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Re-Using Connecting Rod Bolts


GavinT

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Is it worth penny pinching?

Probably OK but short of having them tested you will never know. And testing is probably as much as a new set of bolts.

How much are the bolts, and how much is the cost if they let go.....

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Seems folks may get away with this but I'm of the view that it's best to write off the bolts after 1 use. Just too much loss if 1 lets go. Believe you'll find fewer opinions favouring re-use versus replacement.

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  • 2 weeks later...
On 09/02/2021 at 22:19, GavinT said:

Thank you Gents. ARP replacements on the way!

Don't forget to check the rod end is round or within spec.  Especially if you are going to use different spec bolts and torques to the original spec . This will require torqueing or using stretch gauge for ARP's , Which really makes a mockery out of torqueing rod bolts just once. If out you will need to get the rod end dressed  and honed back into spec which will require removing and refitting the rod bolts a few more times .  Uhmm  .  Personally never had much problem with originals they are quite chunky as rod bolts go and torque matched to the rod spec .   You can do your own stretch test when fitting . Worth remembering there is always more to building and engine than just buying a bit and fitting it ..  You may wish to do a bit of research and checking first.   Two or three tenths of a thou can be big numbers in this area..        

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  • Gold FFM

Where do people stand on this topic with regards to the 918 V8 engine? ARP apparently don't have a suitable bolt and the Lotus ones are not cheap especially when you need 16 of the little monsters.

cheers

-Chris

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For thorough checking of the big end bores at torqued condition perhaps use the oldies for this? Agree the OEM bolts are very substantial. Utmost in all of this must be confidence in the quality of the components and care in torquing/assembling methods.

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Interestingly there are studies that have been done that show how using original bolts and then ARP bolts you can get a different measurements within the rod end .. 

Also worth noting that the rod ends were originally sized perfectly round using original bolts torqued up.  Should you be thinking of using another spec of bolt you will need to do the measurements using the new bolts and having the rod ends re-sized with these bolts torqued in place should it be necessary. 

 

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I will defer to the pro's on this but the question of re-used rod bolt integrity comes down to whether torquing has induced any consequential measure of yield in the metal. This accounts for why some re-used bolts let fly, causing catastrophic damage as one would expect, whereas others will go on serving faithfully. Seems unlikely factory assembly would have pushed too far in torquing yours, thus arguing for re-use if that has been the only history of work. OTH, one might presume torquing those fine ARP's just comfortably short of spec would ensure their ongoing integrity while generating enough force to have the big end bores checked for shape. Oh the joy!  

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Tim Engle’s response when asked the question....

I wouldn't be adverse to re-using the bolts that have been re-torqued twice... "IF" I was confident that they were properly torqued previously. Re-using the rod bolts is all about having confidence that they weren't previously abused. If Lotus was the last one in there, I have no problem re-using the rod bolts. If the engine had previously been rebuilt, did that mechanic know what he was doing? If he screwed-up something else, I might have concerns about what he did to the rod bolts, main bearing studs, and head studs... ie, the critical fasteners. Keep balance in mind. That end of the connecting rod is going through some wild gyrations at 7000 rpm, and any change of mass (different bolts) can have significant balance consequences. The stock rods were reasonably well balanced. If you were building a race engine, you might want to be a little more fussy; but as a stock street engine, the 910 was well built. But when you make changes, like replacing one rod out of a set, or replacing rod bolts, it would be good to have a shop check the balance. Talk to your shop. The bottom of the rod caps have twin, parallel ribs running around them. There is no separate sacrificial pad or boss from which material is ground off to lighten it during balancing, so some shops simply grind the bottom of the ribs. NO!! The ribs are structural, and you don't just cut away at them.

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I actually have two sets of rod bolts. One set from the engine with the failed thrust washer and one set from the replacement engine. The replacement engine bolts have been torqued twice. The original bolts have only been torqued once by Lotus but have been used in an engine that had excessive crank float.

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  • 2 months later...

I asked this question back in 2014 for my GT3 and the consensus was they weren't torque to yeild and could be re-used. I did that and haven't had an issue yet. Car's now running 320bhp and has 4-5k miles since then

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