This is turning into some kind of cosmic lesson (or joke on me), as the formerly “Hotrod CB77” becomes a stocker only to be returned back to the 350cc WEBCO version, once again, by request of the new owner.
If you look back at the last story “Content to de-content… taming the Hot-Rod CB77” the hi-performance parts were removed, as it didn’t sell on eBay as a CB77 Sleeper machine. Rounding up mostly all NOS parts, the fresh top end was installed and the bike ridden about 20 miles in bursts of a few short 4-6 mile break-in jaunts. It is hard to try to keep out of the higher rev range with a bike that doesn’t really kick into the power band until about 6k rpms. After one burst of power on an uphill climb the bike exhibited some signs of overheating, which I put down to the engine paint curing. The power seemed a little bit flatter than normal, but there were no signs of obvious serious distress at the moment. Then the call came in to purchase the bike, but with the roller cam/big bore kit reinstalled, so I took the money and accepted the task of rebuilding the top end one more time.
Most of my engine work comes out well, but sometimes there are little glitches due to a defective part or sometimes my own inattention. As I removed the tach drive housing on the stock engine, after a 30 minute removal process, I was shocked to find no signs of oil on the tachdrive end of the camshaft or inside the drive unit. Something was blocking the oil coming up to the cylinder head, obviously, but whatever could be the cause. It was oiling fine with the WEBCO parts, so the only common denominator would be a blocked oil passage to and through the cylinders. From 1962 onwards, an extra large oil hole was placed in the cylinder block and crankcase to feed oil up both cylinder stud holes which feed the cylinder head end covers. Those covers meter oil up through oiling holes in the tachometer drive and through the rocker arm pins, to lubricate the rocker arms and then splash out to the cam bearings and camshaft lobes. The right side points cover also came up dry. The camshaft lobes were obviously in distress which meant that the rocker arms would similarly be damaged from operating without any oil to the top end.
Once the head was removed, the piston tops and cylinder bores all looked okay, which was a big relief. Pulling the cylinder block off the pistons and flipping it over was a heart-stopping moment as the main oil feed hole (9th hole) in the base of the casting was blocked off solid! This cylinder was a NOS part, shipped from Thailand and was the later die-cast piece, which uses a narrow tensioner. These parts were brought into production around 1966 and used on all three models, as well as being a replacement part for the earlier wide tensioner models. It never occurred to me to look for a non-machined oil feed hole on a factory produced part, much less one that was meant for the 1966 and later machines. All I could do was to drill into the plugged passageway to open up the feed hole. Starting with a small 3/16” hole, the second drill bit selection was a match to the other stud holes and the gasket hole opening. As the drill bit followed the pilot hole into the cylinder base, suddenly the bit tied up, released and tied up again. With a little backing off and pushing in, the bit grabbed one last time and out popped the remains of an aluminum plug! I wasn’t expecting that, at all! The only thing that is remotely possible in my mind is that the cylinder was produced to replace a 1960-61 series cylinder block, which used oil feeds just at the bottom left stud hole opening. The thought of something like this happening never crossed my mind until the plug popped loose. With serious flooding of the oil feed passage with carb cleaner, high pressure water and high pressure air, all the alloy chips from drilling have been flushed out so the cylinder can go back into use, as is; now with a fully-open oil feed passage to feed the cylinder head components.
Well, the main casualties were the cams, rocker arms and cam bearings, which can usually be picked up from eBay auctions for cheap $$, hopefully less than $100 for decent replacements. It was a shame to damage completely good engine components, but thankfully I decided not to continue riding the bike after the deal was made to convert it back to street-racer mode. The engine is waiting for a replacement 350cc head gasket from Cometic, which was ordered last week. The big-bore cylinders and pistons have already been transferred back to the crankcase, so once the head gasket comes in the rest of the motor can go back together in another hour or so.
You can see that attention to detail would have caught this anomaly of a factory blocked off oil feed passage on a replacement cylinder block, but sometimes that’s how we learn… the hard way. At least there was no other serious damage to the engine and it didn’t try to seize up on me, so that is a cause for being grateful for getting the lesson without serious consequences to my wallet or my body.