What Size/Grade Pivot Bolt for a Tilt Trailer?

[minuteman62-64]

I have a early 1980's Dilly tilt trailer. Light weight, constructed of galvanized channel, carries a load of about 600 lbs. fully loaded (boat, motor, gas, battery, gear, etc.). Today, while re-wiring the lights, doing what I thought was the last step in getting it ready to use, I noticed the pivot bolt that allows it to tilt was badly rusted. It is one bolt, looks to be 9/16 inch, with a locknut. It is too rusted to determine if it is graded.

I want to replace this bolt. I'd like to use stainless, which works out to about Grade 5, but don't want to use something that would be under-strength.

Anybody have a Dilly or similar tilt trailer, pivots on one bolt? If so, can you determine size/grade & other specs. and let me know? Any info appreciated.

 

[smokeonthewater]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

grade 5 gets my vote.... 8 is harder but 5 is less likely to break. honestly tho if it really is that light then any grade 9/16 bolt is PLENTY

 

[robert graham]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

A 9/16" Stainless Bolt with Stainless lock nut should outlast you, the boat, motor and trailer. Ace Hardware probably has what you need. good Luck!

 

[minuteman62-64]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

A 9/16" Stainless Bolt with Stainless lock nut should outlast you, the boat, motor and trailer. Ace Hardware probably has what you need. good Luck!

Actually, the rusty old bolt that is in there now will probably outlast me - just thinking ahead if I pass the boat/trailer on to our sone and grandkids

 

[Mi duckdown]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

It is a pivot point. Once the boat is on the trailer it means little. Unless it it worn to God knows what?

 

[dlngr]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

I suspect a 3/8 bolt here- are you talking about a 9/16 wrench size??.Anyway,that's more than 'just a pivot point,it hold the rear half of the trailer to the tongue! I'd use a grade 8 and not stainless.

 

[minuteman62-64]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

This post has a pictue of exactly what I have: http://forums.iboats.com/showthread.php?t=476841&highlight=tilt+trailer

The bolt in question holds the tounge to the remainder of the trailer, so I don't want to scrimp on it strength-wise.

 

[Dewaynep]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

If you think about it, all that is holding your hitch to the receiver is a 1/2" bolt/pin. Your receiver can tow up to 10,000 pounds through that one little bolt, why not the trailer?

 

[minuteman62-64]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

Good point on the 1/2 inch hitch pin. Looking on-line it appears your run-of-the-mill hitch pin is the equivalent of Grade 5. There are also lots of on-line arguements about use of that run-of-the-mill hitch pin vs. a Grade 8 bolt.

Using some of the on-line sources, I did some simple calculations based on a 1/2 inch bolt acting in double shear (as is the case w/my pivot).

Grade 5 bolt has allowable tensil stress of 120000 psi. Grade 8 bolt has allowable tensil stress of 150000 psi. Shear stress is about 60% of tensil stress. So, shear stress works out:

Grade 5: 72000 psi
Grade 8: 90000 psi

So, applying an ignorance factor of "2", the allowable pull, on a 1/2 inch bolt, in double shear would be:

Grade 5: 14130 lbs.
Grade 8: 17663 lbs.
(however, this does not take into account loads from bouncing around, the stress/wear from the trailer members, etc.).

So, it looks like I'd get about 25% more load capacity using a Grade 8 bolt. Given my 600 lb. boat load and the total package weighing not more than 1200 lbs. or so, the stainless bolt, which works out to be about Grade 5, will probably suffice.

I may go the Grade 8 anyways since it will outlast me w/regards to corrosion.

 

[smokeonthewater]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

grade 8 can break easier than grade 5 under some circumstances..... has to do with hardness.... one bends where the other will break

NOW I'm saying this nicely with a smile on my face....

YOU'RE BEING SILLY.... any dang bolt you put in there will last way longer than it needs too.... You could probably get away with a couple big zip ties.....

Just put a bolt in the hole and quit worrying...

 

[The Famous Grouse]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

The bolt in question holds the tounge to the remainder of the trailer, so I don't want to scrimp on it strength-wise.

WARNING: The point above is correct and that bolt is CRITICAL.

URGENT ADDITIONAL INFORMATION: It is critical that you inspect not just the bolt, but also the holes that the bolt passes through in the tounge and in the body of the trailer.

Over time, these holes can become elongated because the trailer is made of softer steel than the bolt itself. If the holes become elongated, they form a "guillotine" such that under acceleration and breaking, the elongated holes allow slippage that can eventually "slice" the bolt in half.

Therefore, it is critical to inspect not just the bolt, but the holes. Also, you must understand that the bolt hardness is not the most critical factor, it's also the hardness of the tounge and trailer body. If there is any sign the holes are becoming elongated, you must get them repaired immediately.

I have personally had this problem of the holes being elongated such that they actually sheared the bolt off!

It was only luck that it happened as I was backing down a boat ramp to retrieve my boat and thank God no one was behind me. I simply stepped on the breaks because I was starting to roll down the ramp faster than I wanted. That simple action was enough to complete the "guillotine" effect and slice through the little bit that remained in the bolt and the body of the trailer tore free and rolled down the ramp on its own leaving the tounge hitched behind the truck. Obviously, the bolt had been damaged by this "guillotine" effect over time and it just happened to break at that point. I had bought the boat used and it simply never occured to me to inspect this part as I was not aware of how critical it is.

The body of the trailer rolled straight into the water at considerable speed and disappeared underwater. Luckily, it did not veer off course and hurt anyone or damage any boats or property. We were able to retrieve the trailer using a tow chain and then I had to haul it home in the bed of a pickup.

The trailer shop that did the repair did so by welding a pipe inside the tounge channel such that the holes are not the only surface area that are in contact with the bolt. The welding shop owner said this is a common problem with tilt bed trailers and he's done over 100 of them in the past 20 years. He said that I got very lucky, he's seen trailers where the failure happened under heavy breaking and the results were very, very bad.

Don't mean to scare you, but I thought it was important that if you are looking at the bolt, you also understand how to inspect the whole system.

Grouse

 

[smokeonthewater]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

good point.... the bolt DOES need to be a tight fit.....

 

[minuteman62-64]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

I'm not sure the elongation of the hole is the problem as much as it is the symptom. Seems like if the hole is elongated there is a good chance the bolt has groves worn in it - resulting in a significantly weakened bolt.

I agree that as a matter of good construction the bolt and hole should be a reasonably good fit. However, it is a pivot. There has to be enough freedom to let it do its thing.

Take a look at your receiver and hitch pin. My pin is 5/8 inch diameter. The hole(s) into which it is inserted are more than 1/32" bigger diameter. I can feel the slop when towing a trailer and braking and accelrerating. The important thing is that I get to look at the hitch pin every time I use a trailer - so I can determine if there is damage and replace if necessary. In the case of my pivot bolt, you make a good point for pulling it for inspection every year or two (maybe more, depending on useage). This would be particularly important if there were any evidence of elongation of the bolt hole(s).

 

[The Famous Grouse]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

I'm not sure the elongation of the hole is the problem as much as it is the symptom. Seems like if the hole is elongated there is a good chance the bolt has groves worn in it - resulting in a significantly weakened bolt.

I agree that as a matter of good construction the bolt and hole should be a reasonably good fit. However, it is a pivot. There has to be enough freedom to let it do its thing.

Take a look at your receiver and hitch pin. My pin is 5/8 inch diameter. The hole(s) into which it is inserted are more than 1/32" bigger diameter. I can feel the slop when towing a trailer and braking and accelrerating. The important thing is that I get to look at the hitch pin every time I use a trailer - so I can determine if there is damage and replace if necessary. In the case of my pivot bolt, you make a good point for pulling it for inspection every year or two (maybe more, depending on useage). This would be particularly important if there were any evidence of elongation of the bolt hole(s).

Elongation absolutely is the problem. The problem is that even a standard grade bolt is harder than the box steel frame of a trailer. That means that the bolt can first act as a hammer on the trailer's steel to elongate the hole.

Then, the edge of the hole begins acting like a cold chisel on the bolt. As the hole becomes more and more elongated, the increased distance that the trailer frame can slide before it bottoms out on the bolt allows the "chisel" to gain more speed. Essentially, the hammer that's hitting the chisel gets larger as the hole's size increases relative to the bolt size because the "chisel" has that small distance over which it can accelerate before slamming into the bolt.

The comparison to a receiver hitch isn't necessarily a valid one. Look at the thickness of the receiver compared to the thickness of the box frame of a trailer. On most small boat trailers that will have a tilt bed, the steel is much thinner on the trailer. Again, like a cold chisel, that means the edge of the chisel is sharper and cuts the bolt with greater ease. Add additional acceleration as the hole gets larger from the hammering, and there's the potential for a major failure.

I can tell you from experience that you do NOT want this major failure to happen to you. I was very, very lucky that the guy I was fishing with was not hit by the runaway trailer body when it broke lose, nor did the trailer damage anyone else's boat.

I shudder to think of what would have happened if that bolt had broken on the freeway on the way to the lake that day. 65 MPH and a runaway boat with no safety chains or anything to control it. Very, very bad.

As it was, I got away with a $100 welding bill and the wiring harness was torn apart such that it was not repairable. I got rather wet wading in to attach the tow chain to the trailer, which had gained enough speed such that it settled in about 3 feet of water. That, ladies and gents, is what you call getting off easy.

Grouse

 

[bigdee]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

grade 8 can break easier than grade 5 under some circumstances..... has to do with hardness.... one bends where the other will break

NOW I'm saying this nicely with a smile on my face....

YOU'RE BEING SILLY.... any dang bolt you put in there will last way longer than it needs too.... You could probably get away with a couple big zip ties.....

Just put a bolt in the hole and quit worrying...

I agree grade 2 or 5 will work fine. grade 2 is more ductile,cheaper and what I would use. If it makes you feel better drill a hole and move the pin to the center of the tongue.

 

[bonz_d]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

Sorry but I'm haveing a hard time with all this! Just sold a 1960s Gator tilt trailer, 50 years old already, that I'd refinished last year and it being that old showed no signs of the mounting holes elongating. As a matter of fact after 50 years the bolt was still tight in the hole and had to turn it out with a wrench!

I also work every day on machines which are exsposed to greater forces and pressures that these trailers will ever encounter and we still do not use grade 8 fasteners! How many have seen a 1.5" diameter stainless shaft snap in half due to fatigue? I have.

 

[minuteman62-64]

Re: What Size/Grade Pivot Bolt for a Tilt Trailer?

OK, project completed (for now). Pulled the old pivot bolt. It was in tight enough that I had to unscrew it. Bolt and holes in trailer frame bracket and tounge showed no signs of wear. The tounge (the element that pivots) was reinforced where the hole is - bringing the total side-wall thickness to a little over 1/4 inch.

Hit the old bolt with a file - it cut easily - I wonder if it is even a Grade 5. If I get more curious I'll hit it with my grinder and see if the spark pattern reveals anything - then again, maybe not.

Installed a new SS bolt with nylock nut. Clamped it down hard on the bracket so it won't rotate. I'll monitor it and see how it goes. However, since I estimate, at most, 10 - 20 round trips per year to the launch ramp, at about 20 miles round trip, I expect it will outlast me.