Why V8 bores crack,,,

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Originally Posted by bgkdavis

It could be indicative that the block wasn't very well aligned with the machine and one side of the bore wall was thinner etc, but this kind of thing is expected with machined castings, and generally these kinds of miss-alignments look a lot worst than they actually are, the scallops are nicely rounded and there is little visible step on the other side.

Someone else may point out that their bore cracked at the point where it was thinnest, but of course it would, the question to be answered is what was the designed minimum wall thickness, did the failed block exceed this, and was the design thickness adequate for normal use.

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I reckon the answer to all your questions is NO....
[wink11]


and really the proof is out there,,

with a 96 thermo and rotten casting is it any wonder every single 4L V8 in the world has failed??

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Originally Posted by Pedro_The_Swift

Ron,, if you paid some guy to rebuild an engine and he WELDED a crack up in the bore and he USED that block for anything other than a coffee table.... :oops2::oops2::oops2:

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I think you're grossly underestimating the power of proper consumable selection, correct welding procedure, and the skills of a suitably trained boilermaker.
Yeah, it's not ideal, but then again, it can and does get done all the time - particularly so in the harder-to-source parts, or pressing deadlines.

Core shift is a real problem wth castings, this is where the sand mould is slightly offset when casting occurs.
I've seen it in engine blocks, I've seen it badly in brake discs, and becomes a problem when things are machined, wall thicknesses can be all over the place.
Old Holden 6 blocks were notorius for it, 300Tdi's are known for it (most have blown up by now!)
Serious race engine builders used to measure block wall thicknesses to make sure they weren't wasting their time before machining.

Wall thickness variations becomes an issue when you are pumping serious torque through an engine, but a FWIW, one of the most famous Formula Ford engines of all time was one called 'Patch' by Minister Engines in the UK.
It won numerous Formula Ford festivals in the eighties, it was their factory engine that was loaned out to gun drivers.
It was a block that a customer's engine had put a leg out of bed, so they sold him a new engine, patched and sleeved the block and use it as a test bed.
The old Kent engine is cast iron, but it shows a repair isn't always a potential issue.

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Originally Posted by Pedro_The_Swift

I reckon the answer to all your questions is NO....

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That would make it a design problem not a machining problem, and the picture showing scallops on a perfectly machined block are pretty pointless.

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Originally Posted by bgkdavis

That would make it a design problem not a machining problem, and the picture showing scallops on a perfectly machined block are pretty pointless.

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All I was trying to show,, is the shift in casting,, [wink11][smilebigeye]
I would hope the machining was perfect, cos the casting was really bad..

I would say that is a manufacturing issue not a design issue - also that machining is not related to the cracked block issue reported with these blocks which is around where the liner seats at the bottom - the cracks are not completely through the block itself but are around the liners.

Here is a pic of my 4.0 block - no issues with it or extra machining like in the OP pic so my take is that the one in the first pic not the norm.


Attachment 134711

very nice Garry,,:cool:

the variation between yours and the other is scarey though,,,