Topic: cb750, '73, has a blank engine serial number plate

[Hondawggie]

I recall the 'drive chain breaks the engine case near the countershaft sprocket' issue on early cb750s but I don't remember what year cb750s that was occurring.  I'm pretty sure it happened with the '69 and '70 but not too long after that beyond that as if Honda fixed the problem.  This bike has a blank engine number plate.

I'm going to buy this clunker cb750.  But I want to know about the motor first -- the frame stamp is also absent and there is a plate that is riveted on the frame near the gooseneck with a California DMV 'special VIN number' stamped on it.  

The owner says it's a 1973 bike because that's what the person he bought it from said.  I'm pretty sure that the unstamped engine case means that part of the engine case was replaced and the dealer didn't stamp the replacement cover.  

I made a very careful detail-oriented and highly vigilant inspection of the left side above the countershaft sprocket engine case -- sure enough the smooth, outlined area where the 'CB750E-xxxxxxx' engine number *should* be present is there where it should be.  It is also 100% flat and unaltered.  It also looks a bit less gamey than the rest of the engine exterior.

  So I assume this is a replacement left rear engine case that was installed due to a destructive chain/engine case encounter, and the dealer did not stamp it.

What year(s) engine could this be?  I'm not worried about the frame.  The DMV has approved it and the seller has the title.  The title shows the year that the frame was inspected and approved by the DMV, in the late 1990s.  No, this is not a 1990s cb750 -- to me it looks like a 1972 or 1971 bike.  It still has the stock hm341s on it.

It's been re-painted non-stock so I can't use that.  Also, it does *not* have a salvage title.  The seller bought it this way and has no knowledge of the engine # and frame # issues.



How can I figure out the correct year?

[MasterChief750]

post lots of detailed pics and there are plenty of people around here that can figure it out. i couldnt tell ya just from the blank cases to my knowledge the crank case replacement happened through the 70s

[754]

Looking at the outer end of the head fins, do the vertical bars joining them look round or oval/rectangle ?

 Do the carbs have cables coming out of the top?

 Is there a shift pattern cast into the left engine cover, the shifter comes out of ?


 My 73 has blank cases, they come as a pair.

[Hondawggie]

Looking at the outer end of the head fins, do the vertical bars joining them look round or oval/rectangle ?

 Do the carbs have cables coming out of the top?

 Is there a shift pattern cast into the left engine cover, the shifter comes out of ?


 My 73 has blank cases, they come as a pair.

The carbs do not have cables, there are linkages and the expected 'butterfly' 2-cable pulley that each carb linkage connects to.

Not only is the engine number missing -- the gearshift pattern is also not there.

I have a '71 head in the garage -- the '71 head has 5 (well it looks like 4 at an angle, but there's actually 5) vertical rods at each end of the head.

On this 'mystery' cb750, there are three verticals at each end of the head, not 5, and they are not rod-shaped -- the verticals are oval shaped.

Also:
- the clutch cover has 9 bolts
- it has hm341s
- the speedo and tach guages are not the later aqua/light green, they're the same darkish color as the early guages
- the speedo is incremented in 10s (10mph, 20mph, 30mph) whereas the earlier cb750s were incremented in 20s?  I believe, but not 100% on this point........
- the ignition is under the gas tank on the left side -- it is flat, not sunken in.

I'm thinking this probably is, in fact, a '72 or a '73.

Didn't the ignition switch go up top in '74?

[754]

 73 and up has the 3 bars in the fins..(early 73 might not)

 2 cable linkage cabs are 71-76

 I used to think 75 and up had the shift pattern in the cover, but I am riding a 74 that has it.. sort suspect it may be changed..

 I think you have a 73, if not its a 74..

[Hondawggie]

73 and up has the 3 bars in the fins..(early 73 might not)

 2 cable linkage cabs are 71-76

 I used to think 75 and up had the shift pattern in the cover, but I am riding a 74 that has it.. sort suspect it may be changed..

 I think you have a 73, if not its a 74..

I think you're right, however here is a 1974 that has the light green gauges:
http://cgi.ebay.com/ebaymotors/1974-Honda-CB-750K-/150497390650?pt=US_motorcycles&hash=item230a57f03a

The gauge faces on my 'mystery' 750 are much darker, not sure what (if anything) that means -- they could have been changed.


The one part I seriously do not get is --- why a frame with no frame number.  I have checked both sides of the gooseneck -- no grinding away of any metal, just a smooth painted consistent-texture goose neck -- with no numbers or ID plate.

The blank engine number I can understand -- seems to be well-understood that these cases came about as Honda replaced the ones cracked by the chain.

How could this frame have left the Honda factory with no numbers on either side of the gooseneck?

[bryanj]

As a spare part the frames also came un numbered for the dealer to stamp in the original and transfer the vin plate, Frame replacements, whilst not common, do happen so its possible that either

(1) Naff dealer replaced frame and did not transfer numbers

(2) Sombody purchased a new, possibly old stock, frame and built a bike out of boxes of bits

I would go for (2) with the Californian "special" vin attached

As to working out the year---its probably from  several so you aint got a hope

[736cc]

9 hole clutch cover on un-numbered engine means its a replacement sandcast motor. The sandcast motors w/ numbers are valuable, w/o numbers they're still worth at least as much a diecast motor, probably a bit more to a restorer. Where u located?

[Hondawggie]

9 hole clutch cover on un-numbered engine means its a replacement sandcast motor. The sandcast motors w/ numbers are valuable, w/o numbers they're still worth at least as much a diecast motor, probably a bit more to a restorer. Where u located?

I checked and I missed a bolt on the front bottom of the clutch cover that is next to some sort of cable or hose coming out of the clutch housing.  It actually has 10 bolts on the clutch cover.   Sorry for the confusion.