Re: [AMC-list] 195.6 leaky head gasket

[Frank Swygert <farna@xxxxxxx>]

I bet the lube was the problem. I don't recall if the TSM values are for dry or "lightly lubricated" threads. I've used anti-seize on head bolts in the past or nothing. But I found this (refers to a diesel engine that the heads are eventually torqued to 345 ft/lbs though!): 

"The AERA Technical Committee offers the following information on
cylinder head bolt torquing procedure on Caterpillar 3500 Series
engines. There seems to be some confusion concerning the correct
procedure for mounting this engine's cylinder heads. This information
supercedes previously published information.

The quality of the joint between the cylinder head and block depends 
on the proper amount of bolt stretch. Generally, the torque applied to 
a bolt determines stretch, but the type of thread lubricant used also 
affects it. The only lubricant that is acceptable for this engine is 
engine oil. Using thread lubricant on the cylinder head bolts other than
engine oil will lead to an improper bolt stretch and possible bolt or
thread damage. It may also provide an inadequate clamping force and
allow leakage."

This seems to indicate that the wrong type of lube can affect clamping force. The chart at this site (a bolt company: http://www.portlandbolt.com/technicalinformation/bolt-torque-chart.html) indicates that if you tighten a bolt that should have been dry (say 100 ft/lbs dry) then it only requires about HALF as much torque if lubricated. So if anything you'd have overtightened the bolts. I think motor oil is the suggested lube for most car bolts, but I don't really know. I do know that I tighten the bolts to the TSM specs whether I have lube on them or not... 

------------
Date: Fri, 29 Jan 2010 18:44:04 -0800
From: tom jennings <tomj@xxxxxxx>

Popped the head off today, and what a mess! Evidence of oil and water leaks.
The head gasket didn't seal for crap. I suspect the head isn't cracked, just
the leaky gasket, but I won't know for sure til I get it magnafluxed.

When I last assembled it, summer? 2007, the head was resurfaced, and the
block I got clean with razorblades and lacquer thinner. Copper Permatex
(brush on I recall now) decent thin coat. It's evident I didn't use too
much.

The most likely thing I can think of is my torque wrench is WAY off (I'll
get it checked or a new one depending on the cost to check) and/or the lube
I used threw torque way off. Do gaskets go bad sitting on the shelf? Hard to
imagine. You can do bad things with too much Permatex, but that's not it
here. Block deck could be not-flat, but I checked it with my Starrett 18"
straight edge (as best I could in the car).


--
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)

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