Hardness test, another BHG prep thread

[Jaguar_5]

So as my N/A is starting to show signs of BHG, with spiking temps, all my lines are good, radiator flows just fine, did a full flush, replaced the thermostat and swapped the water pump off the turbo one which was rebuilt about 20k miles ago (i think) when the previous owner blew the headgasket and parked it, i picked it up about 8 months later. The water pump was in real good condition, seal looked good, turned with some resistance, but smoothly, resistance was the same in the pump off the N/A i replaced, so i assume it's normal. The pump i replaced didn't look too bad, had some signs of white corossion, and the seal looked a bit sketchy, but it should've worked.

Anyways onto the point, i'm starting to realize this car is about to be in the same condition as the one with it's engine on a stand, so i need to start rebuilding this 7mgte!

I talked to a machinist at a good NAPA machineshop, it wasn't the guy i was hoping to speak with though. I asked about a hardness test, and he looked at me weird, tried to tell me i was talking about something called a ... Bernielle test i think he said, which runs about $600... i was planning on dropping my head off today to get prepped, hopefully my preferred machinist is there, how do i approach this? Do i need to look for a new shop? (If anyone knows a good one in the Seattle area!)

Also i've previously asked about headgasket thickness, since i don't know how much has been taken off in the past, it's been rebuilt by a toyo dealer at least twice. They said they can look at specs, do measurements... is this possible?

 

[Jaguar_5]

Nobody? i'm planning on dropping the head off real soon, real curious about this hardness test

 

[IJ.]

The Hardness test for an aluminium head is a very simple procedure using a graduated tube with a captive ball in side which is upended on the head surface and the ball is released.

You watch how high the ball bounces in the tube and this according to the graduations will tell you how hard the head is.

Takes seconds to do and most shops won't charge for it.

Yes you need to measure the head and block to work out how much has been removed.

 

[Shawndude]

Why would you even consider a hardness test? It's a test of the stock material Toyota used, and nothing you can do with the information.

It's a waste of time and money in your situation.

 

[IJ.]

To see if the head has annealed from being overheated Shawn.

 

[boost fiend]

do you want to bolt a head on that has gone soft from being over heated one too many times? and then throw boost/high reving at it?

i say hell no! get the test!

 

[Shawndude]

To see if the head has annealed from being overheated Shawn.

Hmmm. The head should already in annealed condition, for stress relieving after casting. Usually you need to get to 1/3rd of the melting temperature of the material to anneal and ........

Spoon feed me IJ, if you know the details!

 

[IJ.]

Shawn: They're actually bought back up to t4>t6 for use.

I have/had a few 7M heads here that are t0 and not fit for use as the headbolt washers sink into them and you can't keep tension.

I was quoted $1800 AUD to strip reheat treat and refit guides and seats in a casting so just bought a brand new casting for $1900 AUD.

<edit> Forgot to add re: Temps our heads anneal after a BHG when there is either no coolant or only steam in the cooling passages and the combustion temps are unchecked.

 

[Jaguar_5]

Ok, well i almost dropped it off at NAPA but then the machinist was tweaked out and looking at me like i was an idiot when i asked about RA measurements and the hardness test, so i still have it.

I'm about to buy this tomorrow: http://cgi.ebay.com/ebaymotors/ws/e...d=1,1&item=8050756844&sspagename=STRK:MEWA:IT

(Noone buy it please! )

The only difference between the GTE and GE head is the cams right, aren't these actually abit of an upgrade?

 

[IJ.]

Jag: Good move skipping that shop!

 

[Shawndude]

Hey IJ help me some more. Reading my materials text books this doesn't really seem possible, to anneal the aluminum from overheating without melting the whole engine (pistons) down first.

What is the original or proper hardness? What composition is the aluminum in the head? What temperature must be reached for this to happen? Since the combustion chamber sees the 1400F+ temperatures, how far does the annealing go? How can the head bolt washer area anneal, being so far from the chamber without localized melting closer to the combustion chamber first?

Thanks for any info.

 

[IJ.]

Shawn: Sorry no specifics until my shop opens tomorrow.

I tested 4 heads I had here and only 1 passed.

Most were full soft T-0 on the exhaust side and got progressivly harder towards the intake side and this in itself is a problem as the head tries to banana when you unbolt it from the induced stress.

I never got around to testing my brand new head to get a baseline as by then I was very over the whole issue and just pressed on to get it finished.
(My "guesstimate" is T-4)

The Astron 2 litre motors made here in Australia have a very bad Rep for doing this as well and I've seen heads first had where ALL the head bolts had sunk but in a 7M I believe it's only affecting the Exhaust side.

From memory it takes around 270c/518f to anneal 6000 series.

 

[Jaguar_5]

Does that ebay rebuilt cyl. head look good enough for a MHG? I emailed asking for RA values...

The GE one will work no problem on the GTE, right?

 

[Shawndude]

Thank you for the further details IJ, I appreciate it.

 

[IJ.]

Very welcome Shawn!

It only seems to take 1>2 really bad overtemps to kill em as well

 

[Jaguar_5]

Ok so the Ebay cylinder head goes as follows: I called the company, he said they don't have a RA meter but the finish is of very high quality good enough for a MLS HG, and it does have a very soild, 12 month ship up-front warranty.

I think i'm basically decided unless someone can scare me away. I was planning on getting the 7MGE head because it's just a slight upgrade in the cams, right? They have 7MGTE heads for the same price too...