PSA: check your engine mounts

[KnifeySpoony]

Presumably due to fretting of the powder coat on the engine mount brackets, these seem prone to loosening up. I had been checking my paint marks regularly since my build in 2021 and trusting them, but they lied to me. Best put a wrench on them frequently imo. First tested them just recently and needed tightening. After a single track weekend a few were slightly loose again. 

[panamericano]

Torque and retorque frequently.  Beware of paint.  I worked with a motor carrier that had a problem with wheels coming off.  They were extremely lucky not to kill someone.  One wheel/tire went over 1.5 miles down the freeway before coming to rest.  110 pounds x 60 mph = ENERGY.  They were torqued (after the regular air gun, with a 4 foot digital torque wrench.  It turned out that the wheels' paint was applied too thick and not hardened, so nothing was as tight as it seemed.

[MV8]

There are many ways to prevent fasteners from backing off. The simplest is to use specialty (ramp) lock washers that require more torque to loosen than tighten. These are used to hold the prop on many light sport aircraft.

[KnifeySpoony]

14 hours ago, panamericano said:

Beware of paint. 

This is the take home for me. Will be watching any fasteners on painted/coated surfaces closely.

[IamScotticus]

On 6/8/2025 at 7:42 AM, MV8 said:

specialty (ramp) lock washers

Link!

[Anthem]

On 6/8/2025 at 10:27 AM, KnifeySpoony said:

This is the take home for me. Will be watching any fasteners on painted/coated surfaces closely.

Yes, powder coating can hide this well until the hardware is moved, especially on lower torque hardware, the lifted coating has the "bite marks" but the metal surface is clean of any interface. In tight shadowy areas can be a challenge to visually inspect until corrosion, flaking, etc can be seen.

 

 

15 hours ago, IamScotticus said:

Link!

https://www.sherex.com/wedge-locking-washers-and-nuts/

https://www.nord-lock.com/nord-lock/products/washers/

 

Watch out for some of the copycats from china, the ramp edges aren't as "sharp".

 

Edit: spelling/grammar

Edited June 10 by Anthem

[jordway]

What are the correct torques for the engine mounts?  I've seen 41 Nm for the hex bolt to the rubbers and 20 Nm for the 13mm bolts to the chassis.  Does that sound right?

[KnifeySpoony]

Yes and 34nm for the mounts to the engine block. 

[Timothy Keith-Lucas]

Two concerns here, engine mounts and lug nuts. Thank you for the warning and specs on engine mounts.

 

Lazy Saturday morning thoughts: I wonder how many of the 10x20 18-wheeler tires running down the freeway are the product of over-torquing with an air wrench. One killed the wife of a colleague of mine. Related thought- my bet is that bunches of people with wrenches in hand don't understand that the proper torque is a function of the bolt, not what is being bolted. You want the elastic range of the bolt, so it forms a spring to hold your parts together, and god forbid that you stray into the plastic range. I bought an old Jeep with oversized tires a few years ago, and found that some previous owner had torqued the lug nuts at about 200 ft lbs, or about 270 nm. He (I'll bet on he) must have thought big tire, better tighten it more. I'm very glad I got it home without sending one of those suckers down the road.

[IamScotticus]

I torque my wheels off the ground so vehicle weight on the camber doesn't load one side of the wheel.  I do this to my Colorado in which the torque spec is 110 lbs ft.  I found if I torque on the ground, the top lugs will have a 20 lb difference from the lower.

Edited June 15 by IamScotticus

[IamScotticus]

While we're at it, will someone explain torque to yield?

[Timothy Keith-Lucas]

It means to just exceed the elastic limit of the bolt and just enter the plastic range, so the bolt lengthens. Of course, you go a little more and the bolt starts losing strength. To my old engineering school mind, it's damned dangerous, but apparently it is used in bolting down engine heads. I would never risk it with a lug nut.

[wdb]

45 minutes ago, Timothy Keith-Lucas said:

It means to just exceed the elastic limit of the bolt and just enter the plastic range, so the bolt lengthens. Of course, you go a little more and the bolt starts losing strength. To my old engineering school mind, it's damned dangerous, but apparently it is used in bolting down engine heads. I would never risk it with a lug nut.

 

BMW also uses TTY bolts quite a lot in suspension and structural fittings. My Z4s had a thick aluminum plate in front under the engine; a lot of folks thought it was just a skid plate but it was also a structural member of the chassis. All of the bolts were TTY. Torque was to X lb/ft, then another 90 degrees. Standard practice was to use the "single use" bolts two or possibly three times. I wouldn't do that with head bolts...

[Timothy Keith-Lucas]

Ditto with aviation bolts.  Many are single use, single torque, and expensive.