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229 - Engine run in - metal fatigue

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Hi,

I just have a question in regards to using a used block with a full rebuild. Over the lifetime of an engine the cylinder block sees numerous heat cycles which cause metal fatigue.

Do you see issues with using high km engine blocks for builds? I just thought with the amount of heat cycles, the engine block would have alot of stress and fatigue.

Cheers

Why do you think numerous heat cycles cause metal fatigue? I think metal fatigue is purely a function of stress (i.e. loadings). Normal engine operating heat cycles are not going to by themselves induce any stress/strain.

I have raced in a class where the engine blocks were manufactured more than 50 years ago. We still re-build them every year or so, and the blocks & heads are not the problem...

Two schools of though on this.

One is that the thermal and mechanical stresses will remove any residual stress from the original casting and maching.

The second is that the same stresses will potentially cause any casting, or machining, flaws to develop fatigue cracks.

I'm inclined towards the latter as I've seen quite a few heads that cracked and a couple of blocks. Some engines are more prone to problems than others, as they are designed and cast differently.

I would suggest you do a google search for problems with the particular engine you have in mind - on-line forums and clubs for the vehicle is a good place to get some feedback on this.

Failing that, carefully inspect the common problem areas - for the head carefully check the areas around the valve seats, for the block the deck around the cylinder head bolt holes, between the bores and around the main bearing supports where they meet the block, and anywhere else you suspect there may be a problem. If you have the money, you can get them crack and/or pressure tested for a reasonable fee before any machine work is done, for peace of mind - but a careful visual check will usually suffice.

Regarding crack testing, I always get the crank and rods checked and I would recommend pistons also be done, if re-using them.