7MGTE's- tough muthas!

[Typhoon]

As some would be aware through other posts, my engine with a fresh head gasket and ARP head studs had a big overheat due to a popped welch plug.
Well, it's been two weeks, and the residual symptoms appear to be none!
That's right, so far, th eengine that got so hot it MELTED the plug leads to the plugs is running like a top, with no coolant loss, no overpressurising of coolant system, great oil pressure etc.
So, I think it shows that the stock head torque SUCKS and that decent head studs and a good gasket will tolerate a torrent of abuse.
Not that I expect I haven't damaged the engine in some way, it will probably only go to 200k kms now, instead of 300k, but it is a solid display of good engineering.
I persoanlly think the oil squirters and oil cooler helped save the day. Oh, and I am pretty sure the ECU just dumps fuel into teh engine when things get too hot, all the plugs were very dark grey and didn't realy look overheated at al.

Regards, Andrew.

 

[IJ.]

If it was a big overheat the head will be annealed

 

[rumptis]

If it was a big overheat the head will be annealed

How hot does aluminum have to get to anneal?

 

[IJ.]

Rump: 6>700f

 

[ilikebigbutts]

what does anneal mean?

 

[Junior]

http://www.efunda.com/processes/heat_treat/softening/annealing.cfm

 

[mkIIIman089]

Have you actually checked things like compression or done a leak down test? Or just that it "sounds good"?

 

[adampecush]

If it was a big overheat the head will be annealed

what alloy is the head?

 

[IJ.]

Adam: Can't say 100% no one I've spoken to knows.

 

[vas85]

What is the welch plug? I'm just curious. I've heard about it before by a neighbor mentioning something about his welch plug and losing water as it evaporates or something..... where abouts is it?

 

[Typhoon]

Compressions were all good when checked after the event, and head stud torques were all still O>K. I haven't done a leak down test, but I am not losing coolant or getting too much pressure in cooling system. No fumes from crankcase breather either, so blowby has not radicaly increased.
Hopefully head did not get too hot and anneal the bugger.
No way to know for sure without either removing the head or just running the thing. Maybe heat cycles will retemper it.
I choose to just run it! Nothing much to lose.

Regards, Andrew.

 

[IJ.]

Andrew: Well yes there's a way to know for sure

Most machine shops have a simple ping tester (A ball in a graduated tube that they drop the ball and see how high it bounces)

They can perform the test with the head installed and that will tell you if it's soft on the exhaust side.

 

[Typhoon]

Thanks for that info IJ, that tested is kind of a Rockwell hardness tester?
I broke down today and bought a combustion gas leak tester, did the test twice (once when warmed up, once after a 5 min run) and came back negative, so I am pretty relieved at this point!
So now EVERY test says gasket O.K.:biglaugh:

Regards, Andrew.

 

[tte]

Andrew: Well yes there's a way to know for sure

Most machine shops have a simple ping tester (A ball in a graduated tube that they drop the ball and see how high it bounces)

They can perform the test with the head installed and that will tell you if it's soft on the exhaust side.

You know some shops I talked to here do not do that test and some havent even heard of it...and they build performance engines.

I dont know why...

Cheers,
Roy

 

[Frank Rizzo]

What do you mean "what alloy is the head"? It's not 100% aluminum? Then that would explain why the exhaust manifold stud threads strip out so easily....I knew there was something funky about the kind of aluminum Toyota used for their 7M heads..... I've even had a helicoil strip out of the 7M head before. Had to weld and tap completely new threads. I've replaced just about every single one with a helicoil. Sorry for going off topic, glad to hear your motor is still mint!

 

[IJ.]

Andrew: Sort of but it doesn't leave a mark so can safely be used on the deck surface.

Roy: Not all of the shops here have a tester either and in that case I'd think twice about having $1000's of work done on a head that may or may not be soft/useless..

Frank: 100% Aluminium is not very strong at all they alloy it to increase strength. (just not sure what's been mixed into a 7M head)

 

[Typhoon]

Copper is one additive in Aluminium. There are other metals/additives I can't remember right now, will have to dig out a text book.
It should be noted that pure aluminium is very soft and not really good for too much!
Most of the metals alloyed with aluminium are to impart a particular quality, including age hardening, which is how most aluminium alloys that are cast are hardened. They just strengthen as they cool, over several days. Which is kind of what IJ said above!


Regards, Andrew.

 

[IJ.]

Copper
Manganese
Silicon
Magnesium
Zinc
Lithium and I'm sure there are others

 

[Typhoon]

Thanks IJ, that saves a long and possibly fruitless search through some cardboard boxes!

Regards, Andrew.

 

[Typhoon]

Quick update: 400kms on and all is well with the car. Cooling system holding pressure, no coolant use, no weird noises, performance still what it was(both power and fuel consumption).
So I think it's O.K for now...phew!:bigthumb:
Will post if anything else changes, but man these things are strong.
Let's hope it doesn't develop a knock or drop some valve seats!

Regards, Andrew.