Crank taper calculations
Turbo Mini Forums

I was lapping my new clutch hub onto my crank I noticed that the end of the hub only just overhung the end of the crank. When I say just I mean by a 1mm or 2. Does this sound about right?

Does anyone know how to calculate, how much a taper pulls up per ft/lb of torque applied? I was going to try it out by torquing it up and then taking the bolt out, but with the engine split its a bit difficult to get it torqued up.

Cheers
Matt

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

As a point of interest Matty. When you torque up the Flywheel bolt are you doing it with the locking washer on or off..?

Because this will no doubt have an effect on the torque figure. or am I talking bollocks..?

And do people use the lockwasher or do they leave it off.

Si

Edited by Si P on 5th Apr, 2010.

I drill holes in everything..!

I used to use the lock washer until I was advised not to. Now I just use locktite on the threads.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Who told you not to?
I use loctite and a new washer each time

Paul

I seriously doubt it!

I may be talking complete bollocks, but if the crank actually moves up the taper this means that either the crank is being compressed or the female taper in the flywheel is being expanded. Does this seem likely ?

I thought the torque you apply simply increased the pressure on the taper to make it secure.

At the most I would expect a barely measurable movement.

When I am told I AM talking bollocks please explain why.

Was told by Steve Witton many moons ago that the material of the tab washer is softer than both the bolt and the slotted washer that goes in the crank.After some use this can lead to a loss of torque of the retaining bolt then increased risk of fretting or worse between the crank and flywheel .

Is this verto or preverto?

A few people have mentioned it now. It was certainly tight when I went to remove it! l

The flywheel wasn't budging either!



Tadge, thats my thinking aswell, but when people heat the flywheel before putting it on, due to expansion on the hub/taper it would sit further up the taper wouldn't it? Wouldn't appying more torque have a similer effect aswell?

Edited by matty on 5th Apr, 2010.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

well in that case your stuck with a second hand lock washer, unless you rip it off and just use locktite, which i think i would,

as you say matty you could just wind up the bolt harder, but i doubt that you could tighten it enough to get it of as far as if you heated it.

also you should sort your self out a hudraulic puller, pretty easy to make.

The torque applied to the bolt is to pull the flywheel onto the taper. The interference between the flywheel and the crank is what holds the flywheel in palce, and why it takes so much effort to break it free. There will be a certain amount of creap, but not so much that you would take up 1mm axialy.

Its only when you start getting to silly torque that the flywheel starts to move even when it is done up correctly. Adding more torque can increase the tension of the interference, but might yeild the bolt or the threads in the crank. A fail saif to help resist the two parts moving when assembled is some sort of key, which is why we have the key washer. Ultimately it is the interference between the crank and flywheel that transmits the load, NOT the key. A better grade key steel is a good idea though.

I will also go out on a limb and say that lapping in the flywheel is bad, as it creates lots of groves and ridges that resist the parts mating fully. I have done it once, and the taper sufferd fretting in areas right across the taper. I parted another flywheel from an engine built by some one else, and that was the same, so I am confident that its nothing I, or the original builder did, other than lap the parts together with grinding paste.

I am currently waiting on my flywheel centers to return from Turbo Harry after having a bronze bush fitted, hopefuly eliminating this whole fretting problem.

I also do not use the lock washer for the same reasons mentioned above, But, the Verto bolt has the lock washer spot welded to it, and the bolt head is considerably smaller. In this instance, I would use the standard bolt and loctite as a back up

I seriously doubt it!

I thought I had a picture of the taper mod, but I cannot find it and Harry's site looks as though its down at the moment too.

They should be here tomorrow or Wednesday so I'll post a pic then. The idea is that if there was to be any movement for fretting, the softer bronze will be sacrificed rather than damaging what might be an expensive high performance crank.

i believe Carl can offer this (or a similar) service too?

Yes i moved to the darkside

Instagram @jdm_brett

((EDIT, now Four above ^^^ (Sprocket).))

The taper alone is what transmits the drive, just like a morse taper in a lathe or drill chuck.

The bolt is only to set the grip on the taper and the keyplate is to stop the two bits turning as the taper is engaged whilst the bolt is being tightened.

If the taper is engaged right you could take the bolt and keyplate out and run without them.

But back to the original question, there is do direct relationship between torque on the bolt and position up the taper, there are too many variables.

That's why all high integrity bolting is done by extension, not torque.

You could approximate the distance up the taper from the number of turns of the bolt (16TPI I think) but it would only be an approximation as the bolt "stretches" and the keyplate and locktab "compress".

Edited by Rod S on 5th Apr, 2010.

Schrödinger's cat - so which one am I ???

So is the taper of the fly machined out to a larger size?

I seriously doubt it!

I sent some photos of this mod to Sprocket for posting here if wanted...
of course the bush suffers with time as well, but never damages the crank taper or flywheel - I have replacement bushes at hand now...we also regrind damaged crank tapers and fit a bigger bush after that to restore the flywheel position to the correct position...

http://www.minifreunde.at/harry/links/flywheel.htm

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

BTW this season I installed my new selfmade aluminium flywheel without bronze bushing to test if the aluminium dampens the "welding harmonics" enough not to need this bushing...

http://www.minifreunde.at/harry/links/alu_flywheel.htm

Hope it works - could end as an expensive test

Bimmer Twinky headed and turboed A-Series:
http://www.minifreunde.at/harry/projects.htm

May be wrong here but my thinking would be it wouldnt matter if the lock plate is in because the torque value is when the bolts still in the elastic reigon and stretch of the bolt would be after its interfaced the thread, as the shank/thead isnt contacting the washer it wouldnt matter if the washers there because the section of the bolt wont enter the elasic reigon untill other movement has taken place, such as compressing the washer and you wont create the torque required till thats done.
can think it would give a tiny bit more axial resistance on the head of the bolt when tightening though
buuuut...saying that if its what you have been advised and for piece of mind its not alot of hassle to tighten without the washer and repeat propperly

David.

Haha good old halfords ratchets!

I stumbled across this pic the other day and it made me laugh.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi