Let’s continue our story about Honda CB750 SOHC engine.
As original engine was mostly destroyed, we have the only way to restore the bike – to find somewhere another engine. The owner of the ruined bike insisted on finding exactly F SOHC version (F, F1, F2 or F3) so he couldn’t be satisfied by any K-version of engine, which are more common than F. This perseverance may be beyond understanding, but only until you learn subject quite good. You can find information about it in articles such this>>
If shortly, there were a lot of CB750 SOHC modifications, but in fact, F-modification ended the 750 SOHC series, so it had the most modern and powerful engines. For that times Kawasaki made their Z1 or Z2 with DOHC, so even Honda Super Sport SOHC engine was conservative. So if this current bike should be restored, it will be restored with F engine.
But any modification of CB750 SOHC is so rare in Ukraine. For all years I saw only three of them. There was no chance to find it here. In addition, there were no stable engine delivery channel from Europe (ordinary post delivers only parcels up to 20kg out of EU). But we had shipping channel from USA. Not cheaper, 5$ per every Kg for sea shipping and with long delivery time, but quite reliable one. So I began my research on ebay.com.
That was a long search. It was like an everyday fishing. Buy the way, I learned all differences even between F engines. After a long time I found perspective F2 engine, which was declared as one “with low millage”, “in not working” condition (crankshaft won’t rotate) and as “which was inherited with a house and laid for a long time in its basement”.
A short reference about SOHC F2 engine:
F2 – new cylinder head with bigger valves (34/31mm i/o 32/28mm), larger combustion chamber, larger carb mount rubbers, stronger cam chain, new camshaft, stronger valve springs, new retainers, cotters, new pistons compression ratio 9/1. New rod big end bolts and bearings, stronger clutch springs, additional fins on crankcase, larger fins on oil pan, “oil cooler” – finned plate between oil filter case and engine. Final drive 15/43 or 14/43.
After long months of waiting we have got that engine in our garage.
I took a close look at it, and a story unfolded before me. Someone has bought a bike in 1979 and rode it not for a long time, before he had a first crash. In that accident oil pan was broken around drain plug and then repaired. But it looked like the next accident ended a bike’ life. As a result, ignition cover was crumpled, generator cover cracked; clutch, breather and gearbox’ covers were missed (but they might be lost later). One of upper cylinder head’ fin was bent and engine has got different type of scratches. I suppose bike had such damages that it wasn’t worth repairing, so owner disassembled bike and shoved remains into basement, where they laid for good thirty years…
But anyway this engine had original hardware and supposed to be a good base for our Honda CB750’ renovation.
I began to disassemble the engine and that what I saw when took off a cylinder head. There was no spark screwed in the engine for all these years and a cylinders surface above the compression rings turned into a rusty-trash mess. I applied a lot of efforts to remove cylinder block.
The same happened to ignition chamber and valve surfaces.
But in fact the only losses were a cylinder block and piston rings. All other parts were in pretty good condition. There was a bit of rust on some outer parts, like rotor or gearbox shift levers. Whereas all components inside crankcase, such as camshaft, crankshaft, gearbox, clutch, bearings and so on could be used just after the washing.
I made photos occasionally, from time to time, so I don’t have all photos to demonstrate how good was condition of these parts, but take a look at this starter or crankcase surface. They still look like new.
So, I had to do a lot of cleaning, washing, measuring, and searching for cylinders but I also had a good foundation to return this CB750 back on the road.
To be continued.