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I think heat transfer from pump to motor or motor to pump has alot to do with it in my opinion.

I also had wondered was it due to heat transfer.
Maybe kerosine and heat are two causes.
When you look at the shaft seal on oil pumps, it is not surprising that kerosine will leak slightly past the shaft, particularly when oil pump is working and if oil pump is old. I recently had a careful look at a Riello burners oil pump using a torch and noticed very slight trace of kerosine down in between shaft and seal. Motor bearing had gone and that's what I think was causing it.
 
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When you look at the shaft seal on oil pumps, it is not surprising that kerosine will leak slightly past the shaft, particularly when oil pump is working and if oil pump is old.
Used to "metal spray" and machine back to size the shafts on big pump & motors due to wear from bearings spinning on shafts and oil seals going hard and causing damage.
 
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Used to "metal spray" and machine back to size the shafts on big pump & motors due to wear from bearings spinning on shafts and oil seals going hard and causing damage.

That's just too much like real engineering for me! 🙂
One tip I was told about installing new bearings is to mark the shaft where the new bearing will sit with a metal punch to make sure it won't spin on the shaft, which they tend to do with new tight bearings or old seizing bearings.
 
I service boilers at a engineering company that supplies bearings, he recommended SKS to me and i can tell you they are far better than cheap bearings and noticeable quieter and smoother when burner is running.
 
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That's just too much like real engineering for me! 🙂
One tip I was told about installing new bearings is to mark the shaft where the bearing sits with a metal punch to make sure it won't spin on the shaft, which they tend to do with new tight bearings or old seizing bearings.
That was proper engineering but unworkable with small stuff.
The metal punch (center punch) will work however if the raised surface is then too big you can load the bearing causing premature failure as you can if the bearing spins on the shaft.
Loctite make bearing fit which takes up a few thousands of an inch if the bearing has been spinning on the shaft. How do you guys remove and fit the new bearings because doing that wrong can cause premature failure as well.
 
I oil the shaft then put the a small bearing puller on, pull the bearings off, i then clean the shaft, check for damage, seat new bearing and use old bearings to tap down the new bearing trying not damage the new bearing.
 
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Thats cool rpm, where you an engineer or did you work on industrial stuff.
I service boilers at a engineering company that supplies bearings, he recommended SKS to me and i can tell you they are far better than cheap bearings and noticeable quieter and smoother when burner is running.
SKS & NGS (think that`s right, was 20 odd years back 🙂) are the 2 we used.
Did my apprentice in a machine shop (lathes, mills, grinders etc), then moved to machine maint` when I got tired of being shackled to a machine all day then fell into refurbishing commercial pumps & motors followed by plastic pumps today.
 
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Loctite make bearing fit which takes up a few thousands of an inch if the bearing has been spinning on the shaft. How do you guys remove and fit the new bearings because doing that wrong can cause premature failure as well.

On Riello motors, the oil pump side can be too slack for the bearing and a slight bruise on the shaft keeps it tight.
I don't get too fussy anymore with burner motors, but just keep kerosine away from them and avoid damaging motor windings.
I use a bearing puller where possible and tbh I can manage to use two flat blade screwdrivers to prise the bearing on oil pump side off easily. Not professional I know, but does the job.
I use an old 1/2" brass ball valve tail to hit with a hammer to tap the new bearing on as it is perfect fit for centre of Riello size bearings.
 
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I oil the shaft then put the a small bearing puller on, pull the bearings off, i then clean the shaft, check for damage, seat new bearing and use old bearings to tap down the new bearing trying not damage the new bearing.
If you work a lot with the same size bearings then ask a local machine shop to make up a hollow drift from Bronze, an Alloy or even hard Nylon / Plastic, the hollow centre to be a few thou larger than the shaft and long enough so you have a solid face to hit with your mallet, the face that rests on the bearing to be slightly larger than the inner race but smaller than the outer race.
 
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Best i bought a wiper arm puller online to pull the bearing on the pump side, the jaws are small enough to fit under the bearing, but if they are tight the screw drivers are the answer.
 
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Thats high precision work rpm. I am sure you have come across all sorts of faults in pumps and bearings over the years.
Something like 90% of bearing faults result in pump failures.
The condition of the shafts and the housings holding the outer race are so important are all bearings are precision made.
End of sermon. 🙂
 
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