why new rod nuts

[honerboys]

hi - i see on a lot of these posts that you should replace the rod nuts when doing the bearings - why is this - i removed the rods on the 83 - the nuts spun off fine and don't look damaged in any way - not saying i'm against replacing them just wanted to know what exactly is wrong with them - i have reused rod nuts on other cars (no porsches) and never had a problem - just wondering

[John_AZ]

This is why...




John

[JAXTURBO]

No end of knowledge in this forum. I learn something new daily here. Thanks John

[honerboys]

thanks johnaz - now i know

[emoore924]

Doesn't say you can't reuse used "new style" nuts, just don't reuse used (or new?) old style.

Did I read that right?

[89-944NA]

Originally Posted by emoore924

Doesn't say you can't reuse used "new style" nuts, just don't reuse used (or new?) old style.

Did I read that right?

Read under the "Note" on the lower right side of the page John posted.

Porsche recommends that new nuts be used "each time the engine is repaired", the reason for this is that the serrations on the nut become rounded when the nut is removed, thereby reducing the ability of the nut to stay tight. These serrations are to prevent loosening caused by vibration.

Say you just spent a few thousand dollars to overhaul your engine, you followed the recommendation to use new head bolt washers, instead of just scuffing the mating surface of the old ones...now why wouldn't you want to use new rod nuts?

The larger industrial supply houses like McMaster-Carr sell these nuts in boxes of 25 for about $14.00 including shipping....now you have enough spare nuts to either help out a couple of friends or for the next time you go into the rotating mass of your engine.

Me, I look at new rod nuts as cheap insurance against a major repair bill or engine replacement.

[88Silver924S]

I thought the reason why critical nuts and bolts are supposed to be replaced and not reused is that when torqued the threads deform. Once deformed the threads do not fully "spring back" to their original position upon removal and if they are reused they deform a second time which further weakens the threads (work hardening plus shape deformation). This serial weakening of the threads is no big deal on, for example, an alternator mounting bolt but on a rod cap failure is expensive relative to the price of a new nut so full strengh "virgin" threads on each torgue down is recommended. For fun noodle around the web site Bolt Science Web Site they have some interesting articles.

In the old days of my '57 Morris Minor I too reused critical nuts and bolts willy-nilly and got away with it just fine. So I think of it mostly as insurance also. Good luck and have fun.