weak crank query

[matty1275]

Keep hearing about weak cranks and snapped cranks on early 4.2ajp's.
but which exactly are the worry ones?

Surely if a crank has an inherent flaw, it should have snapped within the 15 years plus it has been running so far?

mines a 97 with 44k on the clock, so should I be worried?

[Jubag]

No.

[waveydavey1000]

Been doing a bit of research on this as mine is 96 4.2 with 35k on the clock. It seems there has been a few of these let go but there is no real uniformity of when, in mileage terms.
But there are still alot on the road that haven't let go.

Trackdays seem to be the worst culprit, or a degree of overrevving, ie 7k in every gear everytime

Given that these cars are getting on for 20 years old, I drive mine "enthusiastically" yet with "mechanical sympathy" and its plenty quick enough.
I realise I've probably just opened a can of worms!

[Jhonno]

Mine is a '96 and has had a rebuild due to a snapped crank in 2009 iirc.

[Steve_T]

This is a fatigue failure, so just because it hasn't gone so far does not mean that it won't let go in the future. Unfortunately, it just doesn't work that way.
You can't measure how much of the life of a crank has been used up so far through good or ill treatment, but it's spot on that blasting it to 7k+ rpm repeatedly will use up what is there faster. All that said, if you treat your car with some respect and your engine may well have a long life ahead of it.

[Jhonno]

As it a fatigue? Not a defect failure..? Mine went at 40k iirc.

[Brummmie]

I bought mine at 48K, with a snapped crank, late 97 4.2 model.

[matty1275]

I tend to drive with mechanical sympathy, so fingers crossed!

[Steve_T]

Jhonno said:

As it a fatigue? Not a defect failure..? Mine went at 40k iirc.

I think it is fatigue failure rather than a manufacturing defect since to fix the problem the journal size on the cranks went up from 2.3" to 2.5". However I don't know what happened in your case or the others so I'm happy to be corrected.

[Byker28i]

I have a 97 4.2, still ok. The original clutch has just gone at 55K miles so I'm hoping the engines ok...