loctite on rod bolts

T77911S · 02-18-2020, 08:11 AM

I have ARP rod bolts. going to use the stretch gauge to torque them.
but was curious since torque is not an issue should I or could I not use the thread lube they provide and use Loctite.
and which one, 271?

john walker's workshop · 02-18-2020, 08:35 AM

No loctite, use their lube.

T77911S · 02-18-2020, 09:19 AM

ok
thanks

gtc · gtc's Garage

+1, i had to replace one ARP bolt/nut that galled when i assembled it dry (very lightly tightened) for my plastigage check.

Trackrash · Trackrash's Garage

FWIW. The lube that comes with the ARP bolts will give you a good stretch vs torque value.

I'm not sure what happened on my last build but. I disassembled my motor after a few thousand miles and about half the rod bolts were not seemingly torqued to the spec. They just did not seem to be very tight. Like maybe 20lbs to break them loose. Others were much tighter.

When I re-assembled the motor I used blue lock-tite. I used it generously on the threads and it did take a few more lbs/ft to get the correct stretch.

Does anyone have a theory why they would not stay tight with the ARP lube?

T77911S · 02-19-2020, 03:44 AM

my thought was if a lube reduces friction to tighten it, it would make it easier to come lose.

RedCoupe · 02-19-2020, 07:44 AM

Quote:

Originally Posted by T77911S

my thought was if a lube reduces friction to tighten it, it would make it easier to come lose.

From my understanding, it's the rod bolt stretch that keeps them tight. The ARP special lube keeps the amount of stretch consistent for a given torque value. There are many engine bolts that you can't use a stretch gauge on, so using the lube insures that you have pretty close to the correct amount of stretch just by using a torque wrench. On rod bolts, if you use locktite you for sure would want to use a stretch gauge.

Trackrash · Trackrash's Garage

Quote:

Originally Posted by T77911S

my thought was if a lube reduces friction to tighten it, it would make it easier to come lose.

Since the time I used axle grease on my rear axle nut I have been NOT using grease on any torqued threads. My nut sheared off the cotter pin and backed off at an auto cross. Never had anything like that happen before or after. That is the only time I used grease on a torqued fastener.

That said, I figured the ARP stuff was different. I am not blaming the ARP stuff, but will use lock-tite on rod bolts from now on, checking the stretch.

T77911S · 02-19-2020, 10:31 AM

yes
bought a nice stretch gauge from JEGS, it was their brand.
spring seems sufficient and I can remove it and put it back on and get the same readings.
not a bad price either.
looking forward to using it, just waiting on piston squirters so I can put those in and then put in the head studs.
I also bought a nice set f calipers and have measured all the bolts to get their measurement, just in case.

patkeefe · 02-19-2020, 01:35 PM

Quote:

Originally Posted by RedCoupe

From my understanding, it's the rod bolt stretch that keeps them tight. The ARP special lube keeps the amount of stretch consistent for a given torque value. There are many engine bolts that you can't use a stretch gauge on, so using the lube insures that you have pretty close to the correct amount of stretch just by using a torque wrench. On rod bolts, if you use locktite you for sure would want to use a stretch gauge.

Yes, the stretch is what keeps it tight. If a bolt gets over-torqued (it actually thus is in what is called the plastic range) then it will not go back to it's original shape or length. This may be what we are describing as "galling".
plastic range - The stress range in which a material will not fail when subjected to the action of a force, but will not recover completely so that a permanent deformation results when the force is removed.

ARP says that if you get a stretch that is close to the stretch prescribed by them, then you have achieved most all of the clamping force available. I have discussed the following chart with them: https://arp-bolts.com/p/technical.php

gtc · gtc's Garage

FWIW, a few of us have noted that the 9mm ARP bolts require a few extra ft*lbs to reach the stretch specified in their instructions. They suggest 40 ft*lbs, but mine needed about 45 IIRC. (i assembled mine with a beam-type torque wrench and torque adapter while measuring stretch simultaneously with an ARP gauge)

patkeefe · 02-19-2020, 01:38 PM

Quote:

Originally Posted by T77911S

I also bought a nice set f calipers and have measured all the bolts to get their measurement, just in case.

That is a very good idea, to get the before (and hopefully after) bolt lengths.

stownsen914 · 02-19-2020, 02:10 PM

I'd heard that Loctite is a no-no on rod bolts, but I'm not an expert.

Trackrash · Trackrash's Garage

Quote:

Originally Posted by stownsen914

I'd heard that Loctite is a no-no on rod bolts, but I'm not an expert.

Why would that be?

Wayne in his book (I know), says to use red lock-tite.

Walt Fricke · 02-19-2020, 02:33 PM

I'm with John Walker. Porsche doesn't use a thread adhesive on rod bolts. A properly stretched rod bolt just isn't going to come loose. Neither ARP nor Raceware advocate using Loctite. I don't know what its lubrication properties are, but they can't be similar to those of the lubricants the bolt manufacturers recommend.

The kep for rod bolts is to have the tension created by the stretch exceed the forces acting on the fastener which are trying to pull the joined parts apart. In this case, you don't want the bolt to stretch some more and let the cap separate, even a tiny bit, from the big end of the rod. With gaps, not only is the oiling messed up, but for an instant as things relax there is no tension on the bolt, which is when the nut can back off.

911pcars · 02-19-2020, 02:34 PM

Quote:

Originally Posted by Trackrash

Why would that be?

Wayne in his book (I know), says to use red lock-tite.

The correct torque is based on a known reference lube for the correct amount of material stretch.

Locktite isn't a lube but a thread locker. Thus, what is the suggested torque to be applied to a fastener using thread locker that is equivalent to the specs with ARP or anti-seize lube?

Don't think that's in Wayne's book.

Sherwood

dannobee · 02-19-2020, 07:47 PM

No loctite, only the lube on ARP bolts. BUT, I've found that if you torque to the correct stretch while watching actual bolt torque, it will change if you back it off then retighten to the same torque. Since I started doing that, I've always torqued, then backed off, then retorqued. Once that is done the torque and bolt stretch fall within ARP's guidelines. FWIW, YMMV.