My customer Paul has a bike that belonged to another customer a few years back. He contacted me about finding a suitable CL77 for sale and I hooked them up which resulted in a transfer of ownership.The bike is a 1967 model, originally one of the Candy colors, but Paul wanted the Silver/Black look, so he had the tank and side covers painted. The bike had been in previously for some running issues, thought to have been solved, but arose once again. Plus the nuts that hold the rear sprocket on were never tightened properly and three spun off. He was able to recognize the problem before it put him on his head. He complained that it sometimes idled too high and sometimes died at idle. There was restricted power in intermediate gears and it just wasn’t a very happy machine. He actually rides the bike around San Diego regularly, so reliability is important, of course. One issue was the sudden high idle when the engine speed was above 4000 rpm and stayed high even with the throttle closed.
The bike arrived on the back of a roll-back tow truck. In the unloading process it almost went down before we caught it just in time. I had lined up some nuts and studs for the rear wheel, so that was the focus at first. Then I went through a compression check, which came up with 165 psi on the right side and 90 psi on the left. Checking valve clearances didn’t seem to be related to the problem. I pulled the slides out and raised the needles a notch, checked the ignition timing which was a Pro Trigger electronic conversion and everything looked pretty standard. There wasn’t a lot of gasoline in the tank and the bike has no crossover tube, which was an odd feature of the 1967 models. A quick test ride didn’t feel quite right and a longer one developed a dropped cylinder on the way back. Checking fuel in the bowls, the right side was fine, but the left side was empty.
This gets into a not uncommon fuel flow puzzle where a twin carb engine has fueling problems to one side, even though the petcock is clean and both outlets are open and flowing. Somehow an air lock happens or the uneven length of the fuel lines causes a fuel disruption to one carburetor. As a test, I removed the fuel lines at the banjo fittings and cut about an inch and a half off the longer hose. Taking the same long test ride with an uphill climb resulted in normal performance once again. So far, so good.
I encouraged Paul to hang around and watch what all I was doing and the challenges of working on the CL77s, especially. The next request was an oil change and filter clean. On the later engines with the “big hole” clutch covers, you can fish out the filter and chain for service without needing to pull the whole clutch cover as was required in the earlier models. Well, the oil, which was last changed 800 miles previously, came out with fine metallic particles visible in the oil pan. The filter had a thin layer of debris, but some disturbing signs of tiny pieces of brass embedded in the filter debris field.
I noticed that the engine was louder than normal, somewhat sounding like it had loose cam chain tension, but it was difficult to pin down exactly while running. I hypothesized that perhaps the low gear bushing was wearing out causing brass filings to be deposited into the oil. Obviously something was wearing inside the engine and Paul authorized me to dig into it. This, of course, requires about an hour of dismantling the engine from the chassis and getting it up on the work bench. Paul watched as I heaved all the brackets, bolts, screws and pieces into a plastic bin for the removal process. He helped me haul the 100 lb lump out of the frame and onto a dolly where it was pushed over to my messy work bench. I had just dismantled a CB77 engine (separate story) so there were bits of it here and there. After some 4 hours of wrestling with the bike’s problems and now engine pull, we called it a day and waited for the big reveal on Saturday morning….
Loose/worn camchain does this to the cylinders.
The engine was waiting for me to do some magic and I dug into it with hopes of finding some remedies for what seemed to be unusual wear issues inside. The clutch cover came off and all of the primary chain bits removed to facilitate splitting the cases. I noticed that some of the bottom fasteners and the sealing washer were previously removed, so it was difficult to say what would be found. Once the cases were split, the transmission gear dogs showed excessively deep engagement, which turned out to be that offset gear cotters were installed on the transmission gears. In earlier years, the transmission parts had straight cut gear dogs which didn’t have sufficient engagement. This caused the transmission to jump out of 2nd gear. Honda issued a TSB for this problem and the release of these offset gear cotters which moved the gears closer together ensuring clean gear shift selection. In the later transmissions, the gear dogs were back-cut to promote engagement and secure gear selections. Some gears were updated to reduce the amount of side-play which aggravated the gear dog engagement issues. This alleviated the need for the offset cotters, for the most part. When the cotters, which come in two offset sizes, are used excessively the gear dogs can rub against each other in neutral, generating a clicking noise.
When the bottom case half was inspected, most of the metal debris was right below the transmission gears indicating that some unwanted contact was being made. I removed the offset cotters and installed plain flat ones and the gear dog overlaps were still well within recommendations. I noticed some main shaft side play where it pushes against the edges of the brass bushing in the transmission’s top gear output shaft. I had a new transmission gear in stock but the sprocket splines were deeper than the 1967 shallow spine pattern. That still works as the shallow spline sprockets fit the deep spline versions. The new gear reduced the shaft side play. The end of the bushing is proud of the surface of the shaft so gets contact from the steel end of the main shaft, causing some eventual wear.
The low gear bushing was replaced and fortunately the kickstarter pawl wear was minimal, so it was time to put the cases back together once again. I rolled the engine back upright and noticed a lot of baked-on yellow substance around the head gasket area, as if someone had been trying to seal up an oil leak. I called Paul to let him know that the head gasket was probably leaking and someone had previously tried to seal it up from the outside with an unknown substance. Paul agreed that the head should come off, which also gave me an opportunity to check the wear on the pistons, rings and cylinder walls, along with any valve sealing issues.
Talk about opening a can of worms….. The top cover and breather plate came off easily and the cams looked fine. Once the cylinder head was pulled there was some discoloration on the cylinder walls along with a bit of scuffing on one side. The cylinders were still on STD bore sizes from the factory. When the top piston ring was removed from one piston and inserted into the cylinder bore, the end gap of the ring was about .024” which is at the far end of the service specs. New rings in fresh bores are normally about .008”. I tried a new CA77 top ring in the bore and the gap was .015” so a good hone job on the cylinders and fresh rings should have it running well, saving $300 for new pistons, rings and a bore job. New STD piston rings were sourced from my friend Ed Moore, who is winding down his engine rebuilding business. I had the cylinders honed at a shop about 18 miles away.
The valves were coked over with old burned oil and gas deposits. Removing the valves requires taking the side cylinder covers off, loosening the tappet screws and then pulling the rocker pins out. As usual, what I see on running engines is that the intake valve seats are wide and shiny, with the faces of the intake valves somewhat cupped. The exhaust seats are somewhat wide and often have little dimples in the valve seats where carbon has been trapped at times. The valve seats are part of the cast-iron skull which is cast into the cylinder head. In the days of pre-unleaded fuels, the lead in the gasoline provided somewhat of a coating to prevent wear on the seats and valve faces. When unleaded gas came available, vintage cars and motorcycles often experienced sinking of the valves into the seats, requiring a machine shop procedure to install hardened valve seats in the cylinder heads. This isn’t an option for 250-305 engines and for the most part, it isn’t a problem as these engines are not used in regular transportation these days. Generally, the heads are taken to the machine shop for new valve seat cutting and then new valves are ordered to make it like new again. Honda’s exhaust valves are about $100 a pair and the intake valves somewhat cheaper from www.davidsilverspares.com I do have some factory valve seat cutters that can clean up the seats if they are not too badly worn. But that’s not all!
Looking closely at the cylinder block, I noticed a groove that was worn in the inside of the cam chain tunnel where the cam chain has been rubbing against the alloy block. This was quite possibly the source of the non-metallic debris floating around inside the oil supply. So, now we have to find a new cam chain. Also, the center guide roller was all chewed up, requiring replacement. I keep a few of these in stock for such cases, as Honda no longer produces them. You can see that the bill for labor and parts is continuing to rise exponentially just to rebuild the engine, not to mention the extra hour it takes to reinstall the engine and hook everything up once again.
This job came back to bite me when the engine rebuild was done and installed, the hanging high idle condition remained. I did notice that turning the point cam to check the advance/retard function had a little bit of a click step in it. What I didn’t notice was the point cam plate, deep inside the camsprocket was cracked in half, from some previous repair attempt. I failed to check the condition of the plate inside the camsprocket.. This split plate engaged with the point cam tang okay at idle, but as the revs increased, something got cocked inside and caused the weights to hang open until the engine rpms were reduced either on a long slow deceleration or in gear when the brakes were applied which slowed the engine speed down to where the weight springs took over and returned the point cam back to the idle setting.
I spent another 2 hours extracting the camsprocket, while the engine was still in the chassis. You can only do this with a Scrambler, because there is sufficient clearance above the engine that allows the top cylinder head cover to be removed. The locking nut on the camshaft sprocket was nudged loose with a long flat blade screwdriver that had a plastic handle. It was tightened in the same manner. Both camshafts have to be driven out of the head, but the process of removal keeps the inner camshaft bearings in place. Once the new camsprocket is placed into the head, the master splines on the cams and camsprocket have to be all aligned for installation. It’s probably not a task for beginners, but it did turn out well in this case, as I have done this procedure once before.
With everything all buttoned up, the test ride was unremarkable in that all functions were working normally this time. All it takes is to miss inspecting a critical part like this and everything goes sideways.
Such is the life and trials of MrHonda in 2026!
Bill Silver aka MrHonda
www.vintagehonda.com
04/26
