GM part # 10128213. These are GM 350 pistons from what was supposed to be a marine engine, but I know for a fact that some stuff has been changed. These pistons also have other markings, such as, E-6583 and 95 and 106. Is my best bet the local GM dealership? I am rebuilding the motor out of a boat. This engine looks very similar to the 350 that I had in my '87 IROCZ. The block cracked and I had water in the oiling system, tan milky stuff, 16 quarts of it. Two pistons have damage. One has corrosion around the edge in the upper land and a broken skirt. I am thinking that I should replace all of the pistons, not just two. What do you guys think?

If the block is cracked, what are you rebuilding? Replacing the block and keeping everything else?

Just buy a 350 engine and put the marine camshaft into it. The marine engines are usually reverse rotation so an automotive cam that would come with the engine won't work in a boat.

Marine engines run backwards?

Many do. All they need to run backwards is a different camshaft and a way to crank the engine over backwards. I have no idea how the marine starter system works. I suppose the easiest way to tell since the engine isn't running is to view the timing marks on the balancer/pointer. The advance marks would go the opposite direction.

All automotive engines turn clockwise when viewed from the front. Technically it's considered counter clockwise because all points of view are from the driver's perspective. Many marine engine run backwards and if the boat has dual engines, one runs forwards while the other runs backwards.

I am trying to rebuild the engine at minimum cost. I purchased a ZZ4 4 bolt main single piece rear main seal block from Summit Racing. This new block has the very same GM part # as the supposively marine engine. I also purchased rod bearings, crank bearings, piston rings, and gaskets. I wanted to reuse the entire rotating assembly, as well as, the cam and distributor. So I do not care about if the engine turns backwards or not, that will be transparent to me. The engine is going back into the boat.

I wanted to know what are my options here. Where can I get two pistons with that part number, or should I buy 8 new pistons.

woah woah woah, are you saying even engines in imports turn clockwise? i was always under the impression that hondas rotation was counter clockwise

Stephen, You got me thinking about rotation. So I checked the harmonic balancer, it has a groove in it as our balancers do, and the letters BTDC is to the right of the groove with numbers 4 8 12. All to the right of the groove when viewed from the front cover.

Anyway, back to my piston decision (who gives a crap about imports).

Hondas run backwards. Want to put a Honda car engine in a boat?

From the sounds of your timing marks, I'd say it's reverse rotation.

From the looks of it, that part number is a flat top piston with 4 eyebrows or at least is in the picture I saw. The only way to know if it's available would be to ask your local GM dealer since it uses a GM part number. Although you could replace just 2 pistons, it will probably be easier to order them as a set of 8. If you replace all 8, they don't have to be from GM.

I wonder how much different assembling a reverse rotation engine would be. The thrust side goes to the opposite side of the engine. Rods and pistons would still go in the same way but the rings would be 180* on the pistons. Does it use a different water pump because it would spin backwards as well? The distributor and firing order would rotate counterclockwise. Does it use a different oil pump to spin backwards?

Hey u guy's got me thinking I could sell my buddy and boat motor for his truck and see how long it would take him to figure it out

lol he'd figure it out once he puts it in drive and the goes really fasts in a very undesirable direction

The water pump does need to be reverse rotation. Reverse rotation marine engines usually have timing gears, but with no idler gears, so the cam still turns clockwise, but it is ground for reverse firing order. I don't know about the oil pump though, or the rings, but I assume you are right about the rings.

The balancer has marks on it that are same on my factory 350 that came in my '87 IROCZ. The motor turns same as my car engine. Water pump ---> This is an inboard/outboard setup. There is no water pump, its contained in the outboard stuff.

I am thinking that it would be best to buy 8 new pistons. The rods look very good; how do I get the press-in wrist pins out and not damage the rods?

Usually a machine shop can take care of this for you when you get a new set of pistons. Unless you purchase "full float" wrist pins, they must be pressed on and off. You will want to balance the rotating assembly as well once you get your new pistons. Again, a machine shop can take care of this for you.

lol no no no, i just wanted to know for reference, since you said all automotive engines turn clockwise and i got to thinking if honda's do aswell.

All automotive engines installed inline with the frame turn counterclockwise. Transverse engines are different and Honda runs their engine backwards but also has it so the front of the engine is on the driver's side while most transverse mounted engines are pointed to the passenger side.

Pressed wrist pins can easily be removed from a damaged piston with a simple press but a machine shop should reinstall the new pistons. They use a special torch to heat up the rod end, hold the piston in a special jig to keep it from being damaged then push the wrist pin through the rod while it's still hot.

My engine uses floating pistons. Simply by removing the retaining rings, the wrist pin can be pushed out with minimal effort. It makes disassembly for cleaning or repairs much easier with no special tools.

what do u mean inline with the frame? do you mean transverse?

and as far as removing the wrist pin goes, yes u can press it out if your careful, but as far as putting it back in it requires a special machine, which is basically this little oven basically, you slide in the connecting rod end, and a coil inside gets super hot, making the metal expand just enough to make the wrist pin fit, it takes a while to get the hang out it, once you get the wrist pin in smoothly you leave it alone, if you mess with it too much youll get it stuck and youll have to make a trip to the press again. if you lived close enough id have no problem installing the wrist pins for you, but yeah.

Inline with the frame means just that. Transverse means sideways.

Inline - crank points to front/rear of car - RWD cars/trucks

Transverse - crank points left/right in car - FWD cars

Not always true... Toronado, for example.

so wouldnt our engines be inline with the frame? and they turn clockwise? not counter clockwise, like you stated before

Our engines turn counterclockwise like every other engine. As I stated above, everything on the car is from the driver's point of view, not from standing in front of the car. The left side of the car is the driver's side etc.

A Toronado and an Eldorado are front wheel drive but the engines are still inline with the frame, not turned sideways. They both rotate counterclockwise.

do the pistons look like this? I can get these in singles at the shop i work at, or as a set. they are zz4 350 pistons. We can get them in several over sizes if you are going to bore the block.

There are always exceptions, but what I posted is in-general true, and just posted to give the reader the right mental image.

heff17: thank you for posting (you guys with your motor dirction should start your own post!!!!)

My pistons look very similar, but mine have a small raised lip at the ourter diameter of the pistons. I do have the four "eyebrows". So my pistons are slightly dished with the four eyebrows. PN is posted above in first post.