Is 17ft lbs too much for a 5/16" diameter bolt?

[The motor guy]

The exhaust risers on my boat call for 17 ft lbs and every torque spec chart I look at calls for 13 ft lbs of torque. These are grade 5 bolts Why would the manufacturer call for a tighter spec than what the bolt is designed for?

 

[zrxkawboy]

The charts are probably "on the safe side". I'd listen to the mfr of your equipment.

 

[wag123]

It isn't the bolt that you need to worry about, it is what the bolt is threaded into. If you over torque the bolt you risk pulling the threads out.

 

[The motor guy]

It isn't the bolt that you need to worry about, it is what the bolt is threaded into. If you over torque the bolt you risk pulling the threads out.

Cast iron. Rusty cast iron lol

 

[D60]

Cast iron. Rusty cast iron lol

In that case I'd normally say go less and use thread locker, but is this engine exhaust? If so, the heat obviously won't do any favors for thread lock.

 

[The motor guy]

In that case I'd normally say go less and use thread locker, but is this engine exhaust? If so, the heat obviously won't do any favors for thread lock.

They don't get hot, they have water flowing through them.

 

[Trav]

Check this out, I would probably split the difference do 15 ft.lb.

Tightening Torque Guide

Tightening Torque Guide for Grade 5 & 8 Hex Cap Screws This table is based on IFI 5th Edition Technical Data N-12/N-16, using Equation (1) and a torque coefficient, K=0.20 for non plated steel fasteners and K=0.15 for plated fasteners. These Figures represent an estimate of torque (torque...

www.almabolt.com

 

[The motor guy]

Well what I'm worried about is the bolts are like 6" long and they're being threaded into rusty cast iron threads, so I don't think it would take much for them to strip out and we all know that awful feeling when it suddenly becomes easier to turn. They already have split ring lock washers

 

[clinebarger]

Almost all M8 fasteners on GM products call for 18 ft.lb.....8mm & 5/16" are within .002" of each other.

Don't like using 8.8 or Grade 5 hardware on anything, 10.9 or Grade 8 at the very least.

 

[Blueshound]

The exhaust risers on my boat call for 17 ft lbs and every torque spec chart I look at calls for 13 ft lbs of torque. These are grade 5 bolts Why would the manufacturer call for a tighter spec than what the bolt is designed for?

Why not upgrade to grade 8 bolts and torque to 17?

 

[clinebarger]

ARP stainless is another option, Do you have a more accurate UHL than "Like 6 inches"?

 

[The motor guy]

Why not upgrade to grade 8 bolts and torque to 17?

Not a bad idea honestly. Maybe the next go around

 

[The motor guy]

Not a bad idea honestly. Maybe the next go around

Why not upgrade to grade 8 bolts and torque to 17?

I mean I can still go to tractor supply and grab some grade 8 bolts i think. Or is there a chance the thread pitch would be different?

 

[drtyler]

I mean I can still go to tractor supply and grab some grade 8 bolts i think. Or is there a chance the thread pitch would be different?

Thread pitch doesn't change, but just note if you need fine or course threads. If you can take an old bolt with you to match them, that would be best.

 

[The motor guy]

Thread pitch doesn't change, but just note if you need fine or course threads. If you can take an old bolt with you to match them, that would be best.

What's weird is I have a remote oil filter mount attached to the manifold and they used grade 8 on that one because they needed it to be a little longer to accommodate the thickness of the bracket. Maybe they used grade 8 so people wouldn't mix up the bolts. They are blind holes. The other bolts are all grade 5 zinc plated

 

[paulo57509]

I use torque tables when there is no tightening torque value is specified. Even vehicle manufacturers provide general torque tables in their service manuals. Some things to keep in mind when using these tables.

Fastener Torque | Engineering Library

This page provides the sections on proper bolt torque from NASA's

engineeringlibrary.org

 

[The motor guy]

I use torque tables when there is no tightening torque value is specified. Even vehicle manufacturers provide general torque tables in their service manuals. Some things to keep in mind when using these tables.

Fastener Torque | Engineering Library

This page provides the sections on proper bolt torque from NASA's

engineeringlibrary.org

One thing I didn't think of. Is maybe the fact that they have a gasket in between vs just two pieces of metal coming together is why they would exceed the rating. Not sure if that makes a difference or not.

 

[ElectroMechanoMan]

I absolutely agree with bolt torque on gasketed surfaces. The best example I have is the flexitallic gaskets used in steam service. I believe there’s a couple instrumentation techs here that are familiar with Fisher control valve bonnet bolts. If these gaskets are over tightened, they loose their ability to flex during heat cycles and leak. Plus, if the bolts are under tightened, they loosen under the same heat conditions.

 

[thescreensavers]

Fastenal has a Calculator that I've used in the past.

https://www.fastenal.com/fast/services-and-solutions/engineering-calculators/torque-calculator

 

[The motor guy]

It isn't the bolt that you need to worry about, it is what the bolt is threaded into. If you over torque the bolt you risk pulling the threads out.

I went up to 15ft lbs and then a final crank down to 17. Phheww!!! I thought for sure I was going to be having to order a whole $1200 set of risers and manifolds if these things stripped out. Or atleast have to send them off to be rethreaded