Over torqued stock head bolts, valve lash changes!

Big Blue24

Big Blue24

Comp Diesel Sponsor
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Jan 5, 2008
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I finally pulled all the rockers and torqued my head bolts.

However, before I started, I checked valve lash after 60K miles of daily driving, hot rodding, and 20 or so 3900 rpm 1/4 mile passes. All of the exhaust clearances were between .019 and .020, all of the intake clearances were right at a snug .010. I was impressed that the valve lash was well within spec and dang near perfect considering the motor has 245K miles and it's been 60K since last valve lash job.

On to the headbolts, about half of the bolts moved/snugged up with just 90 ft lbs on the torque wrench. I then took all up to 100, then 110, then 120, then 126 ft lbs. Motor was still warm probably between 75 and 100*F.

I then replaced at valvetrain components in exact original positions and checked valve lash. All of the exhaust lash now came in at .015-.016 and all intake lash came in at .06.
The change in valve lash is proof to me that retorquing the stock head bolts does in fact provide more clamping force on the head gasket. On my well used motor, I feel confident that I compressed the gasket .04".

So Comp and ARP can claim that they tested stock bolts to yield and found no additional clamping load all they want, the truth is in the valve lash clearance changes.


Thoughts, comments, or criticisms?
 
Big Blue24 said:
I finally pulled all the rockers and torqued my head bolts.

However, before I started, I checked valve lash after 60K miles of daily driving, hot rodding, and 20 or so 3900 rpm 1/4 mile passes. All of the exhaust clearances were between .019 and .020, all of the intake clearances were right at a snug .010. I was impressed that the valve lash was well within spec and dang near perfect considering the motor has 245K miles and it's been 60K since last valve lash job.

On to the headbolts, about half of the bolts moved/snugged up with just 90 ft lbs on the torque wrench. I then took all up to 100, then 110, then 120, then 126 ft lbs. Motor was still warm probably between 75 and 100*F.

I then replaced at valvetrain components in exact original positions and checked valve lash. All of the exhaust lash now came in at .015-.016 and all intake lash came in at .06.
The change in valve lash is proof to me that retorquing the stock head bolts does in fact provide more clamping force on the head gasket. On my well used motor, I feel confident that I compressed the gasket .04".

So Comp and ARP can claim that they tested stock bolts to yield and found no additional clamping load all they want, the truth is in the valve lash clearance changes.


Thoughts, comments, or criticisms?
Click to expand...


so you didnt lube them before re torquing?
 
question.....

does the head clamping down .040" mean that there is more "CLAMPING FORCE"?
 
edit: I think the OP meant .004" and not .040", that's more legit

does the head clamping down .040" mean that there is more "CLAMPING FORCE"?
Click to expand...

I would say "not necessarily". I am also curious where this additional .040" was calculated.


Once the yield point of the fastener has been reached, no, there will be no additional clamping force available from that fastener; it will just stretch until failure (assuming it is in pure tension, applying torque to it would twist it off). Aftermarket fasteners, which are intended to have much higher yield strengths, can apply a higher clamping load before yielding.


I think the case here is to determine the maximum clamping load, before yield, of the stock head bolts.
 
Last edited:
well my thought is just because the head was clamped down .040" further doesn't necessarily mean there is more clamping force, but i don't know
 
Hurley said:
I would say "not necessarily". I am also curious where this additional .040" was calculated.


Once the yield point of the fastener has been reached, no, there will be no additional clamping force available from that fastener; it will just stretch until failure (assuming it is in pure tension, applying torque to it would twist it off). Aftermarket fasteners, which are intended to have much higher yield strengths, can apply a higher clamping load before yielding.


I think the case here is to determine the maximum clamping load, before yield, of the stock head bolts.
Click to expand...

Well said... Also there might be a touch of work hardening with the multiple re-torques.
 
It may not be more clamping force but compressing the gasket. After all the heat cycles the gasket goes through it may have room to compress. Hope it works. Do you think there is any benefit to putting head studs on a gasket like my 01 that has 270,000 miles on it and clamping it down harder?
 
Yeah sorry guys, it was very late last night when I made this post. Intake lash went from .010 to .006 after over-torquing the bolts.

Exhaust lash went from .019-.020 to .015-.016 so the head clamped down .004".
 
bsmith said:
so you didnt lube them before re torquing?
Click to expand...

I did not lube or remove the bolts whatsoever, just pulled out the torque wrench and went to town.


More clamping force or not, the gasket compressed .004" so that's .004" more that it has to lift before the gasket can start to move sideways. I honestly think if the bolts were "just stretching", the gasket would not have squished down approximately .004".



Does anyone have thoughts or opinions on setting lash within specified range but tighter than .020 and .010? It would seem that tighter lash setting would result in larger overall valve opening and thus slightly longer valve duration. For example, intake lash could be set as tight as .006" and exhaust lash could be set as tight as .015", netting an additional .004" of intake valve lift and .005" of exhaust valve lift.
 
Tighter lash would change duration. I used to change the lash on a big solid roller in a pontiac from .015 to as much as .030 lash to see if the times changed.
I believe the .004 thousand it tightened down can't hurt, it that much tighter and less wiggle room. Keep throwing boost at it and tell us where it's safe? I'll stop a few lbs. before!:bang
 
Big Blue24 said:
I finally pulled all the rockers and torqued my head bolts.

However, before I started, I checked valve lash after 60K miles of daily driving, hot rodding, and 20 or so 3900 rpm 1/4 mile passes. All of the exhaust clearances were between .019 and .020, all of the intake clearances were right at a snug .010. I was impressed that the valve lash was well within spec and dang near perfect considering the motor has 245K miles and it's been 60K since last valve lash job.

On to the headbolts, about half of the bolts moved/snugged up with just 90 ft lbs on the torque wrench. I then took all up to 100, then 110, then 120, then 126 ft lbs. Motor was still warm probably between 75 and 100*F.

I then replaced at valvetrain components in exact original positions and checked valve lash. All of the exhaust lash now came in at .015-.016 and all intake lash came in at .06.
The change in valve lash is proof to me that retorquing the stock head bolts does in fact provide more clamping force on the head gasket. On my well used motor, I feel confident that I compressed the gasket .04".

So Comp and ARP can claim that they tested stock bolts to yield and found no additional clamping load all they want, the truth is in the valve lash clearance changes.


Thoughts, comments, or criticisms?
Click to expand...



You would be wrong ,

you checked the lash warm, and after a hour or so i
Of retorquing , the valve lash tightened . You think. Warm motor expands heads expand , block expands , lash grows . Then when it cools it dose what .
 
I doubt the gasket squished. I can pull my rockers off and never touch the adjustment nut or anything and when I tighten them back down the lash has changed. The difference could be purely from the oil having drained off of everything or the motor cooling down (most likely).
 
Your change in valve lash was in the temp change of the motor.On motors with cast block and aluminum heads the lash increases with heat.And on motors with cast on cast it will decrease. I have seen up to .010 change in lash from hot to cold changes. mainly .004 to .006 in the average change. After you tourqe the cylinder head once that gasket is fully compressed.
 
purplepuller said:
Your change in valve lash was in the temp change of the motor.On motors with cast block and aluminum heads the lash increases with heat.And on motors with cast on cast it will decrease. I have seen up to .010 change in lash from hot to cold changes. mainly .004 to .006 in the average change. After you tourqe the cylinder head once that gasket is fully compressed.
Click to expand...


Cummins is cast block and cast head so lash will decrease with heat, meaning that if it measured .010 on the intake valves at 140* motor temp, it should read .012 on the intake valves at 80* motor temp.

Great, that means my overtorqued bolts squished the head gasket an extra .008 instead of my .004" original claim, thanks for clearing that up. Then if you account for the approximate 2:1 rocker ratio?? my original claim of .004" of gasket squish is correct. Glad there are so many people on here to walk me through this.
 
Forrest Nearing said:
*shudder*
Click to expand...

I have rebuilt many motorcycle and snowmobile engines in my life. When I was really young and had zero funds, I played around quite a bit trying to reuse head gaskets. Once you let tension off the head bolts, the gasket is ruined. I have tried this many times and even if you exceed torque specs, used gaskets in their original location do not seal.

I have read numerous accounts of guys buying arp studs and replacing them one at a time for "extra insurance." Then two months later they loose a gasket. I have always questioned the practice of loosening and retightening fasteners that clamp down a head gasket. Now maybe, because the head has 26 bolts, most guys get away with it. I felt, however wrong it may be, it was a greater risk to remove and lube each bolt than to torque all bolts as they sat but stay below 130 ft lbs.

I read that Garmon gets away with 150 ft lbs on new lubed bolts so i figured 126 ft lbs was plenty for 245,000 mile bolts with thousands of heat cycles.



Long story short, I feel better about my head that sees 48 psi on a regular basis. Time will tell if I worsened the head's clamp load but it has held up in stock configuration for a year now with 40-45 psi on a regular basis. It wasn't till a few weeks ago that I added more preload to the wastegate to allow 48-51 psi.
 
Forrest Nearing said:
*shudder*
Click to expand...


Forrest, I used to give the old pulling engine an extra turn on the stock bolts every spring.:bow::evil That build was 2002 with -o rings, its still running never blew a gasket.
I think you guys worry too much!!!!!!
 
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