Harrison M300 or M250 pulley/belts problem

Hello,

I have a Harrison M300 which needs new belts. I can't get the old ones off the spindle pulley because they're blocked on by the bolt that holds the head-stock onto the bed - and I'm certainly not removing that. They almost squeeze out but not quite, I could probably force them but it doesn't feel right and I fear getting the new ones on the same way could damage them.

So it looks like I need to get the pulley off the spindle - which is the bit I'm not sure about. The pulley has a cap on the end of it which is held on by two coiled pins and on top of that is an m8 machine screw that goes into the end of the spindle. I don't see a ready way of getting the cap off - I can't get a bearing splitter behind it to pull it off and I'm sure drilling out the coiled pins can't be the intended approach. I could maybe get a big bearing puller and pull the pulley of with the cap in place - but even that doesn't look Ideal as I can't really access the spindle to push against, I'd have to put a screw into it and push against that. I don't know how tightly the pulley is on but it certainly won't come off with hand pressure. The motor pulley came off quite easily with a puller but went back on with hand pressure after a tiny bit of cleaning, I suspect this would be similar.

The M300 manual shows the cap part without coiled pins, but mine has pins and they look original, the similar M250 has the same type of setup and the manual shows the pins. I'm not clear what the cap and m8 screw is actually for - except that it might be belt and braces to stop the key from working its way out.

Obviously I could do without damaging any parts so I'd be really grateful to hear from anyone who has come across this before and can either provide advice on removing the pulley or some other way of getting the belts off and back on.

Thanks

... I guess it's not the 'spindle' pulley - I just mean the big pulley on the gear box not on the motor.

I replaced the belts on mine whilst I was renovating it. I don't remember having any difficulties there, other than adjusting the motor, as the bolts are inaccessible. I certainly didn't have to remove bolts that hold the headstock to the bed. If I had, I'd probably have lifted off the head and cleaned out the ton of swarf thats jammed in under it.

If you could post a picture of what's causing you trouble I'll compare it with mine and let you know what I did.

Rob

Thanks, here's a picture, arrows point to the bolt that the belt won't pass and the two coiled pins (out of focus).

Just to be clear - I'm not contemplating taking that bolt out, just how to get the pulley off.

The coiled pins are rollpins, and will be hard, so drilling is unlikely to be a viable proposition.

They appear to act as dowels between the hub and something behind.

What is behind the central setscrew? It looks as if it does not retain the pulley.

Is it a jacking screw, to remove the pulley? BUT

Any sign of a grubscrew in the bottom of the Vee of the pulley, to retain it?

Howard

If the cap head bolt is your only problem then whip it out replace belt refit job done

Certainly no grub screw and I can't see anything else retaining the pulley so I guess that's what the roll pins are for?

As near as I can tell the pins go into the spindle (or shaft or whatever it's called).

Those coiled pins give the pulley a 'don't take this off' sort of vibe - but then how do you replace the belts?

That screw seems to go into the shaft but came out easily and isn't obviously holding anything, I wonder if it's just used to install the pulley as it would push it into place nicely.

It's a pretty critical bolt and awkward to get to and re-tighten. I'd rather leave it alone if possible.

I would go with Ian’s suggestion. It will not be the only bolt holding the thing together!

I do hear you - but I'd like to hear from someone who's encountered this before too.- it's quite a common lathe and I'm sure someone will have has the same issue.

Michael, have you got or can you borrow a puller large enough to fit the pulley?

If you can, fit that and push on the partially unscrewed centre bolt, I think you will find

the pulley will slide off the shaft. Don't worry about the cap it will come off with the pulley.

You may find you have to replace the bolt with a longer one to get the pulley to clear the end of the shaft.

Keith.

Lathes UK shows a similar pulley / rollpins / setscrew for the M250, but not in the same position as yours seems to be. The M300 does not show the belt drive arrangement.

It looks as if Brochures and parts manuals are available from Tony Griffiths.

Check with him, he will probably provide a solution to your problem.

The setscrew looks to be tapped into the hub of the pulley

POSSIBLY, if you can find and release what retains the pulley, the setscrew could butt against a steel bar held in the chuck, and be used as a jacking screw? Maybe the pulley is pressed onto the shaft?

Howard

Keith, thanks - I was thinking of that as my next step. The main thing that concerns me about that is getting the roll pins back in when I put it all back together - assuming the pins come out with the cap do I knock them out once it's apart and put new ones in? If so how do I drive them into the shaft? I don't imagine hammering them could be right. I guess I could use that screw thread to push them in but I can imagine that going wrong too...

Rollpins are usually put into place with a hammer.and flat ended punch. They are intended to be an interference fit, being springy. The ends are tapered to aid starting into the hole. But do keep them upright until they are well entered. Being hard, you are unlikely to raise much of a burr.

Howard

Thanks Howard. In the M300 manual that I have the pins aren't shown on the motor/pulley page (301/2) but one is shown on the head-stock page (302/2).

I'm not sure which set-screw you're referring to - the motor pulley has one but I can't see one anywhere on the shaft pulley (which doesn't have a hub).

I get that - but can hammering on the end of that shaft (which presumably runs in bearings not designed to take much thrust) be a good idea?

Michael, I wouldn't worry about the roll pins at this stage, if it all comes apart as I think it will you should be able to tap the roll pins back in with a soft drift. Even a mild steel drift would not damage them as they should be hardened. I doubt you will need new ones unless you damage them in some way, but I can't see that happening!

Keith.

Thanks - but it's not damaging the roll pins I'm worried about, it's banging on the end of that shaft with a hammer! I don't think the bearings are designed for that.

You wont be hitting it hard enought to do any damage. ( at least I hope you wont ! ) they should enter with a light tap.

Keith