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Old 01-26-2024, 05:58 PM   #1
Ken/Alabama
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Default 91A Rod
Well, this is a first for me. Been fiddling with flatheads for 40 years now. Checking a set of 91A rods with my Sunnen A300 gauge. Snugged the rod nuts down with a 3/8 ratchet then torque them to 45 with torque wrench. The nut barely got snug and the rod bolt let go. Never had this happen before.
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Old 01-26-2024, 06:12 PM   #2
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Ouch-yeah. You know it did that so you'll worry about the rest of 'em.
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Old 01-26-2024, 06:19 PM   #3
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Default Re: 91A Rod
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Ouch-yeah. You know it did that so you'll worry about the rest of 'em.
I know, now I’m suspicious. I have some extra 91A rods but I think I have enough 21A rods to make a set so I’ll probably go that direction.
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Old 01-27-2024, 08:26 AM   #4
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Was it new?
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Old 01-27-2024, 08:58 AM   #5
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Was it new?
No, they were a used set I’ve had for a while . Supposedly resized and balanced . Now I’m thinking at some point some heavy handed mechanic may have over torqued them so I’m going to dig out another set.
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Old 01-27-2024, 10:03 AM   #6
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Be sure to use NOS for your stroker.
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Old 01-27-2024, 10:48 AM   #7
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Be sure to use NOS for your stroker.
Will do.
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Old 01-27-2024, 11:04 AM   #8
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Default Re: 91A Rod
That is one of the reasons I use the aftermarket rods. Who knows how much those integral "bolts" have been stretched by over torquing. How many guys back in the day even had a torque wrench? It is amazing how well the stock rods have held up all these years. Maybe the rod that broke had a flaw from day 1 and finally let go.
I am glad you found it when you did!
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Old 01-27-2024, 01:27 PM   #9
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Default Re: 91A Rod
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That is one of the reasons I use the aftermarket rods. Who knows how much those integral "bolts" have been stretched by over torquing. How many guys back in the day even had a torque wrench? It is amazing how well the stock rods have held up all these years. Maybe the rod that broke had a flaw from day 1 and finally let go.
I am glad you found it when you did!
So, aftermarket rods utilize actual pass through bolts?
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Old 01-27-2024, 01:51 PM   #10
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So, aftermarket rods utilize actual pass through bolts?



Many use cap screws.
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Old 01-28-2024, 11:52 AM   #11
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Default Re: 91A Rod
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That is one of the reasons I use the aftermarket rods. Who knows how much those integral "bolts" have been stretched by over torquing. How many guys back in the day even had a torque wrench? It is amazing how well the stock rods have held up all these years. Maybe the rod that broke had a flaw from day 1 and finally let go.
I am glad you found it when you did!
This thread was an eye opener for sure. Curious which brand of aftermarket rods you use.
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Old 01-28-2024, 12:08 PM   #12
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Default Re: 91A Rod
WOW!! I have a set balanced in a crank assembly for my last build?? Now what??
Gramps
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Old 01-28-2024, 12:28 PM   #13
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This thread was an eye opener for sure. Curious which brand of aftermarket rods you use.
Tim without getting custom made Scat and Eagle are the only two brands I’m aware of. They are both heavy and the Eagle often need block grinding for clearance. Don’t be put off by one failure. There’s thousands out there running and have been for years.
My favorite rod for a nice hot rod engine. Not a race engine rod.
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Old 01-28-2024, 01:21 PM   #14
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Default Re: 91A Rod
Tim, The 3 sets of Scat rods I am running all had socket head cap screws. I would think they have pictures of them online somewhere.
Mike
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Old 01-28-2024, 02:41 PM   #15
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Default Re: 91A Rod
The aftermarket H-beam rods all use modern cap-screws. Also, there are different quality of cap-screws, so you can even go up to higher strength ones if that makes you happy. Truth be told, at our measly horsepower levels (unblown street engines), there is no head to upgrade the cap screws.
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Old 01-28-2024, 05:32 PM   #16
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Default Re: 91A Rod
NOS stock rods will perform exceedingly well even in 100% nitro burning engines if a few simple things are done to them.
First, magnaflux the rods.
Then shot peen them. Have the caps torqued to spec when shotpeening. Be sure to use shot that is half the diameter of the smallest radius. You will have to determine that number as I haven't done a set in 30 years.
After shot peening and reconditioning the big end, install new pin bushings and align bore them to the big end.
DO NOT use a rod alignment press on the rods after they have been shot peened.
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