Technical Two different sized pistons in a running Flathead. WTF??

Soo I pulled the heads off my little Flatty to put my new heads on... and I seen two of the holes have 050 pistons and the other 6 have 060.... not sure where to go from here... lol I had it cackling over and the pistons fit tight in there holes but it’s driving me nuts now that I know... any ideas fellas?


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Never heard of a . 050 oversized piston.

 

Did you measure the bores? or are the pistons stamped? Pictures?

 

Because before the internet and the "experts" came along, stuff was done to make it work!

And guess what, it worked. So put it back together and keep driving it.

And just so you know, everyone who ever ran a spec motor in a roundy round car ran the front two cylinders that got tested to spec, and the rear 6 cylinders were way over. And they ran, and still run great.

 

it doesn't really alter performance or put any undue stress on the crank..bet you couldnt tell

 

Had a flatty a few years ago to have bad blow by on one cylinder that was over bored a machining error. The engine ran very well, didn’t make sense disassembling the thing and reboring the whole engine because one hole was off. I seriously considered machining one hole to the next size but pulled the engine and sold it as is for 200 bucks.

 

Was it running ok before? Unless you have a bunch of money burning a hole in your pocket just put it back together and don’t worry about it. It’s not a race engine.


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I can remember the Mobil crank grinders. If you were putting new bearings in your motor and had one throw that was scuffed to much to polish out they would grind that one throw to next under size and do it with the Crank in the motor while it was in the Car. Boring just what it takes to clean up a Cyl don't seem all that strange. I can remember grinding just the burnt valve and not touching the others. It was called repairing not rebuilding.

 

About 1962, I had to overhaul the engine in my '52 Ford. The local Engine Rebuilder had a set of 7 take-out pistons from some unsuccessful job they had done that they sold me real cheap. I went to the local junk yard and found a used piston that sorta matched, bought a set of rings and put it together. I don't know if the odd used piston was the same size or even brand as the others, but it fit and I was back on the road.

As "Pist-n-Broke" said above, that's what we did back in those days; just get 'em running again.

 

In 1959, I actually saw a repair like that at the engine rebuilders where my buddy and I used to hang around. When we asked the machinist, he said that not everyone can afford a rebuild, and that was an acceptable repair.
Bob

 

Air cooled engines such as aircraft and motorcycles are sometimes repaired by only one cylinder being worked. If the pistons weighed the same, you’d probably never know.


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People did things to get by. We (people in general) often did not have lots of money to burn (still don't).

 

Not a flatty, but in the 60s i had a 55 Ford six with 1 burned piston. Place where i took it, bored that hole .030 over, installed a new piston & rings. I drove it a long time with no problems.

 

Pull apart a Mexico built GM Target engine sometime, you'd be shocked at how they used to build them. They could have 3-4 different size holes.

 

I'm pretty sure that some of the GM replacement/crate engines from south of the border would have a cylinder bored out or a crank throw ground undersize just to use otherwise good parts.
Edit:
Egads types faster than me.

 

Well thank you for the reply’s everyone! Glad I have nothing to worry about.. this was a first for me and I hadn’t seen a 050 stamped piston before. I’ll post some pictures this afternoon.


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The pistons don't talk to each other, and compare size, if that's what you're worried about

 

Tore down a 340 back in the late 70's. supposedly, it had never been apart. It had one .040 over piston. Just one.

 

There’s a story that my wife’s grandfather had a ‘34 Pontiac coupe he used as a farm truck. It burnt a piston so he pulled out that piston and rod, whittled a wood plug and put it back together as a 5 cylinder. Ran it for years like that and used to haul hogs to market in the rumble seat.

At one time they were just old cars that needed to get back in service.


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In 1972 when I was a broke GI I had a beat up '63 Chevy 4x4 carryall with a 230 six. I drove home on a 3 day pass and burnt a hole in number 5 piston. The local auto machinist pulled a piston from a core exchange engine he had in the shop. The piston and rod bearings were the same as mine. I installed the core piston and rod assembly in my truck and the burnt piston and rod went into the core exchange engine. I just wanted the piston to make the 500 mile trip back to post since I was planning a small block install down the road. The replacement piston worked so well I made another 1,000 mile round trip home on another 3 day pass before the small block install. The things you do when money is tight.

 

I had heard that Chrysler did that "back in the day". I remember reading or hearing that the engine would have a suffix stamped on it to denote this. One character denoted an undersize crank, another oversize pistons, stuff like that. Never seen one in real life, though.

 

Owner bought it new, he was there during tear down. We patched it back together with the one oversize, he sold it almost immediately after that.

 

When I worked as a Harley mechanic, it wasn't all that unusual to find one cylinder bored differently than the other. The pistons were very close in weight so as not to alter the balance of the engine so it really didn't cause a problem- I know several that ran for years like that.
With a V-8 I would think it wouldn't be a big deal at all.

 

I’ve never heard of .050 over either, sure they just didn’t oversize the rings, I mean some jerkoffs do that to avoid a complete boring


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buddy of mine built a race engine, bored all the cylinders out, way past legal, except for cylinder #1. that was the cylinder they tested before and after the race.

 

Lmfao that’s good


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That’s awesome there’s a similar story in my family about a 216 Chevy that my great great granddad used a piece of his belt as a bearing and ran that way for years.


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Yeah it’s odd it’s stamped .050 on the top of the piston I’ll post a picture when I get home from work. It was odd to me as well. The engine was rebuilt at some point because there’s a tag from consolidated engine rebuilders located in Hutchison Kansas on the block. .


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They might have been .020” or .030” over size for some other bore sized engine of another make. Like above rings are rings. As long as the thickness and depth are ok... they don’t know or care what engine they are in..