Worn Myford quick change gearbox lead screw bushes

My quick change gearbox lead-screw bushes are worn and the gearbox oil leaks out until it reaches the bottom of these bushes.

Myford/RDGtools don't supply them, and I'd make them if I didn't have the lathe apart at the moment, does anybody know of another source for these bushes?

C J,

There is a maximum fill level for the gearbox set by the black slot headed screw below and left of the selector ramp.

The bushes are not intended to be oil tight

Regards Brian

If you place a suitable size O ring around the outer collar you can limit the amout of oil that escapes, do not over oil the cups that supply these bearings. Bearing will be a standard size "oilite" type, plenty of suppliers for these.

Hi KWIL,

I have now measured the said bushes, 5/8" inside diameter, yes, but the outside diameter is smaller than 3/4" and my leadscrew is also worn where it runs in the bushes. So I would have to turn the outer diameter of some stock imperial oilite bushes down by "hand feed" and just accept the wear on the leadscrew.

A stick on oil seal housing would definitely help on the chuck side of the box, sorry about the image on the squew?

Regards,

Colin

Better

Edited By C J on 04/07/2018 10:36:35

Hi C J Had a close look at my S7 [1977/8] and there is no bushing in the gearbox casting for the lead-screw it runs in the gearbox main body.

As far as oil leaking out if your oil level is the same as mine then "full" is level with the bottom of the lead-screw hole so little oil should leak out -- is it possible you are overfilling the gearbox or maybe the level plug is in a different position due to design changes over the years? Remember the gears etc are splash lubricated.

The oil level plug is left of your finger in the photo on the end of the gearbox, it is not the large domed screw on the front LHS of the gearbox -- this is there to facilitate fixing the gearbox the machine and allows entry for tightening a screw that holds it against the bed casting.

Cheers John

One trick with worn leadscrew is to add a block to the side of the QC gearbox, or to the existing bracket on non-gearbox models, containing an Oilite bush that bears on the unworn part of the gearbox. It would be easy enough to incorporate a seal or basic o-ring into such an add-on.

No bush is going to be oil-tight. It would seem that the gearbox has simply been over-filled. I would expect JF is spot on as the pic would suggest (from the stamped lettering/numbering) that the level should be no higher than the bottom of the bush. Oilite bushes require the minimum of lubrication as they are either like a sponge or impregnated with virtually a lifetime lubrication at manufacture.

CJ

I had the same problem of a worn bushing on the gearbox of my aged Super 7 some years ago. I extracted the bush, and to my surprise found that it appeared to be steel, I contacted Myford, who were still in business at the time, and spoke to the spares chap (Malcolm?). He told me that he couldn’t help because there was no bush fitted in this position - strange because I was holding it in my hand! Anyway, I turned up a replacement out of phosphor bronze. Fortunately most of the wear was in the bush, not on the leadscrew, so I was able to get a good fit. 15 years later it’s still going strong with negligible play.

CJ,

What you have been told so far is correct, no iolite or other bush will retain oil. The whole Myford lubrication philosophy is one of "total loss".

Oil should be added up to the level screw and not above. after refilling leave the level screw out for a while as it is of small diameter and it will take some time for the actual level to establish its self.

You do not say what grade of oil you use. Never use Esso Nuto or any other H32 grade oil in the gear box. The instructions that came with my gearbox (one of the last made at Beeston) states on page 2 that K68 oil should be used however later instruction in the book (page 15) specifies SAE 30. Both of these oils have a higher viscosity that H32 and K68 is clingy and less likely to leak through a small gap.

Are you sure about the OD of the bush as Myford would surely have used a standard 3/4" OD bush rather than go to the trouble of machining a standard it down for no good purpose?

I have a 5/8” bore x ¾ x ¾ Oilite bush that you can have or a 5/8” x 7/8 x 7/8 if you have to machine one down to an odd size. Send me a PM if you want one.

If the leadscrew is badly worn or has a rough surface it could be reclaimed by having metal sprayed onto the worn area which is then reground to your required size. When I was running an engineering department I had two very good suppliers that offered this serves with very fast return times. One was in Luton and one in Northampton. This is Avery good and accurate way to reclaim worn shafts.

Eric.

F Y I, The Myford QC gearbox categorically did NOT have bushes fitted to the bores where the Leadscrew runs. Any that do are third party, post production modifications to account for wear. All Myford boxes had the steel Leadscrew running in the cast iron of the box at BOTH ends. Malcolm was stating fact.

I imagine that the original casting of the gear box has become worn, and someone has had it bored and bushed.

With reference to a bush looking like steel, Oilite make sintered cast iron bushes. Or some machinery I have seen had steel bushes with white metal as in the bearing shells on an automotive crankshaft.

Oil leaks, British oil warning system, if there is an oil puddle on the floor, there is probably oil in the machine.

Ian S C

Many thanks for all the replies and advice on this subject.

Since buying my second hand lathe I have come to realise that some parts might not be as they seem, as previous owners might have either closely replicated or modified a part to resolve some wear and tear with the lathe itself.

In other words, it has a history which you learn about as you go and try to equal or improve upon.

I have seen many kinds of sintered bushes and also seals and swear I saw a shaft on a Citroen which had no seal but instead a spiral groove which ran counter to the direction of rotation and, I think, encouraged the oil to go back in !

I think I will live with the play after all until the next strip down.

Regards,

Colin

Found in earlier Morris Minor engines at the rear of the crankshaft for another and possibly at the tail shaft of the gearboxes. Made redundant, mostly, by contact seals.

Lots of inclined powder screws employ a fine pitch at the bottom end to prevent powder leakage.

The spiral groove on the shaft type of "seal" was common practice before mid-20th century. My 1942 Harley uses it for the engine mainshaft "seal" in behind the primary drive sprocket. Seems to work ok in use.