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Hot Rod CB77 saga continues… with a somewhat happy ending

Apart and together again... Pistons just removed with carbon layer on top
Apart and together again... Pistons just removed with carbon layer on top
Bill Silver

Since the last report, the cylinder head had been de-carboned and reassembled with the roller rocker camshaft in place. The pistons were shipped off to a local machinist wizard who will attempt to make a set of standard bore CB350 piston rings work in place of the gapped-out, unobtainium Webco rings. The lower engine case has been cleaned with soda blasting and the bottom end can go back together once my oft-delayed transmission comes in from the Mid-West.

The new 12N9-3A battery is all serviced up and waiting for installation. Carburetors will be cleaned and checked for any issues prior to their going back onto the rebuilt engine. The old fuel needs to be dumped out and the tank cleaned with an overhaul of the petcock. Stiff old gas lines will be replaced with OEM Honda 5.5mm fuel hose and the crossover will be routed over the top of the frame to make tank removal a whole lot less messy.

In the past few days, the transmission arrived, the bottom engine case was cleaned and I married all the parts together in one extended afternoon.

This week, the pistons come back on Tuesday, with a seal of approval from the machinist after $90 worth of his valuable time. Apparently one piston chucked up nicely in the fixture which he uses to cut piston rings, but the other one was a bit off the mark, requiring more fiddling to get it round and true in the lathe. The new pistons with 3 piece rings are in the shop waiting for fitting to the WEBCO pistons and then we start putting more of it together. All the ring lands are now round and of the appropriate width to accommodate OEM Honda parts now. This hot-rod engine may just come together by the weekend, however the Thursday-Friday temperatures in Spring Valley are predicted to reach into the 90’s, so extended shop time will not be an option until the heat wave breaks. Because the bottom cylinder bore chamfer is pretty much gone, I plan on loading the pistons into the bottoms of the cylinders first, then sliding the whole assembly onto the crankcase, then finding the rod end holes and driving the pins in from the inside out. It is somewhat tricky to do, but lessens the chance of snagging rings on the edges of the cylinders while lowering the block down over the pistons. I have done this a few times recently and think that is well worth doing in this particular case.

No time was wasted on reassembling the motor’s top end after all the parts came together. By Tuesday night the engine was built with starter on and ready for a Wednesday morning install. There was a lot of last minute parts cleaning before the final bits could be assembled together, but overall the build went smoothly. Getting the cam timing wasn’t quite as difficult as I had imagined, however the camsprocket needed to be pried forward enough to catch the forward side of the camchain which held it steady, while the master link was installed. Valves were adjusted to .005” and it all turned over smoothly with a wrench on the rotor bolt.

Hump Day gets results…

Sometimes, wrestling these motors back into the frames is a chore and they fight you all the way in. This one fairly glided into place with just a small bit of crowbar application to help nudge the cylinder head up into the frame rails. Once the motor was in and bolted up tightly, the rest of the install could proceed. The carburetors were cleaned, floats checked (way off at 26mm, instead of 22.5mm), #145 main jets were still in place from the previous running times. New o-rings were added to the carburetor flanges and the insulators and one-by-one; each little component was attached to the chassis. The replacement kickstarter cover got a new clutch adjuster and new kickstarter gear. EBay sellers supplied a few needed parts, including the kickstart arm, which was missing altogether. The used k/s and clutch covers supplied by the bike seller were in good shape. The clutch cover had already been cleaned and painted, while the k/s cover was grimy, dirty and gouged up here and there. I had the k/s cover blasted with baking soda to keep the finish smooth. Once all the components were loaded up into the k/s cover, it was installed onto cases which had provisions for a full set of screws.

Carbs and air filters went on, battery installed, cables checked and adjusted and the “firing up moment” was coming up soon. With the spark plugs removed, the engine was spun over for a few moments with the electric starter, to help prime the oil filter and begin lubricating the internal parts. Finally, with the fuel tank in place, the choke was put in full ON position and the key turned ON for ignition power. The bike turned over about two turns and lit immediately. The choke was pulled off quickly as the engine seemed to load up, partially from fuel and probably from some leftover oil in the cylinders that was burning off. Left at a fast idle for a couple of minutes, all seemed well. There was a constant clatter of the rocker arms bouncing the valves open and closed at rates unheard of at Honda Motor Corp., but the idle came down evenly at about two thousand rpms. There really wasn’t much smoke coming out of the OEM mufflers and as it warmed up it seemed to settle down, smooth out and behave very civilly. Considering the cam timing specifications, one would think it would be running like a top fuel dragster, just before a full throttle launch, but the engine took throttle cleanly and crisply, settling back to a smooth low idle each time.

I was kind of in shock about the way it was running, just after a full overhaul and with new piston rings to boot. The seat was hurriedly installed and off I went for the inaugural ride. The bike took throttle just like a stocker and gear shifting was smooth. Rounding the corner just up the street, the bike leaned over, but felt a little unsettled. I continued on at a reasonable pace and noticed that when I came to the first stop sign the front end gave a “clunk” sound that could be felt in the handlebars, too. Sounded and felt like the classic “loose steering head bearings” story, so I just took it easy and rode the bike on my little local 2-mile test circuit. The return is uphill and I revved it up a little bit in 2nd and 3rd gears, and then coasted it back towards home.

Shut down after its first run, there were things to attend to, like a small oil leak at the tachometer drive cover, which drooled oil down the cylinder fins towards the front and tossed off oil drops backwards across the side cover and rear shock cover. As it cooled, I removed the tach drive and cleaned the gasket area again, added another gasket and cinched down the four screws again. Brake cleaner scrubbed of the loose oil blobs and then everything was wiped down with clean rags. After humping all day on Hump Day, I was ready to put a cover over it and dive into the front end on Thursday. Checking the steering head bearings by pulling on the forks revealed definite looseness, as well as a discovery that the two lower fork covers had been installed in opposite locations. The little metal tab which holds the speedometer cable to the cover was on the left side doing nothing. So, the next job was basically a front end teardown to switch the fork covers (requires removal of the fork tubes) and tightening up the steering head bearings, as well.

Thursday teardown and wind-down…

After jacking up the front wheel (a small floor jack placed beneath the starter motor), the rest of the front end was slowly disassembled. The front axle nut was just finger tight, so I was lucky that it didn’t spin off on my test drive. Off came the fender bolts, front wheel, front brake cable, speedo cable and all the hardware that attaches everything together. With the fork bridge removed, the steering head bearing nut was turned down by hand a good turn and a half, then everything was reassembled once again.

The bike fired up instantly, once again, with no choke this time and seemed perfectly happy to keep running at idle on a cold motor. Of course the ambient temperature that morning was in the high 80’s so there wasn’t too much for it to complain about. The second full test ride was a success with a dry tach drive side this time and no more clunking noises in the front end.

Assuming that the increased power curve portion is in the 7-10k rpm range, I can’t say that the engine is hugely more powerful than the stock one. The rear sprocket is a 32t version, which increases acceleration, of course, at the expense of top speed. I have to wonder if all the motor mods are not fully compatible with stock OEM mufflers (with baffles installed) and stock air filters/tubes. High rpm performance dictates short intake tracts and exhaust pipe header lengths of a different variety that the ones chosen for the stock cams and compression piston configuration.

I will continue to refine the tuning of the engine with a dynamic ignition timing check and spark plug readout. I am still using stock D8HA spark plugs with points/condenser ignition system for the moment. The first plug checks were clean with a bit of tan showing on the tips. Some of that might be the oil that burned off the cylinders as it was first fired up. So far, the engine pulls upwards towards 8k rpm pretty easily in lower gears with less than full-throttle applied. I do have to give the new piston rings some time to settle in, though. The ring gap with the new OEM Honda rings installed in the WEBCO pistons was about .016”, instead of the .035” with the stock rings. This is still on the wide end of ring gap specs for OEM Honda pistons/rings, however.

Well, so far, so good…. The bike is really a sleeper with stock ribbed front tire, OEM exhaust and intake system, stock carburetors, etc. Only the clatter of the rocker arms is a giveaway that this CB77 isn’t quite like the ones that rolled off the factory floors back in 1965… More fun to come, I’m sure!

Bill “MrHonda” Silver

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