Driveshaft With Bike Engine

[Guest greavesy7]

Bit confused with fitting the prop to my new engine.

 

I've heard that the prop needs to be all in line but what does this actually mean, as the way the prop comes out the bike engine it is almost impossible

 

[sj-bradley]

Prop shafts are not like CV joints which are "Constant Velocity".

 

What this means is that a CV joint rotates smoothly at what ever angle the joint is at.

 

Universal joints (on prop shafts) do not do this. If you have a UJ fitting on your socket set, you can see why. If you bend the UJ through a large angle (90 degrees is the extreme) you will find that the joint "locks" and you cannot turn the UJ.

 

That's why prop shafts have 2 UJs fitted as the second one "undoes" the lumpy velocity through the prop shaft. UJs only work through a small limited angle after which extra vibration will set in due to the constant acceleration and deceleration that occurs.

 

That's basically it

 

Simon.

[Snapperpaul]

[Snapperpaul]

Also on a fixed axle not independant the UJ's at gearbox end move vertically as the axle moves up and down and the axle UJ moves more than the gearbox end

Therefore you can have the UJ angles more acute than the diagram as long as they don't bind

[Guest greavesy7]

I've done a lot of diggin today so I think I should be ok now. My prop has a uj in the middle so I'm planning on having the rear section from the diff to the middle uj straight as poss then there may be. 5-10 degree Angle to the engine

[IanS]

Looking at snappers diagram, has anyone looked at the bedford rascal minivan, the 2 UJs must bend about 20 degrees.

[Guest greavesy7]

It's physically impossible to have it dead straight with a bike engine unless you have a sidecar with the engine in

[sj-bradley]

Re - snapperpauls diagrams.

 

I don't understand why the perfectly aligned propshaft is regarded as "poor". This is the ideal position and the ujs are there to "allow" a slight sideways movement to prevent bending / snapping of a direct coupled drive.

 

Seems like the diagram should read "ok", "good", then two "bad"s. ?? Can someone clarify this ?

 

Simon.

[Peter Bell]

I think it is because the load through the shaft is always in exactly the same position so the UJ needle rollers do not move and the force concentrated in the same place so they fail. By moving slightly the load is spread over a larger area, also the movement allows the grease to get under the rollers rather than be forced out.

[sj-bradley]

I suppose that's possible, but perfect alignment is almost impossible and then there's vibration to consider which tends to move things around.

 

Look at all the older washing machines for example. They tended to wander everywhere ...

 

Simon.

[fry61]

Think it's called "brinelling" Simon, the bearing balls/rollers impacting on the same spot continuously causes a hollow in the outer shell.

[Peter Bell]

Thats the word I was trying to remember Brinelling! its the problem with needle or ball bearings, the contact area is so small

[Snapperpaul]

that's explained it better than I could

Edited October 13, 2014 by Snapperpaul

[Guest Gargoil]

Ok, new word for the day, Brinelling. Must remember..........

Ah, who am I kidding, I'll have forgotten it by lunchtime........

[Grim]

picky alert: It's actually 'false brinelling'.

 

'Brinelling' is caused by whacking your bearing with a hammer and causing dents which, after a while, causes further damage.

'False brinelling' is caused by micro-movements in a bearing causing localised fretting damage and appears very similar to brinelling.