How Does A Crankshaft Work?

How is the crankshaft supported in a modern motorcycle engine? In this video, Cycle World Technical Editor Kevin Cameron explains how skinny little shells clamped in place around the crankshaft’s smooth cylindrical journals help the engine routinely spin as high as 15,000 rpm.

How is the crankshaft supported in a motorcycle engine? In this particular example—removed for this purpose from a late-model Honda CBR600RR—the crankshaft spins at up to 14,000 or possibly 15,000 rpm at maximum performance.

The crankshaft has a connecting rod attached to it at each of the four crankpins. Each rod has a piston rising and falling in its respective cylinder. That rising and falling produces a shaking force, which, to some extent, is counterbalanced by weights on the crankshaft.

The crankshaft is not just a simple zigzag line like my uncle drew for me when I was five. It has the added complication of these counterweights, which are there to reduce vibration and also the load on the main bearings.

Classic motorcycles of yesteryear had roller- and ball-bearing crankshafts. But roller and ball bearings don’t last as long as people would like their motorcycles to last these days. This engine has plain journal bearings.

Smooth cylindrical journals are supported by skinny little shells—a pair of them, split at the centerline, just as the crankcase halves are split—which do the work of great big ball bearings. And they do a better job.

A thin film of oil between the smooth crankshaft journals and the bearing shells acts not only as a lubricant but a damper. So the crankshaft supported in five places by plain bearings and clamped between the upper and lower cases is actually very well supported.

That allows this particular four-cylinder engine to operate routinely at speeds up to 15,000 rpm. That is not an extreme. In fact, that rpm represents the design point for the manufacturer—in this case, Honda. It is normality.

[robbymann]

The crankshaft is too far away from the camera, but knowledge was excellent, thank you ❤️💯

[Twister]

Every time I think about modern car, motorcycle or aircraft engines I am always incredibly amazed at how freaking durable those things are: thousands of RPMs and they run for thousands and thousands of hours. Blows me away.

[emperorofdarkness]

Worth every single second while watching this video as an old subscriber. Ty so much. Knowledge is above the all

[cryalowicki]

If Kevin is impressed, I'm impressed.

[stalwarts]

Just few of the innumerable and Incredible things men have invented!

[nickclayden-rose]

Thank you Kevin! This helped my friend build My Summer Car™. Great video mate.

[mattias]

Damn, Kevin's ending lines are the best!

[joenovak]

I always learn something from Kevin Cameron.

I have a question on fabrication though. When the upper and lower halves of the block are machined for the crank bearings what is the datum - or features - used for location of the block for the cutting tool so that when mated the two half circles match perfectly for the crankshaft?
I would think it is one of the holes - or several holes - from the casting that were honed. This would allow the halves to be placed into the machining jig/fixture thereby locating the halves perfectly for machining.
Does anyone know? Thank you

[monteiro]

As great as always. Grazie Maestro Kevin.👍👍

[bulgingbattery]

What if you use too much boost in your engine?

[jokey]

Love the videos, but I miss the xylophone music

[waypasttheline]

i havent watched the video yet, but when i see an old bald guy with the part in front of him, i hit like and subscribe before i hit play. always listen to old dudes, they got old by not being stupid.

[angelocardoc]

Why are crankshafts never made out of titanium???