IIRC, my original ring gaps (at least top and 2nd and likely oil too) were around 0.040-0.050" on the 64 Dart motor with cast 3.46" overbore pistons (1993 assembly). This motor made some power (14.30 @ 95 MPH in a 3000 lb car in the 1/4) and was not touched until a rering at 50k miles in 2006.

Personally, I would not run less than 0.025" in your application, and might go up to 0.040". My feeling is that any loss you get through those (still) tiny gaps at mid-high RPM will be very small, and will be greatly offset by the durability/insurance you get by running a bigger gap.

Happy building,

Lou

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Home of Slant6-powered fun machines since 1988

Cast pistons don't usually have enough material in them to allow removing more than about 8-10 grams at the max. So there is no point in attempting to do it, you'll just compromise the strength of piston.

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There's no such thing as too much cam....only not enough engine!

I have a horrendously mismatched set of new .030's out in the shop. Bought it off a member here along with a set of .040's.

Let me know how much your piston weighs. If I have a match, I'll trade you new for new.

CJ

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Part of Tyrde-Browne Racing

I also have a bunch of mis-matched used .030s
Post a few more details and photos so we can get a good idea of what to look for.
(Weight, compression height, any distinguishing marks etc.)
DD

BTW...
A good old school machinist can "repair" a bad ring groove.
There are (were) kits out there that had the special tool to widen the groove and then use a thin shim, (much like an oil ring side "rail") stacked with the standard ring.
DD

^^ Ring spacers. Did that once upon a time on a 292 Ford with worn rings grooves.

Weighed a couple of the lighter pistons I have. (They are the 244P's same PN, but quite clearly there are at least three castings, if not more.)

Did the measurement, Pin out. There are variations in pins, so this removes that from the equation. The lightest is 467 Grams, the other is 498 Grams. The heavier one looks the most like your old piston. The lighter one looks like the one on the right, with some differences to the machine work and casting. Make that at least five variations.

CJ

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Part of Tyrde-Browne Racing

Thanks for the info, everybody. Lou, I think we're going to go for something like 0.040".

Here's a bunch of info on the piston I'd like to replace. I'd definitely be open to trading or buying one if any of y'all happen to have one. Weight of the piston (without the pin) is 16.5 oz. or 0.47 kg. This was done with a refrigerant scale, so only accurate to around 1/2 oz. It uses a 0.900" wrist pin, which I presume is the standard size because that's what the new replacement uses as well. Total height from top of the piston to the very bottom of the skirt is 3.005". Height from top of piston to the lowest point directly under the wrist pin hole is about 2.548". Distance from the top of the piston to the top of the 1st ring groove is 0.320". Top of piston to top of the 2nd ring groove is 0.635". Top of piston to top of oil ring groove is 0.835". The width of the openings in the oil ring groove are about 1.375".

The new piston I just bought and can trade away is 18 oz. or 0.51 kg (without the pin).

And here's a deluge of pictures of the piston I need.

Numbers on the top:


Front side, same side as the notch on top.


Back side. On the left it says 244NP and there's a little shield or arrowhead symbol with an S inside. On the right is a number 1.


Close-up of the oil ring groove passage.


The underside. Those 3 punch marks were made by us for indexing. (This was the #3 piston.)


Because this is upside down, I'm assuming this is IH, or maybe 1H. It says USA on the opposite side.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

The pistons I have may be able to match the weight, but won't be exactly the same in appearance.
It's very important to get an accurate scale for this. I had to borrow a buddy's scale to measure the two pistons. My scale is hiding somewhere in my infamous cluttered shop.
Harbor Freight has a scale that is acceptable. It'll get you close enough that we can figure out if one of these pistons will work. Snag one next time you head to the big city. I'm going to grab one tomorrow on my way home to "No retail establishments or automated traffic control here." I'll also use some standard weights to verify it's right. It is after all, the cheapest import available without subverting import controls.

If your building power, there are some better piston choices out there.
If your interested, I'll share my views on this, and I'm sure you can get some great input from many other camps. The minimum piston I'd run in a race motor is a hyper-eutectic, and having been there for a bit, forgings are the only way to go for big power. Just not OEM style forgings. They are far too heavy.

My paradigm could be right, could be wrong. Nothing I've built has blown up. Your results may vary.

2¢

CJ

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Part of Tyrde-Browne Racing

This motor isn't going to be big power. It's got a mild cam and a super six intake, but other than that it's all stock. We're not even bothering to bump up the compression this time around due to time constraints. It's just a motor that will be run hot and beat to hell in endurance racing.

I'm going to take this piston to work tomorrow and use a postal scale. I'll let you know when I've got a more accurate number.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Gotcha. I'll stuff something in a box if the number matches. Doug likely has the closest match, so work something up with him if what I have isn't the same. Matching is the key to finishing the race. The closer the better.

The other piston you have pictured looks like a forged 0.040" piece I gave Doug on my last visit to Sunny Vale. I will be donating yours to the "DD Man/Myth" foundation once he figures out whether he's going to buy an estate on the Riviera, do a vacation for a night or two in Eureka, or will build a pump house out of scrap lumber and a bag of sakrete with his extensive foundation profits.

CJ

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Part of Tyrde-Browne Racing

Alright, CJ. The piston that needs replacing measures 467.5 grams. This aftermarket piston that I bought (pictured on the previous page) measures 513.2 grams. These are both with the pin out, and obviously no rings.

I'll send you a PM with my address. Just let me know where to send this one.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Check your PM's Frank. The light one I have is a Mahle. Not the right piston.

Hopefully Doc can hook you up. The lightest 244 I have out there is 498 Grams.

Give me a ring. I'm digging through my stuff, but it's a pretty whimpy collection as compared to what Doug will have to choose from.

CJ

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Part of Tyrde-Browne Racing

We ended up buying a whole new set of six so they would match. They were cheap ($85 for the set), and they are the same shorter design as our old pistons. So I guess these are just a cheaper design boxed by Sealed Power under the same part number.

Question about orientation of rod bearings. We marked the direction of the rod caps when they came off, and the caps on #3 and #4 were pointing in the opposite direction as the other four. However, the FSM says the rods should be assembled with the oil hole toward the right side of the engine (toward the cam). If this was done correctly, then it means the upper- and lower-half rod bearings on 1, 2, 5, & 6 were installed with the locking tabs on the same side. I was under the impression that the upper and lower bearings should be installed with the tabs opposite each other. Does this matter? Should I reverse the rod caps that were installed backwards, or put them back the way they came out and not worry about where the bearing tabs end up?

On that note, how critical is it that the rod oiling hole points toward the right side? We got in a hurry pressing all the wrist pins out and didn't mark their direction (because the FSM says they are oriented one way), so it's actually possible that the corresponding rods were in backwards as well.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

The rod caps and rods will only go together one way correctly as the bolt holes in the rod and cap will be offset and not bolt together with the housing bores being round. The bearings on most all engines have the bearing tangs on the same side in the cap and rod.

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There's no such thing as too much cam....only not enough engine!