Street 8BA piston question

kegmon

kegmon

Member
Suffering from a little paralysis due to analysis here. My 8BA block is ready for boring and the machine shop says an .080 bore will be necessary to clean up the cylinder walls. I've been leaning towards cast 3 ring pistons as they generate less friction (better cooling) than the readily available 4 ringers but have yet to find a source for them at the .080 size. Egge makes a .125 over 3 ring that Ol' Ron has mentioned, so I guess the rub here is this: Is it better to 'leave a little meat' on the block and go with the 4 ring .080, or to just go ahead and bore it to .125 and be done with it? BTW, This is a budget build so I'll be re-using the 3.75" crank & original heads, if that matters.. Thanks!
 
I would go with the .125 bore as it is very unlikely you will get enough miles on the engine to need another overbore in the future.
 
The only thing I would think about is maybe you would need another rebuild but if not the next guy will. If we all go .125 that is less miles for the future Flathead lovers. Of course I'm just saying that because good Flatheads are becoming more scarce. Is the hp gain of .125 over .080 really noticeable enough verses the engine longevity. But when it comes down to it it's your engine do what make you happy.
 
I agree with Jseery. For a stock engine I'd only bore what's necessary. How Big is it now? Why does it have to be bored to .080"? unless ther's something wrong with the cylinders. 060 pistons are easy to get. OK, as for the 125 over pistons from Egge. Probably the best street piston ring combination you can buy today for a stock street engine. And if 4 rings was better than 3 everybody would use them. That's old tech and rings have gotten better over the past 50 years. Now the next guy can get .020, .030" pistons for the 3 5/16 bore. That's allot of rebuilds. And a 258ci flathead is a fine running engine, use a set of EAB heads milled for .050" piston to head clearance and your golden.
 
kegmon said:
Suffering from a little paralysis due to analysis here. My 8BA block is ready for boring and the machine shop says an .080 bore will be necessary to clean up the cylinder walls. I've been leaning towards cast 3 ring pistons as they generate less friction (better cooling) than the readily available 4 ringers but have yet to find a source for them at the .080 size. Egge makes a .125 over 3 ring that Ol' Ron has mentioned, so I guess the rub here is this: Is it better to 'leave a little meat' on the block and go with the 4 ring .080, or to just go ahead and bore it to .125 and be done with it? BTW, This is a budget build so I'll be re-using the 3.75" crank & original heads, if that matters.. Thanks!
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Hi kegmon; First I'd sonic test, if good, I'd bore the .125 and go with the three ring pistons, less friction, slower ware. The next guy can still bore or sleeve down. Then I'd mill the heads to .050 piston to head clearance. Read JWL's book. Good luck, Craig.
 
BobH - I was wondering about that as well..

Ol' Ron - This motor was bone stock but was stuck hard with extreme rust & pitting in a few of the cylinder walls, it was a real bear getting the old pistons out of there.. Machinist said that .060 might be enough to clean 'em up but .080 would definitely do it but leaning more & more towards the .125 bore after reading the comments here.. Now to find some EAB heads! Thanks guys! Hoping to get 'old blue' back on the road this summer!
 
My idea for a budget engine like yours to get as much poop as you can for the $, It won't cost any more to go .125 than go .080, The 3 ring pistons are good but cost more and takes a lot more balancing on the crank, use the EGGE 4 ring, and use all the rings, I doubt your going to run the salt flats, find an EAB used cam or a Merc cam, there usually in pretty good shape, EAB heads milled for .050 over pistons, usually don't have to mill much with the EGGE pistons, If you can find a Merc intake 4 bolt carb flange and a 283 Chevy Rodchester carb, tapper or bore out the intake carb flange about 1/8in. to match the barb bore. That will be a nice little street engine. Walt
 
I would use the 3 ring pistons, but it is hard to disagree with Walt!! To me the engine needs to be balanced anyway stock or modified. I would never put together an engine without balancing it and if your going to balance it then the 3 ring pistons are a better option. If you choose not to balance it then I would go with Walt.
 
Balance it regardless, with the flywheel etc. Use the .125 over bore 3 ring piston. Absolutely no need for a 4 ring piston or should I say 4 rings on a piston. g
 
Re: Street 8BA piston question / and 1941 A11 ?

This thread comes just as I was about to ask a similar question on pistons,
does ALL this advise equily apply to my original "1941 A11 Tin Can Motor"
to be bored out for replacement pistons of 3-3/16 stalk or should I decide to go ahead and have it cut to over sized to 40-60-80- + ? 53 years old.
Ditto the three ring or four ring for a long distance street - cross country rig if it will be turning a Mitchell 26 % into a 3.78:1 rear end on a pickup...
I do not plan to be / act younger than I am, hot rod, race rice rockets...:D
 
I type in neat evenly spaced rows, but the forum decides to break it up into odd lengths... a bit frustrating, someone please PM me and teach this luddite the trick.
Now back to the important lessons to be learned here with all you good folks. "T"
 
From what I understood the tin sleeve motor is happy at 3 3/16" but not a great deal more according to Walt.
Other than bore size ( as yours will be 0.125" over stock at 239ci) all the above is golden.
Martin.
 
I disagree with Walt. I never re balance an engine, if I use the original crank and rod assy. Never knew a shop that did or does. Yes balancing is necessary when modifying the crank and switching around rods. When I had the Bville engine balanced the rods were so close he didn't have to do anything to them. Egge pistons are with in a gram or two and piston weight isn't an issue when balancing an engine any way. Balancing is a Black art and differed balancers use differed t formulas anyway. BUT!! If it makes you feel better do it. Now we come to flywheels and clutches, On a stock setup I wouldn't bother. However if your going to change pressure plates or anything else I'd re balance it and marl the location of the pressure plate. Especially when re drilling the flywheel.
 
Thank you for your direct reply Mr. Scooder, and both Walter & Ron... as always !
A vigorous and healthy debate is far more interesting and a better education then
a room full of well dressed gents sipping tea... not knowing **** about real life.
 
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