[Skip Fix]

I got a set with a 72 HO block years ago. They just looked to heavy for me and I sold them. Although my Crower billets with similar through bolts and nuts aren't light!

[KEN CROCIE]

IIRC the over the counter SD rods, starting with the "D" series and later were more prone to failure.

Of course, that was the last century, and the memory is a little hazy.

[PAUL K]

Originally Posted by KEN CROCIE

IIRC the over the counter SD rods, starting with the "D" series and later were more prone to failure.

Of course, that was the last century, and the memory is a little hazy.

Hi Ken, thanks for the info. I understand it was a long time ago, do you recall generally what the failures were, rod becoming two pieces, or spinning bearings, or?

[mgarblik]

Originally Posted by PAUL K

Crower rods of that era used the bolt n nut set up similar to the SD rod.... Going from memory Carrillo and Mr Rod (both whom supplied the RAV rods) used a bolt threaded into the rod.

Both can be tightened with the stretch method

Molnar specs. bolt stretch and torque/angle specs. only for their connecting rods. They are cap screw design. (no nuts) . I measured a set of their rods tightening them with both methods and reading the final torque as well with my digital gauge. The bolt stretch method is a direct measurement, so it has to be the most accurate. Torque angle was very close to bolt stretch when cross checked. Torque alone was all over the place, not nearly as close. Through a set of 8 rods, 16 fasteners. The torque varied by +- 15 ft. lbs. It's easy to see why Pontiac specified bolt stretch and so far as to spell it out on a very visible valve cover sticker on every SD-455 produced.

[PAUL K]

Originally Posted by mgarblik

Molnar specs. bolt stretch and torque/angle specs. only for their connecting rods. They are cap screw design. (no nuts) . I measured a set of their rods tightening them with both methods and reading the final torque as well with my digital gauge. The bolt stretch method is a direct measurement, so it has to be the most accurate. Torque angle was very close to bolt stretch when cross checked. Torque alone was all over the place, not nearly as close. Through a set of 8 rods, 16 fasteners. The torque varied by +- 15 ft. lbs. It's easy to see why Pontiac specified bolt stretch and so far as to spell it out on a very visible valve cover sticker on every SD-455 produced.

Good info Mike.... Any thoughts why Pontiac didn't want the nuts used more than once?

[SS-TA]

In 1983 I had Nunzi Romano build my engine with 455SD new Rods I had acquired. Nunzi stated that the problem with many of the SD rods is they were not properly heat treated. He tested every rod for its Rockwell C number, one of my rods did not meet his spec. I believe he was looking for numbers in the high 20s or low 30s. I don't know how often this problem appeared.

[steve25]

It’s been a very long time ( like since 1975 ) but I use to have a full set of new bolts and nuts on my shelf in hopes of one day affording a set of the rods .

My recollection is not clear anymore so someone correct me please if I am wrong , but where not these nuts a bit of a jam nut with how they felt when screwing them on a bolt?

If so then maybe that’s why the factory said they where to be replaced each time even though they did not want you to use the torque wrench method to sinch them up.

I have also seen written that they can quote “ be reused indefinitely “
This makes a bit more sence to me, but still like 5 times of reuse would be the limit for me.

I did some rereading on 8640 steel and despite what I posted earlier 8640 sounds like a good material for use as rods in general, but maybe not so if it needs to be accurately tempered.
This could be an issue .

[steve25]

In regards to this term used of “quenched and tempered “ which is always stated to be at room temperature, I ask, well what the hell is room temperature!?

Is it 62, 68 or 72?

So I need to ask what kind of effect on Rockwell hardness would a 6 degree or whatever difference in temperature make in achieving a given minimum Rockwell rating?

Do higher grade steels need more accurate temperatures to meet a minimum Rockwell number then a 4340 material for example?

[steve25]

With what we are talking about here I feel everyone should read the very detailed info I just found on rod bolts.

I do not know how to post a link unfortunately so I will just tell how I found it so you can do the same.

I searched for L19 rod bolts and info came up.

I scrolled down and saw I listing from the speedtalk site.
When you open it you should see a post by 540 rat.

For me it was the best 12 minutes of reading in terms of info on rod bolts and there usage.

[Elarson]

Originally Posted by steve25

In regards to this term used of “quenched and tempered “ which is always stated to be at room temperature, I ask, well what the hell is room temperature!?

Is it 62, 68 or 72?

So I need to ask what kind of effect on Rockwell hardness would a 6 degree or whatever difference in temperature make in achieving a given minimum Rockwell rating?

Do higher grade steels need more accurate temperatures to meet a minimum Rockwell number then a 4340 material for example?

I don't have my material books here at home but to get the stated Rc, the material is heated to probably 1650 degF, quenched, then reheated and held for a time at the tempering temperature which is probably in the 850-1000 degF range. The "room temperature" statement refers to the temperature when the final strength is measured. So a few degrees matters not.

After quenching, the steel is super strong but brittle. Tempering draws the strength back down but increases ductility (the ability to bend or stretch without breaking). The engineer picks the tempering temperature to get what they feel is the best compromise of strength vs ductility for the final condition. Higher tempering temperature draws the strength down lower than a more moderate tempering temperature does.

For reference, Rc 32 is about like a Grade 8 bolt. 150,000 psi ultimate tensile strength.

Hope this helps,
Eric

[steve25]

Well it looks like untempered 8640 steel does not then gain much strength when it’s at 32 Rockwell, unless I am reading things wrong because I don’t think there’s any section of a SD rod that’s truly 1” in diameter as in the info on this reference sheet I am posting.

[slowbird]

Pic of our broken SD rod

[PAUL K]

Originally Posted by steve25

My recollection is not clear anymore so someone correct me please if I am wrong , but where not these nuts a bit of a jam nut with how they felt when screwing them on a bolt?



I did some rereading on 8640 steel and despite what I posted earlier 8640 sounds like a good material for use as rods in general, but maybe not so if it needs to be accurately tempered.
This could be an issue .

The factory bolts don't have any type of "crimp"

Factory spec allowed the use of three different metals. I wasn't there but I'd certainly think most of the rods left the foundry heat treated properly. Heat treating for a professional is the easiest part.

[PAUL K]

Originally Posted by slowbird

Pic of our broken SD rod

Thanks for that picture. The pin end was certainly stronger than the big end on that rod. I see a heavy TRW piston attached to that rod. Do you know if that bearing spun?

Or possibly the bearing spun as the rod bolts began to crack


Can you see the series letter code on that rod?

[Elarson]

Originally Posted by steve25

Well it looks like untempered 8640 steel does not then gain much strength when it’s at 32 Rockwell, unless I am reading things wrong because I don’t think there’s any section of a SD rod that’s truly 1” in diameter as in the info on this reference sheet I am posting.

The first reference that you posted shows annealed condition. That was heated to the 1650 degF temp and air cooled (not quenched) so it's at its softest condition. The strength of Rc 32 hardness probably shows heated, quenched, then tempered at a fairly high temp (maybe 1150 degF??).

Eric

[Skip Fix]

So a slightly related question since we are talking rod bolts with nuts . I know SD rods were recommended to swap nuts after so many torques as well as most rod nuts.
So does testing several bearing sets and torquing to get the correct bearing clearance and test fitting for block clearance/deck height "burn" one of your torques for the life of the nut?

[mgarblik]

Concerning re-using SD connecting rod nuts: This is pure speculation on my part, not based on published information. Why the caution on not using the nuts again? Think about this at a Pontiac dealership level. 1. The SD rod nuts are NOT National Coarse, OR National Fine thread. They are Unified National Special Threads. No Pontiac dealer would have those nuts in their general hardware bins. They wanted to make sure a new set of the proper, correct nuts were always installed. 2. It's possible the nuts were slightly softer than the rod bolts. So when they were stretched the first and only time they would very slightly deform as they were stretching the bolts. So re-using them might be slightly risky. 3. At the dealer level, replacing the bolts and nuts would be the best idea. BUT, removing the old bolts could cause damage to the rods if they were really tight in the holes. I think Pontiac looked at the cost of bolts and nuts, the chance of damaging the rods and just settled on recommending changing the nuts. JMO. BTW, in today's repair world, GM would just specify replacing the entire piston and rod assembly complete with rings already installed on the piston. Or a new short block or complete engine!!

[PAUL K]

Originally Posted by Elarson

The first reference that you posted shows annealed condition. That was heated to the 1650 degF temp and air cooled (not quenched) so it's at its softest condition. The strength of Rc 32 hardness probably shows heated, quenched, then tempered at a fairly high temp (maybe 1150 degF??).

Eric

Eric when a well meaning shop blues the rod halfway down the beam so they can press the pins, will that affect the heat treat and if so for better or worse?

[steve25]

I did such unknowingly to my own early production forged rods the first time I ever used a rod oven unsupervised on a weekend, and a month later up at 5800 rpm two of them snapped in the beam and took out the complete short block.

I had hours of polishing , lightening the pin end along with shot peening in them, a long with SPS jolts and resizing done to them.
Hell was bummed out.

The only good thing was I had decided to build up a 389 block since it only needed to go .030” over which saved my 4 bolt 400 block from being the victim.

[slowbird]

Originally Posted by PAUL K

Thanks for that picture. The pin end was certainly stronger than the big end on that rod. I see a heavy TRW piston attached to that rod. Do you know if that bearing spun?

Or possibly the bearing spun as the rod bolts began to crack


Can you see the series letter code on that rod?

From what I remember (this was late 80s early 90s) it broke in the burnout after yrs and yrs of service.