head bolt torque

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tufty

tufty

New Member
Posts
214
Location
Leighton Buzzard Bedfordshire
hi guys and gals
I have been busy doing the head gaskets on my 1996 4.6 hse
now the lr manual says torque settings are 20nm then 90 degrees then a further 90 degrees, {in the correct sequence of course } im using new bolts elring gaskets and the heads have been pressure tested and skimmed.
however after tightening the bolts to 20 nm and then 90 degrees it felt really tight. no way am I going to get another 90 degrees out of them, so I decided to measure how tight they were using the torque wrench. the bolts would not move until 145 nm was reached but according to lr they still need a further 90 degrees. what are your thoughts on this surely 95 to 100 nm is plenty tight enough. sorry for being so long winded didn't have this problem with my classic v8. as a ps I broke 5 sockets and rounded off an impact socket removing the bolts and one of them was a snapon socket.
 
Slacken them back off and lightly lubricate the threads and under the bolt heads. Make sure all the bolts screw freely into their positions. Torque as stated, leave a few minutes then make another pass at specified torque to set them all the same. Some may have settled. Then 90 degrees, then 90 degrees. DO NOT just torque the bolts to what you think is correct.
 
Last edited:
tufty said:
hi guys and gals
I have been busy doing the head gaskets on my 1996 4.6 hse
now the lr manual says torque settings are 20nm then 90 degrees then a further 90 degrees, {in the correct sequence of course } im using new bolts elring gaskets and the heads have been pressure tested and skimmed.
however after tightening the bolts to 20 nm and then 90 degrees it felt really tight. no way am I going to get another 90 degrees out of them, so I decided to measure how tight they were using the torque wrench. the bolts would not move until 145 nm was reached but according to lr they still need a further 90 degrees. what are your thoughts on this surely 95 to 100 nm is plenty tight enough. sorry for being so long winded didn't have this problem with my classic v8. as a ps I broke 5 sockets and rounded off an impact socket removing the bolts and one of them was a snapon socket.
Click to expand...

it cant have been the right size socket if you bust a snap-on one,bolts arent std bolts so need correct degrees
 
The bolts are 7/16" UNC with 5/8" AF heads. Many use 16 mm 12 point sockets on them and wonder why they round them off. NEVER use anything other than proper 5/8" AF single hex sockets to remove or tighten them.
 
5/8 hex snapon socket busted the rest were various makes only a brand new cp impact socket shifted them. one had to be drilled out by drilling the head off to almost the same size as the bolt shaft and tightening until it snapped :eek: then it unscrewed with fingers.
new bolts used that are lightly oiled wammers . gonna have another look in the morning
 
As the heads have been skimmed you are now using a "new" bit of thread in the block, not much I grant you but it might be grubby or corroded. I always screw the old bolts in while the heads are off a couple of extra turns more than they'll require when fitted to ensure the threads are nice and clean.
 
StuckAgainSteve said:
As the heads have been skimmed you are now using a "new" bit of thread in the block, not much I grant you but it might be grubby or corroded. I always screw the old bolts in while the heads are off a couple of extra turns more than they'll require when fitted to ensure the threads are nice and clean.
Click to expand...

Or run a tap down if you have one, make sure the holes are clear of any crap, blow out with an airline.:)
 
tomcat59alan said:
Or run a tap down if you have one, make sure the holes are clear of any crap, blow out with an airline.:)
Click to expand...

You can make a thread cleaner by sawing a couple of slots lengthwise in an old bolt and carefully grinding away one side to show a sharp leading edge as the bolt is screwed in and one when the bolt is screwed out. Worked back and forth down the length of the threaded hole this will clean any crap out. Remove bolt and blow out several times as it is being done to prevent jamming. Me giving away trade secrets again. :D:D:D
 
Stretch head bolts are designed to allow for expansion and contraction of the a alloy head. In designs where solid studs with no give were used, expansion and contraction of the alloy head eventually wore into it and caused them to become loose as the alloy was constantly compressed against an unmovable washer and nut due to the differing expansion rates of alloy and steel through the heat range. Stretch bolts are designed to give as the alloy expands and contract as it cools maintaining an even constant tightness. Basically like a spring.
 
wammers said:
You can make a thread cleaner by sawing a couple of slots lengthwise in an old bolt and carefully grinding away one side to show a sharp leading edge as the bolt is screwed in and one when the bolt is screwed out. Worked back and forth down the length of the threaded hole this will clean any crap out. Remove bolt and blow out several times as it is being done to prevent jamming. Me giving away trade secrets again. :D:D:D
Click to expand...

Still keeping your adjustable spanner secret though. For those that don't know it's a bed spanner and a large hammer, beat it to any size you want:D:D
 
ok guys here is a sitrep.
I removed the head that was fitted and cleared all the bolt holes out with a tap and blew them out with an airline. lubricated the bolts with clean engine oil including under the head of the bolt. 20nm then 90 degrees then 90 degrees was finaly achieved much easier this time. then the same on the other head. so all good now thanks guys. mostly back together now, just the exhaust manifolds {needs new bolts as the splines are virtually non existant on some } the pesky heat shields, airflow meter, plenum chamber and cables and hoses to connect :biggrin1:
 
Glad you took advice and lubricated under bolt heads; I was part of an aircraft incident investigation some years back. We used stain gauge washers under the bolt heads and did all sorts of different tests. You wouldn't believe how much variation you get in bolt end load if no under head lubricant is used :eek:
 
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