Rod bolts and Loctite

[ChrisBennet]

The new engine book recommends using Red Loctite before torquing up the rod bolts. This will change the torque won't it? Raceware makes a point of recommending only 30W oil because the lubricant use can make a big difference in torque values.
Is rod bolt torque that critical or not? What's the deal?
-Chris

[cstreit]

With Raceware and ARP bolts, follow the instructions... I think Wayne is talking about the stock bolts...

[ChrisBennet]

Originally posted by cstreit
With Raceware and ARP bolts, follow the instructions... I think Wayne is talking about the stock bolts...

Any torqued fastener will be effected by the lube used. If Porsche spec'd "lightly oiled" for their rod bolts and you use something else the torque will be different. I guess the question is whether the difference in torque makes a difference for Porsche rod bolts.
-Chris

[snowman]

I have never seen loctite recommended for any kind of rod bolt. It won't do any good anyway as the rod will get real hot, hot enough to melt steel, if there is a problem, like lack of oil and the loctite will give out immediately or if over revved the bolt will break. The loctite is of no real use as far as I can tell.

Here is how it is discribed in many books, on cars and on fasteners. The bolt is like a spring. It is tightened up and stretches, like a spring. It is that spring tension that holds things togather, therefore there is no need for any locking devices. THis is true of any MODERN car which a Porsche is.

The bolt will fail if its ultimate strength is exceeded or if the spring tension is exceeded and the bolt undergos a couple of hundred cycles that exceed the initial torqued tension.

There are three tightening methods.

1. Torque only- This depends on using a lubricant, such as oil. To get the correct value one must use exactly the lube recommended by the factory. THe drawback to using torque is that the ammount of tightness or stretch that the bolt sees can vary by huge ammounts, like 50% or more. And worse yet is each time the bolt is tightened the threads are burnished and less and less torque is needed to acheive the same degree of tightness.

2. Torque and stretch. This method is much more accurate than just torque. THe bolt is tightened to a low value of torque, and then turned a specified angle, eg 85 degrees. THis results in a much more repeatable ammount of tightness than torque alone. These bolts are typically only used a single time. These are called Torque to yield bolts. The bolt retains some permanent stretch when it is used.

3. Stretch only. This is the best method and most repeatable. This is the one used by Carillo which uses the worlds ultimate bolts made by S.P.S. (at about $25 ea) and ARP. A U shaped dial indicator is placed on the bolt to measure its length and the length is monitored while tightening the bolt. When the bolt is some number, e.g. 0.006" longer it is considered tight. Again a lube is used, but it dosen't matter much what it is as it will not affect the result. Some of these bolts can be reused.

[ChrisBennet]

Thanks Jack. It seemed odd to me but hey, I don't get out much. Porsche uses the torque angle method (method #2) I think I'll buy or make a rod bolt stretch gauge before I do another motor.
-Chris

[Bill Verburg]

Here are the calculations from my engine using the stretch method and Raceware rod bolts

[snowman]

Bill,
Can you explain?

[snowman]

Chris,
YOu need to go by the bolt mfg recommencation, whatever it is. The best method may not be used, and there is no way to compensate for this except chang mfg of bolts. ( or possibly be an engineer with the expertize to know better).

SPS makes the worlds BEST fasteners, PERIOD. But they are all designed for specific applications. As far as I know only Carillo takes atvantage of the expertize offered by SPS. Their bolts are truly a work of art. every aspect of the thread forming is considered, every radius, everything is xrayed, 100%, the worlds strongest steel is used, some at over 320,000 P/sq in (compare that to ARPs 220,000). Look at one of these bolts, compare it to anything and you know you have Micheal Angelos work in hand. They are truly unbeleaveable. The bottom line, EVERY race team, NASCAR, CART, whatever, uses Carillo rods with SPS bolts. And you do not see engines failing anymore do you?

[Wayne 962]

Snowman is partially wrong. In particular with the case of the rod bolt failures on the Carrera/3.3/3.6 engines, the engine is over-revved and then the rod bolt stretches and becomes loose. This then immediately untightens the bolt, and can cause the rod nut to fall off. The red Loctite protects against loss of torque on the nut due to overstretching of the rod bolt. There is no downside for using the red Loctite and plenty of upside.

Hands down, I recommend red Loctite on the rod bolts to protect against possible over-revs and the rod bolt stretching. The red Loctite will buy you a few degrees of margin, and possibly avoid a complete engine destruction. See the blown up rod bolt in my new book if you don't believe me...

-Wayne

[Bill Verburg]

Jack, No I was in the shop and Dr.T pointed to the calculation page and said that it was the calculation of stretch for the Raceware rod bolts. That's all I know about it.

[snowman]

Wayne,
I cannot agree with the logic on the rod bolt. It the engine is over revved and the bolt is stretched beyond its initial clamping force, it will either
1. count as a single cycle if the bolt returns to its original clamping force (ar nearly so) and the rod nut will not loosen.
2. the rod bolt is permanently stretched so there is very little clamping force left. Here the loctite may "work" but the rod bolt will break in the very very near future.
3. The rod bolt is stretched beyond all clamping force. The loctite will hold the nut, but the rod will soon start to hammer and if un noticed, eventually heat up and ruin pretty much everything.
4. Downside, there are no specs for torquing using loctite as a lubracant. Remember the actual value of clamping varies over 50% with the proper lube. Since the loctite is being used with a torque to yield bolt it is probably much less important, but it still must lube properly so the bolt isn't damaged during tightening.

Like I referenced, ALL the books, automotive classroom, shop, auto mfgs, fastener mfgs, state to use the proper lube, nothing else. I will list, and it is very extensive, all the names of these if you have any doubt. Otherwise it might be better to find one single, peer reviewed, publication that states the benefits of loctite in this application.

By the way I am not saying there is no benefit to loctite, its just there is no one that I have ever seen, and after asking several knowledgeable people, eg the head of the automotive department at the college with over 30 years experience and several other highly reguarded Porsche race car builders. It may be that someone with lots of experience has seen some benefit. But in that case this benefit may be highly process dependant and unless you duplicate everything that person does, in a controled manner you may not obtain the same benefit.

My personal take on the subject, ie gut feeling, is that it probably dosen't hurt anything to use the loctite, but it probably dosen't do much good either, except in the case where it may give you some small warning your engine is coming apart and to stop running it NOW. Unfrotunately my gut feeling is that most people do not stop runnig it soon enough.

[Wayne 962]

Thanks Jack, you just agreed with me!

There is no downside to using the Loctite. I performed plenty of research for the Engine Rebuild book, and this was one of the topics. If the bolt loosens up, you will begin to hear clacking and engine noises, which will most likely cause you to turn off your engine and save it before it throws a rod through the case. 3.2 engine cases can be very expensive to replace. As I said previously, the red Loctite adds a small benefit of added safety. It doesn't hold the whole engine together.

-Wayne

[emcon5]

Sorry to dig up an old post, but the instructions with ARP rod bolts say to lubricate the threads with moly assembly lube, and include a small package of lube for this purpose.

Just muddying the waters,

Tom

[911pcars]

I kinda did both. I torqued the rod nuts using antiseize. After cleaning the threads at the base of the nut, I then ran some green Loctite (perhaps a wishy-washy choice between blue and red) into that area. Who knows?

What does it take to remove red-Loctited rod nuts? 1/2" dr. flex handle or torch?

Sherwood

[ChrisBennet]

At least if you use green Loctite (which is designed to be applied after the bolt is torqued) you aren't changing the torque value.
-Chris

[Wayne 962]

Bottomline is that the people who helped with the book - many use Loctite, and none have ever had a problem with a rod bolt falling off inside the engine. Experience counts for a lot here, the red Loctite is good extra insurance.

-Wayne

[juan ruiz]

I promise my self I could not get involve but I can't.sorry..........

Ok so here goes.........Im sure that Mr.Wayne has done his homework, BUT I will like to offer my point of view and maybe Im misunderstading something,Im looking to learn NOT to create Problems........

I have never heard of this "rod bolt problem" as we all have hear about the valve guide problems (3.2) In this site is the ONLY place that I have seen this mention,so ok, lets assume that if you over rev your car (which I have done in many occassions) the "rod bolt will fail" as mention in here, if you install this "loctite" fine the nut will stay in the bolt,the reason that they break (any rod bolt) is not because the nut fails is because the bolt streches pass his "yield point" there for the bolt breaks and everything goes bad, any bolt regarless they all have a certain % of strech if this point is pass the bolt will let go,so what good is the loctite? the nut still attached to the bolt but the bolt has strech pass the limits and have broke.


Of couse I could keep on and on but I will stop here. thats JUST my point of view.

[Jay Auskin]

I'm with Juan where I wasn't going to get involved, but I need to post a response. I'm no Porsche engine expert, but 6 years of diesel engine design, bolted joint courses, and designing both alot of good and bad bolted joints I can offer the following:
1. The most important part is the bolted joint. Good clamping length, and mimimal overhangs...doesn't seem to be an issue with con rods.

2. The second most important is proper torque. Any time a bolted joint failed I always had to ask, "Do we know exactly how it was torqued?"

3. "Thread locker" is always a last resort for a "borderline" joint or for resistance to harsh environments. Llike Juan said, there aren't an alarming number of rod bolt failures. Hot oil isn't too harsh for a good joint.

On a side note, there was mention of Moly. Unless specifically stated to use this in the torque procedure, do not use it! It is way too slick, and will cause an overtorquing of the fastener (resulting in breaking the bolt head...if you're lucky to catch this mistake). But aside from moly, other oils/thread lockers don't affect the final torque too much. Especially for torque-turn methods.

[Wayne 962]

For proof of failed rod bolts, simply look at page 82 of the Engine Rebuild book. Just because you haven't heard of it happening, doesn't mean it doesn't happen. That's just plain common sense.

Also, the whole point is lost here. The read Loctite doesn't have anything to do with the 3.2 rod bolts. If you are rebuilding your engine, then you are smart enough to use the proper hardward and upgrade to Raceware or ARP. The Loctite is an added measure of protection on a critical joint - it's as simple as that! It's what works from years of experience and practice. If you don't use it, your engine is not going to fall apart. If you do use it, it's not going to mess up the torque spec. Plain and simple, this particular argument is not really rocket science...

-Wayne

[88911coupe]

Sorry to resurrect this but I have a related question. If you are doing a top end rebuild I have heard its a good idea to go ahead and replace the rod bolts since they are supposedly easily accessed with the pistons off. Is this really true and what risks would someone be taking if they decided to not use the EXTREMELY expensive ARP rod bolts and just buy Porsche's rod bolts to be used on a car that only sees redline on very rare occasions?
TIA