Differences - visually between CB72 and CB77 crankshafts

[Dennis Lodge]

I have just purchased a new old stock crankshaft. I couldn't ignore it at the price. However I don't know if its CB72 or CB77.
I was told the balance holes are 20mm (CB72) and 25mm (CB77) but when I measured them they were 23.8mm.
I have checked it is not a CL crankshaft and yes it has the oil hole outboard of the bearing. However it has two oil holes both in line out board of the bearing?
Finally I checked against an old crankshaft. That came out of a CB72 and that has 23.8mm balance holes and one oil hole.
However I am now unsure in case that engine had a CB77 crank fitted, yes vibration problems, but over the years changes happen.
Any help/thoughts would be most welcome.

[e3steve]

Hi Dennis, I wondered when we might get a visit from a VJMC dignitary! Your own personal knowledgebase on both types of machine would be valued also, I'm sure.

I've posted some images, at times, of your beautiful '61 CB72 for all to admire (and my, how they have!); hope you don't mind. I blanked out most of the reg nr for security.

I guess you've seen for yourself, but what I find odd is the difference in price between the CB72 & CB77 crankshafts (see below screenshots); alarming! I can see no earthly reason for that, nor can I think of one for why they'd be different items between two, essentially-similar (similar being the keyword, I s'pose) and identically-stroked motors, but they do have different part nrs -- and 3 different part nrs per model. I'm sure Ed (LM), Jensen or another member who owns / has owned both models may have something to add.

Rgds, Steve

[e3steve]

Different gudgeon pins' lengths, obviously; but I wonder: are they still 15mm dia (& 15.1mm for the -305 oversized pins).

[G-Man]

Dennis

Good to hear from you. I have a couple of NOS CL cranks and a NOS 360 crank without oil hole as well as different balance hole sizes I have seen different sized flats machined on the webs. I think that over the years the design changed a little.

The three I measured came up with:

CB77 used Hole 20.67 mm Flat 63.5 mm
C(A)72 NOS Hole 19.17 Flat 68.0mm ( actually no oil hole so probably a type 2 CL72 ?)
CL77 NOS Hole 23.3 Flat 62.4

Your 2 oil hole crank sounds interesting. I would be happy to provide a small selection of the cranks I have for a comparison. I am in Derby.

G

[Dennis Lodge]

Different gudgeon pins' lengths, obviously; but I wonder: are they still 15mm dia (& 15.1mm for the -305 oversized pins).

Hi Steve,

Yes I still have the 1961. Jensen was in touch a while back and after a few false starts I supplied a large number of images for detail information.

I thought I was pretty clued up on the CB72/77 but never having got involved with crankshafts before I suddenly needed to be having picked up this one at the recent VJMC rally.

I am sure the rods are identical. Obviously gudgeon pins will be longer to suit the larger diameter piston. The os pins are a simple way of dealing with a small amount of wear.

Thank you for the schematics. I do have parts books both No2 and the early one. Amazing how much thinner it is without all the different market information.

You are always welcome to contact me direct if you wish.

regards

Dennis

[Dennis Lodge]

Hi "G Man",

Thank you for the offer. It would certainly be easier than the complete CB77 I have been offered to strip if I wish?
Really I never took much notice of the crank before except to make sure the big ends were good and hopefully the small ends.
Certainly it would be useful to see and measure etc the other cranks.
I am currently tied up on a club magazine. I edit and put the layout together for two clubs but once that is done I will be clear.

regards

Dennis

Dennis

Good to hear from you. I have a couple of NOS CL cranks and a NOS 360 crank without oil hole as well as different balance hole sizes I have seen different sized flats machined on the webs. I think that over the years the design changed a little.

The three I measured came up with:

CB77 used Hole 20.67 mm Flat 63.5 mm
C(A)72 NOS Hole 19.17 Flat 68.0mm ( actually no oil hole so probably a type 2 CL72 ?)
CL77 NOS Hole 23.3 Flat 62.4

Your 2 oil hole crank sounds interesting. I would be happy to provide a small selection of the cranks I have for a comparison. I am in Derby.

G

[Dennis Lodge]

Hi Steve,

Sorry I didn't spot the prices until I enlarged the scans. Ouch!

Yes strange that the CB72 was so much more expensive.

I cannot imagine a reason. Usually changes happened on both.

I am currently building a 1962 CB72. I only bought it because it had a 61 engine but then I decided to restore it having bought some 62 cases plus another engine.

cheers

Dennis
quote="e3steve"]Hi Dennis, I wondered when we might get a visit from a VJMC dignitary! Your own personal knowledgebase on both types of machine would be valued also, I'm sure.

I've posted some images, at times, of your beautiful '61 CB72 for all to admire (and my, how they have!); hope you don't mind. I blanked out most of the reg nr for security.

I guess you've seen for yourself, but what I find odd is the difference in price between the CB72 & CB77 crankshafts (see below screenshots); alarming! I can see no earthly reason for that, nor can I think of one for why they'd be different items between two, essentially-similar (similar being the keyword, I s'pose) and identically-stroked motors, but they do have different part nrs -- and 3 different part nrs per model. I'm sure Ed (LM), Jensen or another member who owns / has owned both models may have something to add.

Rgds, Steve[/quote]