12 replies to this topic

[R1minimagic]

Posting on behalf of my brother.

We stripped his 1380 down at the weekend to find some corrosion/pitting on the crank tail where the flywheel sits.

It isn't mega bad (not sure how this has happened as it wasn't like that when it was built but the car has been sitting unused for about 7 years!), there are 2 small lines of corrosion/pitting on each side about 2mm wide, approx 1" long about 1.5" in from the end of the tail in a radial direction.

He spent a lot of money at MED getting this crank lightened, balanced, cross drilled, bladed etc etc so would rather not throw it in the bin if it can be saved!!

I will post pics later this week, but looking for some advice about whether it is possible to repair crank tails before we go to MED with it on Thursday

Cheers

[Cooperman]

You could try to lap the flywheel on using 'fine' grinding paste. If you get a reasonable seating area it should be fine. If not, then the crank could possibly be metal sprayed and ground back to the original taper although that would be expensive. On ships they metal spray cranks and that's for the big-ends which are rotationg not static. However the revs are very low.
Talk to a metal spraying expert if necessary.

[R1minimagic]

He never had any running issues with the crank so we could give that a go, i would say 95% of the seated area is ok so we may get away with it?

[Cooperman]

He never had any running issues with the crank so we could give that a go, i would say 95% of the seated area is ok so we may get away with it?

It should be fine with a good lapping-in. I've seen them with a lot of pitting and they have always been OK so long as the lapping is done thoroughly.

[R1minimagic]

Can you recommend a paste to use?

[Cooperman]

Just use a standard 'fine grade' valve grinding/lapping-in paste. You will see when it's done enough as you'll have a nice matt grey finish all round the tail and the same on the inside of the flywheel mating surface. With the damage keep lapping until you have at least 75% to 80% matt surface. Wash it thoroughly with brake & clutch cleaner (sorry to state the obvious, but others may want to do the same thing.
If anyone is doing this after a clutch change, don't do the lapping with the primary gear in situ as if the paste gets under the primary gear bushes it's hasta-la-vista primary gear bushes. Take the primary gear and red seal out, lap the flywheel, clean back, then fit a new red seal.

[Spitz]

How do you do the lapping...
Just place paste on the crank tail and slide the flywheel on and rotate one way....or back and forth?

Thanks

[Ethel]

I'd go for back and forth around where the fly 'n crank mate up when assembled

[dklawson]

Lap back and forth... and like doing valves, pull the flywheel "back" every now and then to redistribute the paste. Lap only as long as necessary to get the 80% or so matte finish that Cooperman mentioned. And before lapping, if there are any high-spots on the crank tail. carefully target them with a fine tooth flat file to just remove them (and avoid the surrounding area).

[R1minimagic]

Went to MED yesterday, crank tail should be ok, but ended up spending another £2500 on engine parts!!!

[bmcecosse]

Metal spraying would last about 2 minutes.....just lap it.

[dklawson]

Why is that Roy? Have you had the process done on a crank and experienced a failure?

[tiger99]

Perhaps he is thinking of the "wrong" type of metal spraying, with the gas or plasma gun, which you might use to spray zinc or ali as a coating? The more structural type of metal spraying, as you can use on a crankshaft to restore seriously worn bearing journals, is a close relation of submerged arc welding and should be more than adequate for the taper. But it is not cheap.