650SS crankshaft

Attachment shows variations. Best to know what you have already before you head for a change.

Hello Barry - I've seen a few 650's with the 600's 99 crankshaft and con-rods. A quick check is to look at the con-rod end cap. The 650's have steel caps whereas the smaller Dommies usually have alloy caps. Obviously there are dimensional differences but these are hard to measure when the bottom-end is together. The 750 crankshafts and bigger will not fit in your crankcases without a lot of machining. The 750 Atlas and Commando crank-cheeks and conrods could be paired up with a 650 flywheel if you cant find a useable 650 crank/rods. Good Luck. Howard

I am currently going through this same excersize. The 650 flywheel is the same casting #23316 as atlas. Of course the final maching is quite different.

Both 650 case casting numbers are the same as for my atlas' . Neither have machining inside and are "as cast" in the crank swing area. So why wouldn't an atlas crank alone swing inside 650 cases?

More research to be done....

Don't see why an Atlas crank and rods wouldn't fit. However, the Atlas uses heavier pistons than the 99 or 650, so the balance factor could be out. If you currently have 99 pistons with your 99 crank, they may possibly be too long in the skirt for a 650 or Atlas crank. A Commando crank would certainly need rebalancing as it has a much lower balance factor than the Atlas.

The main bearings will allow the whole range of crankshafts to befitted into any of the cases. However, this does not mean that the associated barrels can be also be fitted to gain a certain capacity.

So an Atlas or Commando crankshaft will sit inside the 650 cases that Barrie has but the barrels for the 750 crankshaft will not go in place due to a stud spacing difference. But .........as the stroke on the 650 motor is the same as the bigger engines these crankshafts can be used to make a 650 motor once the flywheel chunk has been rebalanced or replaced.

Commando crankshafts have a different machined driving side due to the 3 cog sprocket they use. Conversion to belt drive might get around this.

Lastly.....if the engine has been run as a 600cc job and the same barrels are then going to to be part of a 650 motor there is going to be a small problem with the swept area of the cylinder bore. This will probably have worn and left a step at the top and bottom which the 650 pistons will have to cross. A honing or even rebore might be needed to overcome this.

Elderly con rods...

I have just bought a 1963 650SS which seems to have a 99 crank fitted. Can I replace it with an Atlas or Commando crank and rods?

Previously barrie_mundy wrote:

I have just bought a 1963 650SS which seems to have a 99 crank fitted. Can I replace it with an Atlas or Commando crank and rods?

Well you no problems fitting a 750 crank but will need re-blancing to 85% has the 650s where, and fit later type rods Canoe shape has these are stronger rods the Man to sort all this out for you is Steve Maney See his website , Yours Anna J