J&S 540 belt keeps coming off

[David Evans 16Participant @davidevans16]

HI,

I have a new to me J&S 540 surface grinder of 1961 vintage that occasionally throws the belt.

It is a plain bearing head and I have renewed the 4 rubber motor mounting blocks, it has a new belt and the tension is set as per the manual for the original style of belt which requires 0.060" of pre-tension. The head will run for an hour or so with no problem and the oil temperature differential to ambient is around 32 degrees C. If anything the spindle appears to be more free when warm. Spindle backlash is set to 0.0004" and I have tried increasing this to see if makes a difference. The belt does tend to track hanging off the bottom Pulley a few mm when running, but I can't see any means of tracking the belt.

In all other respects the machine is great, surface finish is fine, it just has this annoying habit of throwing the belt occasionally.

Has anyone had experience of this or any ideas on how to fix it?

Thanks

David

[David Evans 16Participant @davidevans16]

[Chris Evans 6Participant @chrisevans6]

With the oil filled head are you using the correct "Felt backed" style of belt ? The latter sealed head uses a yellow looking thinner belt. Try Andmar in Leicestershire for correct information/supply.

[Pete RimmerParticipant @peterimmer30576]

On my (very old) J&S grinder the motor was also rubber mounted. If those rubbers are perished or gone squidgy then the motor shaft won't be parallel to the spindle shaft and that can cause the belt to wander off the crown.

[David Evans 16Participant @davidevans16]

Hi Chris, the previous owner was in the middle of replacing the original belt that had broken, which is when he discovered all 4 rubber mounts had sheared. The new belt is the thinner yellow belt intended for the sealed bearing head. I will talk to Andmar tomorrow to see if the original felt type belt is still available.

Hi Peter, yes I have replaced all 4 rubber mounts with spares from Andmar I also did the 3 that support the hydraulic pump whilst it was out and cleaned.

Today it came off a couple of times in quick succession so had a bit of a play. If I slacken off the two lower clamp bolts and push the bottom of the motor mount away whilst the machine is running the belt tracks correctly. I think if fitting the correct belt doesn't work I will have to shim the bottom of the motor mount to track the belt.

Thanks for the replies, I will update the post if and when I solve the problem.

David

[Clive FosterParticipant @clivefoster55965]

David

Not a J&S I know but I was supplied with one of the thin yellow belts as part of the rebuild kit for my Clarkson T&C grinder.

No rubber mounts to worry about but I was still unable to establish fully reliable tracking of the belt. Not enough room under the guard for it to come off completely but I had to pick it off the floor many times during initial tests. Pushing the motor whilst running to get it tracking sounds very familiar! But it would never stay behaved.

Eventually I got frustrated enough to make a new motor pulley with around twice the crown of the original.

Fixed!

Having watched the movement of both the old and new belts during tests I have the impression that the translucent yellow belt, which has visible reinforcing webbing inside, is stiffer crossways. If this is so it seems logical that it needs more crown to generate the crossways stress variation that produces the self aligning force.

Clive

[David Evans 16Participant @davidevans16]

Ah,

"the translucent yellow belt, which has visible reinforcing webbing inside"

Which way should the belt be fitted, should the smooth "yellow" surface be on the inside or the outside? Mine was fitted smooth yellow side on the inside, visible webbing outside.

David

[Pete RimmerParticipant @peterimmer30576]

Mine had a plain leather belt and ran just fine. It was just about the only past of it that didn't give me trouble 😀

[Dave SParticipant @daves59043]

I just bought a replacement belt from Andemar, had a long chat about various things 540.

The yellow belt is the only available one and is ok for all wheel heads.

Smooth side inward.

Not actually got round to replacing mine yet, as the old belt is currently working.

Dave

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