Garage Door Opener defunct

My old garage door opener seems to have bit the dust today. It's a Sears 1/3 HP model 139.663900, serial number E-154271, circa mid- to late '80s. When I tried to open the door this morning, it lurched a bit, opened the door half-way, then stopped. The motor inside sounds like it's still going, but the sprocket on top doesn't seem to be turning.
I guess I'll take it down and open it up to see if there's something I can fix inside, but I'm not optimistic. I looked around the 'net a bit and it seems that parts for this are no longer available (not surprising.) I'm not upset - this thing has lasted about 25 years with daily use and never been maintained, so I guess we got our money's worth out of it.
What I'd like to know is, can I buy a replacement opener that will work with the existing chain? It would be a lot easier to replace just that unit than to have to replace the chain, springs, etc.
So, any advice about this? Here's some pictures of the old unit, and a parts diagram I found on the Sears web site.
<http://home.comcast.net/~esionder/GarageDoorOpener/
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Nil wrote the following:

they are stripped like mine were. Sears has a repair kit. I replaced them some years ago and the kit cost $21 then. Call your local Sears parts dept. and have your model number handy. It's called a 'Drive Gear and Worm Set'. My Opener does not look like yours exactly, so it may be different.
--

Bill
In Hamptonburgh, NY
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alt.home.repair:

It sounds like that might be it. There are several gears in the parts diagram, and I wouldn't be surprised if some or all are worn. Maybe I'll be lucky and the parts are generic enough that ones from a different model will fit.
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Sears doesn't make anything. Many garage door openers use a nylon gear set between the motor and the shaft that has the chain sprocket on it. It's very commn for them to wear out over the years until they are so thin they just break. It's not hard to find replacements sincethe same gears were used in many models for many years.
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?

Could be stripped gears. It may be worth fixing if that is the only problem.

Doubt it but do you really want to? Sort of like taking that engine from your old Ford Pinto because it is still good and drop it into the 2011 Lincoln. New drives are quieter and faster.
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alt.home.repair:

I'm going to open it up in the next couple of days and see what's in there. It does sound like a stripped gear.

I'm assuming the part that's gotten quieter is the motor unit, and that a new chain would be much like the old. I see there are belt-driven ones - they're probably quieter. Mainly, though, I want to do it as quickly and easily as possible. The noise and speed factors aren't as important to me.
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alt.home.repair:

Yes, you may/it does.
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Nil wrote:

You've got to try repairing the original unit, just for the sake of its fake woodgrain finish that's a vital part of our heritage. That's why I never threw away my vintage-1976 Sears TV (still works great).
A lot of those Sears (Chamberlain) openers crack one of their large plastic gears, but the crack is small enough that the opener works OK when the door is disconnected.
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It can be done as long as sears still sells that type. I did the same as you are inquiring about a few years ago. Your existing rail will hook directly to it. You'll also have to install the supplied door safety lights.
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Nil wrote:

Take heart!
When you open the box, the problem should be obvious. It'll be a broken gear, a wallowed-out shaft, something came loose, etc.
I've fixed two I got off Craigslist in the past year ("Wont work, good for parts..."), each for a nominal sum.
Thirty minutes of searching on the internet will almost assuredly find the replacement parts for under twenty dollars.
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alt.home.repair:

Thank you, all, for your thoughts on this. You diagnosed it accurately: I opened up the motor unit and found wads of what looked like snow all over the place. Turns out that the main nylon gear (#38 on the diagram) that's engaged by the worm gear on the motor axle was completely worn and stripped and shredded. Now that I think about it, I guess it's been getting noisier and rougher for some time.
Sears shows the part as "not available," but I found a similar one that's used in almost all other openers from that era and is still available. I found a Sears parts depot nearby and was able to check it out to see if it was really the same as the discontinued part. It wasn't - the current common gear is much larger in diameter. So, I don't think I'll be able to locate the correct part. Which is OK, I'm prepared to replace it with a modern one. Which brings me to my next question...
Anybody have any recommendations about brands (Craftsman, Chamberlain, Genie) or models to consider or to avoid? Or what technologies? I see that there are chain ones (what I have now), belt ones, and screw ones. I think a 1/2 HP motor would be plenty for this 1-car garage wooden panel door. I'd like to keep the cost around $200 or less, if possible.
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On 1/22/2011 5:12 PM, Nil wrote:

I replaced a Sears chain drive opener a few years ago for the same reason. I got a 1/2 hp Stanley screw drive opener at Home Depot, uninstalled the Sears, and put in the Stanley. It was easy to assemble, install (all by myself) and adjust. It has worked well with no adjustments needed and only minimal maintenance. Screw drive openers are mid-way between chain and belt openers. They are quieter than chain drives, but not as quiet as belt drives. They are more expensive than chain drives, but cheaper than belt drives. As far as durability, it probably depends more on good low-friction garage door maintenance than it does on whether you're using screw or belt drive.
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Nil wrote:

There's a 99.9% chance the gear is still available. Keep looking on the web. For example, I'll bet this one fits: (Amazon.com product link shortened)
You can get JUST the main gear for less than five bucks. It's a good gamble.
Or see here: http://www.opendoorremote.com/v5/go.gnf?s=opendoor&p $3762
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alt.home.repair:

Your links are all to the gear #41A2817 and kits containing it. It's very common and available still, and seems to be used for the vast majority of Sears/Chamberlain openers from the late '80s on. Mine is from a couple of years earlier, and needs gear part #4A1425 which is smaller in diameter. I've been looking around the 'net, but I haven't been able to find one. I've given up and plan to buy a new opener tomorrow.
Thanks anyway. I would rather have spent $5 than $200, but after at least 25 years, I figure the thing is probably ready for replacement.
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