Sonic Check

[67GT500]

Hi, just had my 428 sonic checked.. a little unsure if it would be ok for a rebuild.. it currently is standard bore.. Engine builder says it has bad core shift and to look for another block.. Any advice would be great

Thanks

[cjshaker]

Depending on how much the bores needed to clean up, I'd use it. Often times, your average machinists are only thinking in typical .030 overbores and don't realize, or have experience in,  doing minimal overbores and using custom sized pistons to save an older block. Since custom pistons are easily gotten, it's much wiser to go that route than standard aftermarket slugs in standard overbores. You can get alot more use out of a block than just boring away like they did in the old days. FEs are notorious for thin walls and core shift, so minimal overbores and custom pistons is really the only smart choice, in my opinion. That block is certainly useable for any street build.

[thatdarncat]

I agree with what Doug said and will add that a shop with the proper equipment can also offset bore the individual cylinders using the sonic map to either even out the wall thickness or bias the thickness to the thrust side as needed. And also like Doug said, what are your plans when done, street build or race engine? Is it the original block for the vehicle with matching date codes and possibly a partial VIN?

[Barry_R]

If accurate - those numbers are NOT thin by 428 standards.
That is a good buildable block.

[KMcCullah]

Looks good to me. I'd build it. Even with the core shift shown on the sonic, at .030 over your thinnest spots still would be around .100.

Call Blair maybe he still has some of these trick CP 428 .015 pistons.

http://fepower.net/simplemachinesforum/index.php?topic=745.0

[jayb]

I'd build it too, but it would be worth minimizing the overbore, and going to a custom piston if that was necessary.  Assuming here that you are looking at up to 600 HP; anything over that would be questionable, in my opinion...

[67GT500]

Thanks for the comments.. I'm not looking at going big on HP, around 450. Edelbrock heads, FPA headers and a cam, which i haven't picked yet.. so this is some good news that the block is ok to use. Its not a matching numbers block, just a replacement block that i had been saving for a rebuild, so to get the news that it had bad core shift and that the recommendation was to look for another block, was a bit of a let down..
I will take the advice and look at some custom pistons

[ScotiaFE]

And maybe a different builder?
He may be lacking the knowledge to build 428.

[cjshaker]

Howie has a valid point. If the guy acts like it's a stupid idea or scoffs at it, I'd walk away and find someone else.

[67GT500]

I think he might just be leaning on the "safety advice" side. by providing the sonic check sheet, then leaving the decision up to me.

[turbohunter]

I think what the guys are saying is that even though he may be a great builder, if he knew FEs well, he would be aware that those numbers are pretty safe.
In other words, he wouldn't be giving you the choice to build or not. He would say that those are pretty good FE numbers and there are plenty running around now with numbers not as good (like mine). Now here is what I suggest you think about for this block. Or, here is what I would do with this block.
Get the difference?

[RobMcQ]

Yep, that is a bad sonic test, particularly if you're not used to looking at FE block sonic tests. For an FE block, it's not too unusual though. Not a problem with a good offset bore job and some semi-custom pistons, as has been pointed out here.

Offset boring though may not be nearly as simple as it sounds. The machine shop has to have the right equipment. Many shops are still using old style, three finger air lock boring bars like a Rottler F2, or a Kwick-Way, etc. While the machine shop will tell you they can offset bore a block with these, they really can't, no mater what the machinist believes. He can be very careful in setting up the boring bar, but when you release the air lock, those fingers will move the bar "just a little bit". It's just not possible to be highly accurate with these machines, and there is no way for the machinist to verify the accuracy. Nor can they be used to repeat a cut in the same bore, say doing a small initial cut, then a slightly larger one. They are simply not accurate enough to do so.

To accurately bore a block, a CNC controlled boring bar is needed. It doesn't have to be the latest and greatest 5 axis CNC Multi-purpose machine, an older Rottler CNC F5 can do the job. You can check out YouTube for videos of an F5, or a Rottler F69, an RMC V30, a Centroid, etc., to get an idea of the differences. Not only can you set a CNC bar to offset the bore any amount you desire, but you can use it to creep up on a minimum oversize bore as well. For example, wear ridges are typically heavier to one side of the bore. If you bore the cylinder on center, it may easily take .030" or more to clean the cylinder. But, if you offset the bore center towards the worst part of the ridge by say .005", and then do a small .010" first cut, you can evaluate the result, and maybe make a small correction on a next cut. We've often been able to keep a badly worn block at only a .030" oversize , when other shops have said they had to go .040" or .060" in order to clean the bore.  For their old style equipment, they are probably right. 

So when talking to a machine shop about offset boring your block, find out what type of equipment they are using. You don't need to question their abilities, or denigrate their equipment, but simply inform yourself as to their capabilities so that you can make an informed decision.

Rob McQuarie
Blue Oval Performance

[turbohunter]

Rob I'm curious what made you talk about offset boring.
Was it in the numbers or the core shift comments. Or....
Just trying to learn.

[cjshaker]

That's good info, Rob. Thanks for the education.

[Bolted to Floor]

For the uneducated like me, can someone explain the test result sheet? What I get out of is 8 readings per hole. If your bore it .030 then you loose .015 from each of those numbers. Front and back seem right for location in cylinder, but major / minor makes no sense to me.   

[jayb]

I can't agree with Rob's statements on offset boring.  I had my Shelby block offset bored quite a bit when I built my big SOHC engine.  This was offset boring the aluminum block itself, in preparation for using larger sleeves, spaced farther apart.  I was going for the maximum bore size, so the inboard cylinders (2, 3, 6, and 7) were offset bored 0.035", and the outboard cylinders were offset bored 0.105".  My shop used an old style boring machine (Sunnen or Kwik-Way, I think...), and certainly not a CNC machine; there isn't a CNC machine in the place.  Those bores are perfectly placed; I have checked them multiple times.  Also, after the rod broke at Drag Week last fall, a different shop is repairing this block, and had to touch up those same bores about .003" after the block was welded.  The guy at this shop is extremely meticulous, maybe the best engine machinist I've ever worked with.  Again, no special equipment, and the bores are right on.

There must be a way to do this accurately, without CNC equipment, because I've seen it done on my own stuff, and elsewhere - Jay

[jayb]

For the uneducated like me, can someone explain the test result sheet? What I get out of is 8 readings per hole. If your bore it .030 then you loose .015 from each of those numbers. Front and back seem right for location in cylinder, but major / minor makes no sense to me.   

Major and minor refer to the thrust surfaces of the bore.  If you think about the engine cross-sectionally, and look at the position of the piston, the crankpin, and the connecting rod right after the cylinder fires at top dead center, the force on the piston is directed mostly against one wall of the cylinder; this is the major thrust side.  This is because of the angle of the crank pin and the connecting rod.  For number 1-4 cylinders, this is the outboard side of the cylinder, and for 5-8 it is the inboard side.  Visualizing the engine from the front, and drawing a picture of the bore, the piston, the rod, and the crankpin about 45 degrees after top dead center is the easiest way to see this.

The minor thrust side is opposite to the major thrust side; this is the inboard side of 1-4, and the outboard side of 5-8.  Minor thrust refers to the force on the piston as it is compressing the air/fuel mixture on the compression stroke; there is quite a bit of force required to do this, and the piston pushes hard on the minor thrust side while it is compressing the mixture.

On a sonic check, you can tolerate thinner spots on the front and back sides of the cylinder, but you'd really like to have the major thrust side and minor thrust side as thick as possible.

[ScotiaFE]

There must be a way to do this accurately, without CNC equipment, because I've seen it done on my own stuff, and elsewhere - Jay

An old hand crank hack like me can get the hole pretty close with a dial indicator.

[fairlanegt427]

uae it send it to barry at survival motorsports.  he does great machine work. and more than likely probably has those pistons you need for your 428 in stock.  im not picking on your engine guy but barry knows the fe.

[Barry_R]

CNC does some really great things, and allows a level of easy setup and repeatability that was very difficult in the past.  I can certainly appreciate the value of the latest equipment, and agree that there are things that are "impossible" without it - like CNC porting on a 5 axis machine.

Its rather silly to assume that a good machinist is unable to do something as simple as square decks though.  Its a basic fixturing task.  New and cool equipment will allow you to be working on something else while the machine does the job, it will allow a less skilled (thus less expensive) employee to do the job correctly, and it will free up time.  All of those have great value in a shop environment and justify the investment.  But I can promise that a guy at Holman-Moody in 1960-something was perfectly able to square up a block or offset a bore without a computer anywhere in sight.

[Bolted to Floor]

For the uneducated like me, can someone explain the test result sheet? What I get out of is 8 readings per hole. If your bore it .030 then you loose .015 from each of those numbers. Front and back seem right for location in cylinder, but major / minor makes no sense to me.   

Major and minor refer to the thrust surfaces of the bore.  If you think about the engine cross-sectionally, and look at the position of the piston, the crankpin, and the connecting rod right after the cylinder fires at top dead center, the force on the piston is directed mostly against one wall of the cylinder; this is the major thrust side.  This is because of the angle of the crank pin and the connecting rod.  For number 1-4 cylinders, this is the outboard side of the cylinder, and for 5-8 it is the inboard side.  Visualizing the engine from the front, and drawing a picture of the bore, the piston, the rod, and the crankpin about 45 degrees after top dead center is the easiest way to see this.

The minor thrust side is opposite to the major thrust side; this is the inboard side of 1-4, and the outboard side of 5-8.  Minor thrust refers to the force on the piston as it is compressing the air/fuel mixture on the compression stroke; there is quite a bit of force required to do this, and the piston pushes hard on the minor thrust side while it is compressing the mixture.

On a sonic check, you can tolerate thinner spots on the front and back sides of the cylinder, but you'd really like to have the major thrust side and minor thrust side as thick as possible.

Thanks for the lesson Jay, that makes a lot more sense to me.