What's up, all. I've always heard that putting new heads on a used engine would cause it to mess up sooner or later. Is this an old wives tale or no? TIA for any help.

Never heard that one, or had a bad experience doing it. Short block will wear on out sooner or later. That isn't to be unexpected.

That is an OWT !

But if the short-block is worn-out ...and the heads are high-$$ .. that is kind of a waste.

i swear my old wife never said that, and trust me, the 'tail' is long gone!

old wife ? ... and no-tail ? ... ...

if your old wife see,s this ...no tail for you... hahahahaha dan

Never had a problem with any. Heard that years ago.
Last one I did block had over 280,000 miles on it.

Hot new heads make you want to beat on an engine
If the short block was marginal, you'll hasten its demise by beating on it (old heads or new).

If the short block was solid, it should live just fine.

My 75k mile OE short block is living fine at this point with a fresh set of ported Magnum heads, but I'm only around 3000 miles on the combo... you'll have to check back with me!

I used to think it was BS until I saw it happen.

My dad had a 1980 Crew Cab dually with a 360. This was 2003-2004 or so and it only had 70K miles on it, it had a fair sized cam in it and doug thorley headers. It had been used alot as a tow vehicle and it picked up a miss and it turned out to be a bad exhaust valve. Well I tore it down and he had the heads redone. I put it all back together and fired it up. I warmed it up and shut it down, I had some things to take care of on it so I retightened some things and tried to fire it back up. It cranked like it had no compression and would barelly try to fire. Kind of stumped I called it a day. Well my dad messes with it and figures out it will start if you put oil in the cylinders and it will kind of run...run like it doesn't have any compression. Soooooo it can happen even if you think it is BS lol.

Sounds like the rocker arms are not adjusted correctly, or the maybe the valve job wasn't done right and the valves aren't touching the valve seats all the way.

Thanks for all the replies!

I put a set of aftermarket heads onto an old 440 bottom end that I did an el cheapo hone'n're-ring job one. It ran great after I was done!

There is a bit of truth to the story. If the engine is wore out enough to need new heads then the rest of it is probably on it's way out too.

If you ONLY fix the heads why would it surprise anyone the rest of the worn out engine gives up the ghost not too much later?

Common sense.

My understanding is that if there were no defects in manufacturing, the engine parts usually wear at the same rate. A high mile engine that uses oil and smokes does so because ALL parts are worn. Bolt on fresh heads that seal better and the stressed piston rings are under a greater load and the oil burning actually can increase.
I had a 360,000 mile 305 in a Chevy truck that still ran great and passed CALIFORNIA smog, but 2 exhaust manifold bolts broke off flush to the head causing an annoying leak. I had a pair of 350 heads freshly rebuilt for another project, so I swapped them over since I needed to keep this daily driver operational and smog compliant. The motor actually LOST power with the new heads and the motor spun 3 rod bearings 10,000 miles later. I should have just rebuilt the whole motor instead of replacing the heads, but I only had a weekend to make the changes. Still, 370,000 miles from ANY gas engine is impressive.