72 crankcase questions

Just finished splitting the cases on a couple of 72 engines, What I am trying to do is use the matching number cases that came with the bike that also match the frame and trans. When I purchased the bike this engine was not in it. I found out why, The circlip on the wrist pin had broken and scored the side of the piston. What I would like to know is if a 201470 crank will work in a 2093** set of cases? The crank that came out of the 209 engine dosn't look as good as it seems as though a hack worked on it at one time. And maybe why the clip broke, And also the good crank has an R stamped on it? and the other dosn't? I plan on changing all bearings and bushings and having the crank checked first. Am I going down the wrong path? And I want to thank you all for your advice so far as it has helped, Also do you know of a good shop to check the crank? Thanks and have a great day, Chuck.

I'm sure that you should be able to use any 750 commando crank.

Thanks 79X100 I was hoping that was the case, Because the one looks great the other not so good, Chuck.

Hortons Norton said:

And also the good crank has an R stamped on it? and the other dosn't? I plan on changing all bearings and bushings and having the crank checked first. Am I going down the wrong path?

Click to expand...

The Commando main bearings changed to a (pre-Superblend) MRJA 30 (NF/NJ306) roller type (part number 063114) around late 1971, and a crank of reduced width was also introduced to be used together with the the new bearings, this allowed for a change in the specified bearing end float to suit the new bearing type.
These cranks were identified by an 'R' stamp, and were supplied under the part number 063106. I do not think there would be any problem using an R crank with Superblend bearings, provided it is shimmed to give the correct crank end-float?

Thanks L.A.B., This is great to know. I was wondering why the one crank was marked and the other was not, Do you know if the pre-Superblend and the new Superblend are the same width? Also I have been told I may want to have the crank magnafluxed and balanced any thoughts, The only reason is I don't know the history of these engines and they were not running when I purchased them. And is a visual inspection of the cases enough, I have heard on these Combat cases sometimes the would crack too? Thanks a million L.A.B. and if you or anyone else can think of anything else I should look for or maybe do please let me know, ( i.e.) of brand pistons or bearings ect..... It would be great, Have a great day, Chuck.

Hortons Norton said:

Do you know if the pre-Superblend and the new Superblend are the same width? Also I have been told I may want to have the crank magnafluxed and balanced any thoughts,

Click to expand...

I would think the bearings are the same basic size, I think it was more to do with the MRJA 30 bearing needing a greater running clearance than an actual dimensional change to the bearings themselves? Of course the crank end-float is going to depend on the actual dimensions of the crank and crankcases as well as the bearings. I don't see anything wrong with balancing and magnafluxing the crank.

The recommended main bearings are the brass cage FAG NJ306E C3 type.

My preference for pistons would be original AE Hepolite, but there are alternatives available. The genuine Norton ones are now Italian GPM type I believe?