MC900 help please!!!!

[brainstrust]

My lathe is broke!
Looking at the picture the lower left wheel works fine.
The belt though becomes too loose on higher speeds and actual now I can't move the "speed shifter" at all.
Any suggestions where to start?

https://i.postimg.cc/L4WRfF41/20190731-151310-1.jpg (https://postimg.cc/w3DS8Pmq)

[brainstrust]

Could it just be that the belt has stretched??? With help I can get the speed shifter to move it just likes to be working for it to!!!

[Skew ChiDAMN!!]

Looking at the picture the lower left wheel works fine.
The belt though becomes too loose on higher speeds and actual now I can't move the "speed shifter" at all.

At higher speeds the head (upper right) pulley should be "opening up" to give a smaller diameter, while the motor pulley should be "closing up" to give a larger working diameter. Although you say that the motor pulley is working fine, if it sticks and fails to close up enough (it's only spring loaded after all), the belt will slip at higher speeds.


Could it just be that the belt has stretched??? With help I can get the speed shifter to move it just likes to be working for it to!!!

Yeah, reeves pulleys like to be turning when you adjust the speed lever.

It's possible that the belt has stretched and, from appearances, it's due for replacement soon. Swapping it for a known good belt would answer that question and you could keep the old belt as an emergency spare. It's ALWAYS good to have a spare belt on hand. ;)

Personally, I suspect the pulleys need cleaning and/or a modicum of lube. ideally you'd disassemble the pulleys and clean them individually while looking for signs of wear or blemishes on the mating faces. Keep an eye out for anything that might cause less then smooth operation.

But if that's not an option, I'd grab a can of standard WD-40 or CRC and give them a liberal squirt (with the lathe OFF, of course!), paying particular care to where they mesh with each other. Start the lathe and slowly work the speed lever up and down a few times to work the WD-40 through. I'd repeat this process two or three times at least.

Now, WD-40 is NOT a good permanent lubricant, but it does a good job of washing out any grit between the pulleys while lubing them temporarily. So, when I say a liberal squirt I mean "hose them down." Don't be frugal... and be ready for it to spray off in all directions when you start the lathe! :D If everything seems to come good after this, then a bit of grit in the wrong spot was probably the culprit. I hope it's that simple for you.

After washing with WD-40, you want to apply a real lubricant, something that will stick around a bit longer than WD-40 (or CRC)... I prefer to use Inox, although if I've dissassembled the pulleys I'll wipe them down with Silverglide, but that's a bit on the expensive side for most peoples' taste.

[Redbeard]

Firstly, those pulley wheels are fragile. Resist the urge to force them to move our apply any leverage. They are a zinc die casting and are notorious for breaking. If you do break them, Hare and Forbes normally stock them, Carbatec don't.

When you move the speed control while the lathe is running a pushrod is activated, moving the back side (in your picture) of the spindle pulley along the shaft, thus changing the running diameter of the pulley. On the motor pulley the spring pushes the front side of the pulley along the shaft against the back of the pulley.

When the spindle pulley opens up, the motor pulley closes up and vice-versa. You have to see it to believe it. Try this video YouTube (https://youtu.be/acxU8ItTDUE)

It is the spring loading on the motor pulley which keeps the tension on the system correct. If that spring and pulley are not moving the belt will get loose as the spindle pulley opens up and gets smaller. What then happens is the gap in the spindle pulley gets too big and the belt jams between the pulley. You need to get your fingers in and pull the belt out from between the spindle pulleys. The speed control lever should now work. If not then the most likely cause is the back part of the spindle pulley has jammed onto the shaft. YouTube (https://youtu.be/Vg-M6mCzxV8)

From your photo it looks as if the spring on the motor shaft is fairly gummed up. This will probably translate to the motor pulley not moving, and the tension not being maintained in the system. YouTube (https://youtu.be/Dso7TwHZKAc)

YouTube (https://youtu.be/-JtiDBMBM_8)

Have fun.

[brainstrust]

in the slowest 4 speeds it works fine but from 5 and up the belt is too loose but the spindles do seem to operate as they should. The belt just loses traction.

[Fuzzie]

At a guess I would say the collar on the inboard side of the top pulley might have broken off. Any silvery looking dust around?

[brainstrust]

not that i can see but tomoz i'll take a piccy. i think i'll duck out too and try buy a new belt anyway. I have time off work so i need it to be working now!!!!!

[brainstrust]

ok i didnt realize the drive spindle should move in and out too.
it's not, so on not closing its not taking up the belt slack.
maybe just needs a good clean?????
what makes it expand and shrink though?

[Redbeard]

Quite likely. Just be gentle. I used a couple of zip ties to compress the spring while taking of the circlip. Then the spring can come off, and, if you're lucky, the pulley half should slide off. Lots of lube, be patient, I had to wiggle mine off, fractions of a millimetre at a time. The inner pulley half is held in place with a grub screw and you'll need to get this undone and off to get the key out. Once the key is out and the pulleys are off you can run the motor with some wet and dry paper loosely wrapped around the shaft to polish it off.

If after this your pulley piece doesn't slide freely you can use the shaft with the key left out to clean out the inside of the pulley. Lots of lube (I used wd40) and a firm grip on the pulley half should polish the inside surface quite nicely

[brainstrust]

fixed it!!!! Thanks for all the advice. Pulled a few things off, cleaned and lubed now back to it :2tsup:

out of interest, when I do need to buy a new belt, is there anyone made for cars that is the same size and v shape or must I get the specific one just for this lathe?

[Redbeard]

Excellent!

There should be a product number on the belt you have. Take it into a belt supplier, they'll be able to provide an equivalent.

[Fuzzie]

MC900 belt (http://www.woodworkforums.com/f8/mc900-belt-229147)