Broach Marks
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Le Mans Master
Joined: Feb 2006
Posts: 6,048
Likes: 5
From: "cutesy" TN
When the raw cast block was first machined it left "broach" marks.
This was done by a machine, that in one stroke shaved the block to make it true. The machine that did this is big (I heard it described as big as a locomotive) and uses a blade to do this. As the blade wears it has gashes in the blade that leaves the "broach" marks. (I have also heard the argument that it works the other way. As in: it wears not leaving marks)
The marks run parallel to the crank centerline. Machine shops do not have a machine this big (at least none that I know of) to cut the block. They use a machine that cuts much smaller amounts in an orbital pattern. If the deck (where the heads bolt up) has circles it has been "touched" and is no longer original.
I hope this clears up the "broach" mark reasoning.
This was done by a machine, that in one stroke shaved the block to make it true. The machine that did this is big (I heard it described as big as a locomotive) and uses a blade to do this. As the blade wears it has gashes in the blade that leaves the "broach" marks. (I have also heard the argument that it works the other way. As in: it wears not leaving marks)
The marks run parallel to the crank centerline. Machine shops do not have a machine this big (at least none that I know of) to cut the block. They use a machine that cuts much smaller amounts in an orbital pattern. If the deck (where the heads bolt up) has circles it has been "touched" and is no longer original.
I hope this clears up the "broach" mark reasoning.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Pete, the photo below is of an original '62 pad, and is a good example of the longitudinal broach marks. Some pads had more than others when they were built, and some had hardly any at all. When a block is decked during a rebuild, those marks (and the original stampings) are eliminated, and the pad surface will show curved machining marks from the 12"-18" rotary cutter machine shops use.
Thread Starter
Racer
Joined: Jul 2006
Posts: 270
Likes: 3
From: Montana
Okay guys, I think I'm getting the picture here 
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The 'broach marks' are in the surface finish of the 'stamp pad' before the numbers were actually 'stamped' in ... geez, this makes sense now
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Before now, I had thought it was the imprint integrity of the stamped numbers whether as originally stamped or re-stamped numbers
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Thanks to all for your information and photo's.
Merry Christmas,
Pete
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.The 'broach marks' are in the surface finish of the 'stamp pad' before the numbers were actually 'stamped' in ... geez, this makes sense now
.Before now, I had thought it was the imprint integrity of the stamped numbers whether as originally stamped or re-stamped numbers
.Thanks to all for your information and photo's
.Merry Christmas,
Pete
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