Furnace making loud grinding noise

Greetings,
I have a Lennox 80MGF furnace that is making loud noises from time to time. I first thought that the blower's ball bearings or something was bad and that the motor action is what was producing the loud noises.
The noise happens only sometimes and is rather loud. After standing next to the furnace long enough for the sound to appear again, as it's intermittent, I now think that the noise is coming from a small box near the gas exhaust pipe near the wall where the pipe exits through the wall from the basement to outside.
This little box looks has a flexible metal hose leading to the furnace. It also has a solid hard small pipe line leading to the top of the exhaust. I can't see where it exactly leads because it kind of dissappears into the wall. The box is pretty much square and has a small round thing on the side.
My ignorant mind is making the wild guess that this box takes samples from the exhaust air, and determines that it does not like what it smells, and is sounding an alarm.
I know I know, call in the gas guy. But I'd like to know a few things before the gas guy starts telling me things.
If really needed, I could upload some digital pictures somewhere...
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On 26 Jan 2004 20:37:37 -0800, snipped-for-privacy@whoever.com wrote:

You didn't describe what the noise sounds like. If it squeaks as from a rotation then the only moving parts are the fan axle (most likely) or the motor axle (unlikely). The motor axle runs on dry bronze bearings and the bearings are quite easy to replace. Just go to a furnace or an applicance parts place and ask for them. There is only one standard axle/bearing diameter size.
Don't put any lubricant on the bearings. The heat just dries up the oil or grease so that along the way the worn metal filings forms an abrasive slurry with the lubricant and eats up the bearing. I believe when the bearings run dry the metal parts polish each other to give a low friction mirror surface.
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From your descrip, it sounds like it might be a booster fan to move the flue gasses up the pipe. Sometimes those have an oil hole on each end of the motor. Couple drops of SAE 20 or SAE 30 oil might quiet things down.
Some years ago, I had a blower fan in my trailer furnace start to squack. Really enough to drive me out of the house. I took the blower cage out, and found that it had oil holes. Put in a couple drops of oil, and it never bothered me again.
--

Christopher A. Young
Jesus: The Reason for the Season
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flue
and
You've said in the past that you have to do the oiling every couple of years.
Get your story straight.....
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flue

I couldn't really figure out what it was exactly. My motivation for figuring things out is so that I can have a constructive brainstorm with a gas contractor. This way I feel a little in control and would prevent him from spending time and replace unnecessary parts. CY: Yes, some contractors spend a long time throwing parts at it.
Not being a gas specialist, I only looked and reasoned, to the best of my abilities, and I knew it had to be a 3rd moving part. Not the main fan, not the blower, something else. The loud humming/buzzing was coming from higher up I thought.
So, ok, in the middle of a snow storm, the furnace stopped working. The gas guy took a while, but together, I was able to work through things logically. He started to take things apart, and told me it looks like the large main fan motor. I told him that when I put the thermostat's switch fan position to 'on' instead of 'auto', the fan sounds like it's moving air quite nicely. He measured the amperage how much the motor was drawing, looked normal.
After he took the front of the furnace apart, and started the motor, he now thought the motor was running well, and the noise was indeed coming from elsewhere.
Then, bingo. Right outside the house there is a little box with 'power vent' written on it. It's built into a small metal cage, and mounted on the outside of the house. In it, there is a motor that sucks the air out, and assists in flowing the exhaust out. There is a small solid line that runs inside to another small box with a sensor in it. If the sensor says that the venting is working well, it tells the furnace it's good to go. The motor is stuck and is making a humming and buzzing kind of noise. CY: Please remit $47.50 for diagnosis.
Needless to say, this box being outside results in a shorter lifespan than if this fan had been inside just before the pipe exits the house. By the looks of the manuals of Lennox, it looks like this suction exhaust thingy (power vent thing) is optional, because the other fan normally blows the air out of the furnace. The exhaust is on the side of the house. The exhaust from furnace to outside is about 6 or 7 feet.
Now the fun part. This part is not in stock and needs to be ordered from the manufacturer. The number is SWG-4HD. I have no idea what this thing is going to cost me. If anyone could tell me, that would help. CY: I don't have that information. But I'm sure I could find out with a couple phone calls.
Luckily, I have a gas fireplace, and it keeps half the house relatively warm. The cat looks very comfortable, I think I might join him ;-) Tomorrow I'll find out more about this mistery part. Stay tuned.
Thanks to all giving me feedback btw. I'm not taking any chances and will not risk blowing myself up, and am leaving the real work to a professional ;-) CY: You sound like an informed customer. Hacks hate you, and sincere folks like you.
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snipped-for-privacy@whoever.com wrote in message

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I'd guess about $50 to $75 for the motor. Did you try a squirt of oil? Sometimes that's all they need. I must be too cheap. I didn't call for prices, but I suspect no where near that. But, on the other hand, they didn't get the job. So they got zero.
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Hilarious. Love some of these guys. They probably get maybe a 1/5th of the business with their prices. 1/5th the work - same money. Maybe not exactly, but you get the idea. Gotta give them some credit. Where do I sign up?
$600 is probably more than most installers' cost for an entire super efficient voodoo special top of the line furnace - and it would likely take a good tech in a typical install less than 3 hours to rip out and install an entire new furnace to boot.
Shop around for the motor. HVAC parts warehouses will have cross-reference and application catalogs.
- Nate
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I must be doing something wrong. When my former boss and I used to do furnace installs, it would take us (two men) typically two days to get it all in.
--

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the
take
an
cross-reference
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On 28 Jan 2004 12:44:23 -0800, snipped-for-privacy@whoever.com wrote:

You would be surprised at what some of those small odd ball motors cost...but yes I do agree that $600 is insane whether it really does carry a hefty price tag from the manufacturer or if the seller is slapping you with 500% markup.
My advice is to take the motor to a local place that specializes in selling and rebuilding motors. Every so often when I run into an obsolete motor I'll take it to a local rebuilder. If he can't match it up with a replacement they'll rebuild the old one at a reasonable cost...usually have it back the same day too. Also if you go this route you'll know you're getting the proper voltage, rpm, HP and rotation.
George
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snipped-for-privacy@whoever.com wrote in message
Another update.
I found a motor with a dual shaft. I will saw off the shaft I don't need. I picked the dual one so I can't get the wrong blower wheel. Clock wise, counter clock wise, which combination to pick?
Does a counter-clockwise motor and a counter-clockwise blower wheel make it suck the air in from the inside, blowing it outwards?
So, I couldn't get the old blower wheel off the old motor, and need to find a new blower wheel. Does anyone know where I could find a metal blower wheel of 4 inches in diameter and 2 inches thick in the the Toronto (Canada) area?
Home Depot and Crappy Tire don't have it, where to go...
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Not to be a smartass, but you ARE in over your head, and you are screwing with something that CAN possibly snuff you out and no one know it. Inducer motors are cheap, and easy to get. Get the right damn part before you get hurt, since what you have posted is enough to know that you really need to stop.
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message

I don't think so.

I'm cautious enough that I can work my way through. I did have electric training years ago, so I'm aware of what I can and can't do, and how to do it safely. The system has a air sensor which shuts off the furnace if it doesn't detect a negative pressure, which is why the furnace isn't working. The motor has all the right specs. 3000 rpm, 1/20 hp, shaded pole, 2 wire, no capacitor. I was not sure about the direction, and wanted to have the option to reverse direction. Dual shaft was the only way I could think of.
I detest contractors keeping information from me. The contractor that was here for one hour trying to troubleshoot, checked everything, but stopped short of opening the box outside that has the faulty motor. Had he opened it, I would have seen how simple it really is. I think he didn't want me to see it. Instead, he didn't open it, went away, and told me the next day that it would cost $600 in parts, and $250 of labor because it is a hard thing to replace.
I must and have to solve it myself.

It is, $55.75 for the motor.

The motor has all the right specs, and sawing off the end is not unsafe I believe. I'll smooth off the edges so it isn't sharp.

Many people would probably do it secretly because they'd be afraid of someone ratting on them. Others are afraid of being made to feel stupid and incompetent. I don't really care, I'm quite confident, and being careful. I know not to get into actual gas territory, because for that I believe the proper training is required to know the pitfalls and gotchas.
The part I'm doing is particularly easy, because it isn't near the furnace, it's just mechanical, and it's backed up by a safety shutoff mechanism.
I would have to agree that there *is* oportunity to hurt yourself. The fan rotates at 3000 rpm, and could cause injury. I think I'm ok here.
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I worked for MBB, known now as Airbus in Hamburg but you dont see me in aviation groups...was trained for AB320 series..but am I a pilot? No damn way.

I would have thought about the right motor....complete with blower for under $50.

then you really needed to just kick his ass out to start with.

Funny...I have yet to pay over $45 for a complete assembly..

You fail to see the point.

Good, but you are into CO and CO2 territory... Just because a motor SPECS out right, does not mean its built like the ones that going to be withstanding the heat...think about that for a bit..

And again...cant you find a HVAC supply center to sell you the correct parts? In the time its taken you to write all this, you could have replaced the entire shooting match and been done.
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Yikes!! Some have it, some don't...

Shit - an arctic town like Toronto and you couldn't find an HVAC supplier? WTF are you doing at Home Depot looking for this stuff?
- Nate
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Hi Stormin, hope you are having a nice day
On 26-Jan-04 At About 23:12:58, Stormin Mormon wrote to Stormin Mormon Subject: Re: Furnace making loud grinding noise
SM> From your descrip, it sounds like it might be a booster fan to move SM> the flue gasses up the pipe.
A booster fan is a totally different item than what you are calling it. Now read my lips idiot!! it is called a " Draft inducer or a Power venter" If you were to try to use a booster fan for draft you would cause a fire or maybe carbon monoxide poisoning. you need to stop trying to answer these questions before you get someone killed.
-=> HvacTech2 <=-
.. "Careful. We don't want to learn from this." -- Calvin
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snipped-for-privacy@whoever.com wrote:

bet it is the air handler, motor or the fan hitting, or the bearings or something else that moves.. probably just need some oil in the motor, but with a question like that you better call a service guy out to make sure....if you dont know where the oil goes into the motor...
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