Come the end of summer, there are many room fans out at the curbside for trash pickup. If the bearings weren't loose, I used to flush out the bearing with WD-40 while manually turning the blades. Sometimes, I'd use a needle drop of acetone after that. Then I'd oil the bearing with lawn mower motor oil. I'd get a couple of years of use before the bearings wore out too much.

 

I'd get a couple of years of use before the bearings wore out too much.

Actually sintered bronze has a large capacity for lubrication on its own, coupled with the oil impregnation, even more, I have found the wear is minimal, generally it is not so much lack of oil, but contamination from dust, dirt etc that gums the bearing.
A clean and a oil soak and you can usually get a lot more life.
Max.

 

I was amazed to learn that very large (power plant, nuclear sub) bearings have been made of lignum vitae, a natural wood that is very hard and dense, and contains a high percentage of oil. These bearings can be run at zero free play, are self oiling, and last for decades without maintenance. Truly amazing.

Completely useless information for the OP, but hey.

 

Recently replaced one of the radiator fans in my sister's nissan sentra and it seemed about the same size as your oven fan. Should be up to the task, having been designed to be bolted to a radiator. Only problem is they don't come in 240vac option. But if you're willing to install a 12v smps, the local auto salvage yard might just have your motor...


Edit: sisters car is a 96 model. Took 18 years for the fan to die

 

Agreed, my point was they won't use ball bearings (because of high-temp app), only bush type which are always very lube-critical.

Oils aint oils.

Agree on the oil point. But fans and HVAC blower motors use bushings because they are quieter when running. A ball bearing has a small amount of back round 'rumble' to it when used in that type of application.

 

1 year on and the bearings are seizing up again.

PlusGas appears to free them up pretty well, and there is still no sign of burning or overheating on the rest of the motor.

It is clear that the roasting gases are exiting through the shaft access hole and depositing onto the shaft/bearing, gunging it up.

Does anyone know if the shaft access hole should have a sealing gland of some sort, that may have been omitted in the assembly of my cooker?

Alternatively could anyone sugest what I might make one of?

(I can't trust the manufacturer to answer this question honestly)

 

1 year on and the bearings are seizing up again.

PlusGas appears to free them up pretty well, and there is still no sign of burning or overheating on the rest of the motor.

)

PlusGas/WD40 etc are pretty useless as long term lubricants, the light fraction oil evaporates at room temperature, let alone hot in an oven!

It also dilutes/washes out whatever lubricant the manufacturer put in the bearings originally.

For my oiling jobs, I find the PTFE enhanced lubricants well worth the extra money, GT85 is a popular choice for PTFE enhanced freeing oil.

Slick 50 PTFE engine oil additive works very well as a general purpose long term lubricant.

For tight phosphor-bronze bearings, you can encourage capilliary action by wetting with GT85, also Slick 50 can be diluted with GT85 so it runs into tight bearings easier - the GT85 evaporates leaving the thicker oil in the bearing.

For grease; my favourite is Finish-line PTFE fortified bicycle grease.

 

Did you dismantle the fan & use a syringe & needle to properly fill the bush & its surrounding reservoir with oil, as shown in post 19.

 

Did you dismantle the fan & use a syringe & needle to properly fill the bush & its surrounding reservoir with oil, as shown in post 19.

If they're phosphor-bronze bearings; that isn't enough.

Some manufacturers soak the bearings in oil for a set time before fitting - some people heat the bearings while submerged, the air in the porus metal expands and escapes, when it cools down the oil is drawn into the voids.

When I worked with phosphor-bronze bearings - the specified oil was; Shell Tellus, shouldn't be difficult to cross reference equivalents from other manufacturers.

 

One of the problems I've seen with that type of motor is the welded copper shading ring breaks. It stays in place but the break causes it to run hot. I've tried soldering them back, but to no avail.

 

One of the problems I've seen with that type of motor is the welded copper shading ring breaks. It stays in place but the break causes it to run hot. I've tried soldering them back, but to no avail.

AFAICR: the shaded pole is to make it start in one direction rather than the other.

That type of motor is usually "impedance protected" anyway.

 

The shading is intact and the motor starts and runs well now it is clean.

I have disassembled it and hope to post some more photos tomorrow.

The bearings are plain hardened steed or white metal.
They are neither brass nor bronze.

The outer boss is made of light alloy casting and taper cup shaped.

A sheet metal (steel) rose in the bottom of the cup holds the plain bearing in its centre.
A second rose the other way up is pressed down to lock the first rose in place.

The boss does not contain any oilways or oil points.
These would be pointless anyway since the oil the boss is not liquid tight and any oil would just spew out.

There is no sign of grease, but this may have been washed away by the release agent.

The hardened steel shaft runs in this boss at the end of the rotor block, which appears to be heat shrunk onto it.

Two coil springs mounted on the shaft centre the rotor between these two bosses, which are mounted each end of the stator block.

The shaft then passes through a second similar boss and then has a small cooling fan again heat shrunk onto it.

The shaft then passes through the rear wall of the oven and ends in a shoulder onto which the main oven fan is mounted inside the oven.

None of the fan motor is accessible from the front ie inside the oven.


I am now of the opinion that hot air, laden with carbon rick cooking gases exits the oven around the shaft and deposits onto the works, causing sufficient friction to prevent the fan from running.

Hence my question in post#46 about a seal.

 

Here are some more pics

Firstly the exploded asembly, from left to right

The end boss housing one bearing, stator frame and coil, shaft with rotor, second bearing boss and motor cooling fan.
Note the left hand end of the shaft (shown supported on ruler edge) fits into the left hand bearing boss.




Stator frame and winding.



End view of shaft from end that fits in the outer boss.
Note one of the fan blades is bent aside to allow access to the clamping screws.
(Warning to would be designers)



Angled view of shaft showing locating spring



Inner view of bearing boss with bearing and supporting roses marked



Back view of bearing boss

 

Per post #46, if you were looking making a seal, you could clean oil/grease off the area and make a RTV/silicon seal, this is easily removed later if needed, clean with spirits first.
Max.

 

May be measure the ID of the housing (not the staked areas) and the shaft diameter and see if there is a ball bearing that will work? For each outside and inside diameter bearing there are different thicknesses of bearing so you would also need to check the thickness.

Tried to download this to the site but it was too large -
http://www.google.com/url?sa=t&rct=...aDPaf9s7yNl3gOhNUWhi8zQ&bvm=bv.88198703,d.aWw

 

Hello, max

RTV?

Thanks, shortbus, do you mean fix one of these to the oven wall?

 

RTV = Room Temperature Vulcanizing or fancy term for Silicon Rubber.
Max.

 

RTV = Room Temperature Vulcanizing or fancy term for Silicon Rubber.

But would it work in an oven at 250C around a spinning shaft? ?

 

But would it work in an oven at 250C around a spinning shaft? ?

The temperature range is quite high, it can be used for casting low melt alloys and also Engine gasket substitute.
If you want to get creative you could look at embeding a high temp 'O' ring seal at the bearing?
Max.

 

The seal would be no good at the bearing, which is outside the oven.

My thoughts on the seal is to prevent grease laden hot oven gases exiting the oven along the shaft and depositing on the cooler asembly outside the oven.

If shortbus meant what I think, he was talking about adding an extra bearing at the oven wall.