Thrown fan belt

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Model T Ford Forum: Forum 2012: Thrown fan belt
Top of pagePrevious messageNext messageBottom of page Link to this message  By Don Lyon, PDX, OR. on Tuesday, July 17, 2012 - 12:48 am:

Why does my fanbelt keep coming off? The pulleys are lined up, the tension is as best as I can get it--fan turns with medium finger pressure--book says 5lbs pressure. I do know that the oil (140wt) is leaking out of the top pulley. Is the belt coming off because of oil on the bottom? I'm using a rubber belt, I have a leather one available. Any help is appreciated, Don, Portland, OR.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Anderson, central Wisconsin on Tuesday, July 17, 2012 - 01:04 am:

Is the crankshaft pulley tight and crowned?
Is the fan blade pulley flanged to hold the belt?
Leather is definitely not the answer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Tuesday, July 17, 2012 - 01:17 am:

Unless you do parades or run a waterpump, you don't need no steenking belt.

Removed my fan years ago.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Tuesday, July 17, 2012 - 01:22 am:

Don; Alignment is necessary. The crankshaft and fan shaft must be parallel The center of the fan pulley and the crank pulley must be in alignment and both pulleys must be crowned. If the pulleys run true and the belt is not deformed, there is no need for flanges on either of the pulleys.

Sincerely

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Richard Bennett on Tuesday, July 17, 2012 - 01:26 am:

Don, when you say the pulleys are lined up do you mean they are not one ahead of the other? To prevent the belt coming off, the top pulley needs to be running on a parallel axis to the crankshaft pulley. As the bottom pulley is fixed to the crankshaft, any adjustment has to be made at the top pulley. If your belt runs off to the front, it is likely that the fan arm is bent down a little at the front, and the belt tracks to the front.

If it goes off to the rear, the arm needs to be bent down a little. Bending the arm brings the fan shaft back into parallel with the crank.

Once the shafts are in parallel, the top pulley can be lined up by spacing the fan arm with washers if necessary.

A leather belt can work but these days the quality and consistency are dubious and hence they are not that reliable. To overcome un-equal stretch, some are stitched on each side, but this is a cure for a poor product in the first place. It would seem that tanning leather and producing quality harnessware are dying trades.

Hope this helps.

Allan from down under.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Tuesday, July 17, 2012 - 06:40 am:

Try leaving the belt looser. The main reason the belt comes off is from being too tight.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Doolittle on Tuesday, July 17, 2012 - 06:51 am:

If you are having to manually hold the spark lever down, then it is highly possible that the timer is rotating against the belt, deflecting it, and causing the belt to "walk" right off the pulley.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Tuesday, July 17, 2012 - 08:38 am:

Your profile says that you should have the lever arm type fan pulley mounting.

This can be a bit tricky as you need to have the vertical faces of the two pulley's in a common plane, as that is the only proof that everything made up parallel.

Is the crank pin tight in the pulley? Is there any 'slop' on the fan pulley make up? If there is a water pump, all bets are off, that 3rd pulley can make it a nightmare. The belt could have developed a stress twist also and once they do...they are done.

Check square as other have said...

Turn the belt around for a trial, if it still walks off the same way, something isn't square...and the out of square may be in the make-up of the assembly and it only 'shows' when running...

Leave it as loose as possible as Royce mentions, forget that 5# thing, A flat belt with one set of guide flanges has enough 'flat' that it should bite. (balance here, Goldilocks thing, just enough to get the fan to spin when RUNNING, but not too much)

Another trial is to take two wraps with 1" wide duct tape or 1" masking tape on the running center-line of the pulley on the fan. Starts to track fine...then your pulley has lost its crown.

You go through everything, feel you have done your best and still can't find whatever is making it walk...go to the auto parts store and buy a modern serpentine of the same length in the 15-18mm width. Doesn't look right, but funny how it finds its own center for running, usually more towards the radiator side which also makes it easier on setting the timer cotter pin...lol.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Don Lyon, PDX, OR. on Tuesday, July 17, 2012 - 10:36 pm:

Thanks guys. I've got two or three things to check out and will do that tomorrow. Been reading this forum for about a year now and loving every minute of it, Don, Portland, OR.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Aaron Griffey, Hayward Ca. on Wednesday, July 18, 2012 - 01:20 am:

If somebody twisted the fan blades so it has moore pitch to pull more air that can cause the belt to come off.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Stroud on Wednesday, July 18, 2012 - 04:25 am:

Aaron, ????? Pitch in the fan blade will have no effect on the belt. Dave


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Hoshield on Wednesday, July 18, 2012 - 08:05 am:

My dad problem with the belt coming of in short order on mine, as well. At least now, after it hadn't been running for 5 or 6 years ... I found a shiny spot on the water pump pully. Hand turning the pump pully was a bit of a chore, until I got it loosened up, and new grease in the cups. Now that it's well lubed, and seemingly spinning in concert with the fan belt ... it hasn't come off sense.

Your mileage may vary ..

Dennis


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick on Wednesday, July 18, 2012 - 09:55 am:

We always say that it is best correct to the source of the problem, but sometimes with the Model T when the source of the problem can be elusive, or too expensive or time consuming to correct, you can alleviate the problem by treating the symptom which many original Model T owners did, back in the day, with special accessories designed to correct a particular problem easily and cheaply, which is why Model T's were so popular with the common man, who didn't have a whole lot of money for expensive repairs. In the case of a slipping fan belt it was solved with a fan belt guide, which, are still available from the vendors which is indicative of the fact that this is still a persistent problem.

My '26 coupe originally had one on it when I bought it and though my belt stays in between the guide arms nicely, I kept it on because it is a nice APCO vintage aftermarket accessory which illustrates how Model T vendors created accessories to help old timers deal with persistent problems when they didn't always have the money to buy the necessary new parts to solve the source of the problem. Jim Patrick



Top of pagePrevious messageNext messageBottom of page Link to this message  By Aaron Griffey, Hayward Ca. on Wednesday, July 18, 2012 - 10:41 am:

Dave, Did you think I am just guessing??
I have seen guys put extra pitch in the fan blades to get more heat in the car after removing part of the floor boards (around the top of the hogshead on a '15 touring for example) and later had to bend them back again because the extra load would cause the belt to slip and come off.
I've seen it done for better cooling too, and the belt would keep slipping off every 15 or so minutes..
If you have not tried it yourself how do you know I am a liar or just making up a story???.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Wednesday, July 18, 2012 - 10:54 am:

I added the belt guide also. No more problems with that business.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Wednesday, July 18, 2012 - 04:12 pm:

First, this tale is for illustration. I do not recommend trying it unless you really know your T and yourself.
Model T fan belts need to be run loose. A very good friend of mine (and Aaron's) used to demonstrate proper fan adjustment by grabbing the fan with his hand while the the engine is running.

Also, I know Aaron's comment about bending the blades for greater air flow does make belt throwing worse. I never thought about why before. I suspect that the reason is connected to the same reasons that a too tight belt comes off. Increased resistance due to pushing more air creates a push-pull between the pulleys in much the same way being too tight does by increasing pressure in the bushings. Just guessing.
Drive carefully, and enjoy, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott McBrook on Wednesday, July 18, 2012 - 06:38 pm:

Dennis - I am new to Ts and getting one running that has a pump. It seems hard to turn but maybe its the packing is tight? How much tension is working for you on the water pump packing and bearings? I am going to put new grease in the cups and stuff but w/o running it not sure if I have a problem yet or not. Soon I will know, but wanted to get input on what the pump is supposed to be like.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Wednesday, July 18, 2012 - 06:55 pm:

Generally the packing nut on a water pump has to be tightened just enough to make it stop leaking. Normally that makes it too tight to turn freely, and the belt is thrown frequently. Then the car overheats. Or you can leave the packing nut loose enough to allow the shaft to turn freely. Then water leaks constantly. When most of the water is gone your T overheats.

Best bet is to take the water pump off now and save yourself a lot of trouble. They don't make your T run any better, cooler, or faster. They only hurt your reliability.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Max L. Christenson on Wednesday, July 18, 2012 - 07:02 pm:

What is meant by determining if the crankshaft pulley is "crowned"? What does "crowned" mean?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Aaron Griffey, Hayward Ca. on Thursday, July 19, 2012 - 12:13 am:

Crowned means the diameter of the pulley is larger in the center than on the sides, or front and rear sides.
Imagine what a wooden nail keg would look like if you lay it on its side and put an axle through it end to end. That would be a crowned pulley for a flat belt.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Thursday, July 19, 2012 - 01:01 am:

If you run a water pump, you might consider a crowned crank pulley.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Stroud on Thursday, July 19, 2012 - 04:35 am:

Aaron, take it easy! I didn't say anything about you being a liar or making up a story. WOW, where did that come from? As I said, pitch on the fan blade will have no effect on the belt, load should not have any effect on it. If the belt comes off, the pulleys are not aligned properly, one of the pulleys is not crowned enough, one of the pulleys is loose, or the belt is too tight or too loose. If everything is correct, the belt will stay on no matter what the load is. I have worked with flat belts for over forty years. JMHO. Dave


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick on Thursday, July 19, 2012 - 07:17 am:

The shaft could be bent upward or the rear bushing could be worn which could cause the highest point of the pulley to move toward the front, thereby causing the belt to move toward the fan and off the pulley. Jim Patrick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Hoshield on Thursday, July 19, 2012 - 07:58 am:

Scot ... Ditto Royce's comments! I didnt' take the packing nut off to see what it looked like inside. If I spend too much time on the pump, I'll just take it off. I WOULD like to see what the engine number is, anyway. That might be enough of a reason to take it off, right there! :-)


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