A tough one ! Agree that they should fit each other and perhaps MB has made it larger due to a problem that revealed itself in the field. However, I will also be a bit worried about pushing that new bush home - perhaps heating the housing to enlarge it ? I will still be worried that it may not be enough and would rather put the bush in a lathe and turn it down to the same OD as the old one.
Edit: sometimes the EPC will show if there has been a change - indicated by "part replaced by........."

 

Yes, I think I'll have to take the bushing down and leave the housing as it is.

The old bushing was a tight fit, and because of the shape of the cast iron piece, it would not fit into the press that I have.

So, I rigged up a puller, and that, after I sheared a bolt tightening it, and a long session with an air hammer, the original bushing eventually came out. It was stubborn, but there was no sign of rust or other corrosion.

Given how tight the original was without corrosion, I just don't see the new one fitting.

Something would have to give.

I'd rather turn it than do the "heat and ice down" drill, which I don't think would work here. Plus, the pulley shaft which is still in the housing rides in sealed bearings with plastic shields, so I could see those melting or warping.

And, I'd burn my hand along in there somehow, probably.

 

Update -
In the interim, I checked with Scott, and he got back to me promptly and said he had not had a problem.
He also sent a photo with the calipers on another new bushing showing 45.14mm, just slightly smaller than what I had.

So, I took it to a reputable Auto Machine Shop in Bozeman and dropped it off.
The Machinist managed to press it in,
As it was, but he said it was tight, and at points of the process he was thinking he might crack the housing.
He had the interference at 10 thousandths, and said the ‘normal’ press fit was 4-6 thousandths.
He applied 5-6 tons of pressure to get it seated, but it is done and I can put it back together.
Next !

 

Truktor, How did you notice your bushing dieing? Was it under tension and running or did you have the belt off?
Chas

 

The truck had been parked and sitting,
And it was obvious that the belt did not have
The correct tension.
A little inspection indicated that the toothed metal cylinder at the center of the bushing had become detached from the rubber part,
and it was shot.
Tightening the bolt on the tension arm had no effect, so in order to be able to drive it the 1000 miles or so to Montana, a temporary rig with a spring wired to the tension arm and connected to the grill worked, tightening the belt up and keeping everything running.
You probably know this, but in the interest of having a complete record -
The tension is set
(when the bushing is intact ) by matching up a Mark on the bushing housing with Mark on the arm, with the belt removed.
You tighten the bolt of the arm that runs through the bushing, and then install the belt.
If the belt does not have the correct (5-10mm) amount of give when installed, you can loosen the bolt, clock the arm around another tooth on the bushing core, and tighten it up.

 

 

Here is the photo from Scott which shows the toothed metal bushing at the core of the item, which is what you set the arm tension against.

 

Thanks Truktor,
Good information. Mine has always been kind of bouncy, belt wise and when it first starts up I can hear a light clatter. Thought it was initially the water pump but that bearing seems good. Sound goes away after a couple on minutes. Was wondering if you had the same intitial sounds. Thanks for the particulars.

Chas

 

I have not experienced the clatter that you have described. A lot of things have been moving into and through Bozeman, I hope the Clatter isn’t one of them.

The bushing runs about $52, and it actually cost more than that to have it pressed in. I was a little surprised about that.

 

There is a revised belt that helps eliminate belt slap

 

Some info, this is for the fan bearing but the same brand of belt might help on the other pully?:

 

I will add that by the repair manual, you set the tension with the marks on the arm and the housing, and then you install a new (or not stretched out) belt, and you should be good at 5-10mm deflection.
If you have too much deflection, a new belt is the correct solution, not cranking the arm
Tension up. It is only a temporary fix until you get a new belt.
And my temporary rig with the wire and the spring was a true hillbilly rig,
Devised by two great brothers near Auburn California, and it worked perfectly.

 

And...the ‘Mark’ on the tension arm is not really a Mark, it is the upper corner of the Arm.

 

I mean, even by UNIMOG standards this contraption is a... contraption.

I think it might be the most complicated, but not quite irrational, way to spin a fan behind the radiator.

Converting to SPAL electric fans cost less than the bushings to fix, mine 15 years ago, and its done.

I like many things factory on my truck, but not this finger chopping mess...

Just MHO.

C.

 

Yes, it is weird.

Now, some years ago, around 2001-ish maybe, a UNIMOG specialist in Germany told me while I was there, that the fan belt system was set up this way so that when fording water deep enough for the fan belt to be partially submerged, it is designed to slip,
Shutting the fan off.

The reason for that is to preserve the fan blades, to keep them from breaking or bending against the resistance of the water.
It also stops the churning of water under the hood as a side benefit.

He would certainly know, given his experience and position, and I certainly would not.

I’ve never spent any time analyzing the mechanics of that, I just took it to be true.
I’m not sure this is the explanation, but this guy would know, and is respected.

The other explanation (which always made more sense to me), was that before fording,
the belt system allows for easily removing the fan belt without tools, so you can take the fan out of the system before you go swimming. Simply by pushing down on the tensioner, the belt can be taken off, and then easily replaced when back on dry land.

It is sorta like the (square cab) doors that hang out in space with no rocker panels,
but with large drain holes, so the water will go directly into the doors, and then drain right back out of them.

It is a system, but why not seal the doors against weatherstripping and enclosed rocker panels like virtually every other vehicle out there ?

The UNIMOG designers presumably tried that approach, since it is more or less universal, and decided to do it the way they did, even though it opens the doors up to road wash off of the tires and rust problems.

The size of the drain holes in the doors increased dramatically sometime in the early 90’s when the new dash was implemented,
so the open rocker system was still be tweaked at that point.

I still don’t understand why fording with doors partially filled with water is desirable.
It’s not like the thing is going to float away if the doors are sealed and full of air.
Or is it ?

 

*Still BEING tweaked.
Today’s typo to start the day off right.

 

So much lost in the mists of time.....
Decent powerful electric fans is a recent phenomena - now they are here, it makes sense to go that way. It is true though, that the mechanical fan moves a LOT of air - a lot more than the 16inch DaviesCraig fan I started off with. My new BMW fan moves about 2-3 times as much as the DaviesCraig. Pulling a fuse is also very easy if you want to do some deep fording.

 

So, pulling a fuse takes less than 5-6 tons of force ?
How enlightened.
Just sounds wrong somehow, unless you can use a hammer to pull the fuse.

 

Ah well, there are alternatives for those who want a more Moglike solution;

 

I’ll check into that.

 

Potential problems with that scale of Hardware.

 

Hi Everyone. I know its not quite related to this post, but I'm having belt problems. I think I want to buy the best, in the hope some issues will go away. My steering pump belt keeps stretching. Existing belt is a Gates notched belt and has only done 200km (as new). I have heavy 220kg wheels, and maybe the existing belt cannot handle the load. I think the best for my steering pump would be, Optibelt Truck Power Marathon 2 (EPDM) Belts AVX 13 x 950, but hard to find (I think there are 2 in Australia?). Any thoughts out there ?

 

Another issue I just noticed, with the belt loose, I can move the pump pulley slightly sideways, i..e a bit of wear in the bearing I'm assuming. No oil leaks. But should it be there?

 

Usually when I have had belts not lasting the way the should the culprit is the pulley, if the pulley is worn out of shape, no matter what you spend for belts they won't last.

 

Belt seems in great nick. Just stretching. I've tightened it again. Will see how I go. Maybe because it was new, needed to stretch a bit.

 

You will get an initial stretch out of the belt, but if it wears funny because it doesent match the pulley it will thin up and ride deeper into the pulley making it run loose.

Hopefully its just a little stretch from a new belt!

 

I would be suspicious of a hidden issue - I use Gates Greenstripe and have never had a stretching issue. Be careful about tightening the belt too much......