Long story short, I bought a cheap gen III 4.8 with 12k. It looks very clean, but two of the pistons have very light impressions from where the valve appears to have contacted...but just the tip, you can see about 3/4" or so of an imprint.

I'm already pulling the piston/rods off to clean everything; as the damage is very minimal (?) I wasn't planning to replace. Does anybody think this is a terrible plan? It's just a cheap motor to get my project going.

Sadly, I'm pulling it apart..its, overall, very clean on the inside....except where somebody pulled the plugs and a bug filled #7 with dirt, literally...it was so full it wouldn't even turn over. After pulling heads, etc., I vacuumed...but figured I might as well take it a part and do it right, vs wearing it down in 3k.

 

If you are pulling rods and such, do bearings and maybe rings. That is cheap enough. Dirt filled cylinder? Take it in for a (also fairly affordable) hone unless that cyl somehow looks to have no corrosion.

What caused the valves to smack the pistons on such a low mile engine? That usually tells you what else you have to worry about.

After all of that, you might be better looking for a 100K 4.8/5.3 that will still give you another 150K. Bolt in and go. I have just such a thing(5.3) and I only expect to get $400-$500 or so for it once I get off my butt and sell it. These engines are cheap so it's easy for a "light refresh" to exceed the cost of a seasoned, used engine that's ready to run.

Good luck!

 

hmmm something smells fishy here. are you SURE a bug filled an entire cylinder with dirt? i think something else might be going on here. possibly a hydro lock? maybe joe dirt decided to go mudding...

 

I assume it was dirt dobber as there were 4 other 'nests' under the intake. The other 7 cylinders were clean and the motor outside looked like a motor with 12k (as did the rest of the inside). So...teenage mutant ninja turtles may have gone muddin', popped one plug, then sucked the cylinder full of mud. Or bugs....not sure.

Either way...as the motor was bought secondhand, I'm still curious if anybody's run into the valves contacting the piston during semi-normal operation and / or if these light imperfections are enough concern to worry for a beater motor I plan to use until I build something better.

OBviously it's not worth any $$$ so I don't much want to spend much on it as I could replace with a known-good salvage for $500 or so.

So, bother with pistons or not?

 

Post a pic of the piston damage. Pistons usually aren't wear items..rings are. So if the damage is truly just little dings, I'd say run it. But still valves smacking pistons on a 12k 4.8? Odd. Now do the valves on the same cyl show evidence of hitting the piston? Foreign material(or even a piece of a spark plug) dancing around in there can cause similar results.

 

If you are reusing heads you need to replace the valves that contacted the pistons. Even just thee slightest contact can bend the head of the valve. You might not see it with the naked eye but it is a recipe for disaster.

 

^^^

I mean "run the pistons if damage is inconsequential." I agree that you don't want to run with damaged valves. But on a 12K engine how do we get valve contact with no other damage? (other than a dirt dauber) I imagine maybe a massive over-rev but the PCM shouldn't have allowed for that. Accidental downshift into second gear at 100MPH and pop the clutch out?

Perhaps previous owner had some broken valve springs and made repairs and left the slightly scarred pistons? This situation still has my spidey sense tingling a bit.

 

Agree with you Mercier. I would not be too concerned reusing pistons. Just make sure there are no sharp edges that could contribute to detonation.

How do you get contact? Million dollar question.