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**pbf777** · July 20, 2017, 10:05 AM

Originally posted by Wyldie

Cylinder 6 however has a broken ring which has damaged the bore. Just my luck! Anywho hoping someone can tell me what's the maximum I can bore the block to? What are my options?

Unfortunately, the question of what the maximum amount of material, that can be remove to achieve a required bore diameter with in a particular block, and maintaining a reasonable service life, isn't so simple to answer accurately.

I am of the general opinion that the highly educated and therefore well paid engineers were tasked with the responsibility of creating a product (engine block) that would provide acceptable service life, under the environmental conditions in which outlined, and maintaining costs of manufacturing to a minimum. With these parameters in mind, add the fact that the FE engine was of Ford's newly announced "Thin-Wall-Casting" technique, and the understanding that Ford Motor Company wants to sell new vehicles, not have you rebuilding your old one; why would anyone assume that there is any additional, unnecessary material (iron) added, over and above that required to keep the vehicle out of warranty claims and allow the targeted cycle life by the manufacturer?

Does this mean one can't bore a block to an oversize in the rebuilding process, no, it is practiced; but remember, all things practiced, even if it "works", are not always necessarily correct. I believe this allowance is due to the engineers consideration for manufacturing tolerances and given inaccuracies. Such variables exist in the metallurgy, pouring and casting technique, finish machining, etc.; these considerations cause the addition of materials in order to reduce rejections.

I believe the best advice is to always remove the minimal sum of material from the cylinder walls as possible for best results.

In a more direct answer to your question, if the damage (scoring) in the cylinder will not "clean-up" in reasonable honing, then one would advise a repair sleeve installation process.

"Reasonable Honing", well your block has already been bored .050" oversize (what is required for the other cylinders?); I suppose one could explore out to .060" (check for ring availability), but that's where I would draw the line. And I didn't say that such is an acceptable "maximum", it's just often practiced.

Scott.

**simplyconnected** · July 20, 2017, 01:27 PM

We use a sonic test to determine how much wall is left.

It is ideal to remove the minimum diameter of metal from your bores but that's not the only consideration. I had my Y-block bored +.060" because that was the closest size piston that was available at the time.

So the question is, who will stock all pistons in all sizes and how many sets will they keep on hand? The pistons are cast in batches, then the machining is set up in 'production runs'. They make thousands at a time. When a specific size is depleted, the next run may take a while because NONE of this stock is paid for until it is actually sold.

Alright, having said all that hot air, let's get more practical. If you're already +.050" you're at the end of your rope. Ten thousandths more is only FIVE thousandths per side. That's twice the thickness of a human hair; hardly enough to 'clean up' deep scratches.

I would look for a common 390 short block, either from a pickup truck or a car. If it needs a +.030" bore, so be it. There's plenty of casting left. - Dave

**Wyldie** · July 20, 2017, 05:22 PM

All interesting, unfortunately a new block is out of the question. They are not readily available in Australia, they didn't come standard in anything we have.

Looks like I'll take the block to an engine rebuilder, see if I can get number 6 sleeved, see what my options are. If that can't be done then ummm... Might have to concider moving to a 351 small block. But I really want to keep a big block in it

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