Lubing Fastener Threads
 

Okay, I've admired by beautiful engine parts long enough. I want to drive my car, so it's time to attach the engine parts to each other, starting with rod bolts and nuts.

Porsche says to lube some fasteners. For example, they say to use Optimoly HT on head stud threads, even saying that motor oil is not good enough. Okay, JW was nice enough to throw me the last of his Optimoly, which is a kind of grease.

Wayne's book says to use loctite on rod nuts, though I do not recall seeing this in any Porsche publication. I am concerned that lubing fasteners that are supposed to be torqued dry will result in too much pressure on the fastener. I know we've been over this before (lets try to discuss this in less than 200 posts), but I need to make decisions about which fasteners to lube, which ones to not lube, and what lubes to use.

For example, what if I install a critical fastener, like rod bolts, without lube and the nut creaks and snaps? Obviously this would not be good, and I would be tempted to lube it just to get smooth tightening action. I can report that many fasteners creaked and snapped like crazy when being removed. For example, the main bearing through-bolts made snapping noises you could have heard from outside my garage, when I removed them.

Super...you ask an educated question. If it was my concern I would measure connecting rod length/stretch for perfect torque setting.

Okay. How much are the rod bolts supposed to stretch? Torque spec is 50-55 Nm.

And the better question is this: Why aren't you people fighting over this issue like you did last time? Tired? Lazy? Don't care about fasteners anymore? Heck, I know we still have machinists on The Board.

Supe-

That is a good question (wish I had the answer!). I would hate to dwell on that thought when everything was back together, or after the first run up to 6500 rpm! So, I would be doing just what you are doing: Asking questions. Then again, I would be completely confident with JW's recommendation. If you are still worried, I would email Andial, Jerry Woods, etc..., and get a general consensus.

Superman, I took the Woods & Anderson class last December and Jerry recommended using motor oil only on the rod bolt threads. As far as torqueing the rod bolts he said to use the "stretch" method but mentioned that the supplier of the rod bolts (ie ARP, Raceware) should have the stretch spec included with the bolts. Guess that doesn't help much if you're using OEM rod bolts! I'll check my class notes for other critical fastener info. Pete

Super ...for stock rod bolt stretch I would start with PCNA. Every time I call them I get directly connected to guys at Stoddard, go figure

Hehehe,

Creaking Nuts!

Install with nothing more than light Palmolive lube and all will be super, Super.

Nitpicking at it's finest.

Relax fellas, it's not like these are expensive to machine/rebuild...are they?

Go with JW's advice...afterall, JG would never steer you wrong!

Well, I was a cross between a Nerd and a Socialite/Athlete in high school, which was a LONG time ago, but I still like numbers and science. And I'm a champion worrier, so I know I ask some pretty persnickity questions.

On the other hand, I like the Neanderthal answers. A longtime friend with mountains of hotrod and other experience with V8s starting when he was 15 (he's older than I am) said, when told about our previous controversies around rod bolt torque techniques and possible rod bolt failures said "Bull$hit, I used to put a engines together with breaker bars, no torque wrench, and have had no problems." I tend to agree, at least with SC rod bolts.

I like these kinds of comments and consider them as accurate as the "oh, you CANNOT lube threads unless the mfg says so, otherwise your engine will fly apart and you should ALWAYS measure bolt stretch..." In truth, if I put this engine together using a torque wrench, my failure risk will no doubt be one in 10,000 or less.

Super--you started this subject over concern for proper torque setting. The issue was not over if you should be concerned or not be concerned, IMHO. You raise interesting issues. It doesen't matter, IMO , if it's a book issue or a reality issue. Being provocative probably means you are smatter than you look.[just speculation of course]http://www.pelicanparts.com/support/smileys/wat6.gif

I'm flattered, Ron. I find a lot of things interesting, though the practical impact may not always be significant.

I still don't know how many angels can dance on the head of a pin, but I'm not planning any social events for angels so WTF.

I'm not sure how you would measure bolt stretch without having been able to gauge the length of the bolt after each tightening sequence.

I think the issue with the lube is to take some of the torque load off the bolt so that the threads don't bind under pressure. I don't think the bolts will come out after being properly torqued.

I did a light lube on the conn rod/main bearing bolts when I installed them and tighten them up to specs.

Steve

Storm...the importance of preload sometimes makes me neurotic. The importance of proper torque setting is usually, IMO, more important to bolt strength/fatigue resistance than the ultimate strength of the bolt. If a rod bolt is torqued low it will lossen. A rod bolt torqued high will snap, generally speaking. There are many variables when a torque wrench is used to properly preload/torque a bolt. The spec rod bolt torque numbers are a rough approximation to get the bolt tension preload. I think the desired preload is 60% or 80% of its total strength. IMO, the only way for me to get the desired preload accurately is to measure the exact amount of stretch that the desired preload will cause. If I only use a torque wrench I want my error on the high side rather than the low side, when I consider all the variables, including my technique. IMO, the highest stress a bolt will see happens during tightening, usually. If a bold doesn't fail during tightening, or turn to "plastic", it never should. If I feel a bolt stretching/yielding while being tightened I throw it away. Back in reality when I installed Raceware rod bolts to spec using a torque wrench I didn't get anywhere near the desired stretch. I called Raceware about this and the phone guy tells me "oh yeah, we did not, in our literature, refer to the fact that your 2.7 rod bolts are thicker than the 3.2 rod bolts and more torque can be applied". I stopped at 75# and came close to desired stretch on the low side. I became nervious as the torque numbers kept increasing. All theory be dammed. I'm not a pro so to relax me I did a DE and got the rpm to pull to the far side of redline maybe 10 times. If this 2.7 is going to blow lets do it and get it over with. IMO, any possible bolt damage would have shown in the next 10,000 miles. The 2.7 runs great. I have enough confidence in the total assembly that I'm doing a high rpm cross country ride this May, AGAIN........ http://www.pelicanparts.com/support/smileys/fles.gif