piston size

demingboy

demingboy

Member
So I know I am going to get in trouble but need to ask. In process of doing a re fresh on my 1951 8BA. I am finding more clearance than I want on piston size. Some pistons are smaller and have more wear than others. In fact one top ring had like an 1/8 inch gap. Crazy
So my question is I believe I will gain quite a bit from using new standard size pistons with a 10 over ring. I know its past spec but would be an improvement over what I have now.
Dumb or not dumb? I dont think they sell a 10 over piston do they?
 
I'm not familiar with a +.010 piston option. If your bores are worn as bad as you are describing your machinist may have fun trying to clean things up at +.020.
 
This might be time to consider improving the efficiency of the engine. Considering the fact that the cost of fuel won't get much cheaper for awhile might ad well as improve the milage. You can do this by boring the engine out to at least .060" this add 10ci tot the displacement am 1/2 point in CR. Now angle mill the heads .070" and gainanother 1/2 point in CR.
Now the stock engine in good tune should be much cheeper to run, For this alittle braver bore to 3 5/16, but you need a piston that can be fit tighter in the cylinder. At one time you could get a 4 ring stock type piston . These can be set with .001' piston clearance and modern 3 rings v=can be used.,
 
If you're going to all the trouble of rebuilding the engine, why just try to patch it up with just rings? Now - if this is strictly a money issue, then I get it . . . so I'm not trying to step on your toes.

Why not bore the engine and put in new pistons and rings - as I'm sure the current bores are worn, are tapered, are out of round, etc.. New rings in the current situation might actually run worse than what you have (as they will have a difficult time trying to wear/seat into worn, tapered and out of round bores).

Some inexpensive options:

https://www.speedwaymotors.com/1939...-Ring-Pistons-3-3-4-Stroke-060-Over,1855.html

https://www.speedwaymotors.com/Ring...g-Flathead-Ford-Pistons-3-248-bore,25383.html

There are a ton of piston over-sizes available - with some fairly inexpensive prices if you're going with a cast piston. If it was mine, I'd bore it at least .060, put a decent quality piston and ring package in it and go from there. As Ole' Ron noted, with just a few important steps, you can really improve the performance of the engine (angle milling, tighten up the quench, etc).

Hopefully you're also having a quality valve job done to the engine as well - by somebody who is an expert in flatheads. And then there is balancing - which I always do . . .

You'll have a lot of TIME into this project - try to do the best job possible in the rebuild, while staying within your budget. You'll be very happy in the future that you did things correctly. :D
 
Starting to believe you guys are right. Just gonna have to do it right. Kinda hate to put the money in a tudor sedan but it is fun to drive.
 
I'll buck the trend a bit here, I like thick cylinder walls. I just got done installing (with lots of help from good friends) the 8BA that dad rebuilt 30 years ago. 1951 passenger car motor, +.020 bore -010 on mains and rods, stock cam, lifters, valves, truck oil pan & bell housing. The only deviation from stock regarding power was we milled a set of EAB heads to get .050 over the pistons. The engine is very smooth (dad balanced it) and it pulls great even with the 3.54 rear axle. I like a bit thicker wall for more longevity and fewer cooling problems and the .020 bore of dad's motor meets my expectations for power.
 
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