Conrod bolt re-use - Triumph675.Net Forums
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post #1 of 5 Old 03-04-19, 12:55 Thread Starter
MakinBeer
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Conrod bolt re-use

I compared the length of an used bolt to a new bolt, and they were identical in length - 43.36 mm. I'm aware that the service manual is emphatic about these being a single use part, as they are TTY. However, it doesn't appear that the bolts have actually reached their yield point.

I fully intend to use the new bolts (already bought them, after all), so this is more a matter of curiosity and future reference - I have another build on deck. Given this information, would it be safe to re-use them?
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post #2 of 5 Old 03-04-19, 15:32
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The overall length of the conrod bolts is probably not a tightly-toleranced dimension, and - done properly - the yield deflection is quite small (you don't keep cranking on it until it starts stretching and necking down). I would suggest that it is quite possible - purely by coincidence - for a used bolt and a new bolt to be the same length.


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post #3 of 5 Old 03-04-19, 15:57 Thread Starter
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Fair point. I only checked one new bolt and two used ones. I would have expected them to be measurably longer, even if that was only a few hundredths of a millimeter. I think my initial thought is that these were possibly under-torqued - as in, enough to provide adequate clamping force, but not enough to get into the bolt's plastic zone.

I have some used bolts out of an entirely different engine. I'll have to do some more measuring to get a better sample.
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post #4 of 5 Old 03-05-19, 01:33
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It also has to do with the way the threads are cut. Once tightened they bind enough to hold. I wouldnt trust it twice. I know people that cheap and/or that stupid but its not a gamble Id ever do.
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post #5 of 5 Old 03-11-19, 15:37 Thread Starter
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Quote:
Originally Posted by MacBandit View Post
It also has to do with the way the threads are cut. Once tightened they bind enough to hold. I wouldnt trust it twice. I know people that cheap and/or that stupid but its not a gamble Id ever do.
Thanks. It was more of a curiosity than anything, as to my understanding of TTY fasteners and plasticity/yield/fracture. ~$90/set is practically nothing in the cost of a rebuild, especially considering the possible consequences.
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