Topic: Engine ID assistance

[brett762]

All,

In hopes of starting a new project soon I picked up a CB750 engine on the cheap; trouble is I have no idea what year it is as it seems to be a replace-o-case with a virgin number pad and a California Assigned VIN tag. In my research, the following details appear to be relevant in determining engine year:

The top fin of the head has an early contour.

The cam towers are marked: 44.6.5

The under side of the valve cover is marked: RK 2BA

The head is cast with a 2 on the flat over the second cylinder

The cam is marked R4

Pistons are marked 300

The fin supports on the head are cylindrical.

The plate at the end of the shift drum is not notched for neutral and is fastened by a bolt rather than a philips screw

The rear of the lower case is marked U817

Hoping the experts on here can shed some light on a year/model for this engine.

Thanks!

[Jerry Rxman Griffin aka MuthaF'er]

How many bolt holes in the clutch cover? That's your main question. Most of the other info is not relevant. 76 or earlier. Not an early F. 

[brett762]

The clutch cover is a 10 bolt, but I think it may have replacement cases under earlier top end components.

[Jerry Rxman Griffin aka MuthaF'er]

If it's 10 bolt and not sand cast then......... what's the purpose of your inquiry?

Would be next to impossible to narrow it down to a year and most parts are interchangeable.

[brett762]

Got it. My recent additional research indicated that the cam tower stamps may designate a date based on the Japanese Showa calendar which would place the mfg. date in June 1969.

The purpose of my inquiry was simply to gain knowledge. As I'm new to the CB750, I have much to learn. Beyond that, because I scored the engine for next to free, I am trying to determine if it's a greater benefit to me to rebuild or part out for a profit and put that profit into a more complete project.

Good to know about the interchangeability, though.

Thanks.

[kmb69]

Got it. My recent additional research indicated that the cam tower stamps may designate a date based on the Japanese Showa calendar which would place the mfg. date in June 1969.
.....

That is possibly a Sandcast engine with replacement diecast cases with that build date. If this is the situation, it will probably have many desirable Sandcast internal parts. The 9 hole clutch cover would have been replaced with the later 10 hole version as would the oil pan. You should be able to easily identify if it has the Sandcast cylinder head and cylinders. Post some pictures of the head, cylinder, and alternator cover we might have a better shot at identification.

First dibs on any parts you want to sell if it is indeed a Sandcast motor.

[brett762]

Those are the pictures I had on my phone during tear down. I'll take more if necessary. I thought it was interesting also that everything down to the cam towers was fastened with socket cap bolts. I imagine that was the previous owner rather than factory. I know, the pic isn't of the alt cover, didn't have a pic handy.

[brett762]

Also, kmb69, dibs noted. Thanks for your help!

[754]

Show the underside of valvecover if it has a waffle look .
And ealy shifter mechs are different.
They underside of cylinder will show if its earlier.
 When you can see the crank where tyecoil crossholes were drilled ..are tyey threaded or just have balls in them ?

[brett762]

The valve cover isn't waffled and I haven't split the cases yet. Here are some additional pics.

[754]

Cylinders and shifter look earlier, but nor necessarily sandcast.  Kmb69 should know.

[brett762]

Copy that. Thanks for your help!

[kmb69]

Appears to be a hodge-podge of models. Most parts except the cam holders, rocker arms, and shifter mechanism appear to K1 or later. The shift mechanism appears to be mid-late Sandcast or early K0.

[brett762]

Thanks for your input. Knowing that it's a frankenstein's monster of an engine, I won't feel bad about building it out the way I want.

[kmb69]

After thinking about this a bit, my hodge-podge comment may be somewhat exaggerated. Surely would not call it a "Frankenstein's monster". I would speculate it was a Sandcast or early K0 motor that got replacement cases. Sometime later, the head and cylinder was replaced with newer stuff while retaining most of the original internals. If you split the cases, I would like to see pictures of the rod big ends. Also check the camshaft for a raised rectangular block on one side. I collect and restore Sandcast models so if you decide to update the shifter mechanism and/or transmission, I would be interested in trading or buying that early shifter mechanism and possibly other SC/K0 parts.

[brett762]

Thanks for the follow up. I'll get a picture of the big ends when I split the cases; it won't be for a while. The cam has a raised rectangular block with what appears to be "fy" on it.