My buddy, Scott, has fond memories of his first “big bike” experience on a blue 1962 CA72 250cc Dream, when he lived back in PA as a teenager. For years, he had sought out that bike or one “somewhat like it.” Finally he wound up with a “something like it,” a red, black-plate 1962 CA72, which he bought from the original owner’s family about 12 years ago. It had over 20k miles showing on the speedometer and some extra switches were added on the side of the frame to control the ignition, as the stock ignition switch had failed mechanically. Beyond that and a recovered seat, most of the bike was original, including stainless steel mufflers. The tail light had been upgraded to the later CB72 style, but the welded-on tail light bracket was still intact and able to accept the small rectangular original light assembly used in 1960-62.
Over the years, he rounded up bits and pieces for the bike and for the engine overhaul to come. The time has finally arrived for cracking open this CA72-21075 engine to see what the years have done to this normally sturdy motor. Scott had drained the original oil after purchase and loaded the crankcases with “Sea-Foam” petroleum cleanser to help dissolve the accumulated varnish and sludge that builds up inside these engines. Honda specified non-detergent oils back in the 1960s and that type of lubricant doesn’t suspend a lot of dirt and particles very well.
We removed the engine assembly a few weeks ago and I have been holding it for my friend David, who is an instructor at Hi-Tech High School, here in San Diego. He has access to video equipment and wanted to record the engine teardown process. We tried this once before, but his gear’s hard drive failed to capture all the images, so this is Round 2 with Bill and the 250-305cc Engine Teardown video.
While waiting for David to round up higher specification cameras, I gingerly peeked into the engine through the valve tappets, initially and then finally removing the cylinder head top cover to check the condition of the camshaft and valve train components. There is an alarming amount of some dried out varnish deposits that have turned into a fluffy consistency, which is easy wiped away with a rag. Beneath that layer appears to be some more highly varnished steel components that will need a thorough cleaning.
Typically, the 1962 and later engines use a 12mm spark plug and the lighter style camsprocket assembly, however this engine featured 10mm plugs and the big, heavy “flywheel” style camsprocket unit. The camsprocket change came at CA72-210630 while the spark plug changeover was at CA72-210100. The chassis number is CA72-20057, so probably built the first day or so of production as it related to the 1962 specifications. This bike had an early Yazaki-brand speedometer, which was shipped off to my friends at Foreign Speedo, here in San Diego, who have been rebuilding vintage Honda speedometers and tachometers for many years.
With the kickstarter cover removed, it was obvious that the crankshaft seals must have been doing their job well, as the stator coils were still nice and clean. The Dreams used either Nippon Denso or Kokusan electrics and this one had the N-D products installed. The N-D and Kokusan points and point plates are completely different from each other, so you cannot interchange those ignition parts. The early- generation Dreams also used an ignition coil with removable spark plug leads, which were replaced by epoxy coils with wire ends cast into the body.
It was a 90+ degree day as the engine began to reveal its inner most secrets and in this case, there were a lot of nasty surprises to be found inside. With the top cylinder head cover removed, the massive early-style camshaft sprocket was revealed along with a lot of scaly, oily deposits scattered around inside the engines surfaces. Fortunately, the camshaft lobes looked fine, which means that the rocker arm pads are still okay. Once the camchain was separated the cylinder head was lifted off and inspected for what would normally be very carboned-up combustion chamber and valve heads. Despite all the gunk in the engine, so far the cylinder head’s combustion chambers had virtually no carbon build-up and the valve heads only showed a small amount of carbon, as well. That’s REALLY odd to find in an engine with 20k miles showing on the odometer. What other surprises were next?
The pistons looked somewhat more carboned up then the valves, so perhaps it had a valve job and they left the pistons/rings alone. As the cylinders were lifted up, it was obvious that they were still on STD bore sizes and showed little damage to the skirts beyond normal wear for that mileage. The rings were a little sticky in the piston ring lands, but they were free to rotate, which is unusual to find these days. The early 250 engines used a “thick” set of rings which are 2mm in cross section. In early 1963, Honda switched to using CB72 “thin” rings which are 1.5mm thick instead. The CA72 pistons have a slightly lower piston crown than CB72 types, which began with 10.0:1 compression, quickly lowered to 9.5:1 and finally to 8.5:1 in 1965.
The oil deposits and varnish had a stinky burnt smell to them, which permeated the area, as we continued the teardown. Once all the clutch cover screws were loosened, the oil filter cover was removed and then the clutch cover came away fairly easily. ARRGH! Sludge and varnish were evident everywhere in thick oozing masses. On 250cc engines this early the factory fitted a four plate clutch pack with thick 5mm friction disks. These are uncommon to find, these days, but supported the fact that this engine was mostly as delivered, with few oil changes to show for its service years. The centrifugal oil filter was teased apart and found to have about ¼” of thick rust/dirt/corrosion build-up inside. There was little room left for any more contaminants to be packed inside, indicating that it had probably never been serviced in its life. To be continued…