273 Commando Slugs

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Sorry Chewy, I didn't answer your question. I will reverse the pistons from side to side because of the offset. Your build sounds like mine. Mike
 
Mike...just swapping the pistons/rods bank for bank won't give you the offset advantage you're looking for. You have to flip the pistons 180* on the rods (and in the bore) to achieve this. You can do this with flat-top pistons. You can't do it with the pop-ups as the pistons will hit the heads and/or valves.
 
I had to scratch my head on that one. You're right! By switching the pistons on the rods to the other bank wouldn't do anything with the offset. If they were flat tops that would work. Because of the dome it can't be done. Thanks for wakin' me up! Mike
 
Hopefully its good whiskey. lol.

Thats why I mentioned hitting the head. Also, just swapping banks is ok for short'track racing, but if you were going to run flat-tops that way, wouldnt you have to flip the pistons 180 to get the oil runners squirting correctly up the opposite cylindar??

--tom
 
Egge had mine on the shelf. They sent them out the day I ordered. $400
will get you pistons,rings,pins, and lock rings. Have your machine shop weigh the new pistons as they are lighter than the stockers....enough difference that you should balance the rotating assembly. Mike
 
65 Val said....."Mike...just swapping the pistons/rods bank for bank won't give you the offset advantage you're looking for. You have to flip the pistons 180* on the rods (and in the bore) to achieve this. You can do this with flat-top pistons. You can't do it with the pop-ups as the pistons will hit the heads and/or valves."
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No, the pistons will not hit the heads, and you do not turn the piston 180 on the rod. Figuring piston and rod mounting can really be confusing sometimes, even for experienced engine builders, so one needs to really think things through.

When you take, say, #1 rod and piston (notch to the front) out of its hole, and turn it 180 (notch to the rear) and put it in #2 hole, the dome is still in the correct position for the head, and the pee hole in the rod is still pointing to the cam, with the pin offset is now opposite of where the factory wanted it. There is no reason to take the slugs and reverse them on the rods unless you just want to have a MAJOR problem with flat-tops. You'll wipe the cam out because now the pee hole in the rod is pointing to the side of the block instead of the cam and you'll wipe the cam out.
 
Edit: Of course, with a new build instead of modifying an existing 10.5 "S" motor, you could just mount the pistons on the rods to keep the rod numbers correct, left bank and right banks reversed, notch to the rear.

I know it's a head scratcher, but it does work. I'm trying to activate some old brain cells now, but I read the article in the early '70's, and I think it was the one written by Craig "Twig" Ziegler, owner and driver of the Pizza Haven funny car.

Russ.
 
Russ...I hate to disagree with you, but, the offset is in the pin placement in the piston, not the rod, so swapping the piston/rod assembly from one bank to the other doesn't change the offset...the offset is still to the inside of the block. You have to rotate the pistons 180* ON the rods to get the offset to the outside of the block. The rods stay in the stock position relative to the crank, so the oil hole stays put too.
 
65 Val,

That's what I mean by being a head scratcher. You can't just reverse the piston on the rod because the slug will hit the head. Picture this. #1 piston, you're at the front of the block looking at it. Say the offset of the pin is towards the outside of the block (offset closer to driver's side front fender).

Now, take that piston (and rod, no reversing slug on rod), with the arrow (offset) pointing towards fender and turn the slug and rod 180 and set it on # 2 (opposite bank). Now the arrow just pointed towards the passenger side fender (now offset is towards the passenger side fender, offset just went left of center line instead of right of center line). The offset is reversed, and all oiling holes (rod and piston) are still where they are suppose to be in relating to the motor (cam).

Think about it. I know stuff like this can give headaches, I've got Excedrin bottles everywhere. LOL


Russ.
 
You can't just reverse the piston on the rod because the slug will hit the head.
Click to expand...

Yes, I know this. Thats why I said you cant do the piston reversing thing on pop-up pistons cause they will hit the head. Flat-tops only.

If you line up the piston pins on one bank of the engine and draw a centerline front to back through the pins, you will find the pins are offset toward the inside(camshaft) or outside(exhaust manifolds) of the block. By flipping the pistons on the rods 180*, you will move that offset from inside to outside , or outside to inside of that centerline. Just putting the whole piston and rod assembly from the left bank to the right bank,(or vice-versa) does not accomplish this. Its still on the outside( or inside) of that centerline, on that bank. Again, just taking the #1 piston/rod assembly out of the #1 bore and installing it in the #2 bore, for example, does not change the offset. It is still off-center the same, relative to the center of the engine. Picture a V8 engine as the right bank mirroring the left bank.

It doesnt matter which fender it points to...it matters whether the offset is to the inside (camshaft) or the outside(exhaust manifolds) of the block.

Maybe try thinking of the V8 engine, cut in half down the cam tunnel, turn one side 180*,and then place it side-by-side, as 2 identical 4 cylinder engines. Taking the piston/rod assembly out of the former #1 bore and installing in the former #2 bore doesnt change a thing. Offset is still on the same side. You'd have to flip the piston on the rod 180* to change the offset.
 
Don't forget that the factory pins are THICK and heavy. I replaced mine with some lighter one's on my rebuild. light is good, right Mike?!
 
Pop ups no....flat tops yes. The new pistons are 68 grams lighter. I hope the pins are lighter too. I will drop off the flywheel, balancer, rings, and pin retainer clips on Wednesday so Steve can get things balanced. We had bad weather yesterday so I didn't get the heads delivered. Hopefully this weekend. Mike
 
65 Val,

"Of course, with a new build instead of modifying an existing 10.5 "S" motor, you could just mount the pistons on the rods to keep the rod numbers correct, left bank and right banks reversed, notch to the rear."

"towards fender and turn the slug and rod 180"

Ok, you are forgetting that I said turn (rotate) the piston and rod assembly 180, so that the notch at the front of the piston (meaning that the notch should point towards the front of the block), is now pointing to the REAR of the block, on the opposite bank. Piston and rod assemblies 1, 3, 5 and 7 are now in holes 2, 4, 6 and 8, installed backwards. The piston will not hit the head, the pee hole in the rod is still facing the cam, and the offset is reversed. For both banks.

The pop-up is towards the outside of the block, regardless of which bank it is in, to match the combustion chamber of the head. When taking #1 piston and rod assembly, turning (rotating)(reversing notch from front to rear) it 180, and putting it in #2 hole, the pop-up is STILL towards the outside of the block to match the combustion chamber of the head, and of course the rod will still oil the cam, and the offset is now opposite of factory.

Russ.
 
man this is good read...but damn I'm confused!

Aloha....back to palm trees and Mai tai's!
 
Pins are lighter too.

Great to see several 273's being built. I wish I would have got the HP pistons strait from Egge, much better price than from Hughes.

I went with comp cams XS268S solid cam, balanced assembly as well, squared the block, stock heads, mild porting 1.84 intake and 1.60 exhaust valves and added a cam tensioner.

Heads have been milled slightly and even with MP .028 gaskets my machinist says I am right at 10.5 compression. Heads are 62cc

I am looking into oiling mods.

Love that CD idea for CC the cylinder head! I am going to put the piston down into the block 1/2" and seal it with vaseline and cc the piston dome to double check piston volume. I want to make sure of my compression ratio!
 
65Val, I needed a piston in my hand to understand. I believed too much of what I read about reversing pistons and thought you could do the hp pistons the same way. But no way. The trick started with B and RB wedge motors and they had flat tops from the factory. If you reverse the pistons on the rods and keep them in the same bore the domes would be on the wrong side of the chamber. If you switch sides the offset is the same just on the opposite bank.
Hard to explain and understand. Flat tops are easy. They have 4 valve reliefs so no matter which way you install them they work with the chamber shape and valve angle. Keep the rods in the same bore and twist the pistons to get rid of the offset. Mike
 
Ok, I can see why you're confused. The pistons are bank specific. In other words, the right hand bank pistons are DIFFERENT than the left bank pistons. That's why the pistons Toolman just got have a right bank and left bank set of four each. The pistons for 2, 4, 6 and 8, if you're looking right at them, have the pin offset towards the CENTER of the block. The pistons for 1, 3, 5 and 7 are offset towards the OUTSIDE of the block. That way both banks have the same offset towards the driver side of the car. By swapping banks and installing them backwards, the offset of both banks are now towards the passenger side of the car. The reason for right and left bank pistons is not for the dome or flycut valve reliefs, both reliefs are the same size.

Check with Toolman on his new pistons, and yes, it can be confusing.

Russ.
 
Double M said:
Ok, I can see why you're confused. The pistons are bank specific. In other words, the right hand bank pistons are DIFFERENT than the left bank pistons. That's why the pistons Toolman just got have a right bank and left bank set of four each. The pistons for 2, 4, 6 and 8, if you're looking right at them, have the pin offset towards the CENTER of the block. The pistons for 1, 3, 5 and 7 are offset towards the OUTSIDE of the block. That way both banks have the same offset towards the driver side of the car. By swapping banks and installing them backwards, the offset of both banks are now towards the passenger side of the car. The reason for right and left bank pistons is not for the dome or flycut valve reliefs, both reliefs are the same size.

Check with Toolman on his new pistons, and yes, it can be confusing.

Russ.
Click to expand...

Coming from the toolman: "That really throws a "wrench" in the works".
When I got the pistons I looked at them but really didn't look close enough.
They were marked L and R (bank specific) but I didn't check the offset
difference between sides. I thought the side load for each bank was either towards the center or towards the outside of the block but because of crank rotation the side load for each bank would either be towards the right or left sides. Am I catching on? MIke
 
Too old?? Hell, I heard this in the early '70's when I lived in Hemet, CA. That's after my stint with Uncle Sam. Talk about a guy with a sore and wore out back, that's me!! I hurt in places I didn't even know I had.

But I still play. LOL. Never to old for horsepower.

Russ.
 
I should start my own post instead of hi jacking tcmdowel's start. Oh well, we're
having fun aren't we?. Stopped by the machine shop today and dropped off the flywheel, balancer, and rings so Steve can balance the rotating assembly. The block is bored, honed with a torque plate and chamfered. It looks good. The rods are almost done. The big ends have been reconditioned with new SPS bolts. The small end bushings are good so the just need a very light hone. The crank is done and the last step is the balancing. I need to get the heads to the shop, hopefully this weekend. Sorry for the fuzzy photos but I used my cell phone again. I need to get a Q-tip and clean the lens. LOL Mike

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