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torque for Head bolts -- solution found

36K views 40 replies 20 participants last post by  stubadub 
#1 ·
Hi,

Last weekend I started to rebuild my engine (4.6). In the shop manual I found that the head bolts should be torqued at 20 Nm and then 90 degrees and again 90 degrees.
I 've fastened them on 20 Nm and after that 90 degrees. But I really had to put a lot of force on them to get those 90 degrees (using a tube to get a longer wrench!!). Is there a printing mistake in the shop manual or do I have to ask the Hulk to come and help me with the other 90 degrees?


The Manual said:
* Cylinder head bolts:
- Stage 1 - 20
- Stage 2 - Tighten further 90°
- Stage 3 - Tighten further 90°
I remember that for the RRC, that has the same block and heads, there was no degrees, only torque values in the shop manual.

Could I leave it as it is with 1 time 90 degrees after the 20 Nm? I am affraid to break the bolts if I go any further but at the same time I know how important the torque on heads is and if the book says 2 times 90...
(I don't feel too good about it)
Any expierience?

thanks
 
#2 ·
Not sure about about torque settings I am sure someone will be along soon.

When I had my head gaskets done I read on here that a new set of bolts would be required as they are stretch bolts - good for one use only.

The dealer at first denied this and it was only after a few LR techies joined the discussion that they agreed bolts should be replaced.

Are you using new bolts?
 
#3 ·
Checked in RAVE the infomation you have is correct. Perhaps there is a fluid lock in the threads. Left over cleaning agent or oil maybe. Stretched or not the bolts should be able to be tighend to the specified torque IMO.

My ford 6cyl with alloy head has bolts which are tensioned down to 125ftlb plus 90 degrees so a mere 15ftlb shouldn't be that much of a problem.

If you haven't done so already fork out the extra for new bolts for that added piece of mind with all the apparent problems these engines have it couldn't hurt to have that little extra bit of insurance.

Rob M
 
#4 ·
Used new bolts all right. And the treads are as clean as a wistle. As a good mechanic should, I have cleaned the treads and the new bolts with brake cleaner and have put a drop of oil between the heads of the bolts and the cylinder head (on the bolt of course because otherwise it drips in the treads)
Cannot imagine that I should try to torque them another 90 degs.

Left over break cleaner in the holes? Perhaps but I waited a minute or 5 before mounting the heads and by the time one was done, the other should have been empty anyway.
 
#5 ·
wpr said:
Used new bolts all right. And the treads are as clean as a wistle. As a good mechanic should, I have cleaned the treads and the new bolts with brake cleaner and have put a drop of oil between the heads of the bolts and the cylinder head (on the bolt of course because otherwise it drips in the treads)
Cannot imagine that I should try to torque them another 90 degs.

Left over break cleaner in the holes? Perhaps but I waited a minute or 5 before mounting the heads and by the time one was done, the other should have been empty anyway.
The rave write up is correct. Make sure you are going 90 degrees and not 180 each time. The first 90 is easy. The second will make you think you are going to break a bolt. New bolts are used. Good luck.
 
#6 ·
Torque Value

At Last I am not Alone.

I just did the Head Gasket on the left Bank (4.6 HSE '97) and came across the same issue.
After tightening them initially to 20 nm, I really had give it a lot to make it to the first 90 degrees.
There was no way for me to make it to the 2nd 90 degree turn. I used new Bolts as well and threads are clean also.

Still unsure what to do now, maybe eat some more Steaks :lol:
Honestly, I have no clue what to do now.

Can I just continue to finish the job and start the engine and after idling it a while try to tighten them further? any Ideas?

Hmm.
 
#7 ·
I've got to do my head gasket soon so I've stocked up on the parts and cruised the web looking for information.
There's an interesting graph here
http://www.boltscience.com/pages/tighten.htm that show up to 95% of the applied torque is due to friction so lubricating the threads is essential ( RAVE also says lightly oil them ).
There's a good article here http://www.aa1car.com/library/2005/eb70536.htm about stretch head bolts ( or Torque To Yield as they are also known );

Good Luck , those last few degrees can be difficult :D
 
#9 ·
Torque Wrench

I wouldn't use my torque wrench for the 90 degree turns. :shock:
I marked the heads of the bolts with a white permanent marker,
to determine the angle.

The force needed during that process certainly wouldn't do any good to her.
at least mine wouldn't like it. :lol:
 
#10 ·
Re: Torque Wrench

Blackadder said:
I wouldn't use my torque wrench for the 90 degree turns. :shock:
I marked the heads of the bolts with a white permanent marker,
to determine the angle.
Exactly. Yes, it is very hard to crank the bolts down. I used a 4 foot bar to do it. Marking the heads of the bolts is the way to do it, otherwise you will hose your torque wrench.
 
#13 ·
Right Bolts?

@ p76rangie:

thanks for that, coming to think about your comment, I think that might be the cause.

I have ordered new bolts with the head gasket at landy-depot here in Germany. I think I better call them and check what sort of bolts they delivered.
I recall that Rave stated two procedures, one being the torque method for earlier models and the angle thing for the later ones.

Thanks for your input.
 
#14 ·
Come on guys, this is straight up and simple.
Like someone mentioned earlier in the thread, the classics used a prescribed torque value. The change on Rover V8's occurred in late 1994 when the change was made from 14 bolt cylinder heads to the newer 10 bolt style. At this point Rover decided to use the Torque to Yield, or stretch bolts for reasons known only to the Guinness sodden engineer that thought it up!

This change also introduced the composite head gasket as opposed to the steel shim that was used since dirt. The double 90 degree turns work out to somewhere between 75-88 pounds of torque, but are inconsistent as hell because of the aforementioned "Friction".

I know that most Rover purists have a stroke when I mention it, but a very thorough cleaning of the threads on the bolts, a good chase with a thread tap in the block, and a tiny amount of never seize compound will provide a nice even pull on the wrench and a properly sealed gasket.
 
#15 ·
Bad Apple said:
I know that most Rover purists have a stroke when I mention it, but a very thorough cleaning of the threads on the bolts, a good chase with a thread tap in the block, and a tiny amount of never seize compound will provide a nice even pull on the wrench and a properly sealed gasket.
The answer is to purchase studs and not use bolts at all. This makes the tensioning a lot ore accurate and limits the risk of future issues. You can get the studs from American Racing. In the US the studs would also be cheaper than bolts.
 
#16 ·
I had someone help me on the 90 deg sets. One person watched the angle and held the socket firm on the bolt hex and the other tugged like heck using an 18 inch breaker bar. The resistance to pull was all over the place. Some bolts would turn almost 45 degrees before seating up! It's a crazy process, but I never had a problem getting a second 90 degrees of twist. The lack of torque specifics for this process is probably due to the great variance in running torque vs starting torque when twisting the bolt against the aluminum surface.
 
#17 ·
using a slight drop of oil sure helps but the oil shouln't get on the treads. Only under the head of the bolt as otherwise you risk to break the bolts when dismounting again. What I did notice when dismanteling, was a blackish solution on the treads. Do the dealers use some heat resistant grease or stuff on them? I cannot imagine that one has to use a 4 foot bar to get to the second 90 degs. To my idea that couldn't be good for the treads in the alumynum block. And what about the one bolt that sits under the break cylinder? It is hard to use a 1 foot bar already as it is.

What are studs? If they are what I think they are, it could be a solution, yes. but then you 'll have only 2/3 of an inch of tread to hold all the force. Is that enough?

btw: glad I am not the only one with this problem.
:)
 
#18 ·
Couple thoughts.

-A four foot cheater bar seems excessive for this. Also rather hard to maneuver under the hood, unless you snap the hood back to its mechanics access position.
-Did you blow out the head bolt holes in the block? Sufficient liquid left in these will hydraulically compress and stop the turn down of the bolts.
-Stupid question, but are you using a composite gasket? (ie thick black tar paper lookin' thing)
-I've only seen this done with a new set of head bolts, so if you're reusing them...
 
#19 ·
wpr said:
What are studs? If they are what I think they are, it could be a solution, yes. but then you 'll have only 2/3 of an inch of tread to hold all the force. Is that enough?
The reason that Landrover went to torque yield bolts is due to the inconsistancies in torque when attempting to tighten down steel bolts into aluminium blocks. The condition of the threads in the block also degrade, giving inconsistant pressures. The threads have to be course so as not to strip out of the block, this means that a little rotational movement gives a big downward movement.

With studs you have a steel nut going onto a steel stud. They have a lot finer thread and this leads to more even tension across the head. The torque that has to be applied is a lot lower than the bolts. It significantly reduces the risk of stripping out threads when either doing up or undoing heads.

If there is one thing that you should do with replacing heads, it is using studs instead of bolts.
 
#20 ·
Ceramic grease on the treads seems to be the professional solution.
It explains why there was a blackish product on my bolts.
Ceramic grease does not harden on high temperature so it is safe to use and you don't damage the tread mounting or dismounting the bolts.
8) :idea:

Studs seem to be a good solution also but how much torque do they have to be put on?
 
#22 ·
Studs

@ p76rangie: Thanks for the Link. Looks like the way to go.

One last question though, which ones would i use for the Rangie?
Thanks again for the help.
 
#23 ·
Re: Studs

Blackadder said:
@ p76rangie: Thanks for the Link. Looks like the way to go.

One last question though, which ones would i use for the Rangie?
Thanks again for the help.
I have changed the link. I believe the part number is 124-4003 and they come in a kit for the rover V8 for around $140 to $175US

I cannot find the torque settings on the internet, but testing my memory from the directions that came with the kit, the torque is relatively low compared to bolts.
 
#26 ·
After reading all sorts of horror stories about snapping bolts, oil or no oil, studs or bolts, helicoils etc I just want to clarify one thing.

As I torque each bolt according to the RAVE sequence do you torque to 15lbs in one pass or in say three passes to keep things more even? RAVE makes no mention of multiple passes during the 15lb stage however I just want to make absolutely sure as I've read too much and I'm slightly nervous and don't want to do this twice.
 
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