Difference in 8640 and 8740 rod bolts

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Old School
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Difference in 8640 and 8740 rod bolts

Post by Old School » Tue Jul 17, 2018 1:32 pm

Had a customer bring in a set of rods to be resized. He has a new in package set of Mr.Gasket rod bolts, 7/16 bbc, to use and looks to be mid 1980's. Package says they are 8640 cold rolled threads. Most of the modern bolts are 8740. Just wondering if these bolts are inferior, superior, or about the same. I don't want him to have problems and I don't want to tell him I don't want to use the bolts. Just trying to figure out the quality of the bolts.

Pro-SeriesFab
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Re: Difference in 8640 and 8740 rod bolts

Post by Pro-SeriesFab » Tue Jul 17, 2018 1:47 pm

Shows 10% less yield strength, 1% better elongation at break, same modulus of elasticity.

http://www.matweb.com/search/DataSheet. ... 8a70a1ef69

pdq67
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Re: Difference in 8640 and 8740 rod bolts

Post by pdq67 » Tue Jul 17, 2018 3:46 pm

In other words, imho, they are somewhat, "tougher", but 10 percent weaker so go from there.

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Re: Difference in 8640 and 8740 rod bolts

Post by amc fan » Sun Jul 22, 2018 8:19 pm

Are the letters SPS stamped on the bolts?

Old School
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Re: Difference in 8640 and 8740 rod bolts

Post by Old School » Sun Jul 22, 2018 9:31 pm

amc fan wrote:
Sun Jul 22, 2018 8:19 pm
Are the letters SPS stamped on the bolts?
No, they are not stamped SPS. From the best i can tell looking at the data sheet the 8640 may be a little stronger in yield strength, if I am reading the sheets right.

bigmike
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Re: Difference in 8640 and 8740 rod bolts

Post by bigmike » Mon Jul 23, 2018 3:43 am

Way back when I was in high school back in the late 70s I owned a 1970 Dodge Dart Swinger 340 4 speed car. I rebuilt the engine. At the urging of a local circle track guy I replaced and upgraded to new rod bolts in the 340. I bought the Mr gasket rod bolts and had the big end resized. Admittedly I ran that car fairly hard some of the time. About 1 1/2 years and 15,000 or so miles later guess what went to lunch on that engine? .....It looked like one of the Mr gasket rod bolts broke. That my story with the only time I used Mr gasket rod bolts.

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