Sonic tests back-Too thin for 3 5/16 ?
 

I got the sonic test back from the machine shop, they feel that things are too thin to go to 3 5/16. The bore is currently 0.060 over from a rebuild years ago. The shop feels that they can do 0.080 while shifting the bore centers on some. Am interested in comments guys.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Wow! it's great that a sonic test could give so much valuable info. about wall thickness. Be smart and bore as little as possible. You won't notice any performance difference.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Hopefully, Ronnie Roadster, Bored& Stroked, or Pete chime. My 59L block is 3 3/8 +.030 over. Didn't want to go that big, but we had too. After sonic testing, Ronnie was satisfied that there was still enough meat left.

For the life of me, I can't remember what the numbers were.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Hey Tim,
Yes I am also waiting for the Pros to weigh in on the numbers I posted. I don't imagine I will be overruling my machine shop, but do need to hear from others.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

.100 wall is a safe minimum. Looks like you would average about .010 to spare.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

I was advised the minimum wall thickness ought to be .100 while anything more than this is a bonus.

To go from .060 to .080 would mean .010 (ten thou) off all of those numbers.
To go from 60 thou to .125 thou over would take .0325" off all of those dimensions.

It's hard to read some of them, but what would the smallest number be with .0325 taken off them?

It sounds like the machine shop are being mega cautious but that might be justified if they have to guarantee the over bore will be successful. It might be that .125 is doable but they can't 100% guarantee it will be successful.

It would have to be at your own risk.

Edit: is the smallest number .112 or .172?
What is the smallest number?
I would like a lot more numbers at top bottom and middle.
the thrust face is more critical than the others.
I sound like an expert, but am not. I did get a lot of great advice on here though.

Mart.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Now that Pete mentions it, I believe all of the bores tested at +.100 or greater even after going 3 3/8" +.030"

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Looks to me that 3 5/16" is quite viable.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Your going to fine with the 3-5/16 bore seeing the sonic test wall thickness. If the shop your using will not do the boring I would look for another shop to do what you want.
For piece of mind we ran a top speed of 219.8 MPH last year at Speedweek with a block bored to 3-5/16 with similar measurements as yours and that was after seeing two records over 200 MPH all together 16 miles of all out abuse much harder than anything your ever going to do. That engine will be running again this year at Speedweek.
Ronnieroadster.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Mart, the smallest number is 147

Re: Sonic tests back-Too thin for 3 5/16 ?
 

First off, big Thank You to all who have responded thus far.


This sonic testing is all new to me. Am I correct that I should be taking any of the test numbers and subtract .0325 from them, looking for a result of .100 or better?


On a related note, spoke with Egge piston today, and was told they don't offer a 3 ring piston .080 over (which is the smallest next up for me) nor does Ross, though they can make on custom order.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

The smallest number appears to be on a cylinder that is .188 or so on the other side, so they can move the bore over .020 and center it. Given the measurements, I don't see an issue with a 3.3125 bore.

Couple Points:

1) I don't like to do sonic testing on just one location of the bore (top to bottom). I prefer to sonic test each cylinder on all 4 sides, at 3 different depths in the bore. This helps me see if the readings are consistent up and down the cylinder - the 12 readings give me that.

2) The areas that you need to care the most about are the major piston thrust sides of the cylinder. Given the crank turns clockwise, then the major thrust on the driver's side is toward the intake ports, while on the passenger's side it is closest to the outside of the block.

One caveat, sonic testing won't identify a rust pit or other casting issue in one particular spot. There is really no easy way to know that you might have an issue . . . though you can pressure test the block after boring to make sure there isn't an issue. I always try to look into the water jackets and see how much rust and scale I see. If it appears to have a lot of rust issues in its lifetime, then you may want to be a bit more conservative on the bore.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Here is a picture that shows major/minor thrust. It doesn't matter whether it is a V motor or an inline, the concept is the same (just tilt the picture to the right or left!) - the key is thinking about crankshaft rotation. :D

Attachment 490580

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Dale, thanks for the input/response.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

My trusted flathead machinist used the sonic test so that he would never leave a cylinder wall less then .100.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Years ago, I was visiting Al Sharp at his home getting flathead building tips., He made the Sharp heads and intakes, some of the best flathead equipment made that set many of the records. He claimed to be the only guy with an actual engineering degree in the 1950s that was designing heads and intakes. Super nice guy. He built a 3/8" flathead for his '40 or '41 pickup. The block initially tested fine but when it was installed it overheated. There was a deep rust pit on the back of one cylinder and when they bored it, they barely got into that pit and didn't notice it. After boring the block it's a good idea to pressure test it again. After that conversation with Al Sharp when I'm looking at spare blocks to buy, I look at how much rust is in the water jackets and if it's bad I walk away. I look at the rust pits behind the water pumps first, then the bore size and then look for cracks. That improves the chances of buying a good block.

I also went and talked with Johnny Ryan. He owned Taylor and Ryan engine rebuilding. They built some of fastest flatheads in the 1940s and 1950s. They built the engine that won the 1955 NHRA Nationals against a Hemi, the last flathead to win a NHRA championship. A friend was with me and had an engine that would have needed to be bored to 3 7/16" to clean up. He said guys would come into the shop and want their flatheads bored that big, but he didn't like to do it. He felt the cylinder walls would flex too much. He said he had 16-year-old kids coming in all the time telling him how to build flatheads and that the customer was always right. Another super nice old-timer, I was lucky to a have spent time with them.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

I've bored 3 8BA's to 3 5/16". The only problem I ran into was on the last one that had a hidden pit (casting flaw) that we broke into boring the block. It didn't go through to the water jacket, and the machinist said it would be OK as is. For an extra $80, I had him install a sleeve just to make sure.

As to the extra 1/8" being worth it, consider this : A stock (3 3/4") stroke flathead with an 1/8" over bore yields 258 ci. This is 3 ci more than the vaunted Mercury crank provides, with lower piston speeds, and for less that one quarter the price. Sounds like a deal to me.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

I have plans for a big bore 59AB. I already have all of the parts in hand from scrounging/ Friends.
I don’t think anyone here does sonic testing, are the tools terribly expensive? And what type of sonic tester would you need? As I have never done this before.
I have six or seven complete engines, if I can get one to work I would be happy.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

Hopefully Pete will chime in. I seem to recall him posting about a fairly cheap sonic tester one can get from Amazon for around $100.

Again, if I recall correctly, I think he compared it to a more expensive tester and the results were similar or close enough.

Re: Sonic tests back-Too thin for 3 5/16 ?
 

I haven't done any checking lately but I have had 2 different brands of cheap sonic testers. I got one from Amazon and one from Ebay. I don't know what brand they are as I don't read foreign languages. Both work ok as far as I can tell from simple testing with calibrating blocks.
I have often wondered how much one of those scanners cost that will map a complete surface.