To bore or not to bore?

[JQ-72]

My normal machine shop guy retired after several years and I’ve taken a block and heads to another shop. He measured the cylinders and said the worst one had .010 wear and almost insisted that the block needed to be bored. It is a stock 1972 350 truck motor. The engine will be built back to stock specs and will only be driven occasionally. Can I get by with a re-ring kit or should I get it bored? Thanks for any help.

[Willshook]

Stock would be cast pistons, typically fit .001 +0/-.0005, so yes - the block needs to be bored. No question.

Otherwise the piston will rock in the bore with all the Bad Things that come from that.

Why just the block and heads?

A half-assed “overhaul” is a waste of time and money.

[Dead Parrot]

I would get a 2nd opinion from a different shop. First person may be honest. Or maybe really needs money so he can buy his kid a GI-Joe with the Kung Fu Grip.

Unless your "occasional drives" are screaming runs down a track strip, probably could get by with a good hone job, new rings and put it back together. Optimal, no. Much less costly, yes. Since you have the heads off, might as well get a valve job and new valve seals.

An old repair book I have mentions that "most shops" have equipment that can resize pistons to better fit slightly worn cylinders. Don't know if such equipment or anyone that can use it still exists. Book is from the 60's. It does mention that if the rings are worn, the piston pins are also probably worn. Replace both.

[Willshook]

Originally Posted by Dead Parrot

…have equipment that can resize pistons to better fit slightly worn cylinders.

The book is likely referring to knurling pistons just like valve guides can be knurled. It’s a short-term hack at best, and won’t address a .010 gap regardless.

[Accelo]

The truth is it ran before and will run again without boring.
Machinists love to have everything perfect. Reduces their liability.
Remember, the last guy to touch it gets blamed for everything.
10 thousand is typical of a well-taken care of motor with 100K.
Of course, you will have to remove the ridge at the top.

With all the work required to take the motor apart and clean everything, it makes sense to bore it. But you need to do what works best for you.
Cheers

[JQ-72]

Thanks for the input. I took block, heads, intake, valve covers, timing cover and oil pan. Definitely getting the heads reworked, but was going to get the other parts vatted for cleaning. The engine will be built back to stock specs and put in a restored 72 Super that will only get driven occasionally. Just didn’t want to spend the extra money if it wasn’t necessary.

[Willshook]

...

[Joyridin]

Will it run? Probably. Will it burn oil, lose compression and horsepower? Probably, but it will run.

The question I have is why you tore it apart in the first place? It probably ran fine the way it was. The old rings and pistons were probably shaped closer to the roundness of the bore.

[JQ-72]

Engine was running before I tore it down but had a noticeable miss. Ended up being a worn lobe on the camshaft. Since it was an original greasy motor, I figured the heads needed to be refurbished and would give it a re-ring since I had it apart.

[truckdude239]

id bore it 20 over and be done with it have a good engine and dont have to worry about oil usage and low mcompression

[Dead Parrot]

Originally Posted by Willshook

The book is likely referring to knurling pistons just like valve guides can be knurled. It’s a short-term hack at best, and won’t address a .010 gap regardless.

Probably. Didn't go in to specifics. It did 2nd that a .010 wear was the max the technique could do. It is similar in concept to a Haynes book. A real shade tree mechanic gave it to me when I was a kid after I showed some interest in what he was doing to one of my dad's cars. It was very useful before the Internet became a thing.

OP - based running before disassembly and bad cam lobe, I stick with my hone, re-ring, new cam and lifters and run plan. If you only plan on a couple thousand miles or less per year, probably good for a couple decades. If the bearings are still decent and you kept track of which came from where, might even be able to reuse those. Plus, if your finances ever gift you with extra funds, you will have a project motor where you know much of the history.

Again, not optimal but not every repair has to be a complete overhaul to new specs.