each other on the 1-2 and 3-4 piston sets. /- / instead of the way I had them which was //-// (intakes on top). Not paying close attention will get you into trouble every time. Another wrestling match ensued to get the 73mm pistons and springy ring sets back into their respective bores. Finally I prevailed, but it seemed that the F2 cam timing was still so radical that the valves continued to hit the piston crowns, just at one spot.
I had already backed off the valve springs to OEM stock, so the next thing to do was to put a stock cam back into the engine, ensuring that no more piston/valve contact would occur. A good used eBay cam was purchased and then installed without any further drama. I had to slot the camsprocket to get the camshaft marks on the end –O– to line up properly when the 1-4 pistons were at TDC. Apparently the stack height of the cylinders wound up being different than the stock setup. Perhaps that is why there were two base gaskets under the cylinders when they were disassembled the first time…
Well, eventually everything meshed back together again and all the outer cases were buttoned up with a set of polished Allen-head socket bolts. Turning the engine through by hand gave the impression that everything was going as planned now, but until spark plugs are installed and the actual compression figures are noted, I may not be out of the woods yet on getting this monster motor to spin over with the stock starter motor.
Where I ordinarily go full-bore on getting projects done and back on the road, this one has been dragging on for months and months. Figuring out what I had bought in the first place, followed by my inability to make it start reliably caused the initial teardown for inspection of what engine work had been done and what really wasn’t done, despite assurances from the accompanying documentation. It was certainly a learning experience on several levels and as the project has move slowly forward, various individuals caught wind of the bike and have contacted me about the parts installed and some of the history of the evolution of the components during decades of development.
Apparently these big bore pistons were sourced from local Los Angeles piston manufacturers, including Arias and J-E. Cams were ground to specs from several sources and even the valve springs/retainers had upgrades. The valve spring/retainer set in this bike, built in the mid-1980s, has titanium valve spring retainers, which was a change from the red-anodized aluminum retainers used previously. Russ Collins stamped the parts with “RC Eng” on the parts he actually manufactured/modified, including the cylinders and cylinder heads, after they were completed. My bike does have RC Engineering stamped on the cylinder block, but nothing specifically marked on the cylinder head, despite obvious reworking of the ports and installation of Manley stainless steel valves and the previously mentioned racing spring kit.
So, I’m getting close to dragging the 176lb. lump back into the chassis soon. A recent hernia operation limits me from doing heavy lifting for a few weeks, so I’ll have to enlist some muscle from the locals, when I can catch someone at home and willing to help lift it back into the frame. I just pray that the motor will spin over and start back up without any more drama than we had last time.