Grease for gearbox?

I built a small reversing gear box for a model project using a weedwacker motor. Motor output RPM's is about 3000. Construction is simple with spur gears.
Input and output shafts for gearbox are mounted onto oillite bearings. First used 90wt gear oil but found major oil leakage at bearings. Could grease be used instead and if so could someone kindly point out a good grade and brand? Also if grease can be used should box be packed almost full?

Any comments, help would be welcomed!

BTW, model project can be seen at http://www.geocities.com/eastpac01/index.html

Thanks, Rusty

Pumping grease into a gearbox that won't hold oil is an old maintenance trick that works quite well in desperation.

I would pump it full...any excess will relieve itself thru the open areas and the level should eventually stabilize. Mobil AW2 or any #2 grease should be a good starting point. I've seen #0 grease spec'd for a spur gearbox but that had oil seals.

As it won't be perfectly sealed, there will still be some leakage, but the gears won't be damaged.

You may want to consider oil seals if you can fit them in...Chicago Rawhide (bought by SKF???) is one old-line name.

-Matt

Though it should also be considered that stiff grease will just have neat channels cut in it by the gears and then the grease will just be smiling at the gears which will eventually shed their lube. Soft grease less likely to do this.

Anything that needs to be reliably lubed like a gear box needs seals incorporated in the design.

John

not having had a lot of experiance with grease, but my $.02 worth is:- Hand electric tools always have grease filled gearboxes, my Black & Decker is 36 years old and the grease is still in good shape. One other area is the constant velocity joints splines on front wheeled drive cars are grease filled tho the grease is supplied with the rubber boots that surround the sliding joints (unable to buy it separately?). I would use a LMP graphite loaded grease and only fill the cavity sparingly, if the gears run hot, the grease will melt and run, hopefully into the required area and not out of the seals!

Or wear gloves?

This is an interesting topic. Here is some info from the UK: http://www.lubricants.co.uk/industry_powertools.html

First of all, 3000 rpm on a weedwhacker is below a low idle speed. Most run around 7000 to 10,000 rpm at wide open throttle and idle between 3500 and 4000 rpm.

The function of the grease is to sit out of the way until something gets hot. Then the grease softens and flows to relubricate the gears. High temperature grease can be a bad thing in this case as hi temp grease doesn't soften until after damage has happened to the gear teeth.

If you pump the gearcase full, there must be plenty of venting as about half will get blown out. Most of the heat generated is whipping of the lubricant. I have seen filled gearboxes get hot enough to have all the steel parts turn blue due to heating of the grease.

I was involved for several years in design and testing of a 40:1 worm gear box with 10,000 prm input and 250 rpm output. Initially it was lithium grease lubricated, but most burned up within 25 hours of use. The lubricant was changed to Mobil SHC634 synthetic and lip seals were installed at input and output shafts to control leakage. Anaerobic sealing compound was used on the joints and we got in excess of 300 hours with the gearcase starting at 294 degrees and dropping to about 250 degrees F after the first hour. About 1/2 HP was consumed in the gearbox and about 1HP was actually output.

Hahahha The company I work for hosts chicago rawhide's servers. And i've spoken to people there trying to help them with their equipment. *grins*

The function of the grease is to sit out of the way until something gets hot. Then the grease softens and flows to relubricate the gears.

Click to expand...

WRONG.......

Grease is there to lube, reduce fricton & wear, and keep things from getting hot.
If it gets that hot without any lube, your already SOL. Most of the time its NOT where its supposed to be or hard & old and dried out. Good intentions, but not very effective.

Gentleman,

Thanks very much for the input. I haven't honestly thought about oilseals and will look into some sort of revision for this.

I was trying to use the KISS method...okay I was being lazy!
No, seriously, I haven't really thought about oil seals but instead remebered seeing a grease being used in a transmission used for a riding lawnmower.
The smell of the grease used although I sure it was old reminded me strongly of Johnson Paste Wax.
I used bronze bearings for the output and input shafts for the unit I built based on the Peerless lawnmower trannie I've seen with the paste wax smell. Now I know why it is they used a grease compound.

Oh BTW, make sure the gearcase top cover is in place when hitting the high rev's. You'd be amazed just how far grease gets slung. Oh well, the neighbor mentioned something just the other week about getting the wheel bearings on his boat trailer repacked...

Anyhows, thanks for all the info