It is interesting to watch as waves of certain bikes come to me in cycles mostly unexpectedly. Last year it was a set of CB77s that came through the shop, including my ill-fated white CB77 purchased from Mecum auctions in 2022.
For the past few months I have been rebuilding a “special” CL77 that belonged to a celebrity a long time ago. The bike looked like a $50 parts bike when received and 90% of the engine was replaced. The chassis was all beat up and missing about 60% of the parts. Through various contacts, friends and eBay sellers, it is slowly coming back together, but continues to confound me with mysterious assembly issues.
Not long after the CL77 project arrived, a man from Visalia, CA (about 300+ miles away) got my name from someone else and desperately needed to have his 1963 CL72 engine overhauled. He has family down this way, so it wasn’t a complete trip just for the motor delivery. He dropped it off and it looked very dirty and sad on the outside, only to discover that the insides were worse. Like the project bike mentioned above, most of the engine internals needed to be replaced, including the crankshaft, cylinders and cylinder head, transmission and clutch, due to water damage.
During the same time, another man had been messaging me from the Santa Cruz area with CB92 clutch difficulties and wanted to bring it down for repairs. He also had family in the county, so it was also a dual-purpose trip. When he dropped off the CB92, I was just cracking open the CL72 engine and wondering where I was going to find a donor motor to fix it with. Fortunately, we both knew a friend in the Santa Cruz area who had CL72s stuff. He had given away most of it, but still had a motor sitting in storage that actually turned over and offered it to me for FREE! All I had to do was to bring it down here. So, once the CB92 mysteries were resolved, the owner picked up the CL72 motor and brought it down, then loaded up the Benly for the return trip back to Santa Cruz. Sometimes, it takes a village to get stuff done like this…
So, with a mostly finished CL77 project on my rack and a CL72 engine on the bench, a local friend decided to sell his 1966 CL77 which had been stored in his garage for the past 13 years! The bike was a partial restoration with about 11k miles showing on the odometer. So, on a swing past his N. County home for my monthly chiropractor appointment and a stop in to look in on my friend’s ailing CB350 (another mystery bike), I scooped up the 305 Scrambler and brought it home with instructions to go over it and make it run again.
Day One…
This bike presents itself nicely but has the usual patina in the nooks and crannies of a mostly original machine that had a cosmetic rework to the tank, fenders, and side covers, along with reworked wheels and a set of aged K70 Dunlop tires installed many years ago.
I checked compression and the readings were close to each other at about 140-145 psi, which is a bit on the low side, but this is a post-65 bike where Honda lowered the compression from 9.5:1 to 8.5:1 to lower the risks of piston seizures. The next step was to remove the carburetors, which had been drained back in 2008 along with the fuel tank. Lifting the slides out of the carburetors, I noticed that the needles were bright brass colored, indicative of KEYSTER carb kit parts. Sure enough, they were marked with D13 instead of the desired Kxxx numbers. The old spark plugs were supplied with the bike and they were quite fuel-fouled so it was looking like an uphill battle to get this bike running well again. NOS needles are NLA these days, although I had scored a set of them for the project bike before the seller ran out.
With the air filters removed, exhaust pipes loosened up to get the left side air filter cover and filter removed, the carburetors came out looking a little bit scaly, but serviceable. Back on the bench, the problems were revealed. One of the floats was bent sideways, hitting the inside of the float chamber, and was dented in on one side. One side had the correct 22.5mm float level and the other one was sitting at 28mm! They did have OEM jets installed, still, but there was scale inside the fuel inlet passages and one float bowl gasket was displaced at the front, no doubt causing a fuel leak when fueled up. One of the carb insulators was chipped out where the o-ring channel was formed, so that was probably another issue that caused running problems in the past. Once the carburetors are sorted out and reinstalled, attention will be focused on the ignition system.
Day Two
After several hours of cleaning, replacing parts and reinstalling the carbs to the bike, I hooked up my remote fuel bottle to the carbs. They promptly leaked at the bowl gaskets. Of course the worst one was on the left behind the pipes and next to the oil filler tube. After trying to replace the gasket again, I unhooked the carb, studied the gasket surfaces, changed to another gasket and changed the spring that holds the bowl up to one with more tension… No luck, it keeps leaking.
Prior to fueling up the carbs, I had statically checked the ignition timing after resetting what seemed to be a loose timing chain. There was a lot of slack at the crankshaft when turning it backward and forward to set the ignition timing. The timing was retarded and I suspected that the camsprocket weight springs were stretched and the timing was over-advancing when the engine was running.
I let the carbs fill to where they began to leak then shut off the fuel flow and started the engine. It lit off pretty easily but there was a bit of backfiring in the exhaust (straight bikes with Snuff-or-Nots installed) and the engine didn’t want to idle down smoothly. Checking the timing advance with my automotive timing light revealed spark timing issues as suspected. Retarding the spark timing to rein in the advance back to the II marks on the rotor left the idle timing near TDC (T mark) not at the F mark. And the left side was not advancing as far as the right side. Theoretically, both sides should advance the same amount because both sets of points are running off of the same point cam, which is extended into the right side camshaft and plugs into the slot in the spark advancer plate.
With the engine shut down, I took at a small pointed screwdriver and pushed the end of the point cam around and saw visible side play, which translates into a change of the point gap when the engine is running. Because the rubbing blocks are set at 90 degrees from each other on the point plate, there is a moment where both rubbing blocks push the point camshaft a little bit sideways and when wear occurs (speedo showed 11k miles), the point gap for the left side is different than the right side depending upon how much wear is in the shaft to camshaft bore. This side-play, coupled with the slack return springs on the spark advancer unit results in inaccurate ignition timing and uneven spark timing at idle to compensate for the over-advanced condition. So, the only fix is to replace the point cam and/or camshaft that it rides in, plus replace the advancer weight springs. What often is seen is that the camsprocket which contains the spark advance weights and springs works loose on the rivets that hold it together. The camchain sprocket starts to rock back and forth on the rivets and the ignition and cam timing are compromised. Sometimes the weights are worn at the pivot points, as well, so there are a lot of places for slack to develop in the ignition timing system.
Two possibilities for alleviating the timing problems to some extent are to install an electronic ignition plate that is magnetically triggered and doesn’t apply pressure to the point camshaft as it all turns. This can minimize the unequal spark timing from side to side, but doesn’t address any advancer spring slack or weight wear on the pivots. Beyond that, the cure without tearing the engine down is to install a crankshaft-mounted ignition system from a supplier in Germany, which is highly effective but costs about $500. https://www.elektronik-sachse.de/shopsystem-3/en/digital-ignition-zdg-3-23-for-honda-cb72-77.html
So, after consulting the surprised owner, I offered to remove the cylinder head top cover (which you can only do on a Scrambler with the engine in the chassis) and inspect the camsprocket springs and weights.
Day Three – problem-solving
I grabbed a bunch of wrenches and some paper towels, then went to work in removing the top engine mount from the frame which holds the condensers as well. I removed the spark plugs to reduce the chances of the pistons pushing the top end up off the base gasket, which causes a leak. With the top cylinder head cover off, the baffle plate was found to have been glued in place with Hondabond type of grey adhesive. The cover was pried up a little at a time which caused the gaskets to tear anyway. Once the baffle plate was removed, the camsprocket springs and weights were checked for any slop and wear. In this case, the first advancer weight and spring were actually pretty snug, but when the point cam was turned, the weight didn’t spring back to the beginning position. I turned the motor over with the rotor bolt and checked the other spring/weight. The spring looked like it had been poked with a screwdriver or something to upset the coils and lessen the tension on the weight. I hadn’t tried a “springectomy” with the engine in place before, but doing it on a Scrambler is the only possibility.
The end of the spring was partly lifted up with needlenose pliers and the loop pulled away from the mounting post. The spring needs to be turned 90 degrees to unhook it from the back side of the advance weight. I had stuffed paper towels in and around the camsprocket to prevent any unexpected drops into the cylinder head or the camchain/rollers. Fortunately, I had a NOS return spring in stock, which is used on the CB/CL camsprockets. The Dream sprockets have larger weights and lighter springs to allow for an earlier spark advance curve. With some careful use of the pliers and a hook tool, I was able to hook the spring on the weight, turn it and loop the other end up over the post successfully.
Checking the spring action on the weight gave the desired return function, which was verified when the ignition timing was rechecked after the reassembly of the top cover and gaskets. I used GasketCinch to reglue the gasket surfaces back together and while I was waiting for the glue to set up, I attacked the carburetor one more time. All the surfaces were clean for the gasket to seal the bowl, but something else was working against me. When I rechecked the float level, it was at 22.5mm but the float itself was bouncing up against the roof of the float chamber. I have observed that when the Keyster kit float valves are used, there is some dimension that causes the floats to bounce off the top of the float chamber when the level is set properly. I dug out a good used 2.0 float valve that had a “K” stamped on it (Keihin) and tried it with the rest of the parts and surprisingly the float had an extra 1/8” of clearance before it could be pushed up to the roof.
I hooked up my fuel line system to the carburetor, while it was still off the engine to verify that it wasn’t leaking any further and it had indeed stopped seeping as it had previously. I went ahead and reinstalled the carburetor, hooked up the air filter, installed the left filter cover and then reattached the loosened exhaust pipe set for the 5th time. With the remote fuel bottle feeding the carbs, no leaks were detected! I kicked the engine over and it started quickly, finally settling down to a mostly normal idle. I rechecked the ignition timing with my Sears timing light and had to back the spark timing a little bit more, still with the full advance coming right into the II marks on the rotor, so at that point, the mission had been accomplished.
I installed the fuel tank and seat and added some fuel to the tank for a test ride. The tires had 5 lbs of air so they were reinflated and off I went for a test ride that took about 10 minutes. The bike was a little bit cold-blooded and was snapping back at the exhaust pipes at part throttle. It pulled well under power and went through the gears cleanly. It’s possible that the heavy clutch pull is the result of a Barnett clutch pack and springs, but when I put it in gear with the clutch lever pulled in I could stop the rear wheel with the foot brake pedal and the engine didn’t die.
The spark plug wires had been replaced and a set of SPARKY plug caps were installed on the plugs which require the screw-on tips to make a good connection. The wires were a little bit on the short side and when I looked back into the plug caps I noticed that the little coil end of the plug cap hadn’t been fully pushed through into the corner of the cap, so the spark plugs were getting arcs from the displaced wire ends instead of being solidly attached to the plugs.
The test ride was good overall but the speedometer needle immediately went to 100 mph as I was cruising down the road at about 45 mph. I recommended that the unit be sent to Foreign Speedo, here in San Diego, for one of their meter overhauls in the near future. The bike is for sale, so the new owner might wind up handling the speedometer problem after being informed or seeing what happens on a test ride of his own prior to purchasing.
I loaded up the bike and sprinted up the highway at 2pm which can get busy around that time, but I managed to make the 28-mile trip in 35 minutes and the return leg only took about 45 minutes, which was a relief. The owner had some extra muscle available to help me unload the bike and I lit it up for them and ran it down the road under power with the Scrambler pipes rattling the neighborhood.
I was concerned that I was going to have to tear down the engine to get the camsprocket out and have it sent out for repairs, but with a little patience and some careful work, the end result was a revived CL77 which had been awakened after a 13-year slumber. It feels nice to see it back in action again.
Bill Silver aka MrHonda
2/23
No comments:
Post a Comment