Myford S7 countershaft bush temperature

I have just fitted taper roller bearings to the spindle of my 1981 S7, which I bought little used in 1991. I also fitted a Fenner drive belt to the spindle / contershaft . Finally I fitted new bearings to the electric motor. The clutch and countershaft assembly, were checked and found to be in good order and free running. The S7 is running smoothly and the spindle turns freely without play. Two rings on my test bar were the identical diameter when machined.

The headstock bearings run cool, as does the drive motor and the countershaft bush next to the clutch lever. However the bush next to the clutch runs quite warm reaching 45degrees Centigrade. The 2 drive belts have a small amount of play.

All components are correctly fitted to the countershaft / clutch. They had not been opened since 1981! This lathe has always done light work, as I have a Colchester Student in good condition for the bigger jobs.

Should I look at replacing the bush?

Thank you for any advice you have.

Dennis,

As no-one else has offered any comment I'll add mine. How long does it take for the bush to reach that temperature? I haven't felt mine after a long session but am willing to bet it doesn't reach that.

Is there any sound of distress associated with it? You will of course have pumped some oil in but was the nipple blocked with dried grease? I had to clean mine out in solvents to get mine working after I bought the lathe, it wasn't the only example of grease having been used in the wrong place.

Regards

Brian

Mine gets quite warm after a prolonged period of operation but never having measured this temperature I would not like to say other than I can bear my hand on it. But I wouldn't like to hold my hand on it for very long periods. Just make sure you keep an eye on it and keep it lubricated and as Brian says make sure that the oil is actually getting through to do it's job.

Phil

You could slacken off the spindle drive belt a little. Those link belts are a bit stretchy to my mind and can be deceptive as to tension. They grip quite well so they don't need to be any tighter than needs be. So long as then are not slipping under normal conditions it's no bad thing to have the belt slip when something goes wrong.

regards Martin

Dennis,

I felt my countershaft bushes today after steady use for a hour or more. Both were cool to the touch.

Regards

Brian

Thank you for the feedback. The bush continued to get warm within a couple of minutes without any distressing noises, so more investigation....

The bush was getting oil, but via a passage from the oil cup that passed through the bush directly onto the spindle. The smaller bush at the clutch lever end was fed in the same way. I thought that oil was to be passed through the Oilite bushes to the shaft?

I removed the countershaft today and found both bushes to be acceptable, whilst the countershaft was in excellent shape. Critically the small bush and the portion of the shaft in the bush showed enough oil to be well lubricated, whilst the large bush and its portion of shaft lacked evidence of much oil, even though I had pumped 32 hydraulic oil though the passageway.

I had also slackened the drive belt tension from that recommended by Fenner.

Measuring the countershaft showed its diameter to be 0,8750". The front bush was 0,8775". Is that the correct clearance?

I'd put new Oilite bushes in just for good measure. They are cheap as chips if you buy from a bearing supplier. You have got new headstock bearings and new motor bearings so might as well make it the full set.

2.5 thou clearance is possibly a tad on the loose side. Probably aim for one thou clearance when new.

Edited By Hopper on 26/02/2019 05:22:48

PM sent Dennis.

Does anyone know the dimensins of both bushes as I need to replace them on my MkII 1958 S7 lathe. Whout the dimensions I would need to purchases from Myford. With the dimensions I may find some locally availlable bushes.

Peter

I ran the S7 with the stripped Countershaft only connected to the motor with the clutch operating lever removed. The belt had sufficient play. The countershaft has 2 thou smaller diameter than the ID of the oilite bushes.

For each test I first removed the countershaft and lubricated both Oilite bushes with the correct hydraulic oil. I then repeated this test but with an automatic transmission oil containing Molybdenum disulfide

The large bush still got very hot (70 degrees C) within 5 minutes when the countershaft was running at high speed, but just warm when running at the slower speed. The small bush remained cool throughout.

The next step is to replace the bush.

One thing to check is that the pivoting H frame that holds the countershaft could be bent out of alignment. This often happens on Myfords because of the use of that cheesy Mazak zinc alloy for the casting. (Rolls Royce of lathes my derriere.)

But also because users tend to use the adjusting screw at the right hand end to increase belt tension while leaving the hard-to-access one at the left unadjusted. This - along with belt tension - eventually puts a twist in the H frame, making the bushing out of alignment with the shaft (as in pic below) and shaft running on the edges of the bushing. This would make it run hot. Tell tale is one adjusting screw sticking out further than the other. See pic below.

Cure is easy enough. You can see the twist by eye, or by laying frame on flat bench. So hold the H frame in a good solid vice, or clamp it to the bench, and put a long piece of bar through the bushings where the counter shaft would normally sit and pull on the end of the bar to twist the cheese metal H frame back straight again. Or a longer bar between two pieces of bar through the H frame, as in the pic shown below.

With new bushings in place, you should be able to slide the countershaft, or a longer piece of rod same diam. (It's just a piece of 5/8" bright mild steel bar IIRC) in through one bush and it should enter and slide through the other bush without needed force, If not, pull on the far end of the long bar until the business end is properly lined up with the second bushing and it slides right in.

Edited By Hopper on 28/02/2019 00:15:55

Edited By Hopper on 28/02/2019 00:21:57

From memory the shaft is 5/8" (you can measure that to check it.) and wall thickness is 1/16" so OD would be 3/4".

Hopper

Dennis’s machine is a Super 7, but your last 2 messages appear to relate to an ML7.

According to the Myford website, the Super 7 countershaft bushes are 7/8 I.d. and 1 1/8 o.d. The lengths are not specified.

Mike

Hopper

Thanks for your pointers on the H frame.

I have a good length of 7/8" bar which I used to check alignment when I was doing the countershaft test yesterday. The 2 bushes were perfectly aligned.

My S7 was in very good condition when I bought it in 1991. But your comments are a good warning to buyers.

Dennis

Ah yes. Larger shaft for clutch rod up the middle etc. Thanks for clarifying.

That's odd. Can't think of why a slightly worn bush would run hot if all is in line. But stranger things have happened! Have you checked that belt slip or clutch slip is not heating up the whole large pulley/clutch unit , which in turn is heating the shaft and bush at that end?

Hopper

There is no belt slip. The clutch is not slipping either.

The S7 is running extremely well, silent and very smooth except for the countershaft bush getting hot and pushing out oil. This occurs as 1. bubbles blowing out from the oiler and 2. leaks from the ends of the bush.

The bubbles effect has been reported in this forum a number of times but no one has explained what might cause it.

The bubbling and leaks start while the bush is still cold. It is almost like the shaft is running in an eccentric bush and acts as a form of pump. As the bush loses oil, friction increases and heating occurs. Adding oil achieves some cooling. So I currently need a total loss lubrication system!

The problem is really evident at the high speed setting (740 to 2105 rpm) - at the low speed setting (210 to 600 rpm) the bush hardly gets warm. At 2105 rpm it reaches up to 70 deg C within 5 minutes.

The S7 is usable within these limitations for the work I do. New bushes and thrust bearing will be fitted.

Thanks for your interest.

The symptoms suggest a damaged bearing, perhaps to the point it is indeed acting as an eccentric pump!

In good condition the bush and shaft are both highly polished. When spinning there should be no metal to metal contact at all. Instead the bush and shaft are separated by a thin layer of oil at high pressure, several tons per square inch, over which the shaft floats. The pressure is created by the turning shaft, in effect slowly pumping oil in on one side, and out on the other. When working correctly the flow of oil is relatively slow.

A big problem with this type of bearing is that when the lathe is stopped, there is nothing to maintain the oil pressure and shaft and bush come into direct contact. The two metal surfaces rub badly until the rpm is high enough for an oil film to form. Most wear occurs as the bearing is first spun up to speed and when the shaft grinds into the bush as it slows down. The collisions cause metal particles mix with the oil and have a scouring effect. Eventually the resulting scratches and pits get bad enough to stop the oil film forming properly, and metal rubs on metal more or less continually. When that happens the bearing gets hot, thinning the oil, and progressively causing yet more surface damage. Time for a new bush!

Scoring happens very quickly when the bearing is run dry for any length of time due to a blocked oil feed, wick trouble , or empty reservoir. Even if it doesn't seize, the bearing is soon ruined. Maintenance is important!

Provided it's lightly loaded and kept flooded with oil, a slightly damaged bush/shaft combination might last for many years. However, although most of the resulting wear concentrates on the softer bush, there's a distinct risk that the more expensive shaft will have to be replaced too. I think a persistently over-heating bearing should be changed as soon as possible.

Dave

Dave

Thanks for your explanation.

The bush fitted by Myford is an Oilite which is pre-loaded with oil and supposed to last for a long time (Myford ask that you keep the oil cup topped up as needed). My Oilite bush currently has 1 thou clearance from the hardened steel countershaft which is indeed highly polished. The bush is not highly polished, but the bearing surface is in reasonable condition. The 2 countershaft bearings and their associated ball thrust-bearing are going to be replaced.

I changed the bushes on my early S7 some time ago. As you press them in, they get smaller. After some conflicting advice on this forum, I established that you may ream them as long as the reamer is really sharp, so that it does not rub. This was the advice from "Oilite" themselves on their web site. I bought a new expanding reamer, (cheaper than a solid one) and carefully brought the bushed back to size. Been no trouble since, and neither of them get warm, even with prolonged use.

Maurice