I have heard several people on the forum mention that they have changed the crankshafts in their bikes for added power. I know the crank turns and moves the pistons, but what it is about the crank that causes an increase or decrease in power?

 

The added power would come from changing the stroke for more CI, this requires more changes.
There is also a reliability factor if you go to a stronger composition.
There is more involved than just the crank.

 

Are you sure you mean crank, and not cams? I just recently changed cams and gained a ton more torque and horsepower.

 

To change the crank you can stoke (add stroke to the engine, increasing the total cubic inch displacement), you can de-stroke (subtract stroke to the engine, decreasing the total cubic inch displacement,but gain in the amount of time to reach a set RPM, it turns up faster), or you can decrease the weight of a crankshaft (less weight = less rotating mass = more RPMs and power faster because it turns up faster).

 

I think what you are seeing is they changed the crank so they could do the build and not have to worry about it tweaking on them. Newer Harley cranks are ****. The last of the forged cranks were made back in 2004. And the Timkin left tapered bearing went away in 2003. 2005 brought us cast cranks that have been scissoring ever since. For a crank to be worth using in a build it needs to be welded.

 

Would you explain how welding will increase the strength of a crank?

Does the weld make it stronger due to the increase in area of welding a bead up the length of it? I'm assuming you are talking about welding a cast crank.

Probably a foregone conclusion but I bet it is much better to use a drop forged crank than to modify a cast one. I bet welding a crank invites all sorts of wonderful problems if not done correctly; drawing, warping, the possibility of a bad weld due to inclusions and voids in the original casting, ect.

Interesting subject.

 

The crank halves are welded to the pin. They are a press fit and the welding keeps them from slipping. The crank is trued before it's welded and checked after.

 

Are they talking about some special aftermarket crankshaft?

 

Stock

 

i have heard about welding the crank before.....


sounds kinda risky though.

would have to trust the welder to do it correctly (i can weld to save my life - but it aint pretty..)