.100 or .125 bore without sonic testing the block? How Safe?

R

Riff Raff

Junior Member
Due to budget limitations, my 8BA will be rebuilt with the stock heads, intake, camshaft and crankshaft.
I bought a set of .060” oversized pistons but it still didn't give a clean bore.
The machine shop suggested sleeving the block, but I thought about moving to .100" over, which would be the minimum needed bore to clean the cylinder walls.
The problem is I already have two sets of pistons (.040" and.060"), so it would be cheaper to sleeve the block and bore it .060" (since importing new pistons from the U.S. to Brazil would double their price due to taxes, plus the shipping cost, which also doubles because of taxes).
It seems to be commonsense that most 8BA blocks can be safely bored to .125 over, but also seems to be commonsense that you should sonic test the block prior to doing so.
I’ cannot risk ruining this block, because good flathead blocks are really hard to come by in Brazil, and are quite expensive to.
So, to justify going big bore (and over my budget), I ask:

1) If I can’t sonic test the block, is it safe to go .100 or .125, or would it be safer sleeving the block and bore it .040 or .060 and use the pistons that I already have?
2) If it’s safe, would a .100 bore give a justifiable increase in torque or power even with stock 8BA heads, intake, cam and crank (in comparison to the .060”)?
3) Would .125 be even better (if it's really safe)?

Building this engine has been a long time dream and if I ruin this block I don’t think I can afford a new one, so I really need to be on the safe side.
Thanks!
 
There´s nothing like safe when dealing with 50+ year old engines...if it was run with pure water it may be badly rusted in the waterjackets.
You can get the torq cheaper by raising compression milling the heads then bying a new set of bigbore pistons...
If you have the pistons and sleeves...use them...just my 2c
 
Sonic testing would be way cheaper than messing up a block! It can't be that expensive, what are they asking for the testing? But, I agree with flatheadmurre, sleeve it and you will have a block that will almost last forever.
 
Riff Raff >>>I bought a set of .060” oversized pistons but it still didn't give a clean bore.>>>


You've already got the 60s. So just how UNclean was the bore? I've had blocks with pretty deep gouges and scratches here & there. Not perfect but no excessive oil smoke, consumption or other noticeable side effects except I knew they were there. I got over it. 8^) Jack E/N
 
I bored all my engines to 3 5/16 using Egge 3 ring pistons. Never had a problem. Back in the day we ran 3 7/16 at the track.
 
expect to "maybe" having some overheating issues if this is going into a driver.

No replacement for displacement. But max bore on an engine out the gate seems extreme (if it's a street car). I assume you have pitting that the .60 didn't fix? What about .80 over, if you do whole hog you are still needing new pistons.


If you bore out to .1 and it still doesn't work you can sleeve it. Just be aware of possible heat and thin walls.


Flatheads, joy of spending money. ugh. Best of luck.
 
Last edited:
My engine is bored 1/8" over and have never had any heating problems. This is with a stock radiator with no pressure cap.
 
I have two both at 3 5/16” bore but one has 4” crank and the other 4 1/4” crank ,4”one with electric fan and the other 4 1/4” crank a mechanical fan . Stuck in stop go traffic crawling in summer for half an hour in both cars ,cool as a cucumber , the only frustration was the traffic jam, and on the clutch all the time.
Both blocks were super cleaned and lots of original core sand flushed out, 180 stats , 7Lb caps. 4 1/4” has drake pumps ,4” has Skip Haney pumps. All surfaces decked and square, ignition set right , 97s jetted right. Gotta say the 4 1/4” in a light 32 3W has some torque though it doesnt really rev up quickly.
Overheating is not an issue with proper preparation.
 
Last edited:
I've had two 3 5/16" bore 8BA engines. The first was a 4" stroke that had no problems. The second is my current stock stroke 258" engine. This one tested OK (the machinist said it would go to 3 3/8"). When he bored it out, one cylinder had a pit in it that he said was a casting flaw. He said we could run it the way it was, but I decided to play it safe and had him sleeve that one cylinder. The engine runs well and has no overheating problems.

I guess what you can do will be best determined by the relative costs of sleeves, piston sets, and machining.
 
Why are you averse to doing a sonic test? Is there nobody in your area that can do it? NONE of my blocks have been bored without doing that first. You also can see if there is any core shift as the thickness on one side of all the cylinders on one or both banks are thicker on one side then the other. It won't show you if there are deep rust pits in the water jacket side unless you happen to test in just that spot. My engine machinist doesn't bore a block to wall thickness less then .100. This is why you don't buy the pistons before you check how much you can bore it.
 
I'd keep it simple, sleeve the block & use the pistons you have. Maybe mill the heads to increase compression. Just my .02 cents. Good luck & have fun with it! mike
 
Magnaflux then go for it or scrap if badly cracked. 8BAs are not that hard to come by. Many people have a bunch on the shelf including me. The pre- 59A blocks are another story.
 
As Tinker said, what I have is rust pitting that the .060 bore didn't fix.
I wanted to have the block sonic tested, but no place around here will do it. No machine shop would even magnaflux it. Best I could do was a pressure test (which showed no cracks).
So, I thought I'd ask the ones who know and have experience with this engines to know if it would be safe to do a .100 overbore without sonic testing.
There aren't so many god blocks left here in Brazil. I bought two to find a good one, and most blocks I've seen were cracked or rusted beyond salvation. And the worst part is that even in bad condition they are quite expensive.
As flatheadmurre pointed out, if this engine ran a long time with pure water (which was a common practice here in Brazil) would that indicate that the safest approach would be to sleeve the block?
Seams that without the sonic test the safest choice would be to sleeve the block and have just a mild .060 bore.
 
One more question: if the machining process hit a thin point and exposes the water jackets, can a sleeve save the block or it will be ruined?
I've heard that some diesel engines use wet sleeves, could that be a solution in that case?
 
I would spend about $60 US and get a sonic test gauge from Ebay and test it myself.
Ebay number : 31204599171 is an example.
 
You must log in or register to reply here.
Back
Top