Well, it was an educational adventure, that Hot-Rod CB77 project bike, but apparently it didn’t attract the audience (and a new owner) that I had hoped. A 5-hour wrenching session, yesterday, ended with the Hot-Rod CB77 being emasculated back into the stock OEM Super Hawk model, as Soichiro intended.
The bike, in stock form, certainly has lost the added zip of the 40cc forged pistons, coupled with the H-C roller camshaft and valve spring kit. It was really uncanny how fast the engine would start, hot or cold, when you just touched the starter button. I have never had any bike start that quickly, stock or otherwise. It was really quite tractable at low to medium speeds, but once it was humming over 8k rpms, it was at its happiest place. I think that the full potential was not realized due to the stock carburetors/intake tract length and the bottled-up OEM mufflers, which were complete with stock baffles.
Through a series of bike and parts exchanges, I wound up with a NOS CB77 (or CL77) cylinder head and a set of new late model cylinders, which had been stacked up in Thailand for many years. The parts arrived safely, but with the expected layers of surface rust on anything that was ferrous and some alloy corrosion on aluminum parts, with a good sprinkling of dirt thrown in. I sent the cylinder head to a local friend who has a blast cabinet with soda to de-scale the alloy fins and cut through a layer of rust. Even after the soda blast process the finish was on the dull side so I used some Duplicolor Cast Coat Aluminum Engine spray paint to brighten things up.
I cut new valve seats in the combustion chambers and lapped in the valves for a good seal. I had one last set of NOS valves, so everything was pretty fresh for installation. A good set of used cams/rockers and cam sprocket were installed for a plug and play engine conversion.
The cylinders were rusted in their bores, so they were sent off to be bored to the .75 pistons and rings I had in stock. The cylinders got a spray paint coating as well, as did the engine top cylinder head cover.
Once the engine was extracted from the chassis, the teardown and inspection ensued. The engine had been using a lot of oil, based upon the degree of baked on petroleum throughout the top end. One of the culprits was a .035” compression ring end gap, coupled with old-style single-piece oil rings. My solution had been to re-cut the pistons to use stock 64mm CB350 rings, which closed the end gap down to .016” and featured 3-piece oil rings. Once the head was removed, I could see a nice tan coating on the piston tops and in the combustion chambers, a far cry from what it looked like on the first engine teardown. The pistons looked to be in good condition and the honed cylinders showed a few spots of scuffing, but no signs of impending seizures. The engine only had a couple hundred miles on it, so the rings probably weren’t fully seated to the bores, just yet.
The cams and rocker arm rollers all looked bright and shiny, and everything in general seemed normal other than an odd break in the edge of the head gasket near where the o-ring/locating dowel are located. The engine hadn’t been leaking oil or smoking at all, so apparently all the parts and pieces were playing nicely with each other.
With the hotrod parts set aside, the new cylinder was oiled lightly and prepped for installation after the pistons were swapped into their respective connecting rods. The cylinder block is one of the later die-case units, which uses a narrower tensioner design. Everything came together rather smoothly. It is much easier to get the cylinders down over the pistons/rings when the factory tapered edge is still available on the bottom of the sleeves.
The cylinder head was all setup to accept the camchain without fuss. I have found it easier to loosen up all the valve adjusters, then place the camsprocket in the correct position, level with the cylinder head surface, then use the right side valve adjusters to help center the camshaft position. You can just screw the adjusters down a little bit on each side until the cam is centered in the head. The rocker arms will hold the camshaft steady while you attach the camchain and master link. Then you can turn the engine over one revolution; adjust the right side valves and then another half turn to get the left side valves ready for adjustment. Valves adjusted, tappet covers in place and then squirt some oil on all the top end parts and finally place the top cylinder head cover in position to be secured with the eight sealing washers and cap nuts, all torque down at 15-ft.lbs.
The biggest challenge at this point is to haul the 115lb engine off the workbench and onto my bike lift cart, which I use to hold the engine in place and lift it carefully up into the frame. Sometimes it is a big struggle and sometimes they just slide back together like they remembered just what to do. After that, it is just a matter of reinstalling all the hardware and electrical connections, then bolt up the mufflers and footpegs.
I left the electronic ignition system in place for easy installation, checking the actual timing with a dynamic timing light once the engine was fired back up again. When the ignition timing is within 10-15 degrees before TDC, the engines fire up quickly and then you have to nurse them a little to keep them running while the oil gets pumped up to the top end and the pistons get some lubrication as well. As they warm up the idle speed changes and you have to keep tweaking the idle speed and mixture screws a little bit at a time. Once the ignition timing is set and verified to be correct, then the final carb adjustments can be made and it is time to go for a ride!
The bike was a little bit cold-blooded and sluggish at off-throttle settings, even when warmed up, so a few moments were taken to raise the needles from the 3rd to the 4th clip position, which is recommended in the Honda CB77 tune-up bulletins. The carburetors still had the #140 mains in it from before, but that is a usual setting for even stock bikes, these days.
The bike was running the old D10H plugs, which are too cold and short reach for standard applications, so a trip to the corner O’Reilly’s auto parts store turned up some new NGK D8HA spark plugs for $2.50 each. A fresh set of plugs, coupled with the needle change got the bike feeling much friskier, even with tight pistons/rings working their way into friendship with the cylinder walls. As the engine heated up for the third time, it started smoking a little bit, but the cause was actually the hi-temp paint curing on the engine parts and exhaust flanges. So far, NO SMOKE has exited the exhaust pipes during this initial run-in period. With a proper break-in period and a few oil changes, the fully rebuilt engine should be good for years to come.
It took a good five hours to make the conversion back to stock configuration again. Three hours later I received a question through eBay message system asking if I had sold the “hotrod” CB77 yet. He was keen to buy it all built up and ready to go…. Timing is everything, isn’t it? The potential buyer is now interested in the WEBCO kit parts for sure and perhaps the now-stock CB77 as a package deal. If only he had called a few days ago….