Thread: 300tdi Head Studs

The 300Tdi has bolts not studs.

50 Nm is a very low torque value for the M12 head bolts.

For high bolt pre-load, variation in friction between mating threads and bearing surfaces (under bolt head and the like) gives unacceptable variation in developed tension for a prescribed tightening torque. That is why the prescribed torque method has been replaced by an angle of turn method.

There is computer controlled tightening equipment, but for us there is no useful way to know, what the bolt/thread friction may be for you head bolts that have been in service for so long. Hell you can't be confident for bolts that have been stored on a shop shelf.

I doubt there is a problem with 300Tdi head bolts stretching. IMHO, the problems that occur with loss of gasket clamping load, result from overheating of the aluminium head.

Even when gaskets and bolts are renewed, there can be problems with heads that have been overheated - it is best to have the hardness of the head tested and re-heat treat if soft spots are found.

Bush65
Thanks for your reply bush, and an apology for my nomenclature.
From my background, I have always called a threaded fastener with a nut "a bolt". One that fixes into a "deep threaded hole' (ie, cylinder head or similar) a "stud"'
A little bit like "socket head cap screws", so often called "hex head studs"
So it is the head "bolts" I am asking about.
If the head bolts are prepared as per the W/Shop manual, and the initial torque figure is given as 40Nm for all "bolts", then plus 60* + 60* etc. there is going to be a final rotational torque figure in Nm. for all of them, has to be if only an average. It may vary from bolt to bolt and engine to engine, but I dont think very much.
So the answer will be in my own w/shop, will get some identical "bolts", create a similar hold down situation, and find out exactly what the torque wrench figures are.
And hopefully my head gasket will last the engine out!

You may be able to get similar tightening torque values from a few tests, but that it will most likely be very different when you want to verify the bolt tension by applying torque to a bolt that has been in service, and gone through many heating and cooling cycles.

The simple fact is, as I stated, specified torque is unreliable at high bolt tensions. Even at moderate tension, the accuracy is around +/- 25% of desired tension. Of the common methods for tensioning bolts, it is only better than operator feel in terms of accuracy.

Land Rover and other engine manufactures can easily do what you propose, and if it was suitable, then why have they not used specified torques?

Much research has been done on this and the results are all the same.

In this country, it is Not Permissible to use torque control to tighten bolts in steel structures, except under specific controls that are generally not worthwhile give alternative methods of tensioning bolts (reference Australian Standard 4100 - Steel Structures Code). There are several methods allowed including the part turn method.

It would save a lot of money (many thousands of dollars on some jobs) if it was possible to verify that bolt had been tensioned correctly by someone using a torque wrench. Unfortunately we have to resort to much more expensive methods.

If you want to rely on your torque wrench go ahead - no one will get hurt.

I've recently done a head gasket on mine, if I had to take a guess I'd say about 20-30KG on a 1.2 metre pipe maybe a bit less.
So if my maths is right in the 250-350 Nm range. That's on new oiled bolts in clean threaded holes.

Tony

holy cripes batman you need eat more weetbixDoing up to the specified torque plus doing the angle stages is relatively easy with standard size torque wrench. Extension bar that long you should be able to do it with your little finger

IMHO, Tony's estimated torque is in the ballpark.

And there is nothing wrong with using a long handle for that job, as it allows more control and a better outcome.

Tony says he could have tightened his head bolts to 250-350 Nm.
Bush65 agrees this could be a "ball park" figure.
My conversion indicates that 300Nm (mid point) = 220ft.lb. of torque.
Methinks a trifle much for a 12mm (1/2"nom.) bolt, they would be well stretched at that tension.
The specified torque for the s111 L/R diesel engine 1/2" head bolts, identical configuration, is 90ft.lb. = 122Nm. (I realise it is a C/I head, not al.)
?? still remain.
llandro

Originally Posted by llandro

Tony says he could have tightened his head bolts to 250-350 Nm.
Bush65 agrees this could be a "ball park" figure.
My conversion indicates that 300Nm (mid point) = 220ft.lb. of torque.
Methinks a trifle much for a 12mm (1/2"nom.) bolt, they would be well stretched at that tension.
The specified torque for the s111 L/R diesel engine 1/2" head bolts, identical configuration, is 90ft.lb. = 122Nm. (I realise it is a C/I head, not al.)
?? still remain.
llandro

Hi llandro,
I'm happy to be corrected.
Bear in mind I was paying little attention to how tight I was doing them, just the angles.
I was just trying to help with your question of converting the angle tension to a torque number.
A quick Google search gives 100 Ft/Lbs for a grade 12.9 bolt and 151 Ft/Lbs for Cummins 12mm head bolts, so it would seem that my estimation is probably to high.

Maybe if your worried about them, the head should come off and the problem fixed properly.

A Merry Christmas to All, and may you all get lots of goodies for your trucks.


Tony