My Mac Vacation ...Perfect... Not Really

[kmclemore]

reduce torque by 10%

Metric, SAE, or Whitworth percent??

B.S. *

(And you missed American Unified Coarse and British Association!)

*(British Standard)

[kmclemore]

FYI, pretty good article on torque:

http://www.rockcrawler.com/techreports/ ... /index.asp#

And according to this site, I stand corrected on the 10% figure:

http://www.raskcycle.com/techtip/webdoc14.html

BOLT TORQUE FACTORS
LUBRICANT OR PLATING -- TORQUE CHANGES
Oil -- Reduce torque 15% to 25%
Dry Film (Teflon or moly based) -- Reduce torque 50%
Dry Wax (Cetyl alcohol) -- Reduce torque 50%
Chrome plating -- No change
Cadmium plating -- Reduce torque 25%
Zinc plating -- Reduce torque 15%

Baseline torque is calculated for a non-lubricated, un-plated bolt.

And a case study showing that lubrication of fasteners, without a suitable recalculation of the torque, led to significant failure in service:

http://www.fera.org.uk/cs5.htm

...and a handy torque calculator:

http://www.futek.com/boltcalc.aspx

[Catigale]

So with moly grease film, I should be torquing to only 50 ftlbs....eeeekksss...that seems awful loose

[kmclemore]

So with moly grease film, I should be torquing to only 50 ftlbs....eeeekksss...that seems awful loose

Well, now, that's with a *new* fastener. With an old fastener that has likely been stretched and no longer has the elasticity it once had, you're guess is as good as mine!

[Catigale]

Worth noting - when I travel I stop on the hour, pull off at next rest stop, and inspect lugs for looseness, tires/wheels for heat, and bearings for ooze...

[Matt19020]

You guys are making me nervous now about my 90 mile drive home from the dealer.... I thought I had my share of problems getting the boat there!!

[Catigale]

My point is, Matt, if you detect a problem before catastrophic failure, at a rest stop, its a lot easier to deal with either professionally with a tow, or having someone come bring you parts, etc.

Sitting on the side of I90 with trucks going by at 70 mph 6 feet away is not fun.

[Phil M]

.. went to throttle up and buzzers start going off “Low Voltage Alarm” and boat drops into safe mode 3000 Rpm max…but runs fine all gauges show good charge rates and battery voltage.
About a minute goes by all quiet now throttle up again and same thing happens…two more times this happened. Shut motor off and restarted…same thing happened. Even tried switching over to battery two.
We were approaching marina to refuel and figured I will look at it when we get in there.
You do not want to be disabled in the canal no where to run it is all channel…and narrow.
They do not service Suzuki motors I called a mechanic and he did not recommend running 60+ miles with motor in the safe mode about 6- 7 hour run.

What does a low voltage alarm have to do with motoring at a slower speed for several hours?

Phil M

[albion]

Try this site www.gizmology.net/nutsbolts.htm it will explain how they work.

[Catigale]

On torque, lube, nuts (not Kevin)

Found this while surfing..source not vetted

http://store.curiousinventor.com/guides ... ng/Screws/



How to achieve the required tightness
According to the Machinery's handbook, tightening by feel is only +-35% accurate, and using a torque wrench only improves the accuracy to about +-25%. These uncertainties are massive, and give good reason not to tighten too close to yield, or too loose, and also to design a joint so that it will still work with a huge span of possible pre-loads. A method called "turn-of-nut" can supposedly get within +-10%, but this relies heavily on a reliable starting point from which to start counting turns (see Machinery's handbook).

If the application is critical (and you are not relying on this guide), ultrasonic sensing of the bolt length or drilling a hole down the middle and attaching strain gages will achieve much higher accuracy. Friends in the navy have told us that workers will sometimes heat a very large bolt during installation to utilize its cooling stretch in achieving proper preload.

To add two more variables, additional torsional loads are present during installation, although these usually dissipate shortly afterwords. It can also be assumed that, due to a variety of factors (surface smoothness, uneven loads, thread deformation), some 10% of preload will be lost.

Why is a torque wrench so imprecise? Friction. Some 80+% of applied torque goes into defeating friction, leaving little for actually stretching the bolt. What's worse is that this friction is highly unpredictable and depends heavily on the materials involved and any lubrication that may be present. Most fasteners have a small amount of oil present from the manufacturer to prevent rust.

From the machinery's handbook, the following equation can be used to approximate the required torque for a given preload:

[Matt19020]

Phil... I am not sure what the "Low Voltage Alarm" message means...I called a the marine mechanic and he told me "it is possible to burn diodes out that were located under the flywheel" and he was not sure motor would run in safe mode without more problems for the next 6-7 hours remaining in our trip...
Just decided to play it safe since we were at a marina and it was getting later in the day.
I still have not heard from the shop...they hope to get to it this week.