Belt slip

[AJWParticipant @ajw]

I was turning some 2.25 inch m/s bar today on my ML7 producing swarf by the bucket load when all of a sudden drive was lost.
Motor pulley was slipping so I tightened it a bit and away we went again until, slipping again!
Seemed to only occur after everything got hot I thought.
Last year sometime I changed the motor pulley for a larger diameter item to give a slightly higher top speed. The original was steel and the replacement is aluminium.
I am suspecting the pulley is very polished in its V but would have thought it should still be capable of transmitting power, the belt is certainly tight enough now.
Any thoughts on alloy versus steel/cast iron pulleys?

Alan

[AJWParticipant @ajw]

[I.M. OUTAHEREParticipant @i-m-outahere]

Check the motor shaft key it may have sheared ?

Usually a slipping belt will sqeal -not always though .

Check the contact area on the pulley it may not be contacting the entire flanks of the belt .

The belt may have gone hard and glazed up , check for cracks and if there is any oil on the belt .

Alloy pulleys wear faster than cast also check the pulley alignment , if they are offset it will wear one side out and widen the V over time .

[Mark RandParticipant @markrand96270]

I actually turned a larger pulley for my ML7 because the tiny motor pulley it started with was overheating the belt. the larger pulley was kinder to the belt. That was made from mild steel. A bush was turned to fit the motor shaft and a slot cut in it for the key, then the bush was Loctited into the hole bored in the new pulley. Custom pulley with key seat, simply produced.

As for the belt slipping, check that the belt is riding between the pulley sheaves and not sinking down to the bottom of the pulley groove. It it's doing that, then the pulley is too large for the belt, the belt is worn or r the pulley is worn. Solution as above.

regards

Mark.

[vintagengineerParticipant @vintagengineer]

You could try spraying some belt dressing on the belt.

[Mark RandParticipant @markrand96270]

Belt dressing rarely does a lot of good on V belts. DAMHIKT!!

[HopperParticipant @hopper]

Posted by Mark Rand on 30/12/2017 22:56:34:

As for the belt slipping, check that the belt is riding between the pulley sheaves and not sinking down to the bottom of the pulley groove. It it's doing that, then the pulley is too large for the belt, the belt is worn or r the pulley is worn. Solution as above.

^^^^ This.

The original Myford belt is a Z section, smaller than the more common A section used on the Myford headstock to countershaft belt. Check the new pulley you fitted is not the wider A section and the old Z section belt is not sitting in the groove seating on the bottom instead of the angled sides. If so, the solution is to fit an A section belt, it will ride up on the tops of the Z pulley but will still work OK. I've been doing this for some time with a Z countershaft pulley and A motor pulley. No problems.

You say it only happens when hot. Check the countershaft and headtstock bearings are not getting hot and nipping up after a bit of use. Loosen the belt tension lever and rotate both shafts and the motor by hand to make sure you don't a have a tight bearing somewhere.

Edited By Hopper on 31/12/2017 03:15:37

[AJWParticipant @ajw]

Well thanks for all you replies, had a proper look today, cover off and I could see why.
Oil from the countershaft bearing had found it’s way to the outside of the large pulley and got on the belt!
Cleaned belt and pulleys with a panel wipe product and after drying the belt it looked to be free of oil, although if the worst comes to the worst I might need a new belt.

Alan

[Mark RandParticipant @markrand96270]

That is a bloody nuisance on the ML7. I will admit to have thought about attaching a sheet steel oil flinger to the clutch/pulley of my ML7. I try to wipe oil off it, but sometimes forget.

[AJWParticipant @ajw]

It’s interesting to note that the oil was on both sides of the pulley!
It had penetrated the bore of the pulley and been flung out of the non bearing side!
I must admit to being probably over enthusiastic with the oil can but in all the years I’ve owned the Myford I haven’t encountered this before.

Alan

[HopperParticipant @hopper]

Posted by AJW on 31/12/2017 20:08:58:

I must admit to being probably over enthusiastic with the oil can but in all the years I've owned the Myford I haven't encountered this before.

Alan

Could be you are due for a new belt. They harden up and lose their grip over the years.

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