While carefully torquing these bolts, I noticed they seemed to be getting easier to turn. First thought was the bolts were stretching. Second thought was try it again, maybe I was wrong. Third thought was my first thought was probably right and I should take the bolts out to check before I snap them like a dumbass. I honestly think this is the first time ever I caught it before snapping the bolt.

These bolts started out the same length and shorter than they are now:

This message has been edited. Last edited by: trapper189,

Chinesesium bolts?
That shouldn't happen with a quality bolt.

Oil on the threads that I didn’t catch and no idea how it got there. Suzuki 30hp outboard made in Thailand, so could be Chinesesium.

And of course markings I’ve never seen:



The internet says it’s a Toyota Class 7t bolt which I’m not having any luck figuring out what the means.

Finally found it:
Not just Toyota, but JIS, Japanese Industry Standard, and equivalent to metric 8.8.

This message has been edited. Last edited by: trapper189,

Roughly corresponds to an ISO class 8.8 bolt. A tempered medium-carbon steel.
(Yes I had to look that up)
What material is it threading into?

Aluminum.

Between the intake manifold, exhaust manifold, starter motor, power head, etc, there’s at least two dozen of the same diameter, thread pitch, and marked bolts that all call for 23N-m. It’s at the upper limit of my 3/8 drive inch-pound wrench or the lower limit of my 1/2” foot-pound wrench. I used the 3/8 and none of the other bolts gave me any trouble. That was fortunate as well because they were all blind holes that would have been trouble to get at and fix. These two were the starter motor mounting bolts, they threaded into the starter, and snapping them would just let the starter be removed and screwing the headless portion out would be easy.

My search said that the JIC 8.8 bolt was roughly the equivalent of the standard inch grade 5. It’s hard to imagine why any bolt with that tensile strength would stretch before tearing up the threaded aluminum. You must have got a couple of soft ones. Glad you caught it in time.

Also, some day I’m going to get torque wrenches that have plenty of overlap between the sizes. It’s just not high on the priority list.

^^^ Without looking it up, I'd believe that headstamp to indicate grade 5. Like 400m, I can't see how you could stretch them instead of stripping the aluminum threads. Amazing!

I wondered about the aluminum as well and then figured if there’s enough thread into the aluminum, then the steel bolt will break first. As an extreme example to illustrate the point: it you have an 1/8” diameter bolt with 2” threaded into a piece of aluminum, the bolt fails before the aluminum threads. In my case, the M8, 8mm, bolts were threaded into a 12mm thick flange on the starter motor.

I found a chart that says 23N-m dry produces the same clamping force as about 10N-m if the bolts are lubricated. The threads looked clean and I didn’t notice any oil when I put them in, but they were oily when I took them out. Lesson learned, hit the threads with carb cleaner regardless of how they look.

Just for fun and I don’t know if it’s right:

Tensile strength of grade 8.8 bolts - 116,000psi
Shear strength of 7075-T6 aluminum - 48,000psi

The tensile strength of the M8 bolt is the cross sectional area of the bolt times the tensile strength:

(.31/2)^2 x 3.14159 x 116,000 = 8,755 pounds

This is the part I’m not sure about, but I think the strength of the aluminum threads is determine by the surface area of those threads times the shear strength of the aluminum. The surface area of the threads is a cylinder and the math for that is:

.31 x 3.14159 x .47 x 48,000 = 21,971 pounds

quote:

Originally posted by trapper189:
While carefully torquing these bolts, I noticed they seemed to be getting easier to turn...

Sexy waist on the bolt!

Seriously though, if there is any question whether you have clean dry threads prior to torquing, you should clean the threads with Brake Cleaner, NOT Carb Cleaner! Brake Cleaner evaporates readily and leaves no residue while the same can't be said for Carb Cleaner.

BrakeClean in the red can...There is NO substitute!

Brake cleaner eats things I don't want ate and an outboard is full of those things. I make do with carb cleaner, paper towel, and compressed air.

Both bolts have narrower waists than they are supposed to, but one is better proportioned.

Slim Fastener diet, prolly.

Edited to add:

In my post above where I did some math, I did it mostly right. I actual found some NASA tables that give thread pullout numbers for various materials. According to those tables, the shear strength of 7075-T6 is 45,700psi. My other error was using 8mm as the diameter of the hole when I should have used the pitch diameter of the hole. I also should have used the pitch diameter for the bolt as well. On the other hand, the ratio between the strength of the bolt and sheer strength of the hole would be the same.

Also, NASA divides the result by a safety factor of 3 which wouldn't matter in my case as the torque I used on the bolts' lubricated threads did exceed their yield strength.

This message has been edited. Last edited by: trapper189,

quote:

Originally posted by nhracecraft:

quote:

Originally posted by trapper189:
While carefully torquing these bolts, I noticed they seemed to be getting easier to turn...

Sexy waist on the bolt!

Seriously though, if there is any question whether you have clean dry threads prior to torquing, you should clean the threads with Brake Cleaner, NOT Carb Cleaner! Brake Cleaner evaporates readily and leaves no residue while the same can't be said for Carb Cleaner.

BrakeClean in the red can...There is NO substitute!

Brake Cleaner with tetrachloroethylene and dichloromethane exposed enough heat can generate Phosgene Gas. Inhale that and if you survive for more than a week and you WILL need a double lung transplant. Most do not survive for more than a week. It why I will not EVER use any brake cleaner that has "Chlor" in a chemical used in that cleaner.

Fortunately CRC BrakeClean does not have any chlorinated solvents to the advice to ONLY use the CRC BrakeClean is very sound advice.

Point is, there are cases when the Brand really does matter. You also need to look at the Warnings and ingredients list before using any of these products. You also don't want any cleaner that has a component with "chlor" in the name, because that stuff will kill you if you get it too hot.

Second note is that when you are talking about Chinesium there are a LOT of fraudulent vendors in China selling sub par fasteners and I suspect that bolt that necked down was a Mild Steel part that had been marked and plated as meeting the 8.8 grade specification. This means you are looking at a fastener with about 45-60,000 Yield Strength and that is why it necked down. Basically Suzuki got hit with a batch of bad fasteners and one of them ended up on your engine.

I hate that feeling, once it happened to me when I got a bad torque spec, and using that spec with a proper torque wrench, felt that sick felling, but in this case the bolt wasn't stretching it was the aluminum upper block cover that got stripped out. I had to hire a pro to repair it with a Helicoil. I may have been able to pull it off myself but this was a critical engine part that left no room for error.

But yea that's a sickening feeling, yuck.

For critical applications I go OE bolts, or proper graded bolts of US manufacture from solid industrial suppliers.

Multiple torque wrenches to match the application really help as well.

quote:

Originally posted by rizzle:
Slim Fastener diet, prolly.

That’s some funny chit, right there!