6M torque specs question?????

3154 Views 12 Replies 7 Participants Last post by SupraFiend, Apr 27, 2010

Smitkis

Discussion Starter · Apr 23, 2010

I'm rebuilding my 6M and understand the differences that the 6M brings to the rest of the motor, but my question is what torque specs should I use when putting it back together?

Options are:

A.) Since it's a 7M crank and rods, should I use the torque specs for the 7M when putting the mains and rods together?

B.) Do I use the 5M specs which are all a bit lighter?

C.) Should I just close my eyes and reef on it till my "f'd up wrist from hockey" gives out?

Much appreciated..

As a side note, I'm letting my 11 year old son pick out the paint colors for the motor. this could be interesting and I'll be sure to put up some pics. I'm psyched he'll come out and help me with this so it's a damn good trade off.

Here is a "before" picture:

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Michael764

· #2 · Apr 24, 2010

if the part is a "7m" use the "7m" torque specs. If its a "5m" part use a "5m" spec.

if its an interchanging part.... use duct tape:naughty:

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Road Ripper

· #3 · Apr 25, 2010

Be sure to use the 7M specs for the head gasket. Better yet, torque them to 75 ft. lbs, because even the 7M had headgasket failures from inadequate torque of the head bolts. It's pretty much standard procedure for anyone who's worked on an "M" engine for any length of time. Good luck, and curious to see what color your engine ends up being!

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Michael764

· #4 · Apr 25, 2010

what head bolts are you using?
I dont have a whole lot of 6m experience and the little I have is with head studs.

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Smitkis

Discussion Starter · #5 · Apr 25, 2010

I'm planning on using the head bolts that were born with it. I can't come up with any real good reason to get aftermarket studs or bolts. Bolts certainly can't be the weak link in the head.

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Wolfgang

· #6 · Apr 25, 2010

If you are ever going to turbo it, throw arp studs in now. Otherwise stock bolts are fine when torqued correctly.

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SupraFiend

· #7 · Apr 27, 2010

Road Ripper said:
...because even the 7M had headgasket failures from inadequate torque of the head bolts

you don't say :sarcasm:

Actually IMO its the design of the head gaskets that are the problem in M motors, there's nothing wrong with the stock bolts. The stock torque spec is on the low side however, I went with 70lbs/ft myself.

If you're doing a rebuild, just go with a metal head gasket right from the get go, turbo or not. Its only a matter of time with the stock style gaskets, they're all junk, its a horrible design.

There's a fully rebuilt 7mge in my shop right now with 6000kms on it and a seeping Altrom headgasket (pretty much the same as oem toyota). Both the block and head were properly planed, very nice finish on them.

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D-cat

· #8 · Apr 27, 2010

A 5M & 6m head are the same basic casting. as for the head bolts, check them very carefully for thread damage, and chase the threads in the block. You can torque the original bolts to 75 or whatever turns your crank, but they were designed for 58+ lbs.. It is probably reasonable to torque them to 65 if they are in good shape & you are using a stock gasket, if you use a metal gasket it is really worth while to put ARP studs in & torque them to manufacturer spec.

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SupraFiend

· #9 · Apr 27, 2010

good points, you definitly don't want to overdue to the torque on the stock bolts. But they are pretty beefy mofus. I bet if you looked them up on a standard scale that plots max torq to thread diameter and pitch they probably can handle alot more then the stock 58lbs/ft.

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Smitkis

Discussion Starter · #10 · Apr 27, 2010

I was thinking the same thing. The bolts must be able to handle more than 58ft/lbs torque.

Time for me to geek out a bit:

Reason being, the head bolts are socket head cap screws. These types of bolts are "usually" aircraft grade. Similar to a SAE grade eight bolts.

That means a bolt that's 1/2"x20 SHCS can handle around 126 ft/lbs. I know this isn't the size of our head bolts, but it must be close.

I think the head bolts are 12mm, so here is some torque specs:

Bolt size Low Grade Grade 8.8 Grade 10.9 Grade 12.9
12mm 39 59 83 100

As long as the bolt grade is above grade 8.8 were ok. Since it's a SHCS, my guess would be it is way above grade 8.8

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DRE85PTYPE

· #11 · Apr 27, 2010

With ARP head studs & MHG, I torqued my 6m head to 87ft lbs

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Smitkis

Discussion Starter · #12 · Apr 27, 2010

I think that the newer style head bolts are more of the "torque to stretch limit" head bolts. I was under the impression that the older cars never used these. That's part of my reasoning for re-using the head bolts.

I'm not trying to be a cheap ass. It's costing plenty to rebuild this thing, but I don't want to put on head studs just to make it look pretty either. I want it to make sense.

Let me know if anyone knows if Toyota was using the "stretch" head bolts for these motors.

Weather we come up with the right or wrong answer, I think this thread has some good info and I appreciate it.

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SupraFiend

· #13 · Apr 27, 2010

No, they're not stretch to yield bolts. I've reused 5m head bolts many many times and never had any issues.

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