I've contended for the last few years that the way I have my blocks machined via the BHJ fixtures is better than most on here and other places.

Let me explain further.

Currently I have 2 Olds Big blocks at the machine shop I use in Jacksonville Florida. 1 is a 425 "D" block, the other a 455 "F" block.

Both blocks were sonic checked first, with similar results. That is done at 12, 3, 6, and 9 o:clock as being viewed from the side of each bank. Then it's done at the top, middle and bottom of the cylinders. But in the interest of time and space I will only describe one of the worst of the 8 cylinders on the D block. Block was ultimately bored to 4.180.

Sonic check results, cylinder #4, top to bottom;
12:00 286-263-254
3:00 153-145-139
6:00 291-276-305
9:00 218-200-191

Obviously the 139 is the limiting factor for overbore as you typically don't want any less than .100 on any non thrust side (front or back wall of cylinder)

However the BHJ Bor-Tru plate http://www.bhjproducts.com/bhj_conte...ntfixt/btk.php used correctly locates the bore over the journal and perpendicular to the crank after the block has been align honed and square decked. This cylinder on this block was out .023 front to back, (heavy on the rear) and .020 side to side (intake to exhaust side). Therefore it would take no less than .046 to clean up (from standard by the way) and correctly locate the cylinders in the block. Hence one of the reasons it had to go to 4.180.

So during boring it actually took much less off the front (3:00) than the rear. If someone was going to bore this as "big as they could go" they would have been limited by the 139. As it turns out this block could have gone to 4.210 and beyond with little or no issue after correctly locating the bore as most of the meat came off of the rear (9:00).

And needless to say correctly locating the cylinder over and perpendicular to the crank has it's advantages. The angle of the bore in the block side to side as being viewed from the front is also corrected. This one was out .008 top to bottom.

So now in this case the bore is more centered in the casting. Others have said that these blocks may exhibit "core shift". But here the core was right, however it was bored incorrectly at the factory, by a bunch.

Does core shift happen? Of course, but until it's machined correctly with the right procedure and equipment there's no way to tell for sure where the discrepancy lies. If someone were to favor the "heavy" side without really knowing what was what they could actually be making it worse.

Hope this helps.

P.S. By the way, some machine shops tout a CNC program to machine their blocks. However they use the location of the deck dowels as a reference. Read the text on BHJ carefully. They mention that their plate allows for the correct location of the dowels as they're not always in the right spot from the factory. If you use the dowels as a reference point, and they're off, then so is the rest of your machining process, plain and simple.

 

Thanks.

 

Yes, very interesting. Thanks, Mark.

- Eric

 

Great info!!! many thanks!! i'm about to start on a '455 build and this will come in handy.

 

Thanks

 

Excellent post. Thanks for sharing.

 

You're very welcome, thanks guys.
Both of these are full builds which will be going to the dyno. Of course I'll post the results.

 

Here's the results of the sonic check. Sorry it loaded this way, tried twice to correct it.

 

Here ya go:

 

Thanks Eric.

One note, as per the text, notice the wall thickness on #4 and #6 vs #3 & #5. Notice how much more concentric 3 and 5 are at 3:00 and 9:00 especially.

Obviously one side was better than the other. I find that a lot.

 

That's great info Mark.

I'd personally like to see you take the high road and leave other vendors names out of it though.

 

I see your point, and I somewhat agree. I will change it.
But the reason I mentioned it initially is because some don't know to ask those types of questions when enlisting the services of a machine shop, any machine shop. So I hope this helps.

Thanks.

 

Mark you do make excellent posts I must say ,very informative !

 

So let us use me as an example, my block needs to bored and honed to 4.395 from 4.351". So if I tell them to just over bore it, most will take even amounts from either side, where my block might have significant core shift? This means potentially running too thin wherever the bore shifted? Sounds interesting and important.

 

Yes, I've run into that before. Once you see how far off it is sometimes you just have to make do with what you have or look for another core.

 

Mark you must REALLY hate BTR.Just because he will not give you free advice on cams anymore.....LET IT GO MAN.All you are really doing is hurting the
OLDS community with you're constant bashing of Bill.
I don't have the time to de-bunk your BS,but I will be back.

 

Huh? I don't HATE anybody!

He says his CNC program is the way to go(there are other shops that claim the same, I didn't single out anybody), I don't believe it is and I showed why.
I've talked to Bill more than once, just not recently, no need to really, no issues. He also did my buddys crank, it's in his book. Again no issues.

I think you misunderstood my point(s).

 

Yeah, I didn't see anything particularly "hateful" in anything Mark posted either.

He just contrasted different techniques, and noted that the basis for claims that the other one is superior is not solid.

Mark doesn't even bore his own blocks, so it's not like he's trying to get business for himself this way either. He's just giving information about what he has found.

- Eric