Old piston rings, new valve seats?

Blame it on the "Unfair Advantage" (book)

Mark Dohonue mentions early on in his book that he had his valve seats ground on his Corvette's heads and installed them back on a block that had been running a while. He said that in doing this he accidentally stumbled upon a bit of a "secret" where you run the block as long as possible (to get the molecules "friendly") but install new heads and the result is you end up freeing up some extra ponies.

The backyard beer drinkers always recommended I refresh the bottom end whenever the top was done because "the dad-gum compression will just blow by the rings".

meh, the idea of compression all of a sudden "blowing by the rings" never sounded right to me.

I figured I'd ask the collective since I have the opportunity to do a three-angle job on my Alfa's heads while I'm having the guide seals checked etc. I really do not want to get into the bottom end (I'm dealing with enough "project creep" as it is).

Thanks! -Bill

How do the bores look? If you've got the motor out I'd at least reseal it and roll in fresh bearings.

Hungary Bill wrote: meh, the idea of compression all of a sudden "blowing by the rings" never sounded right to me.

Interesting.

I recently slapped a different head with freshly lapped valves and smaller combustion chambers on my indeterminate mileage Ford and now the crankcase vapors smell worse than it did with the old head and there is oily residue around the valve cover breather that wasn't there before.

There might be something to it afterall

older engines do tend to have worn rings( read as low tension) and worn bearings ( loose bearing tolerences)... so the basic theory is sound.

these days racers dont depend on worn out parts... but parts designed to deliver more power by "taking" less.

a fresh head is still a fresh head... btw if you want to bring it down Id be happy to see if it can use a porters touch...

I did that on an AMC 327.

Ended up replacing the rings later.

Miles on the block/rings is a factor here.

I come from the school of thought of if your already in this deep you might as well.

I did just the top end on a 240SX engine. I ended up taking it back apart because now I had blowby past the rings

Freshening a head isn't going to magically make your rings suck. More likely, the rings sucked before, but now you're overly critical of it because you just put on fancy new parts and didn't address something else that was trashed in your motor.

Interesting. I didn't expect so much "truth" in the "backyard mechanic lore" but the way "swank force" said it makes sense :)

Oldskewl: You may have a PM soon.

Fidelity: man, that train of thought got me in THIS deep. If I keep going, I'm going to have the newest 1985 Alfa the world has ever seen! (not to mention, I'll go broke)

Here's my anecdotal data point:

In november, put a fresh head with some port work and a few other tricks done on a damn near totally blown and heavily damaged bottom end with 220k miles on it.

The power gain was obscene. Easily 40-50whp gains at same boost level over the old worn out head. No weird smells or behaviors that weren't there before. Just lots and lots of tire ripping power.

Was the bottom end trashed? Yep. Before and after the new head.

I'd leave the bottom end alone and maybe tackle it another time at your leisure. Projects cars are more fun when they come to a drive-able conclusion in your life time.

Unless it is a particularly rare block I'd give the head a chance, see how it goes, and build a different block to swap in later. The cost of an extra head gasket isn't a lot for the ability to spread out the costs of the whole works, and you could probably drive it while you block work gets done.

I've bought way too many cars where the owner started to fix something minor, decided to do more while they were in there, then never finished the project because they ran out of time, money, or skill.

In reply to Hungary Bill:

I think in Mark Dohonue's case, the Corvette wasn't terribly old at the time, or high mileage. It was used as a Corvette was intended, so the miles on it probably weren't putting around. The rings would have been fully seated, but probably not worn down. The valves & seats probably had a harder life in that motor, that's why the fresh heads would have made such an improvement.

Your Alfa probably has more miles on it. Did you pull the engine, or are you just pulling the head? Either way, like Kenny said take a look at the bores when the head it off. If there's a giant ridge at the top of the cylinder, I'd plan to refresh the bottom end. If you can still see the cross hatching in the cylinder walls roll with the fresh head and see how it runs.

Swank Force One wrote: Freshening a head isn't going to magically make your rings suck.

While this is true, I think that putting a new head on a block that is in marginal or poor condition can exasperate its problems.

Here's my experience: had an engine that used oil at a rate of ~1qt / 1000mi. I installed a new head (bigger valves, new seals, milled for increased compression) and the oil consumption went up. Way up. Like ~1qt / gas fill-up!

Root cause was stuck oil control rings (found during winter rebuild of the bottom end).

Certainly the new head didn't cause the rings in my engine to fail, it really made the symptom (oil consumption) much worse.

-- Pete

How much swarf are you going to drop down around the pistons, causing them to score themselves and the cylinder walls a bit? I think that's a far bigger factor than "blowing by the rings"

Edit: The aging cylinder block situation was probably true back in the olden days with coarser cylinder wall finishes and crude rings.

I think you're probably right, as he did mention the molecules "getting friendly". In the rotary world we call that "building compression".

I'm with AMG on this one. I'll drop the heads off (since they're out and need checking anyways) and have the bottom end done when convenient. This way I actually get to drive the car in this lifetime.