7m-ge hg torque specs

[87'N/A]

Just read a wikipedia article on the 7m thats says when replacing the hg to yorque the head to 75lb ft instead of factory specs which say 56lb ft. does anyone know this to be true?

 

[87'N/A]

The article: http://en.m.wikipedia.org/wiki/Toyota_M_engine

 

[T3rril79]

That is very true. However, I wouldn't get most of my information for wiki as it is open sourced and people can butcher it however they like. Remember when torquing the head, you must go by a specific torque sequence. I believe it is stated in the tsrm or you can look in the Haynes manual for our cars.

 

[87'N/A]

Thanks I know wiki is pretty unreliable so I figured id come here to make sure.

 

[T3rril79]

Thanks I know wiki is pretty unreliable so I figured id come here to make sure.

That was a good move. Is this your first HG job?

 

[modmonster2008]

when i do head gasket jobs on a 7m typically i do go for 75 ft. lbs torque on the bolts, make sure you torque them up as you go, start by torquing all bolts to 35, then up to 50, 65, then lastly 75. may seem unnecessary but actually helps even out the flattening of the head gasket. btw youre in auburn? you must be local to me if so

 

[T3rril79]

when i do head gasket jobs on a 7m typically i do go for 75 ft. lbs torque on the bolts, make sure you torque them up as you go, start by torquing all bolts to 35, then up to 50, 65, then lastly 75. may seem unnecessary but actually helps even out the flattening of the head gasket. btw youre in auburn? you must be local to me if so

Good catch, I forgot to mention torque up starting from a low number.

 

[Dan_Gyoba]

Factory head bolts are good to 72 ft-lbs. That's the point where they are still in their elastic range (IE, they don't permanently stretch) More than that, and you could end up with less actual clamping force.

 

[Backlash2032]

Factory head bolts are good to 72 ft-lbs. That's the point where they are still in their elastic range (IE, they don't permanently stretch) More than that, and you could end up with less actual clamping force.

Factory head bolts are actually incredibly strong, almost as strong as ARP bolts. That's really the reason I don't get why people buy ARP head bolts. I don't see a problem with 75 ft. lbs.

 

[T3rril79]

Factory head bolts are actually incredibly strong, almost as strong as ARP bolts. That's really the reason I don't get why people buy ARP head bolts. I don't see a problem with 75 ft. lbs.

Oh well that is news to me...i feel cheated lol

 

[Nick M]

Just read a wikipedia article on the 7m thats says when replacing the hg to yorque the head to 75lb ft instead of factory specs which say 56lb ft. does anyone know this to be true?

Factory torque rating was 58, not 56. Just to be picky....

 

[OfnaRcR4]

Factory head bolts are actually incredibly strong, almost as strong as ARP bolts. That's really the reason I don't get why people buy ARP head bolts. I don't see a problem with 75 ft. lbs.

Not to be a dick but how do you know this?

 

[Poodles]

Not to be a dick but how do you know this?

It was tested way back in the day...

I also kind of agree about the bolts...if you're going to go with new hardware, use studs.

 

[JDMMA70]

Not to be a dick but how do you know this?

Makes me feel like Ive been here a long time (even though I haven't) to remember reading that when I got my car in '07

Recently I purchased a pair of new head bolts from my local Toyota dealership. One bolt from the 1995 Supra 2JZ-GTE engines, as well as a new bolt from the 7M-GTE. I then contracted a local certified engineering metallurgical company to perform tensile strength tests on the head bolts to compare yield strengths and torque values.

I have lab data reports based on the ASTM A370 tensile test, giving tensile strength, yield strength, ultimate load, yield load, as well as deformation data and maximum tightening torque values for the head bolts from the 2JZ GTE and 7M-GTE engines. Some results of the test are given below.

7M head bolt is: 12mm-1.25mm thread pitch {Property Class 10.9 grade 8} yield strength=147,353 PSI... tensile strength=160,550 PSI... ultimate load=70,198 N... % elongation=17... % reduction of area=66 2J head bolt is: 11mm-1.25mm thread pitch {Property Class 10.9 grade 8} yield strength=148,948 PSI... tensile strength=162,581 PSI... ultimate load=68,997 N... % elongation=19... % reduction of area=66

The metals used in the head bolts of the 7M & 2JZ engines are identical in metallurgy +/- manufacturing S.P.C. This is a good material; it stretches smoothly in the plastic region of the curve before it snaps.

By calculating the unit strain for each of the different areas of bolts based on the average yield strength, the following total elongation numbers were calculated. The 7M bolt has a total elongation of .0134" {.3399mm}, and the 2JZ bolt has a total elongation of .01093" {.2775mm}.

By comparing the elongation differences of the bolts, related to the corresponding different thickness of the aluminum in the engines cylinder heads, and allowing for the total length of the bolt shank plus 50% of the length of the threads, the only apparent difference is that the 2JZ bolt has 36 percent more thread than the 7M bolt does. The 7M & 2JZ bolts appear to be designed with the same steel to aluminum expansion stretch theory. I believe the bolt designs are different only because of the different ratio of the bolts metal area versus the thickness of the aluminum cylinder heads the bolt is designed to hold down. The torquing procedure for the two head bolts is also different, as is the head gasket

Toyota service manuals say that the 7M engines head bolt torque specification is 52 to 58 ft. lbs. According to my findings the 52 to 58 ft. lbs. specification for the 7M might be too low a torque value to keep the bolt in acceptable tension, not to mention the normal compression of the head gasket after time. As mentioned earlier many 7M engines that experience head gasket failures have many head bolts that can be removed from the engines failed cylinders by hand, or are very loose when removed.

My calculations show that the 7M head bolts when torqued to the factory specifications of 52 to 58 ft. lbs. is in very low tension related to the bolts actual yield curve. Calculations based on my test data show torque values for the 7M head bolt could be as high as 68 ft. lbs. to 72 ft. lbs. without putting the bolt into the plastic region. On a cold engine this extra torque would allow more tension on the head bolts after the head gasket compresses to normal operating thickness.

Many Supra owners that can afford it are upgrading their 7M engine to the expensive HKS stopper type metal head gasket for the 7M engine. This gasket comes in a number of different thick nesses. My Company stocks the HKS gaskets and I ship them all over the world. The HKS gasket will hold well to over 20 PSI of boost over 400 hp as sea level with upgraded fuel and turbochargers. The factory head bolt torque may be satisfactory with a metal head gasket since metal head gaskets do not deform as much as the soft OEM gasket used in the 7M. I would still recommend torquing the bolts to 72-ft. lbs. When upgrading to Metal head gaskets much must be considered with regard to machine work and the finish of the engine block deck and cylinder head gasket surface. See the following link for full details on doing correct machine work to your engine;

http://www.suprasonic.org/public_html/sonictech/mk3/mk3_pmtn.html

 

[Nick M]

Not to be a dick but how do you know this?

I have never seen a weak Toyota head bolt. Just undervalued torque. Even the older 4 Runner and its 3VZE engine that had a real head gasket issue had significantly more torque applied. 33 lb/ft plus 1/4 turn plus 1/4 turn.

 

[Backlash2032]

I just remember reading it somewhere on the forums. And that 160k psi figure rings a bell. I wanna say the arp bolts were around 168k psi yield.

In other words, get the studs haha

Sent from my HTC Droid DNA

 

[Dan_Gyoba]

Makes me feel like Ive been here a long time (even though I haven't) to remember reading that when I got my car in '07
http://www.suprasonic.org/public_html/sonictech/mk3/mk3_pmtn.html

Hell, I remember reading that Reg was going to go buy that set of bolts. I know the engineering company that ran the tests. This is why I said 72, and not 75. As soon as the bolts hit the plastic region, the clamp load goes down, and you don't get to re-use the bolts.

ARPs are good for 85, at least according to the package specs. That's also supposed to be elastic range, meaning that they're reuseable.

Really though the advantage to studs is accuracy. You aren't dealing with a possibly inconsistent length of threads into a block of possibly unknown condition (Even if you DO chase the threads with a tap before installing the bolts.) You have a relatively short length of threads dealing with the nut depth and the nut flange surface on a washer. This smaller, more consistent surface makes the stud much more accurate for clamp force as you tighten the fastener. This means more even clamping force across all of the studs, guaranteed.

I'd go for the ARP bolts, but the difference in cost between them and the studs isn't worth it. I'll go for the studs with a higher clamp load and better consistency.