14 replies to this topic

[bmcecosse]

Can a damaged crank tail be repaired? Is it possible to lightly taper grind it - thus moving the flywheel slightly in towards the block ?

[Dave33]

I suppose it depends on the extent of the damage,if its got a few burrs the you should be able to remove them.
If theres anything more serious than this i would have thought not.
any chance of a picture or better description of actual damage?
Dave

[nickcooper]

i wounldnt have thought so,
because if you do that it means each conrod wont be correctly lined up for the pistons, could cause damage to the bore and rings?
lol dont quote me tho,
ive just got a re-con crank from minisport.com they do a re-ground one with all new bearings and thrust washers, think i payed £160 after the surcharge which i dont think is to bad, and its very well balanced. itll be going in tommorow
hope this helps nick

[mini13]

What!

Ecosse, Surely in your massive experience of doing everything and telling everyone about it you surely know the answer to this!?

what you need to do is remove the block from the gearbox, preferably leaving the gearbox in the car, then carry the assembled block 20 miles to the nearest machine shop, get them to regrind the taper with an angle grinder....



Seriously though the main problem as you mention is the fact the flywheel moves toward the block, IIRC it moves 7 thou for every thou removed, so its quickly going to cause a problem, it must be possible but its not gong to be easy/ cheap, unless its something special crank wise I'd say jut get another crank.

[nickcooper]

ignore my last reply i didnt read the question properly lol, just regrinding the taper wouldnt affect the bore or anything because it wouldnt move the rest of the shaft,
my appologies,

i still dont think i would do it tho, i suppose you could always try

nick

[bmcecosse]

Ho ho ho 13 très amusant So - at 7 thou per thou of taper grinding - do you think the flywheel could afford to move in 70 thou ? I can't see why not myself. Has anyone had the taper reground ? Equally - has anyone had a crank refused for exchange because of a damaged taper ?

[Cooperman]

You could get the crankshaft tail metal-sprayed. The metal-spraying technology is really good these day. The only question is whether it's better to get another crank as one with a worn tailshaft is hardly likely to be 'in its prime' in other areas.
I recently picked up an A+ 1275 crank, standard/standard with excellent journals and no damage to the tail for £60. Taper grinding is likely to ast at least that with the setting-up time costed in.
Of course, if it's a Cooper 'S' EN40B nitrided crank it's a different matter.

[Guess-Works.com]

Think cooperman has hit the nail on the head, it depends how valuable the crank is, yes removing metal from the tail will bring the flywheel/clutch closer to the transfer case and ultimately the starter motor, depending upon the type of clutch being used, I don't think there's an issue with clearance of the flywheel, but maybe when the clutch is depressed as the moving part of either clutch will get ever closer to the transfer case and retaining bolts.

You may however wish to contact MRA-Minis who is making new flywheel centres and therefore without too much hassle could machine a taper in one a little 'tighter' therefore compensating for any movement of the taper...

and yes, I've had a crankshaft refused as an exchange because of a damaged tail, in fact unless the tail is mint, expect it not to be exchanged... think of it this way, if you went in with you minter crank which just needed a grind as an exchange and then received a crank with a less than mint tail back you'd be a little *drunk*... So if the crank tail is not as good as you would expect to receive, then expect it to be refused as an exchange.

Edited by Guess-Works.com, 25 June 2010 - 04:53 PM.

[Shifty]

I may have just imagined this.....

But I recall seeing some "Tail section" parts, ie a new taper that can be fitted to a turned down crank end?

(Morspeed??)

[Cooperman]

I may have just imagined this.....

But I recall seeing some "Tail section" parts, ie a new taper that can be fitted to a turned down crank end?

(Morspeed??)

That might be a bit suspect for a higher performance engine. The machining to take a replacement tapered 'sleeve' would mean that the crank was machined down quite a bit right at the point of maximum bending stress where the flywheel acts on the crank. If you can remember the old 997 cranks which used to break when revved hard until replaced by the ones with the bigger tail on the 998 (and the 850 in fact). The sleeve would need to be, say, 0.070" wall thickness, which would be taking 0.140" off the tail nominal diameter. Not to be encouraged, maybe.
"It don't 'arf make a mess when the end of the crank snaps off at 6000 rpm".

[dklawson]

As stated above, minor pitting and galling can be removed by careful selective work with a file and stones. Once the highest high spots are removed the flywheel can be lapped onto the crank tail to restore a good fit. However, Roy is quite right that the 7:1 taper will move the flywheel WAY up on the crank taper. Before you know it (if you aren't careful) the ring gear will come into contact on the flywheel housing.

I had this happen on an old two-piece flywheel where the hub and crank tail were damaged. It is/was a Cooper-S crank so I didn't want to replace it if I could find a better way. After lapping the parts the flywheel was too far up on the taper. I found a friend who had a used flywheel hub in much better shape than mine and it allowed me to use my crank again. I have considered that if I have to do this again I will investigate the flame sprayers in the area to see who can restore some of the crank tail's diameter.

[bmcecosse]

Thanks all - it was just an 'exercise' to sound out opinions. Having use 'metal spraying' in the past - and found it to be completely useless - I won't be going that route! I do have a crank that is slightly damaged on the tail due to fretting. I would use it - after lapping it in - was just wondering about trying to exchange it - or have it reground and use it! In the past - I will admit to 'exchanging' two broken cranks at BMC garages.. Just made sure the old crank was very dirty and well wrapped up in filthy brown paper - to keep it together long enough to let us out the door........ We helpfully removed the new crank from the box - and carefully fitted the old crank back into the exchange box - to save the counter lad getting his hands dirty you see........The first time - he then just turned round and dropped the box on the concrete floor behind him..... Didn't feel so bad after that - wasn't broken when we gave you it over the counter...!! And - didn't use my local BMC garage for this trick either!

Edited by bmcecosse, 25 June 2010 - 09:16 PM.

[Ivor Badger]

I have used the metal spraying technique and it failed miserably. We then tried a metal welding technique which the local bodging company used to reface rollers for a printing works, that was even worse when the taper bit fell off the crank.

Lapping in has always worked for a road engine.

As far as returning broken cranks. The best method was to weld them back together and then exchange them at a dealer some distance from your home.

[pogie]

An issue that has not been mentioned is that after grinding the crank, the flywheel can move far enough up the taper that it could come into contact with the primary gear "C" washer and you will lose your primary gear end float.

This happened when I built my MED engine kit and found I could not select any gears when I first tried to move the car under its own power and the solution was to send the flywheel back to MED where they machined 10thou off the recess where the C washer and primary gear thrust washer sit. On chatting to MED they said it was not uncommon for this to happen when aftermarket flywheels were used with modified / referb-ed cranks.

Edited by pogie, 28 June 2010 - 07:32 AM.

[Sprocket]

i would be more worried about the flywheel nipping up the c washer and primary gear before the ring gear or flywheel contacts the transfer housing

Edit, Doh! never read the full post lol

Edited by Sprocket, 28 June 2010 - 09:04 PM.