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drumminforev
Guest
If there is a thread about this, direct me to it because I didnt see it but...
Why is it that 7m's always blow the HG. Even NA motors?
Why is it that 7m's always blow the HG. Even NA motors?
The Toyota torque spec is too low 
Plus guys like to turn the boost up on a well used motor...just doesn't last.
Plus guys like to turn the boost up on a well used motor...just doesn't last.
well im not exactly sure but for the most part it was because toyota did not torque the head bolts enough to hold for a long time. I have seen turbo cars stock at 170 k that the head gasket is fine, but if you mod them and beat on them they blow.
I myself retorqued my stock ones to 70 lbs instead of the stock 55 or what ever they are. I just did this for now, and will be replaced the head gasket to be safe this summer. the correct way is arp head bolts with a new head gasket.
hope this helps and anyone who knows more can probably be more help than me.
do a search there are tons and tons of post and info on this.
I myself retorqued my stock ones to 70 lbs instead of the stock 55 or what ever they are. I just did this for now, and will be replaced the head gasket to be safe this summer. the correct way is arp head bolts with a new head gasket.
hope this helps and anyone who knows more can probably be more help than me.
do a search there are tons and tons of post and info on this.
The stock torque spec is 56 ft/lbs. Many cars that have blown have been modded and ran hard, but there are still cases of original owners never really beating on the car, yet it still blows the head gasket in the 120-160k mile range.
If you are looking to save money on a head gasket job, you can pick up a stock type gasket from someone on the forums (they come in the engine rebuild kits, but many don't use them) and get ARP head bolts. The ARP head bolts call for 75ft/lbs (with ARP lube).
If performance is in mind when for a head gasket job, most will resurface the block and head and buy a metal head gasket (matching the thickness of the stock head gasket plus the amount that was taken off during resurfacing). Instead of the ARP head bolts, most usually go for the ARP head studs (better holding ability), which call for 85 ft/lbs (with ARP lube).
If you are looking to save money on a head gasket job, you can pick up a stock type gasket from someone on the forums (they come in the engine rebuild kits, but many don't use them) and get ARP head bolts. The ARP head bolts call for 75ft/lbs (with ARP lube).
If performance is in mind when for a head gasket job, most will resurface the block and head and buy a metal head gasket (matching the thickness of the stock head gasket plus the amount that was taken off during resurfacing). Instead of the ARP head bolts, most usually go for the ARP head studs (better holding ability), which call for 85 ft/lbs (with ARP lube).
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drumminforev
Guest
So even on an NA motor, wouldnt you have to overheat it pretty severely even with undertorqued bolts?
No, it still happens. It even happens to the Cressidas (which generally weren't abused as often as the Supras)
The stock torque wasn't even enough to stretch the bolts properly, so they could loosen - there's been cases of head bolts that were so loose you could pull them out by hand.
72 foot pounds is perfectly safe on stock head bolts, they are reusable, and a stock head gasket with proper torque will hold 320 hp without any problems.
72 foot pounds is perfectly safe on stock head bolts, they are reusable, and a stock head gasket with proper torque will hold 320 hp without any problems.
I'm still lookin to buy my first mkIII, when i do get it, would it be wise to just tighten the bolts that are on there to the higher spec? And if i get a bhg, how much would i be lookin at to get it back to stock form + ARP bolts?
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Ckanderson said:
How many days... Like two
ARP studs are actually suppost to be torqued to 81 ft/lbs with moly lube, but you'd probably still be ok going with 85 ft/lbs like mentioned earlier.
GrimJack said:
76lb.ft's on stock bolts...........320rwhp/362rwtq. You nailed it, Dave.
It's all a matter of how you want to treat it, how well you've prepped it, and just how stupid you want to get with it. :biglaugh:
Just a question, if it was JUST the torque specs on the bolts why do so many still get them even after a proper everything. This whole fix of polishing the block to a mirror finish seems to me to allow the head to slide indepenent of the block (since they both expand at different rates) hopefully keeping a seal and not ripping the gasket apart which it seems is what happens in a bhg. That typically is not whats acheived in most engines. How many of you know the water flow #'s of the impeller at all the different rpm's? Does it cavitate right when you need it most? My thinking leads me more towards HEAT, it isn't being properly removed. I haven't seen any posts on this site from someone that has done any research into this. To me its just a little too odd that this problem has only one fix, proper head bolt torque when many have claimed they torqued them right and still the hg fail. True this hg thing might be a bad Toyota blunder, but is there something else to it?
Geezer, there is a design flaw in the head, and the block, IMO... The water jackets are too close together and teh cylinders are too close together... The other main design flaw is in the HG itself, being essentially pressed wax paper and copper rings... It doesnt take much to push that ring into the paper and right into the water jacket...
Here is a pic of the BHG I had on my old 88... Notice where it happened on the #6 piston... Notice the difference between the make and design of the stock style and the Cometic... Also, notice how close the water jacket rings are in comparison to the piston "rings" in the hg...
To me, yes, heat may play a part, and yes the two metals will expand at different rates, but if they had used a HG that was worth a shit, and torqued the head down to a higher rating and if they had thickened the walls between the piston jackets and water jackets, I dont think you would have near as many BHGs...
Here is a pic of the BHG I had on my old 88... Notice where it happened on the #6 piston... Notice the difference between the make and design of the stock style and the Cometic... Also, notice how close the water jacket rings are in comparison to the piston "rings" in the hg...
To me, yes, heat may play a part, and yes the two metals will expand at different rates, but if they had used a HG that was worth a shit, and torqued the head down to a higher rating and if they had thickened the walls between the piston jackets and water jackets, I dont think you would have near as many BHGs...
Just for the record:
I got my 89T with 50,500 miles on the ODO. Somewhere around 70,000 miles I did a retorque (special thanks to Bob Johnson who welcomed a few Supra owners to his house and we had a retorque party).
My Supra was my daily driver for 10 years and I never went crazy with power like many people have. My Supra now has 186,000 miles on it and has been running since 1998 with a MBC set to just below fuel cut, FIPK, DP and 75mm turbo exhaust, and a type S BOV.
Hell... even the turbo has never been touched and still boosts solid.
Building these cars is like blowing up a balloon. If you go too far your balloon WILL explode - unless you upgrade every part of the balloon to handle more. You can't expect crazy power out of a 7M without doing some hefty upgrades. Even the "Almighty" 2J has a problem with blowing head gaskets - although it is not as common.
I got my 89T with 50,500 miles on the ODO. Somewhere around 70,000 miles I did a retorque (special thanks to Bob Johnson who welcomed a few Supra owners to his house and we had a retorque party).
My Supra was my daily driver for 10 years and I never went crazy with power like many people have. My Supra now has 186,000 miles on it and has been running since 1998 with a MBC set to just below fuel cut, FIPK, DP and 75mm turbo exhaust, and a type S BOV.
Hell... even the turbo has never been touched and still boosts solid.
Building these cars is like blowing up a balloon. If you go too far your balloon WILL explode - unless you upgrade every part of the balloon to handle more. You can't expect crazy power out of a 7M without doing some hefty upgrades. Even the "Almighty" 2J has a problem with blowing head gaskets - although it is not as common.
jake, you're entirely right, and that is why i always blame them for blowing. The walls are waaay too thin to begin with and sadly nothing we can do about it :nono:Reign_Maker said:
Reign, Ya I see where that gasket blew and your right if was wax paperlike and a copper ring I can see that could blow. Now onto the heat thing I see how close the cylinders are and maybe this is where a more stable water flow up and down the rpm range could help out. You pretty much addressed the weak suck gasket issue, now what about the pump cavitating at certain rpms just when you need it most, during a hard run, and after a hard run. These are some of the questions I'd like to see if any of the long time Supra guys have looked into and maybe even benchmarked with some numbers.
I'm not sure I agree with reign about the design cause if you look at rb26 skyline motor it's design is kinda identical to that in the 7m except for one water jacket that's in the 6th cylinder which yes could be a weak point but we're seeing people breaking 600-800hp with a 7m which means if done right there's no problem. If it got a weak point, No matter what you do it will still blow the HG. Just my opinion
Check out the RB26 motor picture
http://japanesejapan.at.infoseek.co.jp/RB27- 1.jpg
And I could be wrong
Check out the RB26 motor picture
http://japanesejapan.at.infoseek.co.jp/RB27- 1.jpg
And I could be wrong
As you can see, there are some major differences in the 7M than the RB... Also, you have to remember, teh RB26 is like the 2JZ to the 7M... But anyway, look mainly at the thickness between the cylinders, and also the size of the water jackets, are much larger... Also, if I remember correctly, dont RB26's come with studs and a mhg? And really, the "problems" with the 7M head/block design can be easily remedied with a proper prep, mhg and arp's torque accordingly... Toyota just effed up, then they recovered with the 1&2JZ motors...
Well does the 7M blow it's gasket between the cylinders?As I know it mosly blows between the water jacket and the cylinderReign_Maker said:
As you can see, there are some major differences in the 7M than the RB... Also, you have to remember, teh RB26 is like the 2JZ to the 7M... But anyway, look mainly at the thickness between the cylinders, and also the size of the water jackets, are much larger... Also, if I remember correctly, dont RB26's come with studs and a mhg? And really, the "problems" with the 7M head/block design can be easily remedied with a proper prep, mhg and arp's torque accordingly... Toyota just effed up, then they recovered with the 1&2JZ motors...