51 Merc belt tensions

hoffernsp

hoffernsp

Member
Reinstalling cooling system. Using NAPA belts 257516 and 257417. Unable to completely tighten the gen/water pump belt. Seems sloppy with extra play.
What should the belt deflection be when properly tightened?
 
hoffernsp said:
Reinstalling cooling system. Using NAPA belts 257516 and 257417. Unable to completely tighten the gen/water pump belt. Seems sloppy with extra play.
What should the belt deflection be when properly tightened?
Click to expand...
The generator belt has to be adjusted first, while the fan belt is loose.
Then the fan belt is adjusted.
 
Last edited:
51 MERC-CT said:
The generator belt has to be adjusted first, while the fan belt is loose.
Then the fan belt is adjusted.
Click to expand...

Thanks right now fighting the generator belt. Everything is loose-the fan is at the lowest on the bracket, the gen strap is undone and the gen bracket bolt as well. The question is what is the gen sequence - if I tighten the bracket bolt then it pulls the gen down. If I tighten the strap bolt first it limits moving the gen up to tighten the belt.
The gen/water pump belt is NAPA 257516 52in circum (OEM 8620) and is supposed to fit.
Am I doing something out of sync or is the belt too long?
Any thoughts?
 
Many of the modern belts are not the same exact width as the originals. This can cause them to ride deeper into the groove of the sheaves. The translation between metric and imperial inch fractions can make more than a bit of difference. I used to use Gates or Dayco belts but I haven't had to replace one for a long time so I don't know if any of them fit worth a dang anymore.

I take the generator out to adjust the cradle height. When I think I have it where I want it, I put the generator nose down on the front of the cradle, put the belt over the sheave, then pull the back down into the seat. It's easier for me to do it this way. Others may not do it this way so it's just a suggestion. That cradle is a heavy *******.
 
hoffernsp said:
Thanks right now fighting the generator belt. Everything is loose-the fan is at the lowest on the bracket, the gen strap is undone and the gen bracket bolt as well. The question is what is the gen sequence - if I tighten the bracket bolt then it pulls the gen down. If I tighten the strap bolt first it limits moving the gen up to tighten the belt.
The gen/water pump belt is NAPA 257516 52in circum (OEM 8620) and is supposed to fit.
Am I doing something out of sync or is the belt too long?
Any thoughts?
Click to expand...
The generator strap must be tight and holding the generator in it's cradle before any up/down adjustments using the center mount stud/nut.
 
rotorwrench said:
Many of the modern belts are not the same exact width as the originals. This can cause them to ride deeper into the groove of the sheaves. The translation between metric and imperial inch fractions can make more than a bit of difference. I used to use Gates or Dayco belts but I haven't had to replace one for a long time so I don't know if any of them fit worth a dang anymore.

I take the generator out to adjust the cradle height. When I think I have it where I want it, I put the generator nose down on the front of the cradle, put the belt over the sheave, then pull the back down into the seat. It's easier for me to do it this way. Others may not do it this way so it's just a suggestion. That cradle is a heavy *******.
Click to expand...

You are right it seems like anything bending over above my waist is a heavy *******. Has something to do with age and gravity!! I did take everything off and found out that the gen bracket had never been removed and was stuck. I was trying to adjust the gen tilting the strap yikes. Thanks for the tip on pre adjusting the gen height and going from there Without the fan attached.
Second question, with the gen off and free spinning by hand, should it squeak with hand spinning?
 
The easiest method I have found is to use your engine hoist and a lift strap. Keeps the task from being a back breaker and mostly eliminates breaking or scuffing parts. As others have said, I would stay on the loose side of things to avoid ruining the generator or water pump bearings.

JB
 
The generator may have some brush noise when rotated and especially when rotated in the wrong direction. The bearings should be quiet if they have some lube left.
 
rotorwrench said:
Many of the modern belts are not the same exact width as the originals. This can cause them to ride deeper into the groove of the sheaves. The translation between metric and imperial inch fractions can make more than a bit of difference. I used to use Gates or Dayco belts but I haven't had to replace one for a long time so I don't know if any of them fit worth a dang anymore.

I take the generator out to adjust the cradle height. When I think I have it where I want it, I put the generator nose down on the front of the cradle, put the belt over the sheave, then pull the back down into the seat. It's easier for me to do it this way. Others may not do it this way so it's just a suggestion. That cradle is a heavy *******.
Click to expand...

THANKS it worked after a few up and downs but eventually I got it to set right.
 
Re: 51 Merc belt tensions/deflection

hoffernsp said:
THANKS it worked after a few up and downs but eventually I got it to set right.
Click to expand...

Ok to keep the thread alive what is the best non tool method to determine the correct belt deflection? I used to use the old finger push/ruler method but wonder if that is still the best way to go? Like the old butcher's thumb on the scale to weigh things he hand a huge thumb pressure than most folks.
But really what is the easiest way?
thanks
 
Re: 51 Merc belt tensions/deflection

hoffernsp said:
Ok to keep the thread alive what is the best non tool method to determine the correct belt deflection? I used to use the old finger push/ruler method but wonder if that is still the best way to go? Like the old butcher's thumb on the scale to weigh things he hand a huge thumb pressure than most folks.
But really what is the easiest way?
thanks
Click to expand...
Don't over think it. 1/2" deflection on the longest span of the belt.

This is the procedure from Mercury shop manual.
403218
 

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For those who don't speak "Flathead Ford" fluently, "valve chamber cover" is what most of us call the "intake manifold". It threw me the first couple of times I saw it.
 
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