I think this topic has been discussed ad-nauseum since the beginnings of time, but I'd like to get some input from the guys that build engines for a living. I ended up getting some old forged pistons for my build, and one of them happens to have the top bead blasted. In my novice opinion, this should be fine and dandy; nothing to really worry about. Of course there's arguments either way on if this is good or bad. The kicker here is it was masked off under the ring lands, so the top and all of the ring grooves were blasted, and the skirt was not. I've always heard that doing this was a no-no, and the only part that can/should be blasted is the top only. What say you race gurus?
Tech bulletin from Hastings, the biggest piston ring manufacturer in the US.. https://www.hastingsmfg.com/ServiceTips/enginering_bulletin_cleaning_pis.htm The issue is you must really pay attention to the cleanup, especially down in the ring grooves. If they are clean, it won't be a problem. JW
That's what I figured Jim. Just make sure they're clean and scrub the crap outta them, blasted or not.
Never attempted, always heard that the damaged bottom-of-groove surface compromises sealing. In all cases, any "pro" will have you purchase new parts if there's ANY risk involved. Their name vs. your $$.
My thought is this was done to clean used pistons only. My engine builder had a set of pistons polished to a mirror finish.
My first choice would be to remove the carbon chemically. Purple Power will desolve carbon if you let it soak long enough,or lacquer thinner or carb cleaner or diesel fuel or an ultra sonic cleaner. If I were going to media blast pistons or any internal engine part, I would use fine virgin glass beads. The beads are only round for one pass through the gun, once they make contact with the surface they break and now they have jagged edges. Virgin beads will give you the best finish. I saw aluminum oxide mentioned, that's what I use to blast exhaust manifolds, I would never use that on an internal engine part! If you do fine glass bead blast pistons, I would submerge each piston in a 5 gallon bucket of water and hose out each ring groove while it's submerged. That would be your best shot at removing any remaining media. The question is: what media did they use, was it too course and did it effect the dimensions and finish of the ring groove.
I can't be certain, but I would venture a guess that this particular piston will be just fine and useable. I got the lot of them from a very reputable engine builder here on the board. :TU:
Purple power will etch aluminum since it's high alkaline with ph around 12-13. Don't overdo it! I've tried baking soda for blasting sensitive parts since it breaks down into dust. Doesn't have much cleaning power but works for spark plugs and the inside of carbs. Do it outside, not in a cabinet. Use it once and it's dust! Easy clean up with water. Biggest problem with using glass beads on aluminum is imbedding glass in the alum, which eventually falls out and into your oil. Fresh beads and low pressure will minimize that problem. I bought some fine steel shot but haven't blasted with it yet.
Bead blasting pistons would be my last choice, but , if your stuck on doing it that way use virgin beads, do not recirculate them. Virgin beads have a very low chance of imbedding. Low pressure is a must. I glass bead blast aluminum and stainless chambers for turbines that go 400K RPM every day without a problem. When I do aluminum I hold the gun 8 to 10 inches away from the part and use short blasts. I'll experiment with Purple Power and aluminum foil to see how long it takes to fall apart, you got me curious. I've done aluminum heads with purple power and it always seems to have it's original luster. My first choice on pistons would be mineral spirits. Probably the person who did that one piston had second thoughts after seeing the results which is why he didn't do the rest.
IIRC, if the part is partly in the solution and partly in air, I saw etching at the liquid/air line. If you see foaming, some sort of reaction is taking place. Also sprayed some AFB carb tops, didn't get all the PP out, and had a white crust develop in the check valve passage, making the valve stick. I should do a test on some scrap alum sheet.... damage would be more visible on the shiny smooth surface.
I've never seen crusting with PP. I flush air and water orifices as small as .030 every day and never have a problem, I use 5 gallons a month. You're not rinsing well enough. I've seen crusting with phosphoric acid which I would never use on anything but ferrous metals and my shop floor.
