CB77 offset crank?

markstertt · Post by **markstertt** » Wed Mar 27, 2013 5:59 pm

Hey, thanks for all the replies, wasn't sure anyone would be interested or see the point. If you read the posts and articles on the xs650 forum on offset cranks and their performance/mechanical advantage you'd understand my interest. I'm considering the 76* offset crank for my Triumph project and that was the offset Phil Irving recommended back in the day and the model billet crank being offered by MAP cycles. 90* would still be preferred but either is better than 360*. Oh and balance factor is usually 50% in either offset.

If I pursue this (after Triumph) idea, I will play with the spare cranks and cams I have, it's just that the cranks are in southern Calif. at the moment. I won't mess with my dad's stock '62 CB77 but have enough spares to make another bike but why stock again? Hence the questions.

Tim, thanks for the offer on using your tooling to reassemble crank...I'll keep you in mind for sure. Texas is easy shipping back and forth.

I do have some spare NOS cams here so will look into spline alinement, time permitting. If I had to, I wouldn't be opposed to turning off the splines, pinning and or welding back together, I really haven't pursued the methods as I wasn't sure, without having a crank here, that it was a feasible exercise. It sounds as though this could be done with parts at hand and little expense, other than perhaps an elect. ignition which would be easiest and most desirable.

I need another project like I need a hole in the head but this kind of stuff really piques my interest and if nobody has a 90* offset CB77 then it's about time, besides the fact that it will sound like a little Ducati and pull like a smallish one can't hurt either...Mark

leonvjames · Post by **leonvjames** » Sat Mar 30, 2013 11:17 pm

Ive had a couple of problems with cams, I managed to break two of them as they sheared off at the splines. It was a long time ago and they were cams from Read Titan, their 3/4 race ones. This could be e real weak point in the cam design.
Leon.
P.S. I managed to ride the bike home on one cylinder but the performance was not good.

markstertt · Post by **markstertt** » Sun Mar 31, 2013 2:37 pm

That's interesting Leon, perhaps the aftermarket cams had a mfg. problem that Honda mfg. wouldn't, who knows. The cams I have available appear to be NOS factory race cams? and stock cams and if I decide to desecrate the old racer H&C roller rocker cams. The good news is one would only need to move one half of the cam set, the timing side could stay installed as per standard so I'd only be messing with one side of the assembly...Mark

jerry · Post by **jerry** » Mon Apr 01, 2013 2:13 pm

I had always thought that extra power was produced through efficient engine breathing and combustion and not firing phasing. All very interesting. All the best Jerry

G-Man · Post by **G-Man** » Mon Apr 01, 2013 2:23 pm

Jerry

I think that the pursuit here is something other than performance. Clearly just changing the interval between the crank pins isn't going to make the bike create any more power. We had a similar discussion on the forum a while back on building a "big bang" 305.

From an engineering point of view, if you cut the engine in half and operate it as two singles the two "engines" do not have any influence on each other.

G

jerry · Post by **jerry** » Mon Apr 01, 2013 5:13 pm

Dear G Man, I do realise. However mention is made of performance /mechanical advantage and it is this part I do not understand. Smoother running potential and different power delivery however I do understand. All the best Jerry

G-Man · Post by **G-Man** » Tue Apr 02, 2013 12:49 am

Jerry

You are one of the few people here who is in a position to measure and understand what creates an improvement in performance.

I think that people get mixed up with the mechanical 'feel' and the perception of performance rather than actual performance.....

G