Should I clean and lube my head bolts before installing and torquing them? Doesn't mention anything about this in the FSM.

Also, Should I make an effort to clean out the head bolt holes??

Brian in Austin

Is the torque stated as a wet torque in the manual? If not then dry and clean. Clean everything, even the threads in the block.
John

A light application of 30w oil for the head bolt threads and under the bolt head - don't forget to wipe some oil from your fingers onto the washers - don't install until after a thorough cleaning of the bolt and block threads. Use a bottoming tap on the block holes. If you have a SOHC 3.0L, torque to 80 lb-ft.

Frank

Where is this technique documented?

In all my years of working on aircraft, and attending college for the same, I never heard anyone that knew something say " hey man, screw what the manual says, just rub some oil on the bolts, it'll torque em up more better. And oh yeah cut the ends of the bolts off because the morons that design these things make them too long". Google wet torque and dry torque and coefficient of friction if you care and be careful what advice you heed...

Oh, Nate, this is gonna be fun...

Before we get going, everybody go read "bolt science" faq's, so we are all at the same state of confusion...

For starters, after you subtract thread friction and underside of the bolt head friction on the washer, I think you are left with something like 12% of the twisting force actually goes to preloading the fastener for a 12mm diameter. The variable list is very large, shaft diameter, fastener material, thread pitch, thread form, thread tolerances (root, crown, axial, lineal), desired clamping load. It's the number of variables that caused fastener engineers to start using angle of rotation instead of raw torque. You preset the fastener to a lower than specified torque, then rotate it a calculated angle to achieve the desired fastener preload.

Well, I feel stupider now....


<img src="/forums/images/graemlins/lol.gif" alt="" />

Possibly only in the book I carry around in my head - based more on working on automobile engines than on airplanes. There's no question to me that oil changes torque value results - and there's no question that a little 30w on the bolt threads will probably do more good than harm.

Do you know why the factory changed the torque value from 72 to 80 lb-ft on head bolts for most of the engines in the '80s? I don't, but they blew a lot of head gaskets and something tells me that the factory guys thought the solution might be to make certain there was enough clamping force.

Here's an opened package of factory head bolts. Take a close look. The envelope has discolored from..... oil. The label inside the package has discolored and become shiny from.... oil. I wiped the bolts on the paper towel and found.... oil residue. Nowhere in the FSM do I see instructions to clean the oil from the bolts before installing and torquing to value:



Whenever I've rebuilt a 3.0L engine, I've found baked oil residue in the deck hole threads. Unless it drained around the threads, that oil came from factory procedures.



In all my years of engineering study and practical experience, one thing I learned was that field mechanics sometimes learn things through the experience of fixing engineering mistakes.



It's not that the bolts are too long, it's that the hole isn't deep enough..... <img src="/forums/images/graemlins/wink.gif" alt="" />

Build a few 3.0L engines without checking - particularly those with cut decks and heads - and see how the head gasket holds up around #4 cylinder.

Frank

Here's what the factory Service Manual says:

(1) Degrease the mounting surface of the cylinder head gasket.
(2) Lay the cylinder head gasket on the cylinder block with the identification mark at the front top.
-Using the special tool (shows picture of a torque wrench), tighten the bolts in the order shown (diagram)in two or three steps.
-Caution: Attach the head bolt washer in the direction shown in the figure.

That's it! That is ALL the FSM has to say,...nothing about cleaning head bolts, bolt holes, or whether anything should be lubed.

So, all the jousting aside boys, what is the accepted way to do this? Surely I am NOT the only one on this forum to ever do a valve job on one of these.

Certainly not - I think I remember doing one somewhere along the way in my life. It does get hard to remember when you're as old as me, though.

As usual, when you have differing opinions, the poison is yours to choose. Remember - you're the mechanic - any problems come back on you.

Here's a tutorial from Victor Reinz - one of the best manufacturers of head gaskets - and they probably want to make sure the gasket doesn't blow:

web page

Frank