[Formulajones]

Ive heard of them twisting like Hoosier mentioned and I've personally seen them snap ears off but the splintered shaft is interesting. As if it had a seam to follow. I wonder what melling is using to make those. The ones I've seen fail didn't happen early on a fresh build either like this one, it was years and thousands of miles later.

The shaft from nightmare is a nice piece. Seems like overkill but an important part of the build.

[peters23]

You can test for hardness using a fine file. It should tend to glide over the material if it is hardened. 30-Rockwell is a medium hardness, so you might get some filing action.

[hurryinhoosier62]

Originally Posted by Sirrotica

This one perhaps? made by Nitemare Performance Products:

http://nitemareperformance.com/pumpshaft.html

It appears that they test for hardness after manufacturing specifying 28-32 Rockwell hardness. Those are the same hardness specs that were used to determine if the Pontiac OEM SD rods were within hardness specs.

I've also taken apart a couple race engines that the tangs were starting to spread, although I never saw one splinter up the center of the shaft as the OP's has.

Brad, it could be a case of the hardness exceeding the spec, making the shaft brittle.

[Sirrotica]

Originally Posted by hurryinhoosier62

Brad, it could be a case of the hardness exceeding the spec, making the shaft brittle.

I entirely agree, QC today is gone from most products no matter what name appears on the box it came in. Names that could be trusted to maintain QC, and deliver a part that could be trusted out of the box, are long gone. The era where someone took pains to deliver quality parts, has been abandoned for corporate greed to capitalize on a companies formerly good name.
.
My reference was that both parts (shaft, and rods) shared the same Rockwell specs to make the most of the heat treated parts being resistant to twisting, and breaking/fracturing stress forces.

Years ago, when I bought my SD rods, the scandal was circulating about faulty heat treat batches from Teledyne (vendor of the rods). I had all my rods Rockwell tested before I sent the parts to be balanced, and all passed with flying colors..........

Someday I should assemble the engine that has been languishing for over 40 years.....LOL

[hurryinhoosier62]

Originally Posted by Sirrotica

I entirely agree, QC today is gone from most products no matter what name appears on the box it came in. Names that could be trusted to maintain QC, and deliver a part that could be trusted out of the box, are long gone. The era where someone took pains to deliver quality parts, has been abandoned for corporate greed to capitalize on a companies formerly good name.
.
My reference was that both parts (shaft, and rods) shared the same Rockwell specs to make the most of the heat treated parts being resistant to twisting, and breaking/fracturing stress forces.

Years ago, when I bought my SD rods, the scandal was circulating about faulty heat treat batches from Teledyne (vendor of the rods). I had all my rods Rockwell tested before I sent the parts to be balanced, and all passed with flying colors..........

Someday I should assemble the engine that has been languishing for over 40 years.....LOL

I’m very familiar with Teledyne’s “spotty” reputation. A lot of otherwise airworthy aircraft got scrapped due to “weak” TCM crankshafts used in their power plants. I had to give the bad news a few times to owners who didn’t know the difference between a VAR forged crankshaft and non-VAR crankshaft. The main difference? Scrap verse $7,000. Non-VAR cranks were known for cracking, especially between the counter weight flange and the main journal. All was well until the FAA issued an AD ( Airworthiness Directive) against non-VAR cranks.

[JSchmitz]

Hardening is a touchy thing. More isn't necessarily better. A lot of people assume that Grade-8 bolts are always better. They are better in tension but nut in shear. Learned that at a very young age. Put Grade-8 bolts in a Brush Hog drive shaft. They broke immediately. I played around with Cherry Red powder hardening compound in the machine shop. I made a T-bolt for the lathe compound rest (just playing around). I hardened it with the Cherry Red. It snapped as soon as I started tightening it. It was made from good quality high carbon steel. If you start with crappy material, no amount of metal conditioning is gonna produce a good product. I suspect this to be the case with the oil pump drive shaft in question here.

[steve25]

Proper tempering to a needed hardness takes time, and that cost money.
You can heat up a grade 5 bolt or any steel for that matter to red hot and then quench it in oil, but the level of hardening will be all over the place!

There is a exact temp needed by the level of redness and then depending on what you want the steel my need to be air cooled breifly before quenching.

Oil drive shaft wise the lesser of two evils for me is a slightly soft one that will twist some before it snaps.

[Shiny]

Yikes, how upsetting was that? Seems you are very lucky it didn't destroy your engine and I'm happy to hear you avoided worse.

I don't expect an answer, but I sent this to Melling on their "tech support" webpage form:

"What alloy is a Pontiac intermediate oil pump shaft IS-54A made from? Is the part through-hardened? To what specs?"

I'm curious about the comment regarding the shaft being longer than expected and in line with chuckies76ta's comment. How much clearance is typical and is it even possible to bind if it's too long? What would bind? The pump? The distributor has a simple thrust washer. I don't know what a pump looks like but is probably another big thrust surface on a driven gear.

The gear on the distributor is retained by a small roll pin. Wouldn't that pin shear before a healthy intermediate shaft broke?

Just speculating about the cause... overstress or defective shaft?

[elefantrider]

Usually a sign of a locked up oil pump. But I also think thick oil not given a chance to warm up before seeing big RPM. Or water thickening oil due to a blown head gasket or leaky timing cover. A few possibilities.

[elefantrider]

Am curious, what weight oil was in this engine? What was the temp of the garage before it was started? Any warm up time?

[John Milner]

I am using 10w30 oil and it was about 180 degrees on the temp gauge.

[Shiny]

Kudos to Melling for a quick and useful response.

Their tech rep said the shafts are made from cold-drawn 1144 they source from Niagara-Lasalle. He pointed me to this description:

Link to Niagara Lasalle Stress-Proof Material Page

This is NOT heat-treated material... it is cold-drawn, then stress-relieved.

Niagara alludes the material being a cost-effective replacement for a heat-treated alloy that was quenched and tempered to Rc 20 to 30 hardness.

IMO, it should NOT be brittle.

I don't know what an overstress failure "should" look like if, for example, the pump locked. Anyone have an example of a shaft known to be "twisted to failure"?

Mike

[elefantrider]

I do but it will probably take me a while to find it in my archived photos.

[Dragncar]

Originally Posted by JSchmitz

Hardening is a touchy thing. More isn't necessarily better. A lot of people assume that Grade-8 bolts are always better. They are better in tension but nut in shear. Learned that at a very young age. Put Grade-8 bolts in a Brush Hog drive shaft. They broke immediately. I played around with Cherry Red powder hardening compound in the machine shop. I made a T-bolt for the lathe compound rest (just playing around). I hardened it with the Cherry Red. It snapped as soon as I started tightening it. It was made from good quality high carbon steel. If you start with crappy material, no amount of metal conditioning is gonna produce a good product. I suspect this to be the case with the oil pump drive shaft in question here.

I deal with that on gear motors. Sometimes on motors with a lot of side loading the grade 8 bolts would shear so we went back to grade 5.
I play around with steel, heating, putting some carbon in it and quenching. Making punches, chisels out of old grade 8 bolts. If you heat them up too much and quench, talking beyond slight cherry red, bright orange that home made chisel will bust a corner off. Dangerous.
The less heat you use the less chance of being brittle while still inducing hardness,
A little light cherry red, then turn off the oxygen and add some carbon to the hot steel surface and quench is good enough. I do it twice.
We have some hex steel of good quality in different diameters I make pry bars out of and heat treat.

Now a broken grade 8 bolt removal vs a grade 5 is a different deal. A old trick is to heat up the broken bolt stub expanding it and then quenching it shrinking it. Many times that is enough to make just enough clearance to remove the bolt with a sharp chisel or other means.
But once you do that on a grade 8 bolt you are not getting a drill through it to use a Easy Out, not happening.
A grade 5 bolt does not get very hard heating and quenching and you can still drill it.
It pays to know what kind of steel you are dealing with first.
And this issue is one of the reasons I have gotten so good at just cutting the bolt out with a torch leaving the base metal. You can weld a nut on the bolt and taking it out with a impact gun.... maybe. If that does not work, cut it out.

[JSchmitz]

Originally Posted by Dragncar

I deal with that on gear motors. Sometimes on motors with a lot of side loading the grade 8 bolts would shear so we went back to grade 5.
I play around with steel, heating, putting some carbon in it and quenching. Making punches, chisels out of old grade 8 bolts. If you heat them up too much and quench, talking beyond slight cherry red, bright orange that home made chisel will bust a corner off. Dangerous.
The less heat you use the less chance of being brittle while still inducing hardness,
A little light cherry red, then turn off the oxygen and add some carbon to the hot steel surface and quench is good enough. I do it twice.
We have some hex steel of good quality in different diameters I make pry bars out of and heat treat.

Now a broken grade 8 bolt removal vs a grade 5 is a different deal. A old trick is to heat up the broken bolt stub expanding it and then quenching it shrinking it. Many times that is enough to make just enough clearance to remove the bolt with a sharp chisel or other means.
But once you do that on a grade 8 bolt you are not getting a drill through it to use a Easy Out, not happening.
A grade 5 bolt does not get very hard heating and quenching and you can still drill it.
It pays to know what kind of steel you are dealing with first.
And this issue is one of the reasons I have gotten so good at just cutting the bolt out with a torch leaving the base metal. You can weld a nut on the bolt and taking it out with a impact gun.... maybe. If that does not work, cut it out.

Cool! Never played around enough to know what I'm doing. Learned A LOT about heat treating in A&P school. But forgot more than I know now. I learned about how the crystalline structure changes at different temperatures, etc. Can use color charts to get temps close. Gotten have right amount of carbon. You can add carbon for surface hardening by heating with an Oxy/Acetylene torch with carburizing flame. Right?

[sdbob]

I remember in metallurgy class in college we had to make a chisel. We used a gas fired furnace if I remember. Then had certain colors to look for,then we had to make a slice on the end with 'scissors'. What this was for so the professor could break off this little piece then be able to judge ,physically see ,whether we properly heat treated the steel. That chisel is the best one I have.

[6point6]

LaSalle 1144 is sold under the trade name "stressproof". It is "notch sensitive", grainy and splits easily. In my opinion, poor choice for a tounge and groove drive system. Manufactures like it because its easy to machine, stays straight and they dont have to heat treat it but its not always a good choice. I designed with and machined a lot it in my career with good and bad results. Most of the guys I worked with considered it cheap junk.

[Shiny]

Originally Posted by 6point6

LaSalle 1144 is sold under the trade name "stressproof". It is "notch sensitive", grainy and splits easily. In my opinion, poor choice for a tounge and groove drive system. Manufactures like it because its easy to machine, stays straight and they dont have to heat treat it but its not always a good choice. I designed with and machined a lot it in my career with good and bad results. Most of the guys I worked with considered it cheap junk.

Thanks for this. To me, "notch sensitive" is more about impact loading than just overstress. No info here suggesting impact loading but hard to know. Being cold-drawn and not really "solutionized", your comments about "grainy" make sense. The web site talks about allowable "seams", which sound like artifacts from hot or cold forming...and can't be good. Maybe what you describe as splits easy?

As to being cheap junk, it is pretty strong without needing heat treatment, so that might be a little harsh, but definitely not going to be the same quality, strength, nor toughness as a quenched and tempered alloy that costs much more.

Personally I think the original slotted design is pretty bad. To your point, GM probably made these parts out of something better but could have at least reinforced the slot or increased the shaft diameter.

[JSchmitz]

I always thought notch sensitivity meant that it would break easily if there were stress-risers like a centerpunch mark or sharp corners. This is a good read on notch sensitivity: https://extrudesign.com/notch-sensitivity/

[Shiny]

Originally Posted by JSchmitz

I always thought notch sensitivity meant that it would break easily if there were stress-risers like a centerpunch mark or sharp corners. This is a good read on notch sensitivity: https://extrudesign.com/notch-sensitivity/

Sorry for the wordy diversion but it's an interesting failure to me and a chance to learn.

Thanks for the link. I'm aligned with your description when there are impact loads. I view stress risers as the effect of geometry and notch sensitivity as a material behavior in the presence of a stress riser. To me, it's about how easily a material fails in the presence of a stress riser. Like the article says, impact loading and fatigue are usually where it comes up.

There is a Charpy Impact test that can be used to compare notch sensitivity. I think of it as a measure of toughness, or ability to absorb energy.

A notch sensitive alloy with a stress riser might bend or yield when loads are applied slowly, but act brittle and fracture if the loads are applied fast (like a hammer). This is like the description of Grade 8 bolts being stronger than Grade 6 yet failing in a brush hog where impact loading is the norm.

6point6 describes 1144 as notch sensitive, which would make it less desirable for the slotted geometry (stress riser) in the shaft than something tough like 4140.

Basic question: was the part inherently incapable of normal loads, was there an unusual/unexpected issue that caused overload, or was the shaft defective? Doesn't seem enough life for it to be a fatigue failure and there is no evidence of the pump being jammed.

Impact loading in this failure doesn't make sense to me unless a chunk of something fell into the pump and suddenly jammed it up. Even high loads from higher viscosity oil wouldn't act like a hammer blow but would clearly increase "normal" loads.

I suppose if the failed shaft was too long as noted, and was actually compressed axially by the distributor, it's possible the loads in that slot caused the shaft to split - like using the distributor as a chisel?? That would be weird and certainly unexpected.

Maybe Melling would be willing to analyze the failure?

Mike