Small Engines (Lawn Mowers, etc.): follow-up question to allis chalmers transmission, input shaft, allis chalmers

Question

transmission, inboard   Thanks Eric for your original answer: http://en.allexperts.com/q/Small-Engines-Lawn-1746/2011/9/allis-chalmers-snowblo  

Unfortuantely there is no obvious fill plug on the side, see attached picture.  I noticed something that looks like a plug at the top (recessed, square hole) but it seemed odd that the whole gearbox would get filled to the top.  Could this be it?  I have a picture of the outboard side but can only upload one picture.



As for forums, they mainly talk about their tractors and the snow blower attachments for their PTO's.  this was the only site where there was any mention of this model # of snow blower.

Answer
Interesting...some of the old units (gearboxes) used to get filled with a lot or 80-90W gear oil...basically filling the gear box to the top.

I've never had an Allis gearbox apart so I'm not too sure how the input shaft gets lubricated.  If it were me I would use a wire or coat hanger and measure (outside the case) from the middle of of the input shaft to the top of the gearbox fill hole.  I would use the wire like a dipstick and fill oil up to the middle of the input shaft...the shaft should be well lubricated if it is sitting half way in oil.

I doubt it is too critical if you over-fill the gearbox other than oil may leak out the input shaft and worst case get on the belt causing it to slip.  The internal gears and/or chains should be able to handle over-filling as most older gearboxes just splashed oil inside the gearbox.

The reason most small engines can NOT be over-filled with oil is because they use oil slingers to splash/throw oil around inside the engine.  Too much oil and the slinger is submerged in oil and can't sling it around inside the engine.

Have you checked any of the message boards to see if an old Allis mechanic is lurking around on the antique forums?

Eric