7 replies to this topic

[JimmyB]

Hi guys,

I have a couple of 1275 cranks that have some damage on the tails/flywheel taper area. I am wondering if I will be able to save either of them with a tail regrind. The crank I use will be subjected to 7krpm and 100hp max. More likely 6.5k-6.8k and 95hp.

This first pic is of an older pre A+ crank that has been ground 10/10. Notice the pitted surface, this is also on the other end where the timing gear slides on (not pictured)
 1275 crank ground.jpg   45.79K   29 downloads

These pics are of an MG metro crank that I would very much like to be able to use if I can. damage to taper and to the flywheel bolt keyway (circled)
 Metro crank1.jpg   84.53K   32 downloads
 Metro crank2.jpg   114.11K   25 downloads
 Metro crank3.jpg   102.24K   23 downloads

Any advice you can give me would be very much appreciated.

[JimmyB]

Hi guys,

I have a couple of 1275 cranks that have some damage on the tails/flywheel taper area. I am wondering if I will be able to save either of them with a tail regrind. The crank I use will be subjected to 7krpm and 100hp max. More likely 6.5k-6.8k and 95hp.

This first pic is of an older pre A+ crank that has been ground 10/10. Notice the pitted surface, this is also on the other end where the timing gear slides on (not pictured)
 1275 crank ground.jpg   45.79K   29 downloads

These pics are of an MG metro crank that I would very much like to be able to use if I can. damage to taper and to the flywheel bolt keyway (circled)
 Metro crank1.jpg   84.53K   32 downloads
 Metro crank2.jpg   114.11K   25 downloads
 Metro crank3.jpg   102.24K   23 downloads

Any advice you can give me would be very much appreciated.

[mayhem13]

I would try and file the end flat and or weld and file and weld and file till you are happy with it. Use a new key washer and give it a go. I have used grinding paiste on the end of mine when the clutch and flywheel got loose and made a bit on mess of it. Worked ok for me.

[JimmyB]

Thanks, I might get the metro crank tail ground and see what it comes out like. I might carefully file the keyway to get rid of the burrs making sure not to take off too much as the key plate needs to be a tight fit. Anyone else have any ideas on this?

James

[Cooperman]

I don't think you can re-grind the tail as it would then put the flywheel in closer to the transfer case and that would be seriously bad.
However, the tail taper is not absolutey critical in terms of surface finish. Clean the tail up with some emory cloth, then 'lap' the flywheel onto the tail using fine valve grinding paste until you have a good mating surfacer on each part, fit and torque-up accurately using a bit of Loctite on the flywheel bolt.

[dklawson]

The pitted crank will not be useful for the power level you are talking about.

The Metro crank does not look like a problem at all. Use a fine flat file to selectively remove the high spots. Mark all the filed areas with a permanent marker or layout fluid, then lap the flywheel as Cooperman said. The object is to develop that "satin grey" lapped appearance on about 80-90% of the surface, particularly right up to the areas you file down. If the permanent marker (layout fluid) remains in the areas you filed, that is "OK" and indicates those spots are now "low" and won't prevent the taper from seating. If the filed areas immediately lose their permanent marker spots, that indicates they are still "high" and you need to work them down a bit more.

I can say from first hand experience that you do not want to grind the crank tail or remove too much from it. As Cooperman said, removing material from the tail moves the flywheel towards the transfer housing. I believe the ratio is 7:1 so 0.001" off the taper diameter will move the flywheel 0.007" towards the transfer housing.

[tiger99]

It suddenly occurred to me wht so many people are having problems with their clutch and needing to lengthen the slave cylinder pushrod. It may be partly due to the flywheel stretching and creeping up the taper each time it is refitted, helped by over-enthusiastic lapping.

But to return to the topic of this thread, I totally agree that getting rid of burrs and protrusions, and a reasonable amount of lapping, will see the second crankshaft fit for use. A few pits and gouges are neither here nor there, if all they are doing is losing a small amount of contact area, but burrs obviously would be unacceptable as they would prevent it seating.

The drive dog is not loaded in normal conditions, and as long as the slot is mostly intact it will not be a problem. The drive torque should be taken only by the tight fit of the taper.

It will benefit from torquing up and leaving for a while (cup of tea), loosening half a turn or so and retorquing. Repeat a few times, then finally do up the locktab.

[JimmyB]

Thanks for all the advice guys, I will use the metro crank and tidy up and lap it to the flywheel. I am collecting funds for a build at the moment and will start a build thread when things get into full swing

Thanks again

James