Tuesday, November 9, 2021

Pretty CL77 Scrambler with a dark secret…

A recent request from an LA-based owner of a CL77 lead to the next big adventure in vintage Honda repairs. The bike had been “restored” by an owner in WA state and posted on Craigslist for sale. The current owner, Mike, had picked it up while visiting his daughter not far away from where the bike was listed, so he went to see it. The bike was not running at the time and the apparently motivated seller sold it for a very cheap price. The bike had been restored with new chrome on the rims and exhaust, new paint on the bodywork and everything looked pretty tidy overall when it arrived on the back of a trailer to Casa de Honda for a “get running” request. I figured that I would just troubleshoot it, fix it and turn him back around to LA within an hour or two…

First step on an unknown bike is to check compression readings. The left side came up at 175 psi, but the right side died off at 60 psi. Not a good start for the day… Next step was to check for tight valves on that side, but when it was brought up to TDC compression, it was evident that there was normal valve clearances on both valves. My little portable bore-scope revealed a coating of carbon on the piston crown and signs of dished valve faces, which seems pretty prevalent these days.

The main issues that kept the bike from starting up were both idle/pilot jets were plugged up and the float levels were at 26mm not 22.5mm. Wrestling with carb jets on a Scrambler are always challenging, especially on the left side near the exhaust system and the oil filler tube. After contorting myself in various ways in order to access the idle jets and reset the floats, I finally got it to a point where it should fire up, all things considered. I checked the ignition timing statically and it was within a few degrees of normal and the points were opening and closing properly. Two kicks and the engine fired right up, filling the neighborhood with the distinctive sound of straight-pipe 305 Scrambler noises.

Unfortunately, the running engine was blowing out clouds of blue smoke out of the breather hose in vast volumes, indicating bad rings, scored cylinder walls or worse. It was time to tear it down and see what had happened to the engine. After unbolting the engine and wrestling it out of the chassis, the truth was about to be revealed on the workbench.

It appeared that the engine had been lightly sandblasted and painted with a light aluminum paint. When the kickstarter cover was removed all the sandy flakes were packed around the rotor and countershaft sprocket area. So, pretty on the outside, but not really cared for beneath the surface.

The engine top cover was removed and checked to see if the breather holes on the plate were oriented properly. If the breather plate holes are installed at the top of the head, then oil gets trapped and blown out of the breather tube. There are arrows on the plate to indicate that the holes should be positioned down/forward, but I suppose you could interpret it as the arrows indicating TOP/UP instead. Anyway, they had been installed correctly, so that was not a contributing factor.

Once the cylinder had nuts were removed beneath the spark plugs, the head slid right off the studs revealing a surprise. The right side piston had a small section melted away from detonation, which extended all the way through the ring pack. Further more, the head gasket fire ring was blown through towards the camchain cavity, so the reasons for all the smoke were quite evident now.

The cylinder bores showed signs of water/corrosion damage in the past, plus there was a chunk of melted aluminum clinging to the top edge of the right side cylinder bore. The pistons were still on STD bore size, but the condition of the bores required over-sized pistons and a rebore to fit them. That lead to the next challenge which was to find some correct pistons and rings at a reasonable price. Ebay sellers were asking anywhere from $50 a piston to $150, with a full set of pistons and rings running from $250 to $400 a pair. My friend Tim McDowell at www.classichondarestorations.com is the distributor for WISECO forged pistons to fit the 305s, but was out of stock and the manufacturer was waiting for piston blanks that were probably on one of the thousands of container ships that were sitting offshore waiting for their turn at the end of the 2021 season. A somewhat reasonable option were IMD piston kits that were engineered in the UK but made in Taiwan. At $169 a set they seemed to be a good option including the 3 piece oil rings that come with modern designed parts. The puzzling part of these piston offerings were that they chose to use the lower compression Dream piston crown configurations rather than the standard higher compression CB series shapes.

I have built up CB engines with Dream pistons, due to lack of proper piston options and they still work fine, but have a bit lower compression readings in the end. This engine was not going to be raced in competition or ridden extensively on the highway according to the owner, so putting the engine together with IMD pistons was the wise option in the moment.

I noticed that when the pistons were removed from the rods, turning the engine over with the rotor left a feeling that something was causing excessive friction on the crankshaft. Rolling the engine over on the bench to remove the clutch cover revealed that the oil filter was stuck on the shaft and the outside cover had been hammered onto the shaft end with the locating pin out of position. This condition was holding the cover just back from fully sealing up the cover to prevent oil drips which were evident as the bike was initially parked.

The oil filter thrust washer had been placed on the inside of the shaft next to the crankcase, which pushes the oil filter chain off-center. This causes side wear on the little filter chain sprocket teeth. Once the filter shaft as extracted from the outer cover and the filter removed from the shaft, the filter was cleaned out of the 1/8” of accumulated grit and debris that the filter had accumulated over the last 50 years.

The cylinder head was dismantled, apart from the cams, so the valves could be removed and inspected. The exhaust seats had a lot of little depression marks and the intakes were quite wide and rounded. All the valves were replaced, with seats re-cut and narrowed to meet up with fresh 45 degree angled valve faces.

As always, considerable time is expended in removing the old, caked-on gaskets from the alloy surfaces without digging into the metal too often. I have found that it usually takes between 1 and 2 hours to successfully clean all the gasket surfaces, particularly on bikes with the original asbestos gasket material.

While awaiting the arrival of a set of pistons to send to the machine shop, any other loose ends must be addressed, which in this case was some kind of solid-state full-wave rectifier cube that had been loosely fitted to the chassis and found to be un-grounded when the engine was removed.

Taking a turn for the worse…

In setting the cylinder block down into a cardboard box for transport to the machine shop, I was shocked to see the right side liner just pop up all by itself. I lifted the cylinders up and grabbed the liner with my hand and it just moved up and down and turned either way easily. This is NOT a good sign. Normally, the liners need a little time in a low-temp oven in order to get them extracted from the cylinder casting. Chilling the liners and heating the cylinder block is the usual way to re-install the liners once again. I called the machine shop and told the owner what the situation was. He said to bring it all in and let him evaluate the situation. His call-back revealed an approximate clearance between the right sleeve and cylinder block at .004” which is not the desired interference fit expected. After washing the parts off in his steam cabinet the other sleeve came out with little effort. After careful measuring, he decided to swap sleeves in the block which ended up with about .002” clearance. He lathered up the sleeves with Red Loctite and let them sit overnight to let the adhesive setup and cure fully. Once he sets the cylinders up in the boring bar, the results will become evident; either the cylinders bore out normally, or the liners break loose and start spinning in the cylinder block which signals the end of the usefulness of this set of cylinders.


The machinist called to say the cylinders were ready and they turned out fine. I made the 25 mile round trip to pick them up and cart them home for installation. The top end was reassembled in an hour or so, then I dragged the big lump off the bench and onto a cart where it met up with the chassis. Some soft rags were taped to the frame to minimize paint damage as the engine was wedged back into the chassis. Scramblers continue to be the most challenging bikes to service and to do big jobs on as far as I am concerned. After another hour plus, it was time to light it off…

Good news, bad news…

The bike started on the 3rd kick, but sounded like a top fuel drag car; a combination of straight exhaust pipes and a bunch of other issues that arose. When the carbs were reinstalled the right side throttle cable adjuster was a 1/4” higher than the other side for reasons unknown. This caused the right side to be pulling the other side along under load, which adds to the stress and overheating of the cylinder. The carb float levels were re-checked before installation and the jetting was all stock. There was no immediately apparent reason for excess fueling of the engine, but the air screws didn’t have any affect on the idle richness.

The spark timing was set for the left side which ran up to the II advancer marks properly. The right side timing was way off at idle and when it was retarded back to the F mark, the engine died a few times, but was noted to exceed the advancer marks by a good 10 degrees, which would certainly cause overheating and seizures under load. After the spark plugs loaded up with black carbon it was time to call it a day and consider all of the possibilities for this suprising outcome. The good news is that the cylinder pressure with the new pistons was 175-180psi on both sides.

Back to basics…

With fresh eyes and better daylight, the re-check commenced. The point brand was verified as genuine ND (Nippon Denso), but someone had replaced the original screws and washers with mushroom head screws that tend to move the point base around as you tighten the screws. The point gap was opened up a little past the .016” to ensure that both sets were not closed momentarily causing a voltage drop to the coils. The ignition timing was set statically with a 12v test light and eventually verified with the engine running to ensure that there were no over-advancing problems with spark timing which causes piston seizures and detonation holes. One step done…

Next, the carburetors were removed again to check the air bleed passages going to the idle and main jet circuits. They were clear, but the emulsion tube holes for the main jet holder were contaminated with some leftover corrosion due to old gas left in the carbs. The float levels were double-checked, the floats tested for any pinholes which leads to sinking of the floats. All the jets were stock Honda, but the carb slide needles were not marked, which is usually due to the originals being replaced by aftermarket Keyster carb parts. I sifted through about 20 needles in a bin and found an actual OEM CL77 needle, plus a Keyster D13 replacement needle. The idle jets were cleaned previously which got the bike to start up, but eventually, the #38 idle jets were replaced with #35 spares to lessen the rich idle condition.

The new needles were attached to the carb slides and the two slides were inserted into the carb bodies.

The sooted-up spark plugs were replaced with a fresh set of D8HA NGK plugs and the bike seemed to finally get its feet again. The air filter and side cover were reattached to the bike chassis before the pipes were installed again.

The bike had been running on a temporary fuel source. Once the engine sounded healthy again, the fuel tank was reinstalled and refilled. I have learned to always check the air pressure before a test ride and sure enough, I was looking at tire pressures of 15 upfront and near zero for the rear. Finally, with everything attached, I ventured out for a quick run about a half-mile away on a road where there are few houses and listening ears to be offended/treated by the sound of a straight-pipe Honda 305 Scrambler.

The rear tail light wasn’t working which was traced down to lacking a good ground from the tail light to the bracket to the rear fender, which is a common problem when freshly painted or powdercoated body parts are reinstalled without consideration of the need for a solid ground path for the electricity. I failed to check the neutral switch condition when the engine was reinstalled and sure enough, it appears to be the source of the non-working neutral light circuit. Checking it requires removal of the footpeg assembly and removal of the kickstarter cover to access the switch and connections. Just when you think you have it done… there’s always something left to do.

I did manage to address the last electrical issues while I waited for the arrival of the owner, who made the trip back down from LA to retrieve his prize CL77. The neutral switch pigtail wire had become unsoldered and the incomplete ground path for the tail light was cleaned and reconnected so that all the lighting systems were once again functional.

The owner took the bike for a quick blast around the neighborhood and rolled it up into his bike trailer for the return trip back home again. It was a far cry from “I can’t get it started” to “Please fix it and let me know when it is done.” These old bikes are full of surprises and this one presented problems not previously seen before. In the end, it lives and breathes again to the delight of the happy owner.

Bill “MrHonda” Silver



  1. I think the sound of a CL77 with straight pipes might have made all this worth it-----maybe.

  2. You are the man! Wish you were closer, and could work on my 67 305 dream

  3. Great work Bill! Been there, done that. All of that!