12 replies to this topic

[govig]

Spent a lot of money on a lightened flywheel and clutch that was supposed to be pre-balanced. The engineer who ground and balanced the crank said it was anything but balanced and I think I know why. A dti on the rear surface of the flywheel shows a 10 thou runout. Is this acceptable considering the £280 price tag? or is it acceptable at all? Have a look at the video..... (click on the pic) What will it be like at 6500 rpm?

Edited by govig, 28 February 2012 - 07:31 PM.

[tiger99]

That is rather poor, but it is just possible that it is not seating well on the taper and needs to be lapped. Possibly as much a crankshaft problem as a flywheel problem, but I suspect that the engineer has already attended to that, leaving the flywheel....,

I assume they machine them on a tapered mandrel, and suspect it was wonky.

For £280, it should go back. You are entitled to something that is fit for purpose.

[ACDodd]

Check the crank tail is true first, then the cover plate mounting points. It is likely these that are the problem rather than anything else.

AC

[govig]

Thanks AC. The crank tail is running out 1.5-2 thou depending where on the taper it's measured. Is this 'normal' ? I'm going to dig out the old verto flywheel this morning and see how true that's running before looking at the new cover and flywheel again.

[govig]

Reduced the runout to half that of yesterday (5 thou) by lapping the clutch centre to the taper. I think that should be OK. The crank had been tuftrided and all the journals had been polished afterwards but not the taper. I don't think tuftriding is very thick but it appears to have stopped the clutch from sitting on the taper properly.

[ACDodd]

If the crank has been hardened that can happen. I have seen this before. 5 thou while not perfect is much better than what you had. I would suspect this is the magnification of the 2 thou at the tail.

AC

[govig]

I would suspect this is the magnification of the 2 thou at the tail

Yes I think it is.

Hindsight is wonderful but if anyone else is going to the expense of having a crank ground, tuftrided and balanced, it might be an idea to check the tail for any distortion first.... At least the MED product has been proven OK.

[jaydee]

Did you send the crank together with the flywheel so they can balance the assembled lot?

[govig]

Yes and the front pulley...

[dklawson]

One additional comment. You need to set your DTI so it is perpendicular to the surface you are measuring. Your picture shows the probe tip at about a 45^o angle to the flywheel. You will not get an accurate measurement until the probe tip is perpendicular.

[govig]

Agreed. A fair point.

Ideally I would have measured this on the furthest position of the flywheel from the centre. Due to the lightening slots and then the taper to the ring gear, this wasn't practical. I did not want to check the runout at the ring gear itself as this is unlikely to be completely concentric to the flywheel so introducing another error (or possibly masking the original one).

I only wanted to see any change thoughout the 360° rather than accurately measure anything as you would when, say, setting the cam timing.

We used to use dti for setting ignition timing on 2 stroke bike engines in the 70s. You could do this via the plug hole (at about 45° to the piston crown) or take the head off and try to get the dti perpendicular to the piston. Whilst the latter is of course better removing the inacuracy caused by the introduced 'triangle' or sliding of the dti tip on the surface, in practice there was little difference.

[Spherix]

_ALWAYS_ balance the crank, it's pulley and the flywheel assembly as one. The flywheel could have been in perfect balance, but if your crank is only a little off, this will affect it.

Nevermind, didn't read last few replies Although, it coming pre-balanced still means nothing.

Edited by Spherix, 02 March 2012 - 10:12 AM.

[govig]

it coming pre-balanced still means nothing.

+1 !