Don Terrill’s Speed-Talk

Two inch bar with spacers in mains,using dial depth gauge with large curved point, and 4 inch base.. easy to find difference end to end.How do you know if the factory cut from lifter side to outside of block is right ? Most shops around my area just indicate that part straight and cut the deck so it is square end to end as measured from first cylinder to last.

Are you trying to see if the left bank is 90º to the right bank with the crank centerline as the vertex of it?

This might help?

Block Tools

Yes John I am trying to see if banks are at 90 degrees,and bores over center line of the crankshaft. I was wondering what other people use/do to get things right.

There must be someone near you with a 4 axis CNC. It's measured on every block that get's mounted.

I'm not sure why you'd want to measure it but so long as the stroke of the crank is the same on every throw, so long as the conrods are all the same length, so long as the pistons all have the same compression height........then all of the piston protrusions will all measure the same.
It's easy to dummy assemble the block, move one piston / rod from one end to the other.


If piston protrusions don't measure the same, then there's a problem somewhere.
It's often the crank.

MotionMachine wrote: ↑Mon Oct 16, 2017 7:00 pm There must be someone near you with a 4 axis CNC. It's measured on every block that get's mounted.

Having that level of precision is kind of a double edged sword. You sometimes find that the factory machining was off enough that you might have to take a block out .060 to clean up when all it would have needed was .030 at most. If it cleans up.

peejay wrote: ↑Mon Oct 16, 2017 7:16 pm

MotionMachine wrote: ↑Mon Oct 16, 2017 7:00 pm There must be someone near you with a 4 axis CNC. It's measured on every block that get's mounted.

Having that level of precision is kind of a double edged sword. You sometimes find that the factory machining was off enough that you might have to take a block out .060 to clean up when all it would have needed was .030 at most. If it cleans up.

Actually that's kind of misleading. Yes, it'll tell you where the bores are in relation to the blueprint but that doesn't mean the machine can only bore on the blueprint, it's an option if the block is close enough to clean at the desired bore size. You can do that or bore on the existing locations or put the bores anyplace you want. If I have a block with 7 cylinders that will correct at the blueprint but one hole needs to be moved .005" to clean up, I can do that easily.

I use a Goodson deck height checker. It's 8" tall for a SBC exactly, kinda shaped like this. ] or this[ . It has a magnet that will hold it against cyl wall. It's set up for a 2" dia bar in mains. So .000 would be 9.000 deck assuming correct doughnut rings installed in main tunnel. The top of the ] is about 3" wide and is 90 deg to cyl wall. Slide your deck indicator on clean
Deck back and forth and if measurement moves on the deck it is not exactly perpendicular to cyl wall. If you have room left you may then correct the deck to be square side to side.

BHJ tooling. Enough said.. They sell tooling for correcting deck squareness as well and gauges to measure from the deck to the fixture.

To answer the OP's question about how to measure deck height and the bores in the Y axis, here is the probe readout for a 440 block I am doing. The machine automatically positions the block so that the cam tunnel is directly over the mainline in preparation for probing. The left column is the factory blueprint bore locations for a 440 in X from the datum, the next column is where they actually are. The Y values are in relation to the crank centerline, 0.0000 being perfect. This block is actually extremely good for a 440, especially the decks. In fact the pass side deck shows only a .0004" height difference in the front. The drivers side is tipped .004" and this results in the positive Y values for all the cylinders on that bank. A traditional boring bar would duplicate that bore error and any surfacer would repeat the deck angle error, if not equipped with a BHJ fixture. A CNC will bore and deck each bank exactly 45 degrees from cam/crank centerline.

SBC Bowtie block with a bad cylinder with a divot. It was set up in a boring mill and cylinder was directly over crankshaft center line to install stepped sleeve. The bore had to be moved away from the center line and moved to one side to place the sleeve in the middle of head bolt holes otherwise the counter bore for the step would have cut into/or get extremely close to the tapped hole for head studs....Just trying to do the best with what we have and trying to see what others do thanks for all the help and replies.

I would say the bore being perpendicular to the crank centerline is more important than being on center. some engines are built with the bore off center of the crank centerline for less friction. remember they used to use pistons the pins were off center and they were rotated 180 degrees to improve performance

how would you set this block up ???

Cylinders are not normally on crank centerline, if they are it is by luck.
The cylinder needs to be 90deg to crank, deck needs to be parallel to crank, and cylinder 90 to deck, so the piston lines up with the HEAD. The other dimensions basically don't matter, because you don't have enough meat to change them unless you are re-designing the whole thing.

Measure deck height with calipers, distance from housing bore to deck. Add half housing bore size.
You need radius on one jaw of the calipers to go in the housing bore. End mill a groove in some round stock and stick it on the jaw. This works on all engines. You could measure DOWN with a depth gauge but in must cases that will be less accurate, why??? because it sure is harder to push a rope than pull one. Depth mic with really long rod....rod very wobbly.

If you have LOST the cylinder location use a deck plate or head gasket and see how that lines up, personally I most often leave the last 1/4 of the cylinder as a step for the sleeve to rest on, so i never lose it, but to do that you do need a way to indicate that in to bore the sleeve, and for old fashoned boring bars that's not included.