What actually causes the Flywheel to fret on the tail of the crank?
Turbo Mini Forums

I have been inspecting one of my spare cranks recently, I did not remove it from an engine and do not know its history, however it is perfect in every way including the journals which are standard.

The only issue is the taper which has suffered from some fretting.

What are the main issues that contribute to this damage?

1. high revs pushing the crank and flywheel assembly through the vibration periods listed in TBASE
2. Poor fit, allowing slight movement - factory machining errors/idiot clutch change.
3. an inbalance in something causing fretting at lower revs.

Heres a picture .

Dirt between tapers,
Not lapping them in,
Bad damper on other end,
Loose bolt,
Badly fitting keyed washer,
Idiots........etc

Lots of reasons really

I seriously doubt it!

could have spun and friction welded to the crank and then someone managed to pull the fluwheel off, including doing this damage

Who you calling an idiot?

I seriously doubt it!

IMO (and this really is just an opinion...) as long as the flywheel is on properly in the first place is thould not fret, I always heat my flywheel and fit it, after lapping it, also I torque to way over 150ft lb, 150 on the torque wrench then a big heave on the breaker bar, probally about 200ft lb...

interestingly I read somthing about morse tapers a while back that recomended lubricating them so that the slide together properly,

Good point joe, could just be a dogdy clutch change. I have been slightly concerned that the fatigue life of the item may have been reduced, but I suppose a loose clutch assembly is the main clupret.

I can't believe how difficult its getting to find decent std/std cranks, I've rejected 4 so far to get to this point!

Maybe a bit of a nupty question, but I searched to find out about this lapping of the crank but couldn't find details.

How does one do this lapping?
First take bigger spikes off of crank and flywheel. Then have the crank in vertical position (if it's not in the car), use some fine grinding paste and rotate flywheel on crank till smooth/dull surface appears on the crank?

I found JohnK saying this in 2007:
"I lap the tapers with fine paste, then clean off with thinners, repeat until all contact area is grey. I use EN24 keyed washer and bolt. Then small dab of thread lock on bolt and a tiny smear of oil under the head of the bolt - then torque up without lock tab to 170/180 lb/ft."

Is this currently still the way to do this?

Dazed and Confused....

yep thats what I do,

lap it on with fine grinding paste till its all grey, after running round the edges where the key sits with a deedle file to remove any dinks from badly fitted keys... ie the wrong way...

Edited by Joe C on 22nd Apr, 2012.

Clear, cheers Joe

Dazed and Confused....

Another engine another damaged crank, this time from a 39k automatic.

Bollocks to it I think when the time comes I'll whack a billet one in there, I can't be bothered to keep messing about.

Fuck it, itl be fine to use that.


rick

Edited by minimole23 on 1st Jun, 2012.

a billet crank will be no different to the above is it is subjected to poor fiting /poor balancing/ poor damping


carl

On 1st Jun, 2012 minimole23 said:
Another engine another damaged crank, this time from a 39k automatic.

Bollocks to it I think when the time comes I'll whack a billet one in there, I can't be bothered to keep messing about.

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

a billet crank will be no different to the above is it is subjected to poor fiting /poor balancing/ poor damping


carl

On 1st Jun, 2012 minimole23 said:
Another engine another damaged crank, this time from a 39k automatic.

Bollocks to it I think when the time comes I'll whack a billet one in there, I can't be bothered to keep messing about.

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

yep, in fact Ive heard billets can be worse due to the different material, probably bollocks though.

Perhaps you need one of these? http://www.minifreunde.at/harry/links/flywheel.htm but you may have to have it re bushed at some point as its the bronze that takes the damage, rather than your super duper expensive modified crank.

Would I be right in saying the problem is more common on vertos than old flywheels ?

Should they be installed totally clean/dry ? or with some slight lubricant ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

I never over torque, especially with the steel flgwheels as they have a habit of sticking on.

Interestingly, someone mentioned that solid mounted engines are not good for fretting.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

With experience of fretting of aluminium centrifugal impellors with a parallel bore on steel shafts, it would appear that it is all down to the torsional vibration or rotating balance.

as pointed out above i thought its caused buy a miss match in grinding at the production stage of both flywheel and crank and as a result any vibrations make the two work on each other and more or less weld together.?.?