torque for generic rod with ARP 3/8 bolt

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steve cowan
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Re: torque for generic rod with ARP 3/8 bolt

Post by steve cowan » Sun May 13, 2018 3:07 pm

RFoll,
I hear ya,
I just done a full year of buzzing a set of scat I- beam rods with 3/8 8740 bolts in my 383 sbc to 7600 rpm
Pulled the engine for some upgrades,bearings could be used again,I was kinda surprised,
327 sbc with heavy pistons and stock rods and bolts torqued to 45 ft/ lbs to 7000 rpm
Some people think I am crazy,maybe I am :D
steve c

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Re: torque for generic rod with ARP 3/8 bolt

Post by groberts101 » Sun May 13, 2018 3:17 pm

Not sure if it's been mentioned yet but overall length plays a role in final torque specs too. Since many of these bolts are custom spec'd for various designs they are slightly different than shelf parts.

For example many are 1.4" lengths(like my scats) compared to the more common 1.5" shelf parts. Iirc, only about 5-6 ft/lbs difference but worth a phone call to be sure. Could also look at the part#'s replacement bolts specs and instructions to get a better idea as well.

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Re: torque for generic rod with ARP 3/8 bolt

Post by clshore » Sun May 13, 2018 4:55 pm

The torque should be the same no matter the length, to create the rated tensile clamp load in the assembly.
But the stretch will be proportional to the length at the rated tensile clamp load.

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Re: torque for generic rod with ARP 3/8 bolt

Post by groberts101 » Mon May 14, 2018 4:56 pm

clshore wrote:
Sun May 13, 2018 4:55 pm
The torque should be the same no matter the length, to create the rated tensile clamp load in the assembly.
But the stretch will be proportional to the length at the rated tensile clamp load.
My bad.. you are exactly right and thanks for the clarification. It's the rod mfgrs that change the torque ratings based on their rod designs(extra reinforcement "meat" in the big ends), and tailored towards the specific ARP bolt which was designed for them, despite the bolts being of similar metallurgy and diametrical sizing to a standardized shelf part#.

So maybe better to say.. IF.. the bolt being used for a specific rod part # is the true and correct replacement part #?.. then use the mfgrs rec'd torque specs. If it is a standardized shelf part#?.. then use the rec'd specs from ARP for that specific part#. Either way though.. mic'ing will be mandatory and you may end up resizing the rods big end depending on its specific big end design and past usage history. And probably moreso true if it's a lower scale/lighter weight rod design and you stray away from the specific replacement bolt # designed for it.

Hope that helps the OP any little bit at all! :)

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Re: torque for generic rod with ARP 3/8 bolt

Post by rfoll » Mon May 14, 2018 9:49 pm

I'm thinking it's getting 60' lbs. with ARP lube. This application could run 305 rods and stock bolts. Thanks to all who responded, Rick.
So much to do, so little time...

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Re: torque for generic rod with ARP 3/8 bolt

Post by groberts101 » Mon May 14, 2018 10:20 pm

rfoll wrote:
Mon May 14, 2018 9:49 pm
I'm thinking it's getting 60' lbs. with ARP lube. This application could run 305 rods and stock bolts. Thanks to all who responded, Rick.
Way too high for an 3/8" 8740 and might want to look over arp's genetal torque spec's before going that route.

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Re: torque for generic rod with ARP 3/8 bolt

Post by steve cowan » Mon May 14, 2018 10:37 pm

groberts101 wrote:
Mon May 14, 2018 10:20 pm
rfoll wrote:
Mon May 14, 2018 9:49 pm
I'm thinking it's getting 60' lbs. with ARP lube. This application could run 305 rods and stock bolts. Thanks to all who responded, Rick.
Way too high for an 3/8" 8740 and might want to look over arp's genetal torque spec's before going that route.
RFOLL says they are 7/16
i am not sure they even do a 3/8 bolt for a H-beam Scat, Eagle rod
hopefully someone correct me if i am wrong :D
steve c

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Re: torque for generic rod with ARP 3/8 bolt

Post by groberts101 » Mon May 14, 2018 10:43 pm

steve cowan wrote:
Mon May 14, 2018 10:37 pm
groberts101 wrote:
Mon May 14, 2018 10:20 pm
rfoll wrote:
Mon May 14, 2018 9:49 pm
I'm thinking it's getting 60' lbs. with ARP lube. This application could run 305 rods and stock bolts. Thanks to all who responded, Rick.
Way too high for an 3/8" 8740 and might want to look over arp's genetal torque spec's before going that route.
RFOLL says they are 7/16
i am not sure they even do a 3/8 bolt for a H-beam Scat, Eagle rod
hopefully someone correct me if i am wrong :D
Ok.. apparently I'm too broke to even pay attention. lol

Well then.. I'll flop the other way and say 60 isn't enough. :lol:

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Re: torque for generic rod with ARP 3/8 bolt

Post by steve cowan » Mon May 14, 2018 10:56 pm

groberts101 wrote:
Mon May 14, 2018 10:43 pm
steve cowan wrote:
Mon May 14, 2018 10:37 pm
groberts101 wrote:
Mon May 14, 2018 10:20 pm
Way too high for an 3/8" 8740 and might want to look over arp's genetal torque spec's before going that route.
RFOLL says they are 7/16
i am not sure they even do a 3/8 bolt for a H-beam Scat, Eagle rod
hopefully someone correct me if i am wrong :D
Ok.. apparently I'm too broke to even pay attention. lol

Well then.. I'll flop the other way and say 60 isn't enough. :lol:
classic GRobs thats funny,
looking at spec sheet 8740 bolt in 1.4'',1.5'',1.6'' between 60-65 ft/lbs
i think RFOLL good to go,
steve c

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Re: torque for generic rod with ARP 3/8 bolt

Post by ProPower engines » Tue May 15, 2018 1:29 am

Back in the early 90's generic sm blk rod hit the world scene of hot rodding as an alternative to stock rods.
scat Eagle and others sold basicly the same looking rods. While the bolts were stamped ARP when you took them apart did they have the ARP lube on the threads??
Scat and Speedway motors offered them with arp lube where Eagle suggested same ARP does as today to use 30W motor oil when no ARP lube is on hand.
If they showed sign"s of their lube then I would bet they are Scat rods and you could use the chart for torque and stretch for the 8740 bolts. Compare to the Eagle chart for other possibilities as the lengths differ between the 2 manufactures.

Back in the 1st days they were offered with a shot peened option and the surface was really rough compared to today's method's of shot peening rods.
Real Race Cars Don't Have Doors

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Re: torque for generic rod with ARP 3/8 bolt

Post by strokersix » Tue May 15, 2018 9:59 am

I would be conservative and go with the smaller torque value, whatever that may be for a mild stock type application.

If you are concerned about that then you need to replace the bolts!

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