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Author Topic: Building a hitch on MCI 7  (Read 4511 times)
dvrasor
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« Reply #15 on: May 31, 2009, 07:48:59 PM »


 If the hitch is going to be seeing
 any tongue weight there is not
 enough torsional strength in that
 design.

   Dave Rasor
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« Reply #16 on: May 31, 2009, 08:03:36 PM »

I have some repair to do to the engine frame, but I need some assistance in welding the stainless steel.  I see one diagonal and 1 upright that it attached to are busted out.  I also need to search for cracks.   Gumpy, you are right that I plan to grind the top center weld at the reciever and plate over it and plate over the bottom of the receiver and use that plate for chain mounts.  


I do plan to haul a 17 ft enclosed trailer with 2 harleys (about 4k total weight) or my flatbed car hauler with car (about 5-6K total weight).

Dave,
Where on the hitch do you see the problem?  Or do you think the problem is in the mounting point?  I'd like some more specifics please. 

Guys, I really appreciate the help.  

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
bobofthenorth
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« Reply #17 on: May 31, 2009, 08:51:11 PM »

This is crude so excuse the lack of drawing skills and remember that I'm no engineer.  But I've built a lot of hitches and a lot of things a LOT bigger than this hitch. 



The black arrow shows what happens to your hitch when you put weight on the receiver.  The effect of the load is to try to torque the two pieces of 2 x 4 tubing which meet at the receiver.  You need to resist that loading.  The easiest way to do that is to apply some reinforcement where the red arrow is.  If you put some form of bracing running forward so that the torque on the receiver is resisted it will greatly increase the strength of your hitch.  Alternately you need to deal with the torsional stress in the tube and I don't have any real world experience with that but I do know that 188 wall tubing isn't strong enough torsionally for what you are doing with it.  The issue is absolutely NOT about how well it is attached to the cradle.  A properly designed hitch can easily be held on with 6 x Grade 5 x 5/8" bolts.
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R.J.(Bob) Evans
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kyle4501
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« Reply #18 on: May 31, 2009, 09:04:49 PM »

What Bob is suggesting will make a better hitch & will likely reduce the stress on the attachment points to the frame.
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« Reply #19 on: June 01, 2009, 05:46:54 AM »

Bob,
I see the issue with that design as you have illustrated.  I don't know how to do those drawings, but I can tell you some differences between your drawing and what I have built.  The support plate comes all the way down to the bottom of the 2x4 which should add strength opposite to the leverage of the hitch and tongue.  Also, the receiver will be inserted into the 2x4 to the point where the bottom of it will be flush with the bottom of the 2x4 which also reduces the leverage applied by the trailer.  The point of greatest twist should be directly against the 3/8 steel plates at the bottom and the greatest point of pull should be the weld at the top of the 2x4 where it meets the plates.

I did find the brackets on the frame that Craig used to help out with this rotational problem on his father-in-law's hitch and I could duplicate that as well.  If I should do that, I'd plan to recess those bars into the 2x4 as well.

I didn't see anyone's take on the idea of attaching angle  stock to the 2x4 and attaching it to the frame like in Richard's picture and I think that might do the job to reduce the torsional stress.

Please don't think that I don't want to hear criticisms, I just want them to be well spelled out so that we ALL understand and learn.  That's what this place is for!  Smiley  I'm looking forward to responses!

Glenn

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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
cody
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« Reply #20 on: June 01, 2009, 06:04:58 AM »

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« Last Edit: June 07, 2009, 06:50:44 PM by cody » Logged
gumpy
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« Reply #21 on: June 01, 2009, 07:10:47 AM »

I understand what Bob is saying regarding the rotational forces on the receiver. Those forces will be there when pulling a trailer, and the longer the hitch bar, the more rotational force there
will be, but for the loads that he's planning to carry and the way it's attached to the bus, what he has is fine.  With the plates extending to the bottom of the cross tube, and welded both top and bottom, and with the overlapping framing under the triangle mounting members, there's little chance these forces will be high enough to cause bending or twisting of the plates or cross tube. That tube is only about 4 feet long and 40% of it is attached to the mounting plates.

On the hitch we built for my friend in AK, we added tubing from the receiver angled forward to the small frame brackets, which will aid in prevention of the rotational forces. Glenn should probably consider doing something similar on his.

I like the large brackets on the forward end of the hitch in the photo Cody posted. They would provide better support than the little brackets we used on my friend's bus. I don't know what those bolt to, though. You'd probably have to add some brackets to the engine. I don't like the rearward brackets, though. Bolting upward doesn't work well on these buses.


« Last Edit: June 01, 2009, 07:15:02 AM by gumpy » Logged

Craig Shepard
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kyle4501
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« Reply #22 on: June 01, 2009, 09:19:53 AM »

On a side note concerning hitch loads, many think that flat towing a car poses little to no vertical load to the hitch. That may true for a properly installed tow bar setup with properly working toad brakes. . . . . BUT, after reading the RV discussion boards & from what I've seen on the road, there are way too many towing with out the proper setup.

The problem with a tow bar comes from it not being parallel to the ground. When the back of the RV lifts during hard braking, the bar is angled upwards & this geometry applies a vertical load to the hitch. If the toad doesn't have proper braking assistance, the vertical load becomes larger since the toad is pushing. Due to momentum & geometry, this vertical load can exceed the weight of the car.

The way the loads are carried by the hitch & frame can be quite involved with a poorly designed hitch. The better hitch design will simplify these loads, but everything is a compromise.
That is why I endorse spreading the mount points towards the front of the bus. They minimize the torque applied to the hitch attachment points.

I don't have much 3/8" plate in the frame of my bus, so now the hitch itself may be strong enough but what about what it's bolted to? The frame was designed to carry the motor (engine) with a certain amount of safety factor, How much of this will be used in the hitch?
This is why one needs to understand how the bus frame is already loaded & make the hitch in such a way that takes all of the loads into account.
This will be simple for some, but impossible for others. Just as some can do excellent in electrical wiring, others in upholstery, others still in engine repair. . . .

Not saying it can't be done. But I am saying one needs to be aware of the 'complications' involved in order to improve their chances of success.


(first edit)
« Last Edit: June 01, 2009, 11:31:56 AM by kyle4501 » Logged

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poppi
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« Reply #23 on: June 01, 2009, 09:46:25 AM »


 Just a FWIW.........

   I was always taught on but welds the metal should be V grooved before welding.
   My own personal preference would have been to go with a larger rod.


   Good luck

Skip
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mikelutestanski
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« Reply #24 on: June 01, 2009, 11:00:54 AM »

Hello:   my first hitch on my 72 7 was like that and it failed after 200 miles pulling a saturn. THe area just above the welds will bend and the box will cantilever down.  I ended up putting a piece of 3/8 angle about 8 inches long on the interior of both sides and welding it to the side rails to get home.  I have redesigned that hitch and their are some pix somewhere here showing that one.    You also need a bar back about 10 or 12 inches back from the front and a piece of channel running foward under the receiver. THat piece will keep the load from pulling the hitch down. Suprising the up and down forces on a hitch while pulling a car.
    Sorry about the bad news but   ...
      Regards and happy busssin   mike
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Mike Lutestanski   Dunnellon Florida
  1972 MCI 7
  L10 Cummins  B400R  4.625R
cody
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« Reply #25 on: June 01, 2009, 11:16:31 AM »

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« Reply #26 on: June 01, 2009, 01:53:01 PM »

That's a heck of a hitch!  I can only say "it's not for an unmodified MCI 7".  There are no downward facing mounting points at the bumper end of the bus.  I think I've seen some bolts going that way on hitches for MCI 9's. 

Glenn
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Glenn Williams
Lansing, MI
www.threemenandatenor.com
1968 MCI 7 Ser. No. 7476 Unit No. 10056
8v71
4 speed Spicer
JackConrad
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« Reply #27 on: June 01, 2009, 02:31:04 PM »

Here are a couple photos of the hitch I made for our bus.  Jack
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gumpy
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« Reply #28 on: June 01, 2009, 04:26:09 PM »

I contend there is no difference between Jack's hitch and Glenn's hitch, regarding rotational forces, and actually, Glenn's design will handle more load than Jack's, simply because of the locations where they are attached. I also know that Jack typically only tows 4 down.


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Craig Shepard
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http://bus.gumpydog.com - "Some Assembly Required"
bobofthenorth
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« Reply #29 on: June 01, 2009, 08:44:49 PM »

I agree with you Craig.  Jack's hitch is depending on the torsional strength of the rear member as is Glenn's.  However, on Jack's hitch, if there was some physical connection between the end of the receiver tube and the bar on the other end of the hitch then it would be what I consider a "good" design.

And Glenn, its your bus, your hitch.  IMO you have a bad design that could be alleviated but never corrected by using heavier metal.  It may never cause a problem but my advice would be to paint it with a high gloss enamel so that the cracks will be easier to spot when they (inevitably) appear.
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R.J.(Bob) Evans
1981 Prevost 8-92, 10 spd
My website
Our weblog
Simply growing older is not the same as living.
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