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HOW TO: Tension V Belts on a HMMWV 6.2 Engine

Tanabi

Member
44
3
8
Location
Raleigh, NC
Hey everyone;

So I did the 60 amp to 200 amp alternator swap, and I bought the 'real' kit so it came with really good instructions. I didn't have a lot of problems, other than my alternator didn't come with all the pieces it was "supposed" to come with (for example, the alternator is "supposed" to come with the nut that bolts onto the pulley, but mine did not, so I had to find it. Hint: Kascar has it).

Let me apologize in advance for a lack of pictures; I didn't take any while I was doing the job. Next time I do it, I'll try to remember pictures :)

When it came time to tension the belts, I'll be honest; this is the first time I've done it on a vehicle without auto-tensioners. I found absolutely 0 resources online as to how to do it, and the tech manual makes it sound like its an obvious process. It's kind of obvious, but, I've got some tips to make your life a lot better if you have to do this.

What you're doing depends on your setup. If you have a 60 amp alternator, you'll have 4 belts; the inner 2 wrap around the power steering, fan, and the big drive pulley. The outer 2 wrap around those things plus the alternator.

If you have a 200 amp alternator, the inner belt wraps around the power steering, fan, and drive pulley. The outer 3 wrap around everything. I'm not sure about the 100 amp alternator, but basically if your alternator has 3 grooves in it, this is how the routing is done.


First, the tools. You need a tension gauge and a belt jack. I used this tension gauge; it's the same type as the one you see illustrated in the tech manual, and sometimes a similar tool comes in "HMMWV tool kits" on ebay:

OTC 6673 Universal Belt Tension Gauge
https://www.amazon.com/gp/product/B000I198J0

The cool thing about this gauge is you can clamp it on your belt, and then adjust the belt, and see the tension reading in real time. I think if you use one of the cheap 'pen' style readers, you can't do that -- I could be wrong. Personally, I would advise against 'winging it' because if the belts are loose you get all kinds of scary sounds and they flap like crazy even at high RPM (of course, even properly tensioned, they flap a lot at idle).

The next thing you'll want is a belt jack, or pulley spreader. This is a tool that you put between your pulleys, and it'll have some sort of nut you twist to extend the tool. As it extends, it pushes the pulleys apart, and you can read the tension gauge as it does this.

You can either buy one or make one; I bought this one:

https://www.mscdirect.com/product/details/35438209?rItem=35438209

The little 'saddles' that push against they pulley are spot welded on there and 100% will definitely break; I broke mine pretty quickly. However, you can fix them; I took mine to a local mom and pop auto shop and they welded it back together for $15. I had them weld both ends (not just the broken end) and use a lot of extra material to strengthen the tool; after that, it worked fine.

I would recommend, if you buy this tool, just immediately go out and get it welded and reinforced before trying to use it. A lot of places can do it, or if you either own or want to own a welder, this is a pretty easy job.

The only other one I've found available for purchase looks like someone's hand-made kit on ebay. I also bought this one as a 'plan B' in case my welded tool didn't work, but it hasn't even arrived yet so I can't comment on it yet. You can try it if you want:

https://www.ebay.com/itm/173278182483


Finally, you could make your own -- a threaded rod, a couple bolts, and 2 chunks of wood are all you need. This was my 'plan C' if I couldn't get something that exists to work, but I suspect most people wind up going this route.


SO ... how to do it! First, put your belts on of course. Nothing special to it, other than working them on around the fan kind of sucks. Remember to disconnect the power steering cable from the front of the fan; mine was a quick disconnect that was easy to detach, not everyone is so lucky. ALSO: REMEMBER TO PUT IT BACK ON LATER! I forgot and lucked out that the fan didn't hit the loose cable in there.

Start with the power steering pump. This bugger moves in '2 axes', meaning it slides horizontally and vertically. This makes it a 2 handed job unless you're using the pulley jack -- I didn't try the pulley jack with this one because mine hadn't arrived yet. So I had my friend get on top of the engine and be ready to tighten the adjustment bolts, while I laid on a crawler under the car and positioned the pump.

Putting a breaker bar or a 1/2" wrench into the little square on the passenger side of the pump, I used that to adjust the horizontal while I just pushed on the bracket with my other hand to adjust the vertical. I put the tension gauge on the belt under the car so I could see it easily.... and then I pushed til the needle went into the black (around 100 lbs of tension is what you're going for), then had my friend bolt it down.

It does take a bit of strength, and pain tolerance if your friend drops the socket on you :) But it's reasonably doable.

Torque up the bolts according to the TM spec -- 40 lb-ft for each bolt. On my bracket, the bolt that goes into the 'back' of the power steering bracket had bad threads :( I went the lazy route and found a self-tapping bolt that would fit (that was REALLY hard to find ...) but I need to go back and replace that whole bracket next time I do this.

If you happen to need this same self tapping bolt, it's here: https://www.zieglerbolt.com/12-13-x...screws-zincunslotted-hwh-type-f-screws-zinc-2

You are better off tapping it properly or replacing the bracket, but you gotta do what you've gotta do.


ON TO THE ALTERNATOR...

I've never tensioned the 60 amp but I imagine the process is similar. Relocate your tension gauge to the belt closest the fan (on top of the engine of course), and face it towards the windshield because you will find the gauge will want to flop over towards the fan in the beginning of this process.

The alternator only moves in one direction, so in that it's easier. However, no amount of pulling or muscle could get the gauge to go more than halfway to the black mark when my friend and I tried this with the breaker bar. Enter the belt tension tool!

Grab yourself an adjustable wrench with a short handle who's 'jaws' will fit around the part of the tool that twists. You're going to have to do this in two stages; the tool has an "extension piece" that you will need to get full tension, but that "extension piece" won't allow the tool to fit between the pulleys at first.

So, we're going to tension the pulleys as much as you can without the extension, bolt the alternator down, put the extension on the jack, then finish the job.

I recommend placing the tool on the *innermost* grooves of the alternator and fan pulleys, and assuming you're standing on the driver's side wheel, you'll want the twisty part of the tool to be on 'your' end. Turning the twisty part clockwise ('towards the windshield') will extend it ... do that by hand til the tool is positioned well between the pulleys, then use your wrench to twist it the rest of the way.

It's a 19mm wrench head that fits on this tool, but my 19mm wrench was way too long to actually turn the tool in the engine compartment; so the adjustable wrench with a short handle was a life saver here.

Once the tool is fully extended, bolt down the alternator -- just one bolt will be fine, the one on the adjustment bracket. Get it down TIGHT because the alternator won't want to stay, but don't torque it yet.

Retract the tool fully, put the extension piece on, and you'll find it fits nice between the pulleys with only a little bit of turning. Tighten the tool between the pulleys, then unbolt the alternator so it rests on the tool, and finish tensioning it the rest of the way to about 100 lbs.

Now, the 60 amp specs are 40 ft-lbs for the bracket and top bolt, and 60 ft-lbs for the bottom bolt. For the 200 amp, I couldn't find specs, but 40/40/60 was too loose and wouldn't hold the tension. I torque'd mine to about 60 ft-lbs all around and that seemed to work. Once it's torqued, retract the tool, remove the gauge, RECONNECT YOUR POWER STEERING LINE TO THE FAN, and you're done!


Hope this helps someone else :)
 

tage

Active member
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Location
LOS ANGELES / CALIFORNIA
You use a half inch breaker bar and have a friend tighten the bolt.
Belts get more tension with heat. Trick is tighten them enough that they don't squeal...
 

Dock Rocker

Active member
980
71
28
Location
Jackson ms
You use a half inch breaker bar and have a friend tighten the bolt.
Belts get more tension with heat. Trick is tighten them enough that they don't squeal...
I read all the info the OP wrote and thought “Oh crap, I have never done any of that!” I don’t remember it being that complicated.

I do remember doing exactly what you wrote though. That made me feel much better.

I am getting a little belt squeal at high speed when the fan engages. I need to give my belts a little love soon.


Sent from my iPhone using Tapatalk
 

Tanabi

Member
44
3
8
Location
Raleigh, NC
I read all the info the OP wrote and thought “Oh crap, I have never done any of that!” I don’t remember it being that complicated.

I do remember doing exactly what you wrote though. That made me feel much better.

I am getting a little belt squeal at high speed when the fan engages. I need to give my belts a little love soon.


Sent from my iPhone using Tapatalk
It could be I'm dumb (I'm fully ready to accept this possibility! :D), but we couldn't get either the power steering pump nor the alternator to budge with just the breaker bar. With the power steering pump, because it moves in 2 directions (at least it does with the 200 amp alternator bracket), it really needed the breaker bar + another hand to move it. With the alternator, it was easy to get the breaker bar on it, but it only moved if you *pulled* the bar (as opposed to try to rotate the bar) and we just didn't have the muscle to get it tight enough.

Maybe you guys are just a lot stronger than me and my friend, or maybe we were doing it wrong somehow. Though with the tensioner tool, you can do the whole job by yourself and make it pretty easy TBH.
 

1993

Member
173
1
16
Location
NY
All of my belts are new and I've tightened them enough so as not to squeal. However,
the two outer ones(alternator) continue to have some serious slop on the top(longest) span.
By slop I mean they flex up and down when engine is running so that there is about 2.5" of difference between the highest and lowest extent of flex. Occasionally I will hear a noise like they're slapping something(probably each other), but definitely no squeaking.
My main concern is about causing too much tension and wearing out pulley bearings prematurely.
If using "slop" instead of gauge reading, approximately how much slop(warm or cold) is normal?
 

Tanabi

Member
44
3
8
Location
Raleigh, NC
All of my belts are new and I've tightened them enough so as not to squeal. However,
the two outer ones(alternator) continue to have some serious slop on the top(longest) span.
By slop I mean they flex up and down when engine is running so that there is about 2.5" of difference between the highest and lowest extent of flex. Occasionally I will hear a noise like they're slapping something(probably each other), but definitely no squeaking.
My main concern is about causing too much tension and wearing out pulley bearings prematurely.
If using "slop" instead of gauge reading, approximately how much slop(warm or cold) is normal?
That sounds like an awful lot to me, but hopefully someone more knowledgeable will chime in :) The belts do flap around a lot at idle -- they should 'look normal' you push on the gas or pull on your throttle lock and if they don't they are probably too loose.

I will say this -- the army specs have them pretty tight. You can try the "twist test" on your belts; if you can take a section of belt and you can twist it a full 90 degrees its probably too loose. On my belts, I can maybe twist it maybe 45-ish degrees, maybe less.
 

Retiredwarhorses

Well-known member
Steel Soldiers Supporter
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113
Location
Brentwood, Calif
All of my belts are new and I've tightened them enough so as not to squeal. However,
the two outer ones(alternator) continue to have some serious slop on the top(longest) span.
By slop I mean they flex up and down when engine is running so that there is about 2.5" of difference between the highest and lowest extent of flex. Occasionally I will hear a noise like they're slapping something(probably each other), but definitely no squeaking.
My main concern is about causing too much tension and wearing out pulley bearings prematurely.
If using "slop" instead of gauge reading, approximately how much slop(warm or cold) is normal?

completely normal....
 

1993

Member
173
1
16
Location
NY
completely normal....
finally decided to remove some of the slop out of the belts since I could occasionally(mostly when glow plugs were cycling) hear them slapping against each other.
So, today I added some tension using the alternator adjustment bracket.
still a little slop.
BUT,
upon starting the truck I heard an occasional creaking sound coming from the belt area. wasn't able to figure out what from because it was not frequent enough and then it seemed to go away.
gonna drive it around a bit later and see if it comes back.
any thoughts of what it might be?
the sound was more momentary with long silences in between, unlike the sound of belts chirpping.
 
Last edited:

Mquirin

Member
40
0
6
Location
Houston, Tx
I just picked up a m1123. The serpentine belt was off of it when it arrived, so I just went to put a new belt on. I had the quick disconnect on the fan clutch, so quickly got the belt inserted and routed correctly. Now, it's time to get it over the final pull, but I can't locate a place for a breaker bar anywhere. The TM talks about the tensioner, but I can't find a place to insert a breaker bar. Does anyone have pics? On my m998, I remember loosening a bolt on the alternator, but im not even seeing that as an option on this larger alternator.
 

Retiredwarhorses

Well-known member
Steel Soldiers Supporter
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Brentwood, Calif
You use a long 3/8 ratchet or 3/8 breaker bar, the tension has a spot on the face.
you also dont need to undo the fan clutch hose on a serpentine truck to install a new belt.
 

Tanabi

Member
44
3
8
Location
Raleigh, NC
I just picked up a m1123. The serpentine belt was off of it when it arrived, so I just went to put a new belt on. I had the quick disconnect on the fan clutch, so quickly got the belt inserted and routed correctly. Now, it's time to get it over the final pull, but I can't locate a place for a breaker bar anywhere. The TM talks about the tensioner, but I can't find a place to insert a breaker bar. Does anyone have pics? On my m998, I remember loosening a bolt on the alternator, but im not even seeing that as an option on this larger alternator.
If you have the 200 amp alternator (huge black cylender with a little silvery box riding on it that looks like a car power inverter) then the place where you put the breaker bar is a little square hole in the alternator mount arm as I recall. You don't need a socket, you just put the breaker's socket attachment square in that hole. Then you loosen the alternator bolt and tension it. I don't remember if its the same for other alternators and my truck is in the shop getting a 3 speed to 4 speed transmission upgrade so I can't take pictures for you.

Alternatively the power steering pump also has a similar detent.

That all said ... serpentine belt truck I thought had a tensioner which is kind of like an idler pully on a spring so you don't have to do the breaker bar thing? I could be mistaken though. My current truck is a v-belt truck.
 

Mquirin

Member
40
0
6
Location
Houston, Tx
You use a long 3/8 ratchet or 3/8 breaker bar, the tension has a spot on the face.
you also dont need to undo the fan clutch hose on a serpentine truck to install a new belt.
Thank you. Yes, I figured that out about the belt.

I found it. Slot was in spring tensioner. Simple 1 man job. Shouldn't take more than 10 minutes on this setup. Thank you all for the help!
 
Last edited:

Tanabi

Member
44
3
8
Location
Raleigh, NC
Thank you. Yes, I figured that out about the belt.

I still can't find a slot for the breaker bar, like on my m998. I'll attach a picture if someone is able to point it out.
Your alternator mount is different from mine so what I know probably won't help you, but in case it does ... on my alternator, there's like a 'saddle' that the alternator sits on and then there's a bracket that connects to the top left if you're looking at the alterantor head on. On my truck, it connects to the bolt that is in the roughly 10:30 o'clock position of your alternator (i.e. the attachment point immediately to the left of the voltage control box).

My truck, the bracket looks like this and you can obviously see where the breaker bar goes in that little square hole in the middle. https://www.worthpoint.com/worthopedia/humvee-m998-military-dual-voltage-1815612436

I'd look real carefully both front and back of that top attachment arm and see if you've got something in there you can plug your breaker bar into. Sorry I'm not more help!
 

Mquirin

Member
40
0
6
Location
Houston, Tx
Your alternator mount is different from mine so what I know probably won't help you, but in case it does ... on my alternator, there's like a 'saddle' that the alternator sits on and then there's a bracket that connects to the top left if you're looking at the alterantor head on. On my truck, it connects to the bolt that is in the roughly 10:30 o'clock position of your alternator (i.e. the attachment point immediately to the left of the voltage control box).

My truck, the bracket looks like this and you can obviously see where the breaker bar goes in that little square hole in the middle. https://www.worthpoint.com/worthopedia/humvee-m998-military-dual-voltage-1815612436

I'd look real carefully both front and back of that top attachment arm and see if you've got something in there you can plug your breaker bar into. Sorry I'm not more help!
Thank you. Mine had the slot in the spring tensioner instead of the alternator where I had been looking. Simple 1 man job. Thank you so much for your help.
 
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