Judging Broach Marks

[Terry M.]

Re: Judging Broach Marks

That would make sense. Cases were stamped before the heads were installed. I would think that the pad was either mask off with tape or wiped off after painting. If the paint was left on it would be hard to see the usage code on it when mated with the chassie.
KEN

Ken, You are painting with too broad a brush.
Small blocks received their assembly stamp near the end of the line -- heads were on when the assembly stamp was done.

Big blocks received their assembly stamp closer to mid-production, and were stamped before the heads were installed.

[Jack H.]

Re: Judging Broach Marks

Judging broach marks is an area that's 'art' versus science... Both engine plants (Flint and Tonawanda) used broach machines and the depth + pattern varied. Here are two factors:

(1) How fresh were the cutting blades on the broach machine when that particular engine block went through it?

(2) How hot/cold was that particular block from the upstream casting process? when it was broached?

On some untouched blocks, the broach marks are SO light, SO shallow, they're VERY hard to see. On other blocks, the broach marks are VERY deep/pronounced and easily identifiable.

Now, throw in confusing factors... If the cylinder case is original to the car and it's aged/used, there's a good chance the pad is going to be discolored from years of exposure to the atmosphere with oxide growing. PLUS, there's a reasonable likelihood the surface will show some degree of damage (dropped tools, Etc.).

BUT, the judging of the pad (engine plant stamp, VIN stamp, and broach mark) applies ONLY to originality. Let me repeat that...

We're not judging condition of the pad (or we're not supposed to be)! But, I'm pretty sure there are judges out there who'll see the presence of dings & swirl marks atop the factory original broach marks (a condition issue) and conclude the pad has been 'dinked' with...

I'm also pretty sure some judges will see blocks that have been sent out for fresh broaching services and let that influence their assessment (too fresh/new to be the factory original).

For these judges, I'd remind them the judging standard for Flight (restored cars, vs. Star/Bowtie--unrestored cars) is as manufactured by GM/Chevy and as delivered to the original owner with then current dealer prep.

So, we should NOT let the issue of condition (too fresh/new OR aged, abused, damaged) of the surface of the stamp pad influence the decision/judgement call. What would a pad have looked like when the car was actually freshly delivered?

Plus, since condition isn't an issue, ignore those stray dings and swirl marks + the oxidation/age of the surface. Can you see evidence of the factory original broach process by reading between the lines?

[Roy S.]

Re: Judging Broach Marks

Guys you are painting with too broad a brush, the pad use to be worth 88 points and it was all or nothing or anything in between in some cases, that was changed to 38 broach and 50 remaining items because we were encountering some decked blocks that had no broach marks but still had original fonts and characters in the remaining machine code or machine code and VIN derivative. The breakdown was to give those pads with missing broach marks some points not an 88 point deduction. It was not done to assign anymore points to anything it was done to keep a full deduction from being made when partial should be given.

[Jack H.]

Re: Judging Broach Marks

Hum, since you reply to my post, can you clarify what I've said/done that's wrong?

I said:

(1) Judging the pad is an artform that's not so easy to obtain experience in doing correctly.

(2) The condition of the pad is not a consideration; it's factory originality (or the appearance thereof) that counts.

(3) The three issues of engine plant emboss, vehicle VIN derrivative emboss and broach marks are independent scoring considerations.

Waz did I do/say wrong, boss?

[Kenneth B.]

Re: Judging Broach Marks

Ken, You are painting with too broad a brush.
Small blocks received their assembly stamp near the end of the line -- heads were on when the assembly stamp was done.

Big blocks received their assembly stamp closer to mid-production, and were stamped before the heads were installed.

TERY
I stand corrected. I should have said BB'S were stamped with the heads off before painting.My main point was that there would be no paint on the pad so it would be easy to see the usage code to get the right engine in the Corvette that was ordered .
KEN

[Roy S.]

Re: Judging Broach Marks

Jack,

I replied to a thread that involves broach marks, if it looks like I replied to your post then your computer is set up different than mine! The last I knew posting a reply that started off Guys did not mean I was responding to Jack, sorry if my computer ineptness offended you.

[Stewart A.]

Re: Judging Broach Marks

I just come back from a machine shop and while I was there I had a look at heaps of chevy blocks.
Around 25 of them, none of them were Corvette blocks, but were still Chevrolet blocks. Most were 350 cube and every broach mark was different. Some were coarse and very obvious, some were so faint that they almost looked smooth.
I even saw one that come out of an original 57 Chev 2 door that was meant to be an unopened block, standard bore and it was as smooth as a baby's bottom, no broach marks. Some had rusty dots on them. This exercise would be very hard almost impossible to judge. I even put broach marks into one with heavy sandpaper and looked pretty much the same as the heavy broach mark blocks.
I feel it's black magic to judge these pads I don't think I could ever do it. Stewy

[Mike M.]

Re: Judging Broach Marks

Sure you can, Stewart, if you dedicate yourself like several in this organization have. Your trip to the builder would be a good start. If that had been on the Judging Field, you would have earned one or two judging points for OJ'ing.
Repeat that process at an NCRS Judging Event and the other events all over the country, attend the Judging Schools and Retreats, with the tutorage of Master Judges, say for 10 or twelve times a year for fifteen or 20 years plus and earn 300 or 400 Judging Points or more and you should be able to Judge a pad at a glance.
HaND

[Rob M.]

Re: Judging Broach Marks

Broach marks on this pad look very authentic to me!!! I wouldn't deduct for it...

regards,
Rob.

[Warren F.]

Re: Judging Broach Marks

Joe Greer,

I pretty much specialize in 1971 big blocks. Your 'before' rebuild picture of the stamp pad is definitely what I see as original pad and stamping.

Your 'after' rebuild photo because of the block surface being prepped by the machine shops method of cleaning the cylinder case gives the pad broaching surface a different appearance, the 'broach lines' appear much more intense.

A terrific example of how an appearance can look different without any physical changes done to the pad surface.

[Joe G.]

Re: Judging Broach Marks

Hi Warren,
Thanks for the comments. Photos can be tricky sometimes. That second photo, the "after rebuild" was taken with a flash which I think highlighted the marks. Here is another without a flash for comparison. It is more subdued.

Joe

[Michael W.]

Re: Judging Broach Marks

I just come back from a machine shop and while I was there I had a look at heaps of chevy blocks.
Around 25 of them, none of them were Corvette blocks, but were still Chevrolet blocks. Most were 350 cube and every broach mark was different. Some were coarse and very obvious, some were so faint that they almost looked smooth.

Excellent observation and makes the point that not all broach marks were not created equal(ly)!

[Ted S.]

Any Pictures of Original Machining Process

Anyone out there have a picture of original blocks being machined. I assume the broach was like a wide flat file (broach) that moved front to back or visa versa along the deck surface. Is this correct?

[Robert E.]

Re: Any Pictures of Original Machining Process

Anyone out there have a picture of original blocks being machined. I assume the broach was like a wide flat file (broach) that moved front to back or visa versa along the deck surface. Is this correct?

[Terry M.]

Re: Judging Broach Marks

Beautiful Bob.

Too bad there is nothing for size reference. Those tools were about 15 or 20-feet long, and the whole machine with the transfer line was well over 50-feet long.

BTW: I was watching "How it is Made" on the Science Channel over the weekend. They showed Channel-Lock pliers being made, and the use of a broach machine to cut the teeth. A somewhat smaller machine than the above.

Another of those programs showed tubular shock absorbers being made, and the tool that welds the tubes closed. It made the same welds we see on the original C3 (and I suppose C2) Delco shocks.