The Stovebolt Site Forums The Shop Area Engine Shop installing pistons

this is going to be a dumb question, but which way do the pistons go in a 1962-63 327. yes i know the flat part goes on top! i have flat top pistons and i forgot weather the recesses for the valves go twards the intake manifold or twards the exhaust manifold side.

Do you only have one set of valve reliefs? Most replacement pistons have four notches, so there doesn't need to be dedicated pistons for right or left bank. Either way, there should be a small notch cut into the top of the piston that is supposed to face the front of the engine. There is usually the letter "F" cast into the skirt area of the piston, also indicating "front".
Jerry

If there is only one set of reliefs cut, then they would go towards the exhaust manifold.

Don't these pistons have an offset on the wristpin?

no, the wrist pin is centered. there is a notch in the top of the piston, but all 8 of them are exactly the same; if i put the notch forward on both sides then the driver side would have the reliefs tward the manifold, and the passenger side twards the exhaust. i got a pic of the first one i put back in, maybe it can help. its on the driverside. http://i831.photobucket.com/albums/zz233/Toste_bucket/66%20chevy%20C-30/0615101820.jpg

What brand are the pistons? If all of them are the same, you've got four of the wrong part number.
Jerry

I believe the sixes had offset piston pins in 1955 or so. It is quite surprising that the V8 didn't.

Virtually all engines built in the past 60 years have had offset piston pins- - - -they're just not obviously off-center. The only exception to that rule I can remember would be some of the Ford industrial V-8's made in the late 50's and early 60's. They had round piston skirts, not cam-ground, and no wrist pin offset. They sounded like Diesels because of all the piston slap. I doubt if anyone on the forum can eyeball a 1/16" or so off-center situation unless he knows exactly where to look on the wrist pin boss of a piston. EVERY Chevy V-8 made since 1955 has had the wrist pins offset!
Jerry

It doesn't matter where the locating dimple is, just get all eight with the valve reliefs in the right spot. The pin offset will be correct for each side, just the dimple will facing backwards on four of them. The pistons don't know which way they are facing, and since the wrist pins will be on the same side of center, it will work just fine.

Think of this way, if the wrist pin was offset 1" from center (towards the valve reliefs), the rod would always be 1" closer to the outer wall of the block, as long as the valve reliefs were all on the exhaust side. The indicating dimple makes no differene.

We used to run our Pontiacs with all eight pistons facing backwards, this made them stay at TDC longer due to the off center of the wrist pin. Don't know if ever really helped, but the Chrysler guys were doing it, so we did.

Joe

Joe, that advice is so far wrong, I can't even begin to point out all the errors! Wrist pin offset has to do with putting the load of compression against the thrust face of the piston before the spark plug fires, and it's different from one cylinder bank to another on a v-type engine. I'm out of this thread, too many self-appointed experts!
Jerry

The way I see it, all eight pistons were made on the same machine, so all eight are the same piston. If all eight are placed on the rod so the valve reliefs are under the valves, then all eight will be on the rods in the same orientation. What difference does it make where the front facing dimple is?
We have to assume the forward facing notch is aligned with the chamfered side of the crank end of the rod, then each piston and rod could be swapped hole to hole and still be right. The chamfered side of the rod bearing end is the side that rides against the crank, the other side rides against the other rod.


http://www.amazon.com/Engine-Bluepr...books&qid=1276986201&sr=1-1#noop

Here is a quote right out of the above linked book, Engine Blueprinting & Practical Rebuilding guide book by S-A design. I have the book, this is from page 70.

"All most all overhead valve engines require reliefs or notches in the piston tops to provide clearance for the valves. With out these notches the valve lift would be severly limited. Installing a camshaft with longer duration and higher valve lift increases airflow through the engine allowing the engine to produce more power. As the valves move farther off there seats and are held open longer, the location and depth of the valve pockets in the piston tops becomes more important.

The valve notches found in stock pistons are usually the wrong size and in the wrong places. Factory flat top pistons for the smallblock Chevrolet, for example, have four equal-size valve reliefs-even though each combustion chamber has only two valves with unequal valve head diameters. With four notches, however, the pistons are "universal"-they can be installed in any hole on either bank of cylinders, and there will always be a valve pocket where its needed. High performance and raceing pistons yeild more compression by eliminating the two "extra" valve reliefs. And once the sizes of the pockets is reduced to fit the exhaust and intake valve heads precisely, then each piston must be assigned to a cylinder with the same valve layout."

Please explain, what am I missing? What is the author missing?

Joe

"Stock" pistons have four valve reliefs AND a "front" notch, so the pistons on one bank can be installed with the wrist pin offset toward the outside of the block, and the other bank with the offset toward the valve lifter valley. As the piston approaches the top of the stroke, the connecting rod goes "over center" slightly before TDC. When the piston reaches the top, the rod is at a slight, but measureable angle, and the thrust of the compression pressure holds the piston skirt tight against the cylinder wall- - - -the "outside" wall on the passenger's side, and the "inside" wall on the driver's side cylinders. This allows the piston skirt to load itself against one cylinder wall due to compression slightly before the spark plug fires. When the plug fires, there's no "slap" as the thrust of firing reaches the piston. If a piston is installed with the offset wrist pin facing the wrong way, the piston is "floating" at the top of the stroke, and the piston skirt will make nasty noises as it hammers itself into the cylinder wall as the plug fires. The piston skirt, and/or cylinder wall will fail in a short time. If a V-8 piston is made with only one set of valve reliefs, it MUST have a different wrist pin offset for right and left cylinder banks.

Actually, a set of custom race pistons such as Keith Black forged pistons, will have four, not two different part numbers, because the valve reliefs will be custom-cut to match individual cylinders as well as being set up for right or left cylinder banks. The intake and exhaust valves are in different places in cylinders 1 and 3, for instance, and need different-sized relief cuts, also 5 and 7. Ditto for 2,4,6, and 8.
Jerry

I have a diagram from GM showing the differences in the 1954 six cylinder piston and explaining the offset. So my point was that it does matter which way the pistons go in. Now I just finished installing new pistons in my 1951 216 and I measured and determined that the pin was not offset. There was no mark to indentify the fromt either.

Apparently, the cast iron 216 pistons did not have offset wrist pins, while the "split skirt" aluminum pistons did have. Ford used aluminum pistons with offset pins as early as 1932 in their 85 HP V-8. The 235's and 265's with aluminum pistons used offset pins and cam-ground piston skirts to allow closer tolerances and quieter engine operation.
Jerry

well i got all 8 in, they are GM pistons- everything i have taken out of or off of this motor seems to be stock! i bumped the starter several times- nothing is hitting or grinding. i know the truck ran ok before i dug into it, so im just going to pay very close attention to any nocks, pings, dings, or what have you. thanks for all the help!

The 1954 Chevrolet Truck Engineering Features booklet indicates that the offset pins were introduced in 1954 for the 235 and 261 engines. This reference comes from Tim's 1954 truck site.

Hoyt

I'm with Jerry. If my opinion differs from Jerry's....I'm with Jerry.

Jerry's right.

Glad you got it worked out.

Joe