Lycoming rebuilding guildance

[flyingriki]

I almost made the rookie mistake of orienting the rods all out when lining up the direction of the caps etc. per the manual. Just happened upon a web page where the guy said if yours looks like this it's WRONG! Mine looked like that.

Had to buy 4 new bolts, since the old school opinion was to never reuse them, another $100 down the drain....and turned in two of the rods to orient them correctly. Didn't see that warning anywhere else and assumed most knew enough about engine operation not to need the warning....

[j-red]

About the connecting rod bolts, i've read Lycoming instructions to replace them when the rods are removed, but i've always assumed that this was more a reference to removing them at overhaul time. Anyone with some experience have an opinion on this? Would they really need to be replaced if only just installed for a day or two?

[lr172]

Originally Posted by j-red

About the connecting rod bolts, i've read Lycoming instructions to replace them when the rods are removed, but i've always assumed that this was more a reference to removing them at overhaul time. Anyone with some experience have an opinion on this? Would they really need to be replaced if only just installed for a day or two?

In the auto world, some engines use a "Torque to Yield" type rod bolt. These can only be torqued to spec once and cannot be torqued again. They have a unique stretch property. I don't believe that I would call these standard. I have not seen any reference to Lycoming using these types of bolts. If they did, you would likely find a warning in the Overhaul manual to this effect or at least an SB, warning mechanics. The fact that many believe it to be true doesn't hold a lot of water with me. I have found many incorrect "facts" that seem to be in the urban legend category. I don't routinely dismiss, but use my own research to validate them.

Have you seen a reference to disposing the rod bolt any time it is removed or when it is removed at overhaul time of for component replacement? The former would imply a torque to yield bolt. I would expect most mechanics install the bearings prior to installation to measure for clearance and if they use new bolts for this, they have torqued twice. I would think this would be more common knowledge if there was a limitation related to torque to yield bolts. I also don't think they existed back in the 50's or 60's when these engines were designed.

I can think of countless reasons that a rod bolt would be torqued more than once during an overhaul/assembly. Lycoming would need to provide clear guidance to the maintenance community that this is not allowed or would be subject to serious liability in a court action. "replacement at removal" doesn't cover someone re-torquing just to be sure they got it right. A standard bolt can be torqued many times without risk. If the rod bolt is unique and can't tolerate that, Lycoming has an obligation to point that out to avoid liability and they have shown a clearly conservative approach in this area.
Larry

[Mike S]

When the bolts are torqued, they stretch. There is even a special dial indicator designed to tell you the correct stretch amount.

https://static.summitracing.com/glob....jpg?rep=False

http://www.hotrod.com/how-to/engine/...-stretch-tool/

Some manufactures dont want to reuse a bolt that has been stretched due to potential fatigue issues when it gets stretched the second time it is used.