[PAUL K]

Any first hand, or factual second stories about SD 455 rods breaking? Any details about the incident?

[steve25]

I think I have heard of some breaking ( trying to recall for sure ) but I think the failure was due to spun bearings which may have been due to over used rod bolts .
Might have also been due to replaced rod bolts that were not pressed in right.

Once again I can’t recall for certain, sorry.

[Dragncar]

I don't have first hand info on thembreaking. I did run them for quite some time and no issues. When I went to a roller cam I bought some cheap H beams and re balanced everything.
But, the reason I got rid of them was Dan told me he had a couple guys break them right under the pin during the burnout. He told me to keep my burnout RPM to 5500 or less and that is what I did except for one time when it went to 7200.
Jim Butler told me once you can break them "looking sideways" at them, Had people break them under the pin too. He used them just on 455 SD spec builds.
I sold my set of 455 SD rods to a local guy who ruined one in his race car he was trying to sell. He tried to buy only one but I sold him the whole set.
If I had a real 455 SD engine I would run aftermarket rods. No one knows they are in there but you.

[242177P]

Originally Posted by PAUL K

Any first hand, or factual second stories about SD 455 rods breaking? Any details about the incident?

Aren't there preferred letter codes? I was under the impression
they were several different batches of SD455 rods, some better
than others.

[steve25]

One thing I have never figured out about these rods is why they chose to make them out of the 8640 material that they did.
Even back then 4340 seemed to be the way to go.

In reading some of the above , I think that breakage below the pin would have been due to inflexibility of the 8640 material.

I have seen comments over the decades in regards to staying away from the A thru C batch rods, that is if your only running a 3.750” stroke and not buzzing over 6400.

[sdbob]

My experience. I found a SD 455 short block in a salvage yard junk pile,1975era.No crank or heads or intake. Just block SR, #5 hole sleeved,8 rods,SD distributor, I took block and rods to Arnold Hines. I bought newSD rod bolts.He said I didnt need them. Engine has many 200+ runs usually shifting at 5400. When I first ran it I was shifting about 5800. John Herslow gave me some pointers. I've hit 6400 in the water a few times. Street car shifting at 5400.i tried 6000,engine didnt pull. I had an SD 455 block that came out of an early 74 4 spd car. That engine was built with roller cam for a street car.Owner lost interest. Sold engine to a stock car guy(old H-O racing newsletter with 2n d gen
Firebird on cover like 1977) The guy wasnt making enough power so he decided to rpm higher,broke one of the SD rods. Bent the thrust main outside short bolt,cracked cap. Block was ok. I ended up with the bottom end block,cam,lifters. Jim Miller built the engine(also thesmall journal RAV dirt GTO). He told me the reason why engine broke.I found the original car tried to buy it,nope. Then by accident a guy called me. Long long story. Here he bought the
car,that block is back in car. I do have 16 nos rods.i was buying all the SD parts I could afford at one time.

[Half-Inch Stud]

...i had an SD rod nut spin down, off in the pan. Yea that led to. A spun bearing. And you know it could have spun the bearing 1st, then the rod nut got relieved of TQ duty and spun down. The rod cap let go.

Otherwise, never had an SD-rod let go

Uhm, i might need a set soon. Details soon if so.

[Dragncar]

When you look at how thin the meat is around the pin its hard to imagine anyone ever full floating them. I know they did with very thin bushings.
I used red Locktight on all my rod nuts.
I found mine new. But they had used nuts on them. Bolts were new.
Dan said they needed shot peening so I sent them to the same place in NH that shot peened F-18 turbine blades. I had enough money into them to buy Crower billets.

[steve25]

Exactly!
Some folks seem to take grate pride in being able to say that they have 455SD parts in there motor.

The facts 5 decades down the road now show that in a motor with a 4.210” stroke or greater you should limit the rev’s to very safe 6500 with stock weight pistons and pins.

Especially if the rods are used and you don’t know the history of them.

One needs to keep in mind that the rod bolts neck down twice as they pass thru the rod and this concentrates the G force loads right in those two locations.

To this day knowing the engineer that went into these rods I can’t understand why they chose to use bolts and nuts to clamp caps to the big end.

I guess they felt that having threads in the big end weaken it.

[Half-Inch Stud]

Also wondered why the 8640 wasn't tapped for bolts. Bolt-stretch must have been a major priority in the Engr's plan.

Bolt middle acting as a Cap alignment Dowel was novel enough. Friction there moght have called for Stretch, not TQ friction.

[PAUL K]

Originally Posted by Dragncar

I don't have first hand info on thembreaking. I did run them for quite some time and no issues. When I went to a roller cam I bought some cheap H beams and re balanced everything.
But, the reason I got rid of them was Dan told me he had a couple guys break them right under the pin during the burnout. He told me to keep my burnout RPM to 5500 or less and that is what I did except for one time when it went to 7200.
Jim Butler told me once you can break them "looking sideways" at them, Had people break them under the pin too. He used them just on 455 SD spec builds.
I sold my set of 455 SD rods to a local guy who ruined one in his race car he was trying to sell. He tried to buy only one but I sold him the whole set.
If I had a real 455 SD engine I would run aftermarket rods. No one knows they are in there but you.

I'm trying to weed out the wives tales and the actual events, thanks for the information.

[PAUL K]

Originally Posted by 242177P

Aren't there preferred letter codes? I was under the impression
they were several different batches of SD455 rods, some better
than others.

That's a good question. The later series are nicer looking forgings but I'm thinking the earlier units passed Pontiac's QC test also.

[PAUL K]

Originally Posted by steve25

One thing I have never figured out about these rods is why they chose to make them out of the 8640 material that they did.
Even back then 4340 seemed to be the way to go.
.

Both 8640 and 4340 were acceptable metals for the forging company to use. The metal would need to be analyzed to know for certain what material was used. That may have changed over the years also.

[PAUL K]

Originally Posted by sdbob

My experience. I found a SD 455 short block in a salvage yard junk pile,1975era.No crank or heads or intake. Just block SR, #5 hole sleeved,8 rods,SD distributor, I took block and rods to Arnold Hines. I bought newSD rod bolts.He said I didnt need them. Engine has many 200+ runs usually shifting at 5400. When I first ran it I was shifting about 5800. John Herslow gave me some pointers. I've hit 6400 in the water a few times. Street car shifting at 5400.i tried 6000,engine didnt pull. I had an SD 455 block that came out of an early 74 4 spd car. That engine was built with roller cam for a street car.Owner lost interest. Sold engine to a stock car guy(old H-O racing newsletter with 2n d gen
Firebird on cover like 1977) The guy wasnt making enough power so he decided to rpm higher,broke one of the SD rods. Bent the thrust main outside short bolt,cracked cap. Block was ok. I ended up with the bottom end block,cam,lifters. Jim Miller built the engine(also thesmall journal RAV dirt GTO). He told me the reason why engine broke.I found the original car tried to buy it,nope. Then by accident a guy called me. Long long story. Here he bought the
car,that block is back in car. I do have 16 nos rods.i was buying all the SD parts I could afford at one time.

Thanks for your response. Do you know where the rod broke? Any idea if it had spun that bearing?

[PAUL K]

Originally Posted by Dragncar

When you look at how thin the meat is around the pin its hard to imagine anyone ever full floating them. I know they did with very thin bushings.
.

Thin compared to a cast rod?

What is too thin?

[PAUL K]

Originally Posted by Half-Inch Stud

Also wondered why the 8640 wasn't tapped for bolts. Bolt-stretch must have been a major priority in the Engr's plan.

Bolt middle acting as a Cap alignment Dowel was novel enough. Friction there moght have called for Stretch, not TQ friction.

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

[misterp266]

I ran a set in my 406 in the late 80s early 90s. I polished the side beams and bushed them for a .927 SBC full floating pin. Light weight Arias pistons. I don’t recall what letter they were. As I understand, the heat treating was different for different batches. Ran a 389 crank. The car ran low 10s @ 130mph. I shifted it at 7500rpm on every pass. The motor got freshened up a few times and I never replaced the bolts. At the time I don’t think I was aware that they should have been replaced. Never any issues and they are still in the same motor that was relegated to street use. Still have the original bolts in them too.
I’ve never personally seen a broken one.

[PAUL K]

Originally Posted by misterp266

I ran a set in my 406 in the late 80s early 90s. I polished the side beams and bushed them for a .927 SBC full floating pin. Light weight Arias pistons. I don’t recall what letter they were. As I understand, the heat treating was different for different batches. Ran a 389 crank. The car ran low 10s @ 130mph. I shifted it at 7500rpm on every pass. The motor got freshened up a few times and I never replaced the bolts. At the time I don’t think I was aware that they should have been replaced. Never any issues and they are still in the same motor that was relegated to street use. Still have the original bolts in them too.
I’ve never personally seen a broken one.

Thanks ..... You mentioned you're still using the original bolts, have you re-used the nuts or were they replaced?

[misterp266]

Originally Posted by PAUL K

Thanks ..... You mentioned you're still using the original bolts, have you re-used the nuts or were they replaced?

Original nuts as well.

[steve25]

When you look at photos of a 455SD rod and even a 1957 forged production rod you see that in the pin to beam transition area no less in the pin hole itself shows there’s far less meat in the 455SD rod.

The earlier produced RAV rod has more meat in the traditional area then the SD rod does and these where used with far less of a loading due to the 3.750” stroke.

Looks like SD rod production stopped at the H series and all production motors go the A series.

All the SD rods where shot peened before sizing which was deadly for many of the over the counter sold rods because many of them where not cleaned out properly before being boxed up for sale.

I think I recall HO racing having problems with these over the counter SD rods they sold due to this issue.

Maybe Ken can confirm this for us.