Unusual gearbox noise

[ldh04]

I have a 85 ton hoist with dual gearboxes that have started making a semi-grinding noise on lowering and raising with little or no load. The gearboxes are over 50 years old, but the operation is very limited(say 200 hours per year)

The oil was just changed (possibly for the first time) using a 90 weight oil as recommended by the crane manufacturer. Any thoughts?

 

[hacksaw]

you have to check the bearings...

 

[ldh04]

The bearings appear to be fine. It has been suggested that the noise is due to the oil change and that possibly we should put the old oil back in????? I have just never heard of this type of problem.

 

[automatic2]

No need to put the old oil back, but it could tell you something. It's probably too polluted to say anything about box condition but it's consistency will have established a reference that you are likely comparing too, as in, it sound different than before. Assuming that no mechanical shortfalls occured during oil change (contaniments)it may be that the new oil has flushed deposits within, in solvent fashion, and in fact may lead to excellerated wear of the box. Don't despair however as the box has likely given you good service for many years and just needs a little TLC to make sure it gives many more years of service. I would apply a couple of observations;
- audio, with a stethiscope to try and identify area of concern
- drain and refill oil after a week to inspect it's metallic content. Make sure you have high EP content in replacement oil.
- visual inspection if you have port access. Earlier the better so you have that reference.
- compitence, don't injure/pollute the box unintentionally.

The beauty of older boxes is the opportunity for repair. Gearsets can be expensive but bearing housings and shafting can typically be reworked to restore boxes without replacement costs.

 

[quark]

Did you flush out the gearbox with solvents before changing the oil?

 

[ldh04]

Flushing was not performed prior to oil change

 

[hacksaw]

what oil weight was recommended by the manufacturer?

 

[ldh04]

Originally it was around 30 weight, however, they are now recommending a 90 weight, which is what was put into gearbox. Now they say it is okay to return to the 30 weight.

 

[NickE]

is that 30wt motor oil? which was replaced with 90wt gear? IIRC the viscosity of 30wt motoroil is the same as 90wt gear. its the EP additives that really make the difference.

 

[ldh04]

Since I am electrical, What is EP??

 

[NickE]

Extreme Pressure -- IE why gear lubes stink so bad.

 

[hacksaw]

EP oils have a high film strength and keep metal to metal contact down

 

[tygerdawg]

I did a short term contract with a gearbox manufacturer...gearboxes always used MobilGear 630 oil. I would think SAE 30 motor oil is too thin for gearboxes. I saw SAE90 once, and it was like syrup, maybe too thick. Gear oils are formulated for the "EP" , heat, film thickness, etc. I would guess this is the root of your noise problem.

TygerDawg

 

[ldh04]

Thanks everyone for your replys. We are looking at the oil types and may replace the oil with the older type. Will let you know the results.

 

[MintJulep]

Did the noise start immedieatly after you changed the oil, or did it take some time?

Are the bearings oil lubed, or greased?

If oil, how is the oil supplied to the bearings? Is it splash lube?