Technical Heat Cycling and Re-torquing N54 Head Studs? Thoughts?

[IQraceworks]

It seems like there are people who say it’s a must, and people who say it’s really not needed. What’s the consensus on this? After installing ARP head studs in my engine (with OEM BMW Head Gasket), do I really need to put it all back together….run the engine in order to get it up to operating temp, and then pull it all back apart in order to get to the head stud nuts so that I can retorque them all? Such a royal pain having to pull the cams all back off again…..

Thoughts?

 

[jzx_andy]

That Aussie bloke with the diy built engine/8hp70 E92 made up a bench cooling loop for torquing up the head. I'm sure you've seen his videos if you built yours somewhat recently.

He pumped 100c water through it. I think it's a smart idea to have the head torqued up with everything as close as possible to engine operating temp.

If I was in your position and had already put the engine together, I'd probably just leave it unless it was something that really bugged me personally.

 

[IQraceworks]

That Aussie bloke with the diy built engine/8hp70 E92 made up a bench cooling loop for torquing up the head. I'm sure you've seen his videos if you built yours somewhat recently.

He pumped 100c water through it. I think it's a smart idea to have the head torqued up with everything as close as possible to engine operating temp.

If I was in your position and had already put the engine together, I'd probably just leave it unless it was something that really bugged me personally.

Yep...Mark Heyward. When I talked to him, he said that it didn't really work as good as he thought it would have...and he ended up just running the motor to get it heated up. I'll see if I can get some more details from him on why he didn't like the"heat it up with coolant" method he used....

 

[wheela]

Yep...Mark Heyward. When I talked to him, he said that it didn't really work as good as he thought it would have...and he ended up just running the motor to get it heated up. I'll see if I can get some more details from him on why he didn't like the"heat it up with coolant" method he used....

I think with that setup, it's not representative because you're just equilibrating temp of the head with the coolant temp vs. actually running the engine you'd have very high temps (much higher that coolant temp) on the head's combustion chamber surface, with active heat removal via coolant.

So running the engine, you'd have a decent temp gradient of high (>> than 100C) at the combustion chamber and exhaust port surfaces down to around 100-ish C in the coolant chambers. Probably hot spots in the coolant chamber surfaces > 100C too, since 100C is just the average coolant temp. Plus I believe coolant temp is measured at the thermostat after the radiator, correct?

Without hitting actual running temps at the combustion chamber and exhaust port surfaces, the head would not thermally expand in the same manner by flowing 100C coolant on the bench as it would if you were actually running the engine in the car with 100C coolant temps. Especially going WOT.

One would think some heat is probably better than nothing, but maybe he felt that there just isn't enough thermal expansion by running hot coolant on the bench to yield an effect worth the time and effort vs. just running the car and tearing it back down to re-torque it. After thinking this through a little more, I think that's my position on this (probably not worth the effort of running 100C water on the bench).

 

[IQraceworks]

I think with that setup, it's not representative because you're just equilibrating temp of the head with the coolant temp vs. actually running the engine you'd have very high temps (much higher that coolant temp) on the head's combustion chamber surface, with active heat removal via coolant.

So running the engine, you'd have a decent temp gradient of high (>> than 100C) at the combustion chamber and exhaust port surfaces down to around 100-ish C in the coolant chambers. Probably hot spots in the coolant chamber surfaces > 100C too, since 100C is just the average coolant temp. Plus I believe coolant temp is measured at the thermostat after the radiator, correct?

Without hitting actual running temps at the combustion chamber and exhaust port surfaces, the head would not thermally expand in the same manner by flowing 100C coolant on the bench as it would if you were actually running the engine in the car with 100C coolant temps. Especially going WOT.

One would think some heat is probably better than nothing, but maybe he felt that there just isn't enough thermal expansion by running hot coolant on the bench to yield an effect worth the time and effort vs. just running the car and tearing it back down to re-torque it. After thinking this through a little more, I think that's my position on this (probably not worth the effort of running 100C water on the bench).

So do most people just run the engine to get it up to temp, and then tear it all down again to get to the studs? Or do most people just not ever worry about it? Honestly, I've never heard of people re-torquing ARP head studs after heat cycling the engine on anything other than the N54. I've used ARP studs on SBC, LS, and Diesel applications...and never done that, and never had any issues.

 

[wheela]

So do most people just run the engine to get it up to temp, and then tear it all down again to get to the studs? Or do most people just not ever worry about it? Honestly, I've never heard of people re-torquing ARP head studs after heat cycling the engine on anything other than the N54. I've used ARP studs on SBC, LS, and Diesel applications...and never done that, and never had any issues.

That I do not know. I can't really say if re-torquing after running is necessary. I wouldn't think the head, block, or studs would creep from running, but perhaps the head gasket could, depending on its construction? I'd wager there is no run and then re-torque procedure when assembling engines at the BMW plant.

But I do feel comfortable with my assessment that running hot water through the head on the bench would not result in heat distribution or expansion representative of what you'd get by actually running the car. So if one believes that it should be re-torqued after running, I don't think that the hot water bench flow treatment would be a meaningful substitute for actually running the engine.

 

[IQraceworks]

I think with that setup, it's not representative because you're just equilibrating temp of the head with the coolant temp vs. actually running the engine you'd have very high temps (much higher that coolant temp) on the head's combustion chamber surface, with active heat removal via coolant.

So running the engine, you'd have a decent temp gradient of high (>> than 100C) at the combustion chamber and exhaust port surfaces down to around 100-ish C in the coolant chambers. Probably hot spots in the coolant chamber surfaces > 100C too, since 100C is just the average coolant temp. Plus I believe coolant temp is measured at the thermostat after the radiator, correct?

Without hitting actual running temps at the combustion chamber and exhaust port surfaces, the head would not thermally expand in the same manner by flowing 100C coolant on the bench as it would if you were actually running the engine in the car with 100C coolant temps. Especially going WOT.

One would think some heat is probably better than nothing, but maybe he felt that there just isn't enough thermal expansion by running hot coolant on the bench to yield an effect worth the time and effort vs. just running the car and tearing it back down to re-torque it. After thinking this through a little more, I think that's my position on this (probably not worth the effort of running 100C water on the bench).

Yes, I completely agree with everything you are saying. Still makes me wonder if there is any actual science behind the "you must heat cycle the engine and then re torque the studs" thing...or if it's just like some of the other internet rumors that have gotten started years ago. Plenty of other aluminum head and block motors using MLS head gaskets and ARP studs that don't require any re-torquing. ARP will tell you they don't need to be re-torqued.