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Author Topic: Grabbing Drive Belt Problem  (Read 879 times)
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Jeff McKelroy #55A
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« on: January 04, 2014, 01:47:01 AM »

Hello Everybody~

I'm in a quandary here, and I seriously need some help with this issue.  I have exhausted all ideas at this point. I will do my best to go through everything I've done to try to correct this problem so far.  This is a 2001 Craftsman chassis, G/P class, 700 transmission.  EC engine and transmission pulleys.  EC clutch assembly.  Fully welded/frame, EC tranny plate with support bushing as well.  68" drive belt.

This chassis was originally raced as a C/P and the belt drive system was flawless.  No thrown belts, no seized bearings, nothing. I always tried to take the time to repack the bearings and replace the belt every three months whether it needed it or not.  Then last September I converted it to a G/P.  That's when stuff started wearing out.  I had never experienced a worn engine pulley, and after 3 years of racing it finally gave up the ghost.  Belts were "wearing out" in 30 laps, and just flat wouldn't pull.  Anyway, I tried to compensate with shorter belts before I realized the engine pulley was severely grooved and wouldn't let the belt seat properly, (I was in the middle of figuring out the right gearing for G/P class, swapping sprockets back and forth with different 4" and 5" tranny pulley combinations before I found what worked.) at which time I replaced the engine pulley, and finally went back to the 8" and 5" pulley setup with the original 68" belt.

But the problem changed.  No longer am I replacing belts every 30 laps, but when I press in on the clutch, and then shift into gear, the whole mower bucks and jerks from the belt acting like it is not fully disengaging.  I have blown up two transmissions so far because of this, and I'm getting pretty frustrated.  It doesn't take long to ruin a good 700 when you are experiencing this issue.  I verified the correct belt length using George's trick, all is well (as far as I can tell).  I lengthened the clutch pushrod to allow for more adjustment.  I can literally pull the belt off in any direction I please, it is so loose.  I noticed the v-groove clutch pulley was worn as well, so I replaced it.  I verified the pulleys are on the level from front to rear, clutch included.  Afterwards I replaced the transmission pulley just to see if that would make any difference.  No change.  I tried running without belt guides at the transmission and the v-groove clutch pulley, no change, however I noticed the belt didn't fall off when I disengaged the clutch, and it jumps around a TON, not simply slowing or stopping like it should.  Without using a measuring tape, I visually looked at the crankshaft in relation to the hole in the frame, and it appears centered.  I've flipped the mower before, but I never noticed any belt related issues after that.

The only thing left that I can think of is possibly the crankshaft position has changed when I went from the flathead twin to the G/P engine, but you would think that issue would have been revealed long beforehand, by verifying the proper belt length.  The only thing I haven't tried yet is a 69" belt, but I'm afraid it will be TOO loose. Would too loose of a belt cause this issue as well, when it is trapped inside the belt guides?  The guide bolts are the same ones, and in the same original locations, so I don't think that's the issue.

I know I have given a bunch of information, but I believe it will help to a good diagnosis.  I hate making stupid mistakes, and overlooking the simple stuff, but maybe you have run into the same issue and might have an idea.  You can poke fun if you want, that's not as expensive as a new EC transmission.

Thanks for your help as always,
Jeff
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Jeff McKelroy
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« Reply #1 on: January 04, 2014, 01:53:04 AM »

Jeff, I'm sure you are aware of this already but an easy mistake with mower turned upside down. Which side is the clutch on if you are setting in the seat? What belt type?
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« Reply #2 on: January 04, 2014, 06:10:44 AM »

Did you install any belt guides? Without them the belt will grab and do what you are describing.
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« Reply #2 on: January 04, 2014, 06:10:44 AM »

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« Reply #3 on: January 04, 2014, 08:12:57 AM »

When  I have had problems like this it was usually the belt guides.  We have also had to put guides on the tension side of the belt to the outside to keep the belt from just going in a big circle and not letting the clutch disengage.  I have a stand that I can run the mower on and be underneath and watch what's going on at a safe distance.  Centrifugal force wants the belt to push outward you just need to make it go outward on the ends only.
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« Reply #4 on: January 04, 2014, 08:35:53 AM »

I do have belt guides, three per pulley, with the exception of the clutch. I have a belt guide bolt on the flat side pulley, but not on the v-groove pulley. The reason was when I extended the travel of the clutch, the guide bolt would pull the belt back and the grabbing was even worse. I forgot to put that in my novel...

Tank, the clutch is on the slack side.

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Jeff McKelroy
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« Reply #5 on: January 04, 2014, 08:47:02 AM »

Try taking off the center guide on the engine and trans pulley and just use one on each side, that lets the belt push out more on the pulley an yet stay on. That's all I run. I make a flat L bracket that bolts on the pan and slides up to the pulley. Other than a brand new belt grabbing slightly on the first use, I now have no hang up issues.
We also had one chassis that the clutch pivot had egged, and caused the belt to grab the guide when pushed in and would cause it to pull the slack tight. We work on ours on open tables, and I had my brother in law turn the engine over by hand while the clutch was in, and that's how we found it.




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« Reply #6 on: January 04, 2014, 09:14:31 AM »

Trans pulley did you replace that if the motor pulley was wore out so was the trans pulley. ALSO I had this issue way back with new pulleys the setup was one where the belt barley fit on and when it was new it would do this once a couple races were on the pulleys it went away. The V shape of a belt and a pulley rarely are a dead match this all new items I noticed that intially the belts rode on the top of the V with about 1/2 of the V flat side surface not initially making contact Some belts brands are worse than others but thats what I come to relize the one time I experianced this for myself. and new aluminum pulleys are far more grippier than a steel pulley of same size.
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Jeff McKelroy #55A
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« Reply #7 on: January 04, 2014, 01:36:01 PM »

Guys, I found it.  Redline, your trick worked nicely, but didn't completely solve it. George, I had bought the engine pulley from a racer at a swap meet. It looks EXACTLY like an EC pulley, but plain aluminum, not anodized. It very well may be some kind of knock off of the real thing? I had just dismissed it as "One of the first made" and thought nothing of it. I borrowed an EC engine pulley from Jim Burk and installed it, now the belt just stops like its supposed to.  I was thinking I was getting a killer deal on what looked like a new EC pulley, which has now cost so much more in lost time and money. Never again.

Thank you guys so much for your input and advice. I knew I can count on you. Thanks again!!!

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Jeff McKelroy
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« Reply #8 on: January 04, 2014, 06:12:24 PM »

No problem Jeffery, anytime...  bigsmile
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« Reply #9 on: January 07, 2014, 06:15:39 PM »

Thanks for the lesson Jeff! No I don't want to buy a almost new aluminum EC look alike pulley! LOL Seriously glad you got it figured out!
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