Overheating problem...

[jetjock]

Not sure I follow that logic .

 

[starscream5000]

A used set would be heat cycled already (assuming they were on the engine for any decent amount of time) so once you reach final torque, that's it. This is all assuming the studs are in great shape.

 

[ryanday]

There is nothing wrong with stock head bolts, Assuming of course they are not corroded or damaged the whole "stretching" issue is foolish. if they stretched so easy they would never stay torqued.

 

[Supracentral]

Back in 1998, Reg Reimer did the research. I'll let Reg's words speak for themselves:

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 thicknesses. 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.

So those of us (like me) who have owned Supras for years (I bought my first new in 1990 and I've owned ten of them) know for a fact this issue exists. We've seen it many many time. Reg went the extra step and had the ASTM A370 tensile tests done in a lab to prove it.

Edit: Removed rude comments.

 

[ryanday]

Mabey i read that wrong and correct me if i did, but i believe what he found was that the stock torque specs were too low to place the head bolts under ideal tensions. ..If you are trying to say that arp head bolts are stronger and stress less under certain tensions, i agree with you. what i was implying was that the stock head bolts are fine. I understand that they can stretch but Mabey i should have said something like "torqued to proper specs."

 

[Supracentral]

Yea, jetjock just pointed out to me that I was not catching your meaning.

I edited the nasty out of that post above, shit day at the office and you caught the heat from it, that was uncalled for.

I apologize for that.

I'm going to go watch a movie or something. I'm far too grumpy for humans tonight. ;p

 

[Nick M]

I missed the nasty edit, oh well.

People need to stop saying the headbolts stretch, and are no good. This, like other issues, has been covered. The stretching is what gives the clamping force. They are supposed to stretch. Dean Marcum on his site mentioned seeing headbolts that could be removed by hand also. That is the one true "flaw" the car has. I don't know why Toyota wanted that lower number. Perhaps fear of warping the head or block.

So what he is saying is that the stock head bolts are good quality. Unless I am mistaken.

 

[CACressida]

I experienced a bhg about 8 months ago in my Cressida, and for the first time ever out of all my bhg experiences in any 7M, when I went to loosen the headbolts, the ones in the rear were loose enough to twist off by hand. I was stunned by this because I did a compression check 2 months prior to the bhg and all compression was good. I reused my headbolts and torqued them down to 72lbs. I retorqued after a month of driving to 72lbs, and retorqued a 3rd time. 4th 5th and 6th, the bolts weren't loose anymore. 7th time I went to retorque the headbolts 2 months afte the last retorque and the headbolts were still tight.

Factory bolts worked out for me.

 

[jetjock]

Best to stop looking at it as a head bolt and start looking at it as any clamped joint. "Stretching" itself isn't the issue. The real issue revolves around the elastic versus plastic regions of a material and into which the elongation ends up putting it. It's mechanical engineering 101.

 

[PROJECT N00b]

OR you can check your radiator to see if its dirty and clogged...if it is then go ahead and change it out.

 

[CACressida]

OR you can check your radiator to see if its dirty and clogged...if it is then go ahead and change it out.

I bought a Cressida off an old man for 1k bux super clean. The guy was told it had bhg, opened the hood and took the radiator out and replaced it with one out of my other Cressida. Sure enough, the 7M it had in it was still in excellent shape. Sold the car to my cuz for 3500

Most likely the overheating is caused by a bad radiator. The temp gauge on that Cressida made it seem like it was BHG but it wasn't. Swap out a radiator or have your cleaned. Even tho its not the radiator, atleast you have a clean one for your next hg

 

[suprahooked]

ok sure will. these are the bolts i would need right??

Those are connecting rod bolts

 

[7-m-g-t-e]

Ok i decided to just completely start from scratch... Im gonna rebuild the whole engine... JE Pistons, Crankshaft, Oil Pump, Walbro Fuel Pump, 550CC PTE Injectors, completely brand new Gaskets, Malory 4 port FPR, Flush Radiator, Change Thermostat, Lexus AFM, and Ebay XS Power Intercooler, New Timeing Belt, New Rod Bolts and New Head Bolts... Any thing else i might need new that might cause the overheating to continue?? Thanks ahead of time!

Marvin

 

[Nick M]

Flushing the radiator isn't as effective as having the radiator shop take it apart. A new one is expensive, but effective also. Make sure your fan clutch is still tight, and you use its shroud.

Why the new crank?

 

[JustAnotherVictim]

A new stock koyo isn't that expensive, should be <$150.
Well, not expensive to me anyways...

 

[7-m-g-t-e]

Flushing the radiator isn't as effective as having the radiator shop take it apart. A new one is expensive, but effective also. Make sure your fan clutch is still tight, and you use its shroud.

Why the new crank?

The crank needs to be replaced, srry and i didn't flush the radiator, i took it to a shop they opened it up and cleaned it out so its pretty much brand new... Clutch fan i just installed one and also a brand new fan shroud from the dealership... Anyhting else i might need to raplace that might cause overheating problems?

 

[Nick M]

The stock cooling system is designed to deal with the stock characteristics of the engine.

If the engine has problems, the cooling system will not completely do its job.