Well, it just never ends… My friend Mario, an avid vintage Honda collector, brought a 1964 CB77 to me to “get running” and change the tires to a more correct size. Usually, this is not a big problem, but when I was in the process of changing out the big, tall OEM Honda bars (probably CB350-450), I pulled the clutch lever and it felt stiff. The bike had been sitting for many years, so I assumed a “stuck clutch” condition when I removed the clutch cover.
I had an inkling of something being wrong when I removed the tappet covers to check the valve clearances and the inside of the tappet covers were coated in a dark, brown-ish coating that didn’t just wipe off with a rag. Even so, it was shocking to see the entire inside of the engine covered in the same brown coating, that looked like burned oil or perhaps that gasoline had contaminated the oil and it sat like that for many years. Obviously, the next step was to pull the engine and take it apart.
Unlike a Scrambler, the engine comes out of a Super Hawk in about 20 minutes. It just drops down out of the frame and onto the work bench. The oil had been drained out before the clutch cover was removed and it looked pretty dark like it hadn’t been changed in decades. I hoisted the engine up on my work bench and began to tackle the disassembly. Once the clutch side parts were all removed and the starter motor pulled off the front of the engine, I anchored the engine on the bench and removed the top cover. There were signs that the engine had been worked on previously and reassembled a bit incorrectly with some bolts and nuts in the wrong locations. The oil seal for the starter clutch had been installed backwards. Additionally, I noted that the right side carburetor was a 1967 specific square bowl replacement and paired to the original left side round bowl carb, which had an aluminum slide needle commonly used in the early days.
With the top cylinder head cover removed, the camsprocket and point cam were in better than average condition. The bike’s speedometer showed about 11k miles and overall it seemed to be about right for the year. One cool factor was it was still fitted with the OEM stainless steel mufflers, although the left side was a bit flattened out from low-speed crash. Apart from the bobbed front fender, the rest of the bike was pretty much as you would expect a 1964 CB77 to be.
The camchain had a link, so that was removed and the chain dropped down inside the engine for the moment. Once the cylinder head was removed, the whole valve train was coated in the brown gunk. The cylinders were lifted off and when the top right side piston ring was removed for end gap checking in the bore, the ring turned out to be a crescent shape due to wear. The end gap was about 1/8” instead of something in the. .010” range. I had a new STD ring and put it in the bore. The ring gap closed down to the .020” range. The cylinder bores were still on 60mm size. Once the top end was removed, the engine was flipped over to access the oil pump and then to split the cases.
The crankshaft throws were all coated in brown, with the connecting rods covered in a fluffy, flaky oil residue. Surprisingly the wrist pin holes were still pretty tight when the pins were inserted. The transmission shafts were removed for cleaning and to check the condition of the low gear bushing and the gear dog overlap. The cases showed the original greenish sealer from the factory, so it was obvious that the bottom end was never disturbed. I did discover a camsprocket return spring and the tiny bit of the anchor that held it in place. This was sitting inside the crankcases. Fortunately, the oil pump screen would have kept it out of the pump, but as the parts were breaking off from the camshaft sprocket, they could have landed into the camchain causing catastrophic damage.
I tried putting the clutch hub in a tub of paint thinner/mineral spirits to see if the brown would loosen, but there was no sign of it softening the coating. All I could do was to call my buddy Brian at his “Small Engine Repair Service” shop and ask if he could fire up his hot tank blast cabinet to see if that would melt off this grimy gunk. He agreed to have me come down on a Friday afternoon to give it a try. We loaded all the biggest parts into the cabinet and he set the timer for 20 minutes. The temperature is 240 degrees and he throws a bit of cleaner into the 50 gallons of water to help cut the crud. After the first go-round, the parts came out looking very shiny! We had to reload the parts into a big basket so they could be blasted once again, especially on the areas that hadn’t been touched by the nozzles. One last round of heated steam even got much of the crankshaft crud removed. We sprayed it with WD40 after it was removed to keep the bearings from rusting up. The bigger questions is going to be if the oil feed passages inside the crankshaft are totally blocked, which happens even in the best of conditions and maintenance. Scrambler expert, Tim Miller, in TX has pulled NOS crankshafts apart and found the factory lubrication has congealed inside the crankshaft throws. UK crankshaft expert Graham Curtis routinely rebuilds pressed together crankshafts of most 1960s Honda twins and find that the oiling passages are always blocked which creates a lack of lubrication for the small end of the rods and elsewhere.
Brian honed the cylinders and measured the bores and the pistons coming to the conclusion that one piston would wind up with a.. .005’ clearance which is well out of spec for these engines. He felt that the bores were good so suggested finding some STD pistons and rings to freshen up the engine’s compression. I gathered up the engine bits and drove them home to ponder what was going to be needed next. Checking eBay sellers, the STD pistons were being offered for silly $80-100 each! I mean really? How many engines are going to be rebuilt with standard bore pistons and rings? I finally sifted through the listings and found a seller with a pair of slightly used STD pistons and rings for $30!
In the meantime, the inside of the clutch cover showed signs of the primary chain touching it during operation. And the poor little oil filter drive chain was so sloppy that I was surprised that it hasn’t jumped off the sprockets. Back at eBay, the “going rate” for both the big 56 link primary chain and the tiny #25 pitch oil filter chains were $150 each! Choosing the Cappellini oil filter conversion, also at $150, does away with the oil filter and chain, using inexpensive Suzuki cartridge filters to screen out the contaminates. A OEM NOS primary chain was listed with a seller in TX , so Mario ordered that one for me. The original oil filter was, as you can imagine, caked with dirt and debris.
In the meantime, the cases and engine external parts were shipped off to my friend John, who lives about 8 miles away. He has a full-on blast cabinet dedicated to vapor blasting alloy parts, once they have been degreased. I dropped them off on Sunday afternoon and they were ready on Monday. This will give the engine external surfaces a nice shiny look, but the real work will be to chip off the OEM asbestos base gasket from the cases, which is exceedingly tedious. It can easily take an hour to get the gasket material off the alloy surfaces. Single-edge razor blades, gasket scrapers and a tungsten scraper were all employed in the removal process. Ultimately, more than 2 hours were spent in asbestos gasket removal from the crankcases, cylinder head top cover and breather plate and one side of the cylinder head side covers, which holes the points and point cam.
Once the upper case was cleaned, the crankshaft was installed with an endless camchain looped around the middle. The transmission gears were cleaned with a plant-based cleaner that worked amazingly well on the brown crud that was attached to all the rest of the internal shift and clutch parts. I have to say that this has been the most challenging engine repair I have attempted, given the amount of clinging oil deposits that attached to all the internal parts.
Amazingly, the transmission parts were all in decent shape after cleaning. Even the notorious low gear bushing still had the ridge in place. The gear dog engagement was marginal but acceptable. I replaced the shift drum with one with less wear and reused the shift forks. I had to hone the inside of one of the gears where the bronze bushing was binding on the shaft for some odd reason. Ultimately, the bottom end was reassembled, along with the clutch which had been fitted with a version of Barnett fiber clutch plates. The fiber plates were probably some of the Kevlar bits attached to the backing plates but with little round holes in the center of each contact patch. The thickness was around 3mm, but for a 5-plate clutch, the requirement is about 3.5mm. I had contacted Barnett about clutch plate kits during this time and they did show an unusual fiber plate pack that had both red and gray fiber material that was just bonded to the backing plates. I paid a bit over $100 for the set and had them set aside for the possibility of use in an engine project.
I used the older plate set in the clutch build, but added another metal plate to make the stack height more correct. 5X a .5mm thickness is a 2.5mm overall change in the clutch pack height. No matter which of about 5 different clutch packs that Honda used in Dreams, Scramblers and Super Hawks, the clutch pack stack height is always the same.
So, you can convert the early 6-plate clutches to a more desirable 5-plate setup, but the height must always be the same. A change in the stack height leads to issues with the clutch adjuster and clutch lifter parts in the kickstarter cover. When the height is altered, the index marks on the slotted clutch adjuster and also the angle of the clutch lifter arm don’t match the original setup and that can cause clutch release problems. Ideally, the clutch lifter arm should be pulling through an arc, below and through horizontal. When the pack is too tall, the lifter arm loses it’s leverage advantage and the clutch pull effort increases.
I have seen some over-tall clutch packs rub up against the inside of the clutch cover, as well. So, there is only one correct way to setup the clutch assemblies in these old bikes, no matter how many clutch plate packs it has. Ultimately, once the bike was up and running, the clutch slipped under high rpm loads and finding neutral was difficult. When the clutch was removed, the little rivet holes seemed to serve as suction cups, sticking the steel plates to the surfaces unnecessarily. I prepped up the new Barnett clutch discs and installed them. Because they were the correct thickness, the extra steel plate was removed and the stack height was just about right. The index marks on the kickstarter cover were close to factory alignment and the clutch didn’t slip under load and finding neutral was much easier. I always use the little steel retainer springs which are NLA in the world now. Depending upon the original clutch plate pack, the retainer wire grooves are machined in different locations to accomodate the thickness of the plate sets being used. The early 6-plate hubs have three grooves to set the Plate A, then two sets of steel and fiber plates. The later 5-plate hubs only have 2 grooves; one to set the thicker 3mm steel plate A and then one set of steel/fiber plates. You can’t mix and match these parts when changing the fiber plate count. It all has to match up correctly. Also the last version of the pressure plate has angled relief holes on the outer cover surface to help evacuate the trapped oil inside the clutch assembly. That last generation 5-plate clutch for CB and CLs are the way to go for good clutch performance.
Okay! Well, back to the bike’s challenges. The installed 3.00 x 18 front and 3.25 x 18 rear tires were placed with a set of 3.00 x 18 tires, which normally give sufficient clearance under the back tire when the bike is on the centerstand. As received the bike was sitting on all 4 points, so the rear was changed out first. In order to get some clearance on the rear wheel, I have to drag out a 1/2” steel plate that weighs about 15 lbs to slide under the centerstand feet, raising the bike up enough to R&R the rear wheel assembly. I changed the tire and reinstalled the wheel assembly, after cleaning rust out of the rear brake drum, and added a new rear brake cable. The tire was still kind of skimming the work stand, though. I put a jack under the starter motor which raised the front end enough to allow removal of the front wheel assembly. This was easier than usual, as the front fender was bobbed back about 6 inches.
Finding a correct 2.75 x 18 front tire is getting more difficult, so I just went with another 3.00 x 18 tire that matches the rear tread pattern. The new tire profile was shorter than the removed tire, so finally I got some ground clearance under the rear tire when the bike was sitting on the centerstand. Puzzling this out further, I noticed that the rounded feet on the centerstand legs were flattened out from wear, so that accounted for some of the clearance issues at the back. The bike still had the original rear shocks, set at the lower pre-load setting, so that wasn’t an issue.
After finishing off the now bright looking engine assembly, I tucked it back under the frame. It’s a delicate process and I do have a little sideways bike lift that I have used in the past to hold it steady while raising the 115 lb lump into the chassis. I also use a little Harbor Freight hydraulic jack that can be used with great care to avoid having the engine fall off sideways. I put the foot of the jack under the drain plug area to help give it some stability and slowly raise the engine upwards with a couple of long Phillips screw drivers to use to hold it steady as the holes align. Putting the breather hose on the cylinder head top cover and routing the points wiring lead up over the cylinder head first, saves a few steps later on. After re-attaching all the mounting bolts, the bike was finally coming back to correct appearance.
Watch for Part 2 coming up next....
Bill Silver aka MrHonda
www.vintagehonda.com
No comments:
Post a Comment