Thread: High-tensile bolts for winch mount

As you are talking imperial you will not find 8.8 grade bolts as that is a metric measure of tensile strength.

What are the markings on the heads of the bolts you already have? I would venture that being 3/8 UNC bolts they would be SAE grade 5 at the very best. With a UNF you get a much greater thread contact areas for greater strength at that point. If the mounting instructions don't come with torque values then again they haven't considered it to be that important to put high tensile bolts in there where they are being worked hard.

Just be sure to ensure that they are zinc coated, use washers and have at least three threads visible after the nuts are done up. For greater corrosion protection, paint over the bolts when they are done up.

Originally Posted by POD

I'm planning on mounting a warn 8,000lb low-mount winch that I have had sitting around for a while. The existing bolts are not quite long enough for the new application, i.e. the base plate is thicker so need longer bolts. The existing bolts are 3/8 UNC and there are original square nuts in that size with the winch, so i need to get 4 suitable 3/8 UNC x 1 1/2" bolts. Are 8.8 grade high-tensile bolts high enough strength for this?

check this site

American Fastener - ASTM, SAE, and ISO Grade Markings

I don't see as how the bolts will be under any tension at all ?

Doesn't the winch bolt behind the bar (winch mount) using bolts through the fairlead into the winch .

When you are winching you will be trying to pull the winch through the winch bar, or have I missed something ??


Martyn

Martyn, some bars have the holes vertically oriented, which means good winches like the Warn Hi Mount just won't work on them. The Rovacraft bars are like this. And hence why I now have an ARB style bar

Originally Posted by Bushie

I don't see as how the bolts will be under any tension at all ?

Doesn't the winch bolt behind the bar (winch mount) using bolts through the fairlead into the winch .

When you are winching you will be trying to pull the winch through the winch bar, or have I missed something ??


Martyn

The bar that the winch has been mounted in for several years (and has seen some heavy winching) has the holes mounted in the horizontal section, so that the winch sits on a flat base rather than being bolted behind the fairlead. The new bar that I'm fabricating for the rear of the 130 has the same arrangement. Most of the load on the bolts in this setup is shear, as the winch pull is at right-angles to the bolts and a couple of inches above them, depending on how much cable is on the drum.

I emailed Warn's tech department and got a very helpful reply overnight; they use grade 5 bolts as these will give a little stretch before breaking compared to grade 8. They are 3/8 16tpi.

I'll check the markings on the old bolts against the chart that slug-burner has linked.

See bolt orientation in this clip:

[ame=http://www.youtube.com/watch?v=d0LHtChhXK0]Jeep Winches Winner: Installing a WARN PowerPlant Winch - YouTube[/ame]

Originally Posted by POD

The bar that the winch has been mounted in for several years (and has seen some heavy winching) has the holes mounted in the horizontal section, so that the winch sits on a flat base rather than being bolted behind the fairlead. The new bar that I'm fabricating for the rear of the 130 has the same arrangement. Most of the load on the bolts in this setup is shear, as the winch pull is at right-angles to the bolts and a couple of inches above them, depending on how much cable is on the drum.

I emailed Warn's tech department and got a very helpful reply overnight; they use grade 5 bolts as these will give a little stretch before breaking compared to grade 8. They are 3/8 16tpi.

I'll check the markings on the old bolts against the chart that slug-burner has linked.

For your reference Grade 5 is approximately equivalent to Property Class 8.8 and Grade 8 is approximately equivalent to Property Class 10.9

Originally Posted by Bush65

For your reference Grade 5 is approximately equivalent to Property Class 8.8 and Grade 8 is approximately equivalent to Property Class 10.9

I suspect the guy in the bearing supply who sold me the bolts last week mistakenly told me they were '8.8' meaning they were grade 8. Or maybe he said 'grade 8' and I heard '8.8'. I was unaware of the different metric & imperial classifications. Will check the markings. Grade 5 seem a little harder to find, a bearing supply near work only has grade 8.