dsolomon

In the process of tearing down a 350 that I purchased to determine the quality of the build and get some idea of the specs. Can anyone ID this piston? It is .030 over cast piston. Other than a B410 cast into the inside, there is nothing else that I use to ID it.

Any ideas?

Rickman48

Did you check the bore? Is it oversize?
99% of aftermarket pistons are stamped on the face with a part# and size [+.030, 040, 060]
They could be factory, or factory oversize.

MDchanic

The dish diameter looks a bit small to be factory, from the limited amount I've seen.

I'd suggest cc'ing the dish (or just measuring depth vs diameter and calculating) to see what you've got. Visually looks like a small dish in the picture, which is good for high compression, but needs to be measured.

- Eric

dsolomon

Yes they are marked +.030 on the top. I was planning to CC the heads, I will try the same on the piston. Can I just cc the piston from the deck? If so, what fluid would I use that doesn't leak past the rings?

MDchanic

The good thing about the regular shape of Olds piston dishes is that their volume can be calculated easily (no valve pockets to account for, etc.).
½ of diameter x ½ of diameter x π x depth = volume. (π = 1.314159)
You can get the rest of the cylinder volume by doing the same calculation with bore and deck height.

To actually measure cc volume, any liquid with low surface tension (minimal tendency to form a meniscus) is good - rubbing alcohol is used a lot, lacquer thinner and gasoline can work, too - it really depends on how you're doing it, for instance, if you're using a plastic syringe, anything that will soften the plastic would be a bad idea, and if you're indoors, minimal odor is helpful.
It is common for folks to use a piece of plexiglass with a small hole drilled in it to lay flat on the gasket surface to be sure that the the liquid's meniscus doesn't bulge out above the chamber, then fill it through the hole.
Vaseline can be used to help make a seal in places where the liquid might run out.

Others may have better advice, and probably do.

- Eric

cutlassefi

You can use white lithium grease as well, doesn't break down as easy. And I use Windshield washer fluid to fill it, easy to see.

To figure piston dish cc I use the following;

Diameter X diameter X Depth x 12.87, example, 3.00 diameter x 3.00 X .250 depth x 12.87= 28.95cc.

MDchanic

I'm a dummy and not paying attention because I'm at work.
Used circumference formula instead of area.
Fixed now.

- Eric

olds 307 and 403

Those look like the big dish 24cc replacements. Get ready to mill your heads a lot.

dsolomon

I cam up with 10.52cc using the formula given above. The dish is only .100" deep. With a 64cc head, .038 deck clearance and a .039 gasket, I am calling it 9:1.

MDchanic

Dan,

So, I'm assuming that you measured the dish out at 2.854" diameter by 0.100" depth, and you've got a true measured deck height of 0.038".

9:1 seems like a good ratio, but I'm a bit surprised by the dish volume of 10.52cc, as I am under the impression that the choices are 6cc, 14cc, or 24cc. Interestingly, the 24cc piston dishes are theoretically supposed to measure 2.85" x 0.230".

I'm planning on repairing / rebuilding (depending on what I find inside) a 350 over the next year, so I'm paying attention to your build and trying to learn from it.

- Eric

dsolomon

Eric

Yes I used 2.85 which is the measurement to the edge of the dish. There is a radius which would reduce volume but then there is the slight cut taken out of the center. I called the two a wash. The depth is .100
I couldn't find these pistons anywhere. That is why I posted this.

MDchanic

Weird

(at least as far as I've read so far...).

Maybe someone with more experience can explain this anomaly, but my guess would have to be that you've got a custom-modified piston from someone who had a flat-top machined to fit his personal specifications.

- Eric

dsolomon

No the dish has a cast finish. The only machine work is the small diameter in the center.