False torque spec given for motor mount bracket??

Ethan Barr said:

Hey all, back again. Almost done with the motor. Broke my first bolt today on it.

I found a factory is300 manual and am confused on the torque spec needed for the motor mount bracket that attaches to the block.

book read it was 44ft-lbs and I just snapped the bolt.

anyone know if this spec if correct and I had a weak bolt? If not what’s the correct spec?

also anyone know what bolt it is as well? Can’t find much discussing the bolts themselves only the monts And using the different trd ones for the supra but I’m not interested in that.

I need the torque spec and the bolt size/thread pattern please

I have more bolts and can hit up Home Depot as they have the best bolt selection around besides where I work but it’s closed for the weekend now and I’d rather buy them.

the bolts on my 5.9 Cummins 12v were grade 8, I can’t tell the grade on these. Has anyone upgraded them to grade8 so it’s safer to run more power? My Cummins broke the grade 8s and I went to 10.9’s

thanks in advance.

photo below for reference.

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The bolts for this bracket it looks like? Book does calls for 44ft lbs. that’s what I torqued them to as well. I also reused the oem bolts. I can’t tell if you did as well.

Assuming you did, maybe someone over torqued them at some point? Or your wrench could be off. I used a digital gauge alongside my click type wrench just to make sure. (And also because my smaller torque wrench is 20ft-lbs low because the handle got misaligned somehow.)

There are no grade 8 bolts anywhere on the car. That would mean imperial threads. Either grade 10.9 or 12.9 will work. m10x1.25 would be my guess from brief searching. you have the bolt. Just measure it. It’s either 10mm or 12mm.

The thread pitch is almost certainly fine (1.25 either way I think) so you might not find it in Home Depot. Ace hardware has AMAZING metric hardware section if you have one of those. Fastenal, despite its name, does not. McMaster Carrt has amazing hardware section as well but they’re “online” only. (Though I live close enough to do warehouse pickup)

AlwaysBroken said:

View attachment 145019 The bolts for this bracket it looks like? Book does calls for 44ft lbs. that’s what I torqued them to as well. I also reused the oem bolts. I can’t tell if you did as well.

Assuming you did, maybe someone over torqued them at some point? Or your wrench could be off. I used a digital gauge alongside my click type wrench just to make sure. (And also because my smaller torque wrench is 20ft-lbs low because the handle got misaligned somehow.)

There are no grade 8 bolts anywhere on the car. That would mean imperial threads. Either grade 10.9 or 12.9 will work. m10x1.25 would be my guess from brief searching. you have the bolt. Just measure it. It’s either 10mm or 12mm.

The thread pitch is almost certainly fine (1.25 either way I think) so you might not find it in Home Depot. Ace hardware has AMAZING metric hardware section if you have one of those. Fastenal, despite its name, does not. McMaster Carrt has amazing hardware section as well but they’re “online” only. (Though I live close enough to do warehouse pickup)

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good find!!
Yes I did reuse the the oem bolts. I kept tightening using my big 1/2” torque wrench (I just torqued the main crank bolt so maybe setting it to 240ftlbs threw it off?) and it didn’t feel right. Just kept going and going and going and I was getting nervous. Didn’t feel like it was snuggling up at all.

my digital only goes up 22ftlbs, maybe it’s time to invest in a 3rd party digital torque assist that sits on the end of the click type one so I have two things telling me the torque rating?

my 1/2” is new this year and has been taken care of immaculately and only used up to 135ftlbs for my dodge wheels. So I’m hoping it isn’t off as I used it on the whole motor :/

I’ll check all of those stores, thanks for the reply! Would you say it’s worth it to upgrade the bolts while I’m at it to 10.9? I mean if Toyota didn’t then they are the pros so it makes sense to just leave it as a stock bolt.

Theneil300 said:

I only use the torque spec for main caps, rod bolts, head bolts and flywheel bolts. Gotta have your arm recalibrated brother

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I think your right!
I’m notoriously bad at breaking bolts, especially JIC fittings and over tightening them when I first started my job.

I thought my arm was in spec but I have been working out a lot more so maybe it’s been throwing it all outta whack?!

I’ll send my arm off to snap on to get an analysis lol.

Ethan Barr said:

good find!!
Yes I did reuse the the oem bolts. I kept tightening using my big 1/2” torque wrench (I just torqued the main crank bolt so maybe setting it to 240ftlbs threw it off?) and it didn’t feel right. Just kept going and going and going and I was getting nervous. Didn’t feel like it was snuggling up at all.

my digital only goes up 22ftlbs, maybe it’s time to invest in a 3rd party digital torque assist that sits on the end of the click type one so I have two things telling me the torque rating?

my 1/2” is new this year and has been taken care of immaculately and only used up to 135ftlbs for my dodge wheels. So I’m hoping it isn’t off as I used it on the whole motor :/

I’ll check all of those stores, thanks for the reply! Would you say it’s worth it to upgrade the bolts while I’m at it to 10.9? I mean if Toyota didn’t then they are the pros so it makes sense to just leave it as a stock bolt.

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I don’t think using the torque wrench, even at the high range, would make it out of whack. Regardless though, I do like to check the wrench before working on something critical or a pain to replace. Torquing to high values always feels weird. The torque is high enough where the car feels like it’s moving around a lot.

As for the bolt grade, 10.9 is good up to ~50ft lbs depending on where you look whereas grade 8.8 is good until ~40ft lbs. grade 12.9 is higher albeit with drawbacks that’s too complicated for me to truly understand. The OEM bolt would be equivalent to a grade 10.9 bolt. Stick with 10.9.

As for “calibrating” your arm, that’s probably how the bolt got messed up if you aren’t the 1st owner. Someone else decided good and tight is a value. 44ft lbs ain’t a lot when someone’s being a gorilla.

The only real thing to keep in mind is how the bolt feels when it’s coming to target torque. If it feels like it’s not increasing that much or feeling easier as you “increase” in torque, take the bolt out and check the threads for stretch. if you have another bolt, it’s easy to check. The threads if they’re stretched won’t line up with a new bolt. (You can see the stretching in your photo too)

I’ve managed to prevent snapping a arp head bolt before like this. A bolt should never feel like it’s plateauing in effort to tighten as the torque goes up. (Terms and conditions apply but in general it’s a good description)