Replacing the lower drive belt on an MTD 660 series tractor - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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post #1 of 25 Old 08-31-2019, 04:47 PM Thread Starter
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Replacing the lower drive belt on an MTD 660 series tractor

For a year or so this tractor will hesitate when going forward, but if you back up then go forward that works. I was looking in the space by the gear shift lever last summer and noticed the belts down there are in rough shape so I ordered replacements. But that belt from the bottom of the crankshaft to the variable speed pulley near the transaxle is a dealer-replace item I think. Parts list: http://manuals.mtdproducts.com/manuals/769-00642b.pdf

The main problem is that there are belt keepers. The pulley on the crankshaft has a bolt holding it on, but take that out and nothing happens because that double pulley goes onto a keyed shaft. And there are keepers on 3 sides of that deck under the engine holding the belt on that upper pulley. At least one more on the back end. I suppose I could bend them out of the way but the right approach would seem to be to cob together a puller and take that double pulley off the bottom of the crankshaft. Anybody done this?
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post #2 of 25 Old 09-01-2019, 08:40 AM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

Welcome to the forum.
Ideally the pulley will slide off the crankshaft when the bolt is removed. I would try a puller first before bending the belt keepers.

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post #3 of 25 Old 09-01-2019, 09:39 AM Thread Starter
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Re: Replacing the lower drive belt on an MTD 660 series tractor

I'm not sure what I've got for pullers, never had one that worked very well.

No, taking the bolt out did nothing, or some careful tapping around in there with a 1 lb hammer. Impact wrench zipped that bolt right out pretty slick. I could almost cut a pair of wooden wedges and drive them between the big pulley and the deck under the engine. I worry about bending that big pulley trying to get it off. I'll squirt some WD-40 or whatever I can find at that space between the shaft and pulley, let it soak in.
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post #4 of 25 Old 09-03-2019, 09:24 PM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

Tapping side of shaft part can help. Maybe even heat the shaft. I suggest a real penetrating oil like pb blaster or fluid film rather than wd40. Heat and then spray at top. Those belt guides #34 shoulds screw out. Ends are 1/4 hex usually. But your issue is the guide pieces that are part of the chassis. That is why pulley needs dropped. I have once just bent them way back. Have known people who have lifted engine up to get the clearance from those guides to remove the belt. Not sure why backing up makes a difference. Belts always go in same direction. Transaxle is single speed. Either forward or reverse. Maybe issue is the FNR shifter.
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post #5 of 25 Old 09-03-2019, 10:00 PM Thread Starter
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Re: Replacing the lower drive belt on an MTD 660 series tractor

I'm going tomorrow to the store to buy a 7/16-20 x 3 bolt (if that's the size). My puller can't deal with a dished pulley so I'll screw in a long bolt to have the bolt in the puller push against, maybe center-drill it in my lathe so they don't sip.

There's at least 1 keeper in the back by the transaxle , I'll probably bend that out of the way. Yes, the screw-in keepers are out, I used to have the snowblower attachment so every year the mower deck came off and the snowblower went on, those keepers always got unscrewed and screwed back in twice a year. The hex is stripped on one, had to use Vise-Grips to turn it this time.

Backing up, I haven't tried to work out the math, but one time I looked in there it seemed like big chunks had come off the inside of the belts, leaving just the backing. They're 17 years old, both original. So by backing up you get onto a different part of the belt. Sometimes shifting up will do it, but you can't always do that.
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post #6 of 25 Old 09-04-2019, 07:14 PM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

Still confused about the backing up. Belts are always going in the same direction. If you stop belts with clutch then they restart in motion exactly same whether you have stayed in forward or shifted into reverse or from reverse to forward.
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post #7 of 25 Old 09-04-2019, 08:34 PM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

In your case that would not be a dealer replace item. Probably dealer would charge more than your mower is worth to flog that one.

It's quite common for that pulley to become seized/rusted and stuck to the shaft. (not a fun job when that happens) The Keyway is built into the pulley shaft. Sometimes you can lock the engine and take a pipe wrench and wiggle the shaft because if the deck ever hit something hard the keyway jammed in the crank slot. I have had to just sacrifice the pulley and use a very large bearing puller, then get a used pulley from flea bay.

Now days when I find a rough contrary stuck pulley, I just drain the oil out of the motor. drain the gas, remove the battery and turn the tractor upside down, add penetrating oil, let it soak, try pipe wrench, then pulley puller and torch. (you can get too all really easier with the tractor upside down. You can use some padding underneath if you want to keep from scratching up the hood, etc.

When going back use good smear of anti-sieze lube on the engine shaft. If new correct size belts don't make it go check the spring loaded clutch idler pulley area, it should swivel really easy. The center sheave on the variator drive pulley should move up and down freely with the belts off. Sometimes just little bit of oil will free it up and when it's free the belts are easier to install. You can see you tube videos of how it should operate.

When you first install new belts push the rig outside and get ready for a fast launch in high gear. Sometimes it won't even move until you place it in max speed usually #7 on the vari drive and don't try making any adjustments for the lower speeds until the belt have run in.

Replacing those belts is not a fun thing the first time, next time will be somewhat easier.
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post #8 of 25 Old 09-17-2019, 12:16 PM Thread Starter
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Re: Replacing the lower drive belt on an MTD 660 series tractor

I had this idea but it took me a while to get around to go buy the bolt. And then it didn't work. I got a 7/16-20 x 3 bolt, made a little depression in the head with my lathe so the puller wouldn't slip off. But the puller is mostly just bending up the edge of the pulley. Looks like the pulley slid less than 1/4" on the shaft, but it's got a long way to go.

Yes, in 17 years the blades have hit things, I've replaced them maybe 4 times, so the key's jammed. I'm about out of time for this year, I need to get the tractor down off blocks and move it so a couple truckloads of wood can go there, then pile that. I've got the front wheels up on a pair of 12" wide John Deere rims. I can actually get under there. But I don't lay on the ground and get up again as easily as when I was younger.Click image for larger version

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post #9 of 25 Old 09-17-2019, 01:31 PM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

If it moved a little, squirt with more penetrating oil and tap the pulley back up. Keep doing that until it comes off.

Chuck L

3 Late Model MTD 990s - (2 1980 Farm Kings and 1981 Wizard), 1979 Farm King, 1978 Farm King, 1973 Farm King for parts. Craftsman DTY4000, DLT2000.
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post #10 of 25 Old 09-17-2019, 04:24 PM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

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Originally Posted by VTXRider View Post
If it moved a little, squirt with more penetrating oil and tap the pulley back up. Keep doing that until it comes off.
For the tough ones like you are into I use a husky tough bearing separator puller that is about 4 1/2 inches between the spreader bolts and I have a yoke puller (cross T puller)


I made most of it myself with a cutting torch and welder but HF has a separator at this link.
https://www.harborfreight.com/bearin...tor-63662.html
Turn the bearing separator backwards )concave side up) so as it won't touch the curved bell part of the pulley to keep from damaging the lower pulley's bell shape.

Mine is so tough that I have pulled the lower pulley off of it's shaft collar and then had to weld a piece of metal pipe to the pulley shaft collar to get a bite with the puller and then heat the shaft and collar and hoss it off. If your pulley is already ruined, you can cut the lower pulley off and grind the pulley shaft collar so as to split the shaft collar. or weld a large nut onto the pulley shaft collar as a pusher for a threaded bolt.

If you apply any serious heat you will need to replace the lower sump seal, usually.

Too late now but sometimes you can remove the engine mounting bolts and move the engine just enough to replace the belt.
Best to not bend on the metal frame belt keepers, they will break off.
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post #11 of 25 Old 09-17-2019, 09:30 PM Thread Starter
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Re: Replacing the lower drive belt on an MTD 660 series tractor

Shh, as far as I know I could still bolt the pulley back on and move the engine instead. This is all the damage I've done so far, bent one side of the pulley out a little. And I just looked back through my pictures, the amount of the inside of the pulley showing around the bolt is about the same as 16 pictures earlier when I'd just gotten the puller arrangement on there and I was showing that it worked. I don't think I actually moved the pulley on the shaft at all, now that I look at that. It looks like it's moved but it looked like that before I started, I just didn't notice.

A cheap new one on ebay at $40 (shipped)
https://www.ebay.com/itm/For-MTD-Eng...ty!01346!US!-1

or new at MTD
https://www.mtdparts.com/en_US/pulle...956-04023.html
$78.71 (free shipping because it's over $50)

But to replace the pulley I've got to get it off, pullers and all. To just replace the belt I don't need to. That probably has its pitfalls too but it's uncharted territory.
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post #12 of 25 Old 09-17-2019, 10:58 PM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

If you have an impact air hammer there's a guy on YouTube who hammers that bolt you put in while holding pulley with pry bar or something to impede its upward movement. Sometimes the pulley just walks down. Principle is that he's driving crankshaft up it's endplay amount .
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post #13 of 25 Old 09-18-2019, 01:14 AM Thread Starter
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Re: Replacing the lower drive belt on an MTD 660 series tractor

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Originally Posted by 38racing View Post
If you have an impact air hammer there's a guy on YouTube who hammers that bolt you put in while holding pulley with pry bar or something to impede its upward movement. Sometimes the pulley just walks down. Principle is that he's driving crankshaft up it's endplay amount .
Nope, no impact air hammer, used to use one at a job in the 70s though. No air compressor. I have a Hitachi cordless electric impact wrench but that doesn't seem useful for this. If I spent a year with a regular hammer that might come close. Some kind of slide hammer like for pulling dents maybe.

This is like a bent key in a flywheel in a lawnmower engine I think, and Briggs recommends a puller for those. The weak point seems to be pulling on the edge of the pulley. It's all flimsy.

I wonder what happens if I can make a punch (ground down sheetrock screw) and pound on the key itself. I could only move it towards the engine though. Oiling it from the top would be good, no way to get there. I do have a bottle of 3-in-1 oil with a spout about a foot long. I don't think I can even see the spot I'm aiming for though.
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post #14 of 25 Old 09-19-2019, 09:57 AM
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Re: Replacing the lower drive belt on an MTD 660 series tractor

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Nope, no impact air hammer, used to use one at a job in the 70s though. No air compressor. I have a Hitachi cordless electric impact wrench but that doesn't seem useful for this. If I spent a year with a regular hammer that might come close. Some kind of slide hammer like for pulling dents maybe.

This is like a bent key in a flywheel in a lawnmower engine I think, and Briggs recommends a puller for those. The weak point seems to be pulling on the edge of the pulley. It's all flimsy.

I wonder what happens if I can make a punch (ground down sheetrock screw) and pound on the key itself. I could only move it towards the engine though. Oiling it from the top would be good, no way to get there. I do have a bottle of 3-in-1 oil with a spout about a foot long. I don't think I can even see the spot I'm aiming for though.
IIRC key is built into pulley so that won't work. Neighbour has opposite problem. When I was changing her deck belt last year I noticed that the pulley had dropped. The key was worn away so I got her a used pulley. Yesterday she called to tell me that pulley was loose again. I may use loc tite on the bolt this time.
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post #15 of 25 Old 09-19-2019, 10:38 AM Thread Starter
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Re: Replacing the lower drive belt on an MTD 660 series tractor

Well, last night I got 4 bolts out that were holding the engine in, and this morning 2 cords of wood got dumped, the tractor got shoved out of the way by the wood guy, Maybe before snow flies I'll get back to it.

Having the key built into the pulley limits the options. Hack saw blade and cold chisel maybe, split the pulley off and throw it away. I got the bolts out but the engine still resisted moving. The screw-in belt keepers are out but there must be throttle linkage and all that, didn't look up top.
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