If you can go with aluminum pistons, I would.  Reducing rotating mass is always good.

Posted by: @dunfire

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If you can go with aluminum pistons, I would.  Reducing rotating mass is always good.

X2! I also converted to insert bearings.

The 1928 car engines came with aluminum pistons. That was one of the changes that caused the '28 engine to have 35 hp versus the 21 hp of previous Chevy four bangers.

When I rebuilt Lurch's '28 engine, I used four new pistons from Egge that were .060" oversized.

I was very happy that three pistons weighed exactly the same as each other and the fourth was only 1 gram heavier. This was handy for balancing purposes. I also ground some material off three rods and caps to make them equal in weight. For the one piston that was 1 gram heavier, I ground that particular rod to be 1 gram lighter than the other three rods, so the net weight of each piston/rod pair was equal to all the others.

In Ray Hollands "School is in Session" '28 engine rebuild, he also bored the block out .060" oversized, and used four new pistons that were meant to go into a Chevy 261 engine.

As an aside, I suggest that you have the crankshaft polished and balanced (with the flywheel attached). This, together with the balanced pistons and rods, made  for a very smooth-running engine.

Cheers, Dean

I wonder when they went back to cast iron? My 38's were cast iron before the rebuild.

"The 1928 car engines came with aluminum pistons. That was one of the changes that caused the '28 engine to have 35 hp versus the 21 hp of previous Chevy four bangers."

X2...

If I'm remembering right... for 1928, Chev originally used what they called an Invar Strut aluminum piston, which besides just being aluminum, also had several "windows" cut out of the pin boss area to lighten the piston even more.

@tiny 

Hi Tiny

1929

I think the Invar Strut aluminums were a 1 year thing.

When Chev went to 6 cylinders, cost of production was a major consideration so they went with cast iron pistons and stayed with just 3 main bearings.

Except for weight, cast iron was actually an excellent material for pistons.

The fat kid learned something today. You coming to Rapid City Ole? @ole-olson

@tiny 

Unfortunately, most likely not.

My wife has us lined up for a trip to Vancouver Island around the same time.

We toured through that area many years ago.

We camped at the Grace Coolidge camp ground in the Black Hills, survived a VERY close lighting strike that night, and saw many of the nearby points of interest.

I would love to go back, and actually meet you and the other fine people of the VCCA.

Who knows, sometimes plans change.  🙂

Lou when you get it back and start putting it back together, I caution you not to mix up the bearing cap bolts meaning keep them in the position they had them to line bore. I didn't have a line bore job done as the bearings I used still had shims to take out but I didn't keep track of which bolts were where and I found that the bolt shanks are not concentric to the bolt threads and in some cases (not all) the bolts go around in a slight cam like motion and can cam the bearings into a misalignment.  It was especially problematic on the center main.

David

I appreciate all the feedback, very helpful. If new pistons (aluminum or otherwise) are installed, the cylinders would need to be bored, to round them and match available pistons. However, that would increase the compression ratio i think, which would increase the forces on the bearings. I don't know if that is significant increase, but it would be increased. I was also, as mentioned, considering converting to regular bearings, but was concerned about the lube system being sufficient to support them. Some folks say I think too much....maybe so!

Anyway, David, good point, thanks.

and, of course, one must always keep an eye on the wallet! 

Lou,

I don't think you need to worry about the bearings not being able to handle it.  I know Ray in his build was totally comfortable with using the 261 pistons which are 60 over standard and I believe have a 1/8in taller deck height. I think???? It wasn't his first rodeo either when he built that 4 banger.  And if you haven't, the Schools in Session thread is a great one to study and then study some more as well as Deans Resurrecting a 4-banger.  

I hear ya on the money part too.  I am fretting over whether or not I want to have my cam ground and lifters faced.  One has to get the cam gear off to get it ground and you either trash the cam gear and or the retainer plate behind it and have to fork out more cash. 😑 What it comes down to is how many miles am I really going to put on driving the old guy at those high rates of speed he's going to be able to go lol.

David

@lou 

Hi Lou

Boring oversize alone does NOT usually increase your compression ratio on engines with essentially flat combustion chambers.

There will be some increase in engines with odd shaped chambers cast into the head, but I don't think that really applies here.

There will be a very slightly increased load on the bearings due to the increased surface area that the same pressures are acting on.

Compression ratio WILL be increased by reducing the size of the combustion chamber at TDC, most often via planing of the head or block surfaces, or using a piston with an increased distance between the wrist pin and top of the piston when there is room to do so.

I don't think you need to worry about overloading the bearings in the bottom end anyway.

Keep in mind that there was a time when people hot-rodded these things without bottom end modification.  🙂

@lou  @tiny

I just did a little research, and the 1928 combustion chamber was configured such that no compression ratio increase will occur with boring oversize.

Regarding the Invar Strut aluminum pistons... interesting stuff from the 1928 Chevrolet Service bulletins!

Invar was a nickle-steel alloy with a very low thermal expansion rate.

It was used in a strut that was cast into the aluminum piston to bridge or connect between the pin bosses and the upper skirt of the piston.

The skirt was isolated from the head of the piston by slots, so heat traveling from the head of the piston to the skirt had to travel through that Invar strut.

The result was an aluminum piston with a skirt that expanded so little with heat that it could be fitted as closely as .002" to the cylinder bore.

That's the same clearance as was used with cast iron pistons, was far closer than normal aluminum pistons of that time were fitted, and controlled piston to bore clearances much better.

This was no run of the mill aluminum piston and obviously this would have been expensive, and would be the reason Chev went back to plain cast iron pistons in the '29 six.

Just a little trivia that some may find interesting.  🙂

Have you guys forgotten that 4 cylinder Chevy heads have no combustion chamber. They are flat on the bottom. The combustion chamber is the unused part of the bore. The pistons don't come to the top of the block. If Ray used 261 pistons that were 1/8" taller from the pin to the top, he would have increased the compression by doing so. My late friend, Les Mades, from Washington, Missouri, made longer rods for his High Performance 1928 Chevrolet engine.

Mike