connecting rod bolts with loctite?
connecting rod bolts with loctite?
(OP)
hello,
I have point I am trying to make to a friend , but I'd like to be a litle more sure of my answer than just , my opinion and the way I do things, and have a knowledgable answer to back it up.
A friend who happens to be a heavy equipment mechanic, claims that in every engine he's ever built, he uses blue loctite on the connecting rod bolts.
I not only don't do this, but am of the mind that this could really give a false torque reding , even hinder the ability to get proper torgue with a stretch gauge if he is using one.
I was taught to use oil or even the moly type lube (I think) that ships with quality aftermarket bolts such as ARP, etc., or you can't get the proper tension on the bolts.
Can anyone tell me if I am correct here, and explain so that I might inform this person why this is not a good thing? (if I am am correct that is)
Thanks
I have point I am trying to make to a friend , but I'd like to be a litle more sure of my answer than just , my opinion and the way I do things, and have a knowledgable answer to back it up.
A friend who happens to be a heavy equipment mechanic, claims that in every engine he's ever built, he uses blue loctite on the connecting rod bolts.
I not only don't do this, but am of the mind that this could really give a false torque reding , even hinder the ability to get proper torgue with a stretch gauge if he is using one.
I was taught to use oil or even the moly type lube (I think) that ships with quality aftermarket bolts such as ARP, etc., or you can't get the proper tension on the bolts.
Can anyone tell me if I am correct here, and explain so that I might inform this person why this is not a good thing? (if I am am correct that is)
Thanks





RE: connecting rod bolts with loctite?
4th result in google for "arp rod bolt torque" the other 3 from arp also contain information.
In the case of your friend old habits die hard and I'm sure some where that will be atributed to another smokey yunick secret trick. The locktite should not hinder the bolts ability to stretch. Should hinder the ability to torque it with a torque wrench alone.
RE: connecting rod bolts with loctite?
I, personally, would use oil on rod bolts only with French locks.
Mostly, like your friend, I use Loctite of some kind. In recent decades, I've been using Loctite PST, which feels better in the torque wrench than blue Loctite.
Mike Halloran
Pembroke Pines, FL, USA
RE: connecting rod bolts with loctite?
If no recommendations are available, or on engines with stock rods I use Loctite instead of oil on the threads, but a drop of oil under the head of the bolt.
Regards
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RE: connecting rod bolts with loctite?
RE: connecting rod bolts with loctite?
RE: connecting rod bolts with loctite?
Mike Halloran
Pembroke Pines, FL, USA
RE: connecting rod bolts with loctite?
RE: connecting rod bolts with loctite?
I'd use a GOOD moly paste with a lot of moly, not a moly chassis lube. ARP moly or Dow Corning GN paste is fine. It is the PRELOAD and only the preload that prevents fatigue cycles and fractures on something like a rod bolt.
Loctite is good for non-rigid connections, like soft gasketed joints. I use it between the rod/main bearings and the rod/block to help avoid spun bearings--along with the bearing crush on the high side.
Naturally if a journal bearing is starved for oil it can seize and spin no matter what you do.
"I'm that dog who saw a rainbow, only none of the other dogs believed me." from "Kate and Leopold"
RE: connecting rod bolts with loctite?
With no spec, oil is the most likely the presumed method. Loctite still works as a reasonable lube until it starts to set.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: connecting rod bolts with loctite?
I have used the 'stretch' of my rod bolts as a guage to determine what the 'torque' should be, it can vary from specs a bit, but I have not needed the info for quick repairs in the field lately (knock wood). Rod bolt stretch is still my main method, oddly (or perhaps not), the ARP and SPS specify the same .006" in my case (two totally different engines). Maybe I'm a little old fashioned, but if I have fasteners that tene to loosen frequently I generally search out some alternative to "just using Loctite". I tend to use it, but only as a last resort (which does happen). On the other hand, I use it extensively on all my chassis and suspension bolts and nuts, along with safety wire when applicable. I use AN flat washers only, no split lock washers...hate them thangs!
Rod
RE: connecting rod bolts with loctite?
Friction keeps the bolt or nut tight and not a thread locking compound. Friction on threads and nut/bolt base is key to non-rotation during engine operation. If sufficient stretch is applied to the fastener so that the assembly never "feels" the loading which is proper design, then the fastener will not "un-screw".
As far a these lock plate devices on any high load fastener--------bad idea. In order for the lock tab to bend it needs to be ductile----soft. If soft and used under a rod bolt or nut, it will compress over time and the bolt stretch will diminish. BANG/CRASH/BOOOOM! :(
RE: connecting rod bolts with loctite?
I agree with Patprimmer; if the spec says oil, use oil, if not, go dry. To me, loctite is OK, and won't hurt anything, so why not use it?
I think loctite on the shells is bad news, as it could affect heat transfer between shell and rod/block.
Jeff
RE: connecting rod bolts with loctite?
Mike Halloran
Pembroke Pines, FL, USA
RE: connecting rod bolts with loctite?
RE: connecting rod bolts with loctite?
RE: connecting rod bolts with loctite?
With steel rods I'd first take pains (and measurements) to get the bores round and straight and repeatable, the right size and surface finish (finish for HD use used to be in the TRW and Sealed Power bearing books, and the Chevy power book), and forbid the balance shop from reducing the "footprint" at the parting line or any area that reduced Big end stiffness.
I never did the experiments, but I'd kind of expect heat transfer from shell to rod thru loctite might just be better than thru all that "air" in a typical interference joint anyway.
Oil flow is a powerful tool to cool bearings of many types. Clearance has a direct influence on oil flow thru a journal bearing. http://w
RE: connecting rod bolts with loctite?
Not wanting to start a fight, but I have read and have practiced sizing my con rods at the parting line 0.0005"- 0.0007" larger than my vertical measurements. The theory being at high rpm/load the rods stretch vertically and tighten the clearances at the parting lines. Have I been missinformed?
By "reducing the footprint at the parting line" do you mean removing material from the outside of the rod where the bolts pass through?
Carl
RE: connecting rod bolts with loctite?
Footprint is the total contact area at the parting line.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.