REPLACING CAP SCREW STYLE ROD BOLTS.

Old 12-29-2009, 02:29 PM
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Tod74
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Default REPLACING CAP SCREW STYLE ROD BOLTS.

If you want to replace the rod bolt/cap screw in an H BEAM style rod,do you have to have it re sized afterward? Obviously I am talking about the kind where the rod is threaded and the entire bolt comes out, not a pressed in stud with a nut like stock rods have. Also I am speaking of putting better bolts in a brand new rod, not just putting new bolts in a used rod that could be out of round etc... Thanks
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Old 12-29-2009, 03:05 PM
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zipper06
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NO
and L19's are best choice in my opinion. i think it's a good idea to change the rod bolts on every rebuild including magnfluxing the rods.
My friend who has the Biscyne, still carry's the stretched/broken rod bolt in his pocket from the 477" motor he lost in 2008 from not changing the rod bolts on the rebuild.

Zip.
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Old 12-29-2009, 03:50 PM
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Tod74
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Thanks ZIP. That was what I thought just confirming.
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Old 12-29-2009, 04:22 PM
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hammertime
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If you ask most motor shops yes they should be resized after installing a different rod bolt then is already in there. I just had this chat with a big engine builder, he explained to me the torque specs are different between the bolts and once you trq it down more with the good bolts it throws it off just a little bit, enough to get them resized.

I've upgraded in the past and didnt take my chances. Some get away with it some dont chance it .. my thoughts its cheaper then losing a motor for something stupid.
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Old 12-29-2009, 07:40 PM
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markdunlap
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Default Replacing cap screw type rod bolts

Dial bore gage the rods with the original bolts torqued up / stretched. Remove and replace with new bolts and torque / stretch to new spec. Dial bore gage again. If they are the same as before, good to go. If not, take them to machine shop and have them resized.
If you don't have the required tools, the machine shop can do it with their rod checker and be even more precise.
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Old 12-29-2009, 08:00 PM
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Tod74
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Ok so that presents another question...just a thought...what if you somehow mixed up bolts from one rod to another? Not likely but suppose you have them apart on the bench and a few get mixed up. They should be the same since they are the same kind of bolt but are they?
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Old 12-29-2009, 11:48 PM
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cepx111
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How is a bolt going to change the dimesions of a rod?

I am upgrading to the L19 bolts in my motor this winter.

With the crank rods still in the block I'm just going to loosen up the old bolts one by one, lube and torque down the new ones, cant see that as changing anything but the bolts, and no I dont use a stretch guage either.

My buddy done his this spring, know of several others that have in the past using the same method, none had any problems.

Call me crazy but thats what I'm gonna do, least till someone can convince me other wise.

Anybody?
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Old 12-30-2009, 12:14 AM
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cepx111
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[quote="hammertime"]If you ask most motor shops yes they should be resized after installing a different rod bolt then is already in there.[quote]


One must remember they are 'trying' to sell work, they make money off your/our paranoia.

I used to work at a machine shop years ago, I wasnt a machinist, just the helper/teardown guy.
Oh boy believe you me I seen a many motor/parts with nothing wrong with them get the works.

Their motto was whenever in doubt machine it out.

Cp
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Old 12-30-2009, 02:25 AM
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zipper06
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The theory behind the possible out of round comes from the fact that 8740 bolts call for 62/63 ft.lbs. for the proper stretch, where as the L19's require 70 ft.lbs. for the proper stretch due too the higher tensil strength of the bolts 180,000 VS 240,000. Those torque values come with using moly lube, not regular motor oil.
That's what torque was called for on the Lunati promods rods that i bought with L19's and all Eagles with 8740 calls for 63 ft.lbs.

Funny thing is that RMS, doesn't change out the bolts on their engines, they claim that the 8740's are good enough as long as you change them on every rebuild.

JMO

Zip.
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Old 12-30-2009, 07:17 AM
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hammertime
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[quote="cepx111"][quote="hammertime"]If you ask most motor shops yes they should be resized after installing a different rod bolt then is already in there.


One must remember they are 'trying' to sell work, they make money off your/our paranoia.

I used to work at a machine shop years ago, I wasnt a machinist, just the helper/teardown guy.
Oh boy believe you me I seen a many motor/parts with nothing wrong with them get the works.

Their motto was whenever in doubt machine it out.

Cp
They werent trying to sell me work as it wasnt Nyes it was another big name shop I had a oil pan deal through.
Every shop I know wont even replace them without resizing the rod. It has their name on it and wont take a chance is why I am sure. Like mentioned above if he doing it himself just measure them before and after.

Zip I know lots that replace the 8740s every freshen up and have no issues.
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