CL77 & CB77 crankshafts

Tim Allman · Post by **Tim Allman** » Sun Oct 04, 2015 12:48 pm

I have a CB77 with a lot of distance on it. The centre main bearings are showing a bit of pitting on the rollers and the bottom end connecting rod bearings seem perhaps a bit sloppy although without pulling apart the crankshaft it's hard to know. Given that some (most?) of you have more experience than I, I'm looking for some advice.

Used crankshafts, at least ones that aren’t obviously rusted, are scarce and buying one seems a bit risky because you can’t see inside. I have however found that there are more and apparently better CL77 shafts available on Ebay. Could I replace the right side section of a CL77 shaft with the one from the CB77 shaft to avoid drilling the hole for the starter sprocket bearing? Is there anything I need to be aware of?

Thanks.

G-Man · Post by **G-Man** » Sun Oct 04, 2015 1:00 pm

Tim

Yes you can replace the outer wheels but make sure that you get a 305 crank rather than 250. The 250 has smaller balancing holes (20 mm vs 23).

If you are going to the trouble of pulling off one wheel you might as well get someone to pull the whole crank apart to check the bearings and possible blocked oilways.

The centre main bearings have an easier life than the big ends as they don't have the out of balance and combustion loads to deal with directly. I have been stripping some cranks this weekend and high-mileage cranks tend to break through their case-hardening on the big end eye. It's difficult to know how many miles you could get from a crank that is starting to 'go' but I suspect that most of the cranks out there now are in a similar state.

These pictures are from a crank I just stripped. The big-ends felt pretty good.......

This is contact fatigue. The maximum stress is just under the surface layer and the cracks eventually grow leading to small flakes breaking away.

This is a roller from that big-end.

Centre shaft was pretty good.

I have just reassembled this crank with new con-rods and it should last a good few years more.

G

Tim Allman · Post by **Tim Allman** » Sun Oct 04, 2015 2:42 pm

Thanks for the info. It is in fact the inner bearing rollers that are showing some pitting when I slide the outer races towards the centre so perhaps that doesn't bode well for the rest.

Where did you get the con rods? I found an NOS pair with bearings on for €400 but this seems excessive.

G-Man · Post by **G-Man** » Sun Oct 04, 2015 2:53 pm

Tim

I've had the rods for quite a while. The cranks I've stripped (quite a few) seem to have more damage on the alternator side than the primary side so it is sometimes possible to build a good crank out of two....

G

Tim Allman wrote:Thanks for the info. It is in fact the inner bearing rollers that are showing some pitting when I slide the outer races towards the centre so perhaps that doesn't bode well for the rest.

Where did you get the con rods? I found an NOS pair with bearings on for €400 but this seems excessive.