New fan belt on 8N 12 volt snapped within 5 minutes

Just moved to a new property and it came with an 8N in good shape. Don t know the model year but it has the 12 volt conversion with side mount alternator. Took it for a spin and noticed that fan belt was torn up and hanging on by a thread.

Took the old belt into auto store and they matched the numbers on it to a "15417AP" measuring 3/8 by 42 1/4"

Got the new belt on and headed for another spin. It snapped within 5 minutes. Was able to get the tractor back before it got to hot but now wondering what went wrong.

A few things worth mentioning...did a lot of research on the forum regarding the correct fan belt size/length. Seems as though a 5/8 by 41-46" are used depending on model and alternator/generator set up. At 42 1/4 I could barely get the belt on and alternator was snug up to engine in order to get it to fit. The belt had some play once attached and seemed snug. 1/2 inch is recommended and I didn t measure but I would say it had no more that 1/2 inch play max.

Here are my thoughts/questions and I appreciate any incite from y all...

Not sure what size I need for my setup. I matched what previous owner had on there but maybe it was to tight/small to begin with? It was also a 3/8 belt and everyone recommends a 5/8? What belt size would be best with my set up? 12 volt 8N with side mount alternator.

Grease/W-D 40 on pulleys once I get a going? What do you think? Just a smidge?

Im paranoid the crankshaft pulley was not turning now. I just remember not being able to get it to spin during install. Alternator and fan pulley turned freely but I kinda overlooked if crank shaft was turning. Would it even turn with engine off?

Thanks folks.

5/8 should be the correct width, a 3/8 belt will go on and tighten up but it will bottom out on the pulleys and constantly slip. A slipping belt will get hot and eventually break. Make sure the alternator pulley is 5/8, or same width as w/p and crank. Also make sure the water pump/fan spin good too.

Gates # TR22425, 5/8" x 42.5"

The 22425 should cross to other brands if not the same part #

As 4play mentioned alternator pulley needs to be 5/8 to match the other pulleys. If it has a 3/8 pulley that may be why the previous owner was running a 3/8 belt.

When the belt is installed, sight down the runs between the other pulleys. It should be straight and the alternator pulley must be in the straight line as well. If it appears cocked out of line it needs to be straightened, by adjusting the alternator mounting.

Your crankshaft pulley drives the belt, it should not turn when installing a belt (at least not without a good bit of force as the engine has to turn over for it to turn).

Do not put oil, grease, WD40, etc. on the pulley surfaces. They should be clean and dry for best belt life.

Welcome to the forum! The belt width should be 5/8 as stated.
The alternator pulley needs to be that width too. The length of
the belt depends on which style of distributor you have. Which
side of the tractor is your alternator on when sitting on the tractor?

Even the wrong belt should last quite awhile sounds like you have more issues than a belt are incorrect pulley...

98-NAA5825 pulley would be the correct alternator pulley

https://forums.yesterdaystractors.com/viewtopic.php?t=1326598&highlight=pulley


Correct Alt pulley pix


https://forums.yesterdaystractors.com/viewtopic.php?t=1368023&highlight=pulley

You stated the tractor has been converted to 12 volts and has an alternator. These tractors did not come from the factory with alternators; that means you can not search factory literature nor can a parts store determine the length of belt needed. The fan and crankshaft pulleys were made to work with a 5/8" wide belt, there are special (5/8" wide) pulleys made to fit alternators for use in these conversions - check this site....? You will need to determine the belt length that can be tightened for your alternator mounting position. Also, check the alignment - all pulleys must be in the same plane (alignment). Good luck - you might make note of the belt required so the next person that gets the tractor does not experience the same problem you are having.

(quoted from post at 05:59:59 07/21/19)Which
side of the tractor is your alternator on when sitting on the tractor?

Click to expand...

Alternator sits on right side.

My 48 8N broke a couple of belts and ran hot a few times because of belt slippage. I finally figured out the alternator pulley was a "combination 5/8 - 3/4 inch". The 5/8 belt rode too low in the pulley and would snap eventually. So I finally got a 5/8 pulley, and the best belt for my money is the Gates Tri-Power BX-42, which is 21/32 inch wide and 45 inches long. Cogged belts work much better with small diameter pulleys. The belt sits slightly proud of the pulley OD, just like it does on the water pump pulley. This setup has worked great for me - no more broken belts and no more overheating.
<img src="https://www.yesterdaystractors.com/cvphotos/cvphoto30372.jpg">

Great info everyone you have my many thanks. I didn t mention at the beginning that I went with a 5/8 41.5" generic belt. Wouldn t fit not even close. Then I brought in the remains of the old shredded belt and they were able to match the number.

SlimB has got my ear. Maybe there is an odd pulley in the alternator complicating matters.

I think I m gonna go with the Gates Tri-Power BX-42. As I had mentioned previous in order to get the 42.25" on the loosened alternator had to be hugging the chasis. Absolutely no wiggle room at that length. Maybe my conversion requires a longer belt?

(quoted from post at 11:49:29 07/21/19)

I think I m gonna go with the Gates Tri-Power BX-42. As I had mentioned previous in order to get the 42.25" on the loosened alternator had to be hugging the chasis. Absolutely no wiggle room at that length. Maybe my conversion requires a longer belt?

Click to expand...

after my 12 volt conversion, the alternator was touching the manifold, and i had to pull the bolts so i could angle the alternator to get the belt on or off. i switched to a belt an inch longer. iirc, i still have to pull the bolts - but i now have a gap between the alternator and the manifold. u might consider a two inch longer belt, but don't go for three inches. don't ask me how i know

(quoted from post at 09:55:51 07/21/19)

(quoted from post at 05:59:59 07/21/19)Which
side of the tractor is your alternator on when sitting on the tractor?

Click to expand...

Alternator sits on right side.

Click to expand...

So that would be a front mount distributor engine. It takes a longer
belt than a side mount but the actual length could vary based on
your mounting brackets. With the YT mounting kit, they say it is
44 1/8 inch. [b:13a01afb33]Link to the belt[/b:13a01afb33]

(quoted from post at 05:59:59 07/21/19)
So that would be a front mount distributor engine. It takes a longer
belt than a side mount but the actual length could vary based on
your mounting brackets. With the YT mounting kit, they say it is
44 1/8 inch. [b:aae575d83e]Link to the belt[/b:aae575d83e]

Click to expand...

Front mount, side mount, was trying to figure out what was what and thank you Royse for clearing it up for me! Changing my plan and going for the 44 1/8

B belts will screw with your head...

http://www.seekbelts.com/beltsizes/bsectionvbelts.html

B Section V-Belts are measured on the inside diameter.

Exp: B100 has a 103 inch outside length.

What I do is measure the outside and deduct 2" if it measured 45" get a B43 belt...

(quoted from post at 12:04:08 07/21/19)

(quoted from post at 05:59:59 07/21/19)
So that would be a front mount distributor engine. It takes a longer
belt than a side mount but the actual length could vary based on
your mounting brackets. With the YT mounting kit, they say it is
44 1/8 inch. [b:917a0a135f]Link to the belt[/b:917a0a135f]

Click to expand...

Front mount, side mount, was trying to figure out what was what and thank you Royse for clearing it up for me! Changing my plan and going for the 44 1/8

Click to expand...

Side mount distributors look like a car distributor with a round can
coil, also like a car would have. They are on the right side, so the
generator/alternator is on the left side. 1950 1/2 through 1952.

As Royce said no lube on belts. 1/2 inch deflection between pulleys measured in the center. If there was no smoke or squealing noise, it may just have been a defective belt which is not common. Belts need to "lock into" pulleys to prevent slippage. This is accomplished by having different angles between the belt and the pulley. I like my belts in the middle of the swing slot when properly tensioned.