Thread: Cast Iron heads for 300TDi?

Originally Posted by isuzurover

How do you do that on bolts that were angle tightened (as per 300tdi head bolts)? You can retighten by a specified angle, however you don't know when the bolt will snap.

Measuring tension in bolts is not simple - I have encounted good methods but they are not cheap or applicable here.

In this example, what I have done is loosen one bolt at a time, then re-tighten. Repeat the process for all head bolts and use the recommended sequence.

I have discovered that 300Tdi head bolts can be tightened well beyond the recomended angles without failing.

I dispute the often stated claim that they are torqued to yield - no one has convinced me that using a specified angle proves that yield was reached. That simply defies logic, and to be pedantic, the alloy steel used for 300Tdi head bolts will not have a yield point.

Originally Posted by Bush65

Measuring tension in bolts is not simple - I have encounted good methods but they are not cheap or applicable here.

In this example, what I have done is loosen one bolt at a time, then re-tighten. Repeat the process for all head bolts and use the recommended sequence.

I have discovered that 300Tdi head bolts can be tightened well beyond the recomended angles without failing.

I dispute the often stated claim that they are torqued to yield - no one has convinced me that using a specified angle proves that yield was reached. That simply defies logic, and to be pedantic, the alloy steel used for 300Tdi head bolts will not have a yield point.

Thanks John - very helpful and informative comments as always.

In general wrt torquing to yield - something I have never fully understood... Once you reach the yield point the stress vs strain curve flattens out or even goes down. So if you did indeed torqued a bolt to (just past) yield, the clamping force would/could be lower than just before yield???

And I am not sure what you mean by no yield point? Do you have a stress-strain curve for such bolts to demonstrate?

Steve and Rick - I don't have a Manuel for the Tdi - I was (foolishly) going by statements on here that that was what the manuel said.

Originally Posted by isuzurover

Thanks John - very helpful and informative comments as always.

In general wrt torquing to yield - something I have never fully understood... Once you reach the yield point the stress vs strain curve flattens out or even goes down. So if you did indeed torqued a bolt to (just past) yield, the clamping force would/could be lower than just before yield???

And I am not sure what you mean by no yield point? Do you have a stress-strain curve for such bolts to demonstrate?

Steve and Rick - I don't have a Manuel for the Tdi - I was (foolishly) going by statements on here that that was what the manuel said.

Low carbon steel (AKA mild steel) has a definite yield point, high strength alloy steels do not.

I don't have pics with me, but will attempt an explanation of what happens in a tensile test, starting with low carbon steel.

As tensile load increases, the elongation (stretch) increases proportionaly until the proportional limit is reached - the slope of this straight line corresponds with the elastic modulus (E = stress/strain where stress = load/area and strain = elongation/original length so E = (L x l)/(A x e) ) curve. Near limit of proportionality the elastic limit is reached - where original length will be achieved if load is released. Just after the elongation of the test piece will start to increase with no increase in load - this is yielding and the curve goes horizontal. As further elongation occurs the load starts to drop (because cross sectional area has become smaller - waisting) and the curve dips down. The material begins to work harden and the load starts to rise again to increase elongation. Load starts to fall again because waisting becomes severe. During the last 2 stages the curve resembles an arch. Finally the test piece breaks.

With high strength alloy steel, the curve starts the same and the slope until the limit of proportionality is reached is the same because with steels E is much the same (small differences do occur but are usually neglected except for stainless) regardless of alloy or heat treatment - the value of load at proportional or elastic limit is higher but slope is same. Then as waisting occurs the curve has a similar arch shape until the break occurs. There is no yield point where elongation increases for no increase in load.

Because yield strength changes (material property) we commonly base design strength = 0.nn x yield strength. We avoid yield because it will result in permanent deformation (also formation of a plastic hinge which can turn a ridgid structure into a mechanism (resulting in collapse).

As the high strength steels have no yield point, we create an approximate value on the load/elongation curve by drawing a line parallel to the linear slope, but offset by 0.2% elongation. Where the 0.2% offset line cuts the curve from the tensile test, we have a value to use with our much loved equation (design strength = 0.nn x 0.2% offset strength).

For bolted joints in steel structures, it has become normal and more economical to use high strength structural bolts these are different to common high tensile bolts which are called hexagon precision bolts in the relavent Australian Standard (AS1110 from memory). HSS bolts are designed to be tensioned to the prescribed proof load (near as damb the yield or more correctly 0.2% offset) and the bolt proportions (particularly the head) were developed after much research by the international committee - the Aus Standard is identical to the ISO standard.

The Steel Structures Code (AS4100) and it's commentry have a section on tightening bolts. For bolted joints designed as fully tensioned (tension to the proof load) one of the acceptable tightening methods is part turn (snug tighten then further angle as given in table for bolt length). The other acceptable methods involve tension measurement and torque control (e.g. tension wrench) is generally not permitted.

It is well documented that the part turn method often results in tension exceeding the proof load, but it is not an issue. The standard allows bolts that have been fully tensioned to be re-used once, but only if they are used in the same bolt hole as they were removed from - because permanent deformation of threads, etc. can prevent proper tension being achieved if used in a different location.

With mechanical equipment, where parts are required to be pulled apart and re-assembled more than once, the bolted joints are usually designed for bolts tightened to approx 65% proof load and tables give tightening torque for achieving this tension.

When bolts are tightened to the proof load, the friction forces become so large that torque control results in errors of resulting bolt tension something like 25% - this error has been found in many tests making it unacceptable.

To avoid fatigue failure of bolts subjected to cyclic loads, the best practice is to use bolts (quantity and diameter) so that when tightened their pre-tension is at least 2 times (up to 5 times) the external applied load (in the bolt). Together with this tension, the joint must be designed so that it is considerably stiffer than the bolt. Then during pre-tensioning the bolt elongation is much more than the elongation of the joint. During the load cycles the variation in the tension in the bolt will be small and the variation in the compression of the joint will be large (in proportion to the relative stiffeness). The sum of change in tension of bolt and change in compression of joint equals the external applied load. So fluctuation in the bolt tension (the most important factor for fatigue strength) is much less than the fluctuation in applied load.

Note: it is not a requirement to tighten bolts to yield to achieve ar pre-tension 2 to 5 times the external applied load (we normally use 65% proof load, but where it is not possible to use more bolts or larger dia bolts then we use greater pre-tension, but achieving the pre-tension becomes more difficult.

Originally Posted by Bush65

Low carbon steel (AKA mild steel) has a definite yield point, high strength alloy steels do not.

I don't have pics with me, but will attempt an explanation of what happens in a tensile test, starting with low carbon steel.

As tensile load increases, the elongation (stretch) increases proportionaly until the proportional limit is reached - the slope of this straight line corresponds with the elastic modulus (E = stress/strain where stress = load/area and strain = elongation/original length so E = (L x l)/(A x e) ) curve. Near limit of proportionality the elastic limit is reached - where original length will be achieved if load is released. Just after the elongation of the test piece will start to increase with no increase in load - this is yielding and the curve goes horizontal. As further elongation occurs the load starts to drop (because cross sectional area has become smaller - waisting) and the curve dips down. The material begins to work harden and the load starts to rise again to increase elongation. Load starts to fall again because waisting becomes severe. During the last 2 stages the curve resembles an arch. Finally the test piece breaks.

With high strength alloy steel, the curve starts the same and the slope until the limit of proportionality is reached is the same because with steels E is much the same (small differences do occur but are usually neglected except for stainless) regardless of alloy or heat treatment - the value of load at proportional or elastic limit is higher but slope is same. Then as waisting occurs the curve has a similar arch shape until the break occurs. There is no yield point where elongation increases for no increase in load.

Because yield strength changes (material property) we commonly base design strength = 0.nn x yield strength. We avoid yield because it will result in permanent deformation (also formation of a plastic hinge which can turn a ridgid structure into a mechanism (resulting in collapse).

As the high strength steels have no yield point, we create an approximate value on the load/elongation curve by drawing a line parallel to the linear slope, but offset by 0.2% elongation. Where the 0.2% offset line cuts the curve from the tensile test, we have a value to use with our much loved equation (design strength = 0.nn x 0.2% offset strength).

For bolted joints in steel structures, it has become normal and more economical to use high strength structural bolts these are different to common high tensile bolts which are called hexagon precision bolts in the relavent Australian Standard (AS1110 from memory). HSS bolts are designed to be tensioned to the prescribed proof load (near as damb the yield or more correctly 0.2% offset) and the bolt proportions (particularly the head) were developed after much research by the international committee - the Aus Standard is identical to the ISO standard.

The Steel Structures Code (AS4100) and it's commentry have a section on tightening bolts. For bolted joints designed as fully tensioned (tension to the proof load) one of the acceptable tightening methods is part turn (snug tighten then further angle as given in table for bolt length). The other acceptable methods involve tension measurement and torque control (e.g. tension wrench) is generally not permitted.

It is well documented that the part turn method often results in tension exceeding the proof load, but it is not an issue. The standard allows bolts that have been fully tensioned to be re-used once, but only if they are used in the same bolt hole as they were removed from - because permanent deformation of threads, etc. can prevent proper tension being achieved if used in a different location.

With mechanical equipment, where parts are required to be pulled apart and re-assembled more than once, the bolted joints are usually designed for bolts tightened to approx 65% proof load and tables give tightening torque for achieving this tension.

When bolts are tightened to the proof load, the friction forces become so large that torque control results in errors of resulting bolt tension something like 25% - this error has been found in many tests making it unacceptable.

To avoid fatigue failure of bolts subjected to cyclic loads, the best practice is to use bolts (quantity and diameter) so that when tightened their pre-tension is at least 2 times (up to 5 times) the external applied load (in the bolt). Together with this tension, the joint must be designed so that it is considerably stiffer than the bolt. Then during pre-tensioning the bolt elongation is much more than the elongation of the joint. During the load cycles the variation in the tension in the bolt will be small and the variation in the compression of the joint will be large (in proportion to the relative stiffeness). The sum of change in tension of bolt and change in compression of joint equals the external applied load. So fluctuation in the bolt tension (the most important factor for fatigue strength) is much less than the fluctuation in applied load.

Note: it is not a requirement to tighten bolts to yield to achieve ar pre-tension 2 to 5 times the external applied load (we normally use 65% proof load, but where it is not possible to use more bolts or larger dia bolts then we use greater pre-tension, but achieving the pre-tension becomes more difficult.

John, thanks for your informative post, I don't pretend to understand it all, but I get the Gist of it.
I was wondering if you could offer advice, I am contemplating purchasing a new (alloy) head for my 300TDi, the original has developed a dish like depression around 3 to 4" in diameter and about 8thou. deep. This area is right in the middle of the head straddling #2 and #3 combustion areas. The first time the gasket blew (and it had never run hot until the gasket blew) this depression was noted I had the head skimmed to remove it.
The next time the gasket blew (exact same circumstances) the depression was back, first and second time I used new bolts and torqued to Factory specs.
I didn't have the head skimmed again and fitted a new composite gasket, when it blew again I fitted a laminated metal gasket and old bolts, the depression in the head was still there and the previous composite gaskets all blew in the same spot, at the depression. So far, about 12 months now, (knock on wood) everything is OK.
I intend using ARP head studs and a new laminated metal gasket, I always tap the threads in the block before fitting head bolts. Would you have any suggestions on how to Torque these nuts and washers, would I do it to Factory specs. I cant see where TTY would work on head studs, washers and nuts, I will be using the lube oil for the washers and nuts as supplied by ARP, any information would be appreciated, Regards Frank.

Originally Posted by Tank

John, thanks for your informative post, I don't pretend to understand it all, but I get the Gist of it.
I was wondering if you could offer advice, I am contemplating purchasing a new (alloy) head for my 300TDi, the original has developed a dish like depression around 3 to 4" in diameter and about 8thou. deep. This area is right in the middle of the head straddling #2 and #3 combustion areas. The first time the gasket blew (and it had never run hot until the gasket blew) this depression was noted I had the head skimmed to remove it.
The next time the gasket blew (exact same circumstances) the depression was back, first and second time I used new bolts and torqued to Factory specs.
I didn't have the head skimmed again and fitted a new composite gasket, when it blew again I fitted a laminated metal gasket and old bolts, the depression in the head was still there and the previous composite gaskets all blew in the same spot, at the depression. So far, about 12 months now, (knock on wood) everything is OK.
I intend using ARP head studs and a new laminated metal gasket, I always tap the threads in the block before fitting head bolts. Would you have any suggestions on how to Torque these nuts and washers, would I do it to Factory specs. I cant see where TTY would work on head studs, washers and nuts, I will be using the lube oil for the washers and nuts as supplied by ARP, any information would be appreciated, Regards Frank.

Some people have not had luck with the laminated steel gasket in the 300Tdi. You need both head a block to be flat, then all surfaces need to be very clean, nothing that will reduce friction, including finger prints.

I have ARP studs for the head on my 4BD1T, but have not used them with a 300Tdi, which they should help.

When I fitted them (4BD1T) I used the tightening torque that ARP recommended. They had a finer thread pitch for the nut end of the stud than the stock bolts, so using the stock bolt tightening angle would have given a different tension, thus clamping force on the gasket.

I used a tensioning method recommended by diesel engine builders with much more experience than I. Use many small tension steps, much more than the 2 or 3 stages often used (tighten in the same order as stock).

When all studs/bolts are tensioned to the usual 2nd from last stage, release the tension (reverse the normal tightening order and do this in stages). The reason for this is that the mating threads (male & female) settle better. Then tension the bolts by stages as before, to the final tension.

Thanks John for the great tech (nice to have you back)

Ben, as an aside, I often find AULRO similar to Fawlty Towers
"I was (foolishly) going by statements on here that that was what the manuel said."

The Manuel in both FT and AULRO will often lead you astray, laughing of course

Steve

John, thanks for that info, I figured ARP would have there own torque figures.
I used the metal laminated head gasket (even though I didn't machine the head, it had a dip in the middle about 7 Thou.).
The composite gasket on each occasion that they blew did so between and 2 and 3 cylinders and surrounds, each time the composite material was missing. I figured at least the metal gaskets wouldn't get blown away, been good for over a year now, knock on wood. Would loved to have been able to get hold of a cast iron head, but not to be. I will buy a new alloy head, laminated metal gasket and ARP studs and hope I get some reliability, Thanks again, regards Frank.

Originally Posted by Bush65

Some people have not had luck with the laminated steel gasket in the 300Tdi. You need both head a block to be flat, then all surfaces need to be very clean, nothing that will reduce friction, including finger prints.


[snip]

That was JC's advice to me, so I have a new Elring composite gasket here + stems seals, etc. for a precautionary change very soon (which is something I've been saying for the last six weeks )

I reckon 285,000km on the original gasket with 17psi of boost and silly EGT's at times over the last 130,000 km or so, it hasn't done too badly.