The engine build went along pretty well, as planned, but there were issues to solve that required some creativity to some degree. Starting with the bottom end, the transmission did receive a set of offset cotters to help improve gear dog engagement. The low gear bushing was refreshed, as well. Once the cases were bolted back up, the unit was flipped back over for top end and clutch side assembly. I discovered that you could stick a 3/8” drive extension with a medium sized socket on the end and poke the whole thing through a connecting rod to keep the engine from turning over while tightening up the big crankshaft nut. Using a ½” drive ratchet and extension on the 4 prong special tool gives a nice snug tightening experience without the usual hammering with a dull chisel on the nut flats.
The engine had 15k miles, according to the speedometer, so the primary chain was somewhat slack, of course. Once the clutch plates were all cleaned and sorted, the primary side was all assembled with no major traumas. The shift shaft did turn out to be one of the “short” ones, but the splines are good enough to reuse the shaft once again. The oil filter was actually fairly clean, so someone had serviced it at least once in its life; perhaps when the top end was rebuilt.
The oil filter drive chain was REALLY loose and sloppy when the filter was fitted up in the crankcase hole. These little chains are hard to find as they are a few of those “universal” parts used on ALL 250-305 wet-sump twins. None of my usual resources had a spare chain available, but research revealed that the chain is a fairly common #25 chain pitch. The factory chain is endless, but these small chains can be purchased with a master link, allowing for building a custom chain for this application. An eBay seller offered a 3’ long chain with master link for less than $14 delivered. The chains are used on those little pocket bikes, so they should be sturdy enough to just spin a little oil filter round and round, I hope.
When the original chain was measured with digital calipers, the length was about 18mm. The new chain showed an overall inside length of 16.5mm and when fitted to the engine resulted in a very nice fitting chain with minimal slack. I am in contact with a company in the UK who apparently has these chains in the correct endless lengths as well as a potential replacement primary chain, which is another hard to find part now.
The cylinders were honed and looked mostly good except for an area of staining about mid-travel down the bore. New rings showed nice end gaps, so the piston/ring package should be good to go this time. The endless chain is somewhat easier to wrangle during engine assembly, once it has been looped over the camchain guide roller. Those rollers are NLA from Honda, but were beautifully reproduced by CMSNL in Holland.
The original cylinder head had a large section of broken fins, so the hunt was on for a correct “U” shaped fin replacement. A check on eBay showed a decent looking head up for auction of the correct type and miraculously it was located right here in San Diego. It turned out to be perfect for my needs and at $60 a bargain, as it included valves and springs. The fins were all perfect and combustion chambers/spark plug holes all in great shape. Honda Dreams had their own exhaust valves until CA77E-1025681, when Honda just installed regular CB72 (268 code) exhaust valves in the rest of the production run. Both of these heads were early version (the front fin shape cutaway is U shaped, instead of V shaped), so all of the valves were the same. The best four valves were cleaned and installed, although the intake valves had a little step in the valve face angle, they seemed to seal up after a little lapping work.
The cams were like the rest of the internals… all varnished up, but not scored, worn excessively or damaged. Even the camsprocket was in decent shape, so was reused after the return springs were checked for nice return action on the weights. The cam bearings were all replaced from stock on hand. The rocker arms and shafts were all installed and the cams lightly started into each end of the head. While it is possible to slip the camsprocket in and under the camchain with the head in place, it is probably easier to insert the camsprocket into the chain before dropping the cylinder head down onto the cylinders.
Care must be taken to ensure that the pistons are both at TDC, before the camsprocket is positioned into the camchain. To hold the whole top end down in place, a couple of short 3/8” sockets were slipped over the exposed stud ends and secured with some 8mm nuts. This helps to clamp the gaskets down in place and gives just enough slack to allow the cams to be installed into the camsprocket, which was positioned with the 0 mark at 12 o’clock and the flats parallel with the cylinder top cover surface. The left side cam (right side as viewed during assembly) is tapped into the awaiting camsprocket’s master spline first. I did install both of the inner cam bearings into the head first, with the outer bearings pushed onto the camshaft shoulders for insertion. Once the camshaft catches the sprocket’s splines, it will hold the camsprocket in place while the piston position and cam timing landmarks are all rechecked one last time. When the proper cam timing is verified, the right side camshaft, with the point cam mark pointed upwards can be gently tapped into place. After the cam has engaged the splines, attention must be made to ensure that the point cam’s shaft tang end engages the inner plate of the spark advancer unit. On a 360 degree firing engine, the point cam has double lobes, 180 degrees apart, so you can get away with installing the point cam shaft in “backwards” and not suffer any timing issues. You cannot get away with this on a 180 degree firing engine, however. If you make that mistake on a CB/CL 180 degree motor, then you would have to install the points plate in upside down in order to get the engine to run. That makes for a very untidy installation, so do it right the first time.
Once the camshafts are installed, the end covers have to be placed over the ends of the camshafts where the edges push the cam bearings deeper inside the cylinder head openings. I usually install each cover without the gaskets at first and secure each cover with 2 screws, mounted diagonally to hold them in place. At this point the camsprocket position can be checked to see if it is in alignment with the bottom chain sprocket on the crankshaft. You can sight down the chain and see if it is pulling to one side or the other. Small adjustments can be made by tapping the camsprocket slightly to one side or the other until the camchain run looks to be straight.
Once this is achieved, you can snug down the camshaft nut tightly. I have an adjustable hook wrench which works perfectly for this function, but the old “dull chisel” or a wide flat-bladed screwdriver can be used as a tool as long as the handle is strong enough to endure some hammering on the end. Remember, that in most cases, the camshaft nut is a left-handed thread! Once the nut is secured, you can remove the end covers, tighten down the left cam’s through-bolt and then install the gaskets correctly and tighten all 4 screws on each end.
All that is left is to install the top cover gasket, breather plate (drain holes for forward/down) one more gasket and then the top cylinder head cover. Torque the cap nuts to 15-16 ft lbs. and you are ready to install the camchain tensioner on the back of the cylinders and adjust the camchain tension. This engine still had the “early” style camchain tensioner, which has the tensioner bolt on the left side.
There is more work to do on the right side; of course, installing the rotor with fresh starter roller springs positioned inside the starter clutch hub outer, which should be tightly screwed to the back side of the rotor. The starter chain, if showing excessive slack, can be shimmed by using thin washers beneath the starter motor mounting points. Otherwise, the chain is the same pitch as the camchain, so a replacement can be made from a spare camchain and master link. OEM starter chains are endless, but using a replacement with a master link is perfectly acceptable. Remember that this chain only turns when the starter motor is activated; otherwise it just sits quietly in place when the engine is running.
Tim McDowell http://www.classichondarestoration.com/index.php has quite a few replacement parts on his website, so an aftermarket air filter and tube were ordered from him, along with new chromed cap nuts for the head and an engine screw kit.