[Pav8427]

Back when I used the 'shake-n-bake method, it was my understanding that the shot peen does releive some stress. Although I think itbwas mostly surface stress and help reduce stress by smoothing sharb edges. Haveing ro line hone was due to the shot peening doing just that. Peening the surface. Kind of the same as smacking a piece of steel with a hammer.
Always displaces material. Therdor making line bores smaller.

[mgarblik]

I heat cast iron to 625 degrees F in our oven cleaning process. Then it is blasted with .030" chopped stainless steel wire to remove the scale . The required line hone and block surfacing is due to the peening from the wire blasting process. I have not noticed the line bore/cam bores/deck surface moving from the process with the tools I have available to measure, .0001" resolution. The peening process makes all the holes smaller, that's why a little clean-up hone is required. The cam tunnel and lifter bores just need a tiny clean-up with a ball hone, a couple strokes. The deck needs proper surfacing because so many people like to use Cometic type gaskets that need a super smooth surface to seal.

[Shiny]

The chart I posted shows not much happens below 750F so the lack of common major distortion from heating below that is consistent.

And yes, peening will relieve residual casting stress at just the surface. More importantly, it will create residual compressive stress at the surface and as Pav8427 notes, smooth sharp edges. Both of these will reduce risk for fatigue failure.

[pastry_chef]

Originally Posted by Pav8427

Would be interesting to deck, bore, torque plate hone and line hone a run of the mill block. Record dimensions. Then stress relieve and re-check to see if anything actually moves.

From Joe Mondello.

So, I took an Oldsmobile block that had about 150,000 miles on it and measured everything; then put it on my Stress Relief Engineering Vibratory 62 Load Master 2000 shaker table and gave it a massage for about 2 hours at 100 hertz frequency and guess what I found? It still moved around significantly. The total deck changed .003”; the bores .0025-.0035”; the main line .001”; and cam tunnel .0005”. These measurements show that everything shrunk significantly from prior measurements. This observation blows the theory out the door that older components are stable, maybe more so than new but not quite there yet!

Some engine builders also have the theory that machined green blocks, when assembled and run, will relieve their own stress; especially in the fields of drag, circle, boat, and Bonneville racing. My extensive testing proved time and time again this is simply not true. One of my mottos is “machine it straight, keep it straight – machine it round, keep it round”. Most shops cannot do this using old school technology. The most amazing thing I found is how much I helped the 5 HP Briggs & Stratton flat head Kart engine on Methanol and running on a dirt track. That engine is the most expensively built, unstable one that I’ve ever seen but I shook it and cryogenically froze it fully assembled (less the magneto and rubber seals) using the same material and thickness engine base plate as OE. It includes the side cover and gasket, head and gasket, fasteners and gaskets, all torqued to specs as a final assembly. I shook the assembly first and then put it in the freezer at minus 300°F before bringing it up slowly to + 275°F for the heat treat cycle. After doing so, that engine lasted a full season without a rebuild!

I have built a lot of engines in my “hobby” job of 52 plus years and shaking with freezing have been two remarkable breakthroughs in high performance or even for stock engine building for quality shops. The most remarkable part is the shaking, as it changes sizes. Therefore never shake after the final machine work is done. You can freeze after final machining but in my opinion it is better to do the work after both processes. That way all parts are free of stress and one to two points harder on the Rockwell C-scale.

http://mondello.com/page23.html

[coupeute]

My two cents worth.... Back in the early days of Pro Stock , I remember a rumor that a well known racer would leave his blocks out side in the open for quite some time to stress relive them with the use of the sun in the day and the cooling of night. If this sounds strange, it was also rumored the Bridgeport milling machines that were built in Singapore under license had the best cast iron because they too would leave the casting out in the open for at least a year before machining them.

[Pav8427]

Joe Mondellos tests on blocks is what I was kinda thinkin. That much mass has got to move around a bit.
Most of the discussion has been related to heat and cold.
Being more of a backyard engineer would be interesting to hear what all the book learned engineers think.
A side note. The Meta-Lax relieving we did on the aluminum dorgings sid the trick. No more warpage after machining.
I know forging and casting are different. And they are aluminum. But it is kinda amazing that some controled shaking cured it.
They used to make gauge blocks and gauge pins by leaving them in drums for years to 'normalize'