Replacing Oilite Bushes in ML7 Countershaft bracket

[Chris Evans 6Participant @chrisevans6]

William. it looks like Richard is closer to you as I am up in the Midlands. Keep us posted on how you get on.

[not done it yetParticipant @notdoneityet]

Morty,

I expect your method was ‘rough ’n ready’ and clearly worked well enough.

In this instance, the part may not easily be held by a vise and this is a bearing with a relatively thin wall, so your method, using twice the force required (by removing and inserting simultaneously) may not be the best plan.

[Howard LewisParticipant @howardlewis46836]

I would advocate make removing and fitting bushes separate operations. Trying to do both in one operation risks damaging the new bush. It is thin walled and the forces involved might crush it and cause it to distort..

No point in saving ten minutes at the cost of damaging new components

Howard.

[Martin of WickParticipant @martinofwick]

I have had to do this for a 7 and S7, and confirm it is not a trivial job, especially if you intend to fit a new shaft. Hammering them in, using G clamps etc is not recommended, oilites will distort in a heartbeat.

You absolutely do need to make up a pulling mandrel, find lengths of threaded bar and have some appropriately sized tube washers and nuts to use as pullers.

Your mandrel should be stepped to conform to the exact external diameter of the shaft (avoid being smaller) with the wider portion say 10 thou less than the id of the bearing recess. The part upon which the bearing sits needs to be slightly (4-5 mm) longer than the bearing. Tap the mandrel for 8 or 10mm threaded pulling rod.

Pulling the old bearings out is easy, pulling the new ones in needs a bit of care on the initial alignment. Soak bearings in oil and use lots of oil when placing bearing on mandrel (it may be tight)

You may need to wring the mandrel back out of the bearing, or even need to pull it out.

My nasty experience came when I discovered the new shaft was a wringing fit in the new bearings. I tired slow running the shaft as a bearing run in, but it was clear that it was seizing.

Now here is the thing, you don't want to ream this type of bearing and even if you did, how would it be possible to do it accurately in situ? I solved this problem by making up a polished olive that was a couple of thou bigger than the shaft id. This is pulled through the tight bearing making it conform to the required size (process may have to be repeated). These bearings have a porosity, so within reason can be 'squeezed' to size.

Eventually, the shaft fitted albeit a little tight, but easily enough that after a bit of running in, all was well. The running in consisted of: run the shaft at min primary speed, as soon as the bearing gets cup of coffee hot, say over 50 C. stop and allow to cool. Repeat until happy that the heat build up is reducing.

With the lathe back in service, keep bearings well oiled and monitor temperature, ceasing operations if getting too hot until well bedded in. A year or so after fitting, my countershaft bearings get just slightly warm after a couple of hours run. I make sure the oil cups are full before every use.

[GeorgineerParticipant @georgineer]

Posted by not done it yet on 06/02/2021 09:47:37:

… your method, using twice the force required (by removing and inserting simultaneously) may not be the best plan.

NDIY, since the bush being inserted displaces the bush being ejected at exactly the same rate, wouldn't it remain constant at once the force required? (Ignoring all the other variables.)

George B.

[not done it yetParticipant @notdoneityet]

Posted by Georgineer on 06/02/2021 18:30:43:

Posted by not done it yet on 06/02/2021 09:47:37:

… your method, using twice the force required (by removing and inserting simultaneously) may not be the best plan.

NDIY, since the bush being inserted displaces the bush being ejected at exactly the same rate, wouldn't it remain constant at once the force required? (Ignoring all the other variables.)

George B.

Constant – yes (well maybe, but dependent on the force required for each separate operation being identical), The same – no. Total Work Done would be the same, but all in one operation. Same Displacement, so Force must be increased (WD = F x D).

Edited By not done it yet on 07/02/2021 07:00:43

[GeorgineerParticipant @georgineer]

Posted by not done it yet on 07/02/2021 07:00:07:

Posted by Georgineer on 06/02/2021 18:30:43:

Posted by not done it yet on 06/02/2021 09:47:37:

… your method, using twice the force required (by removing and inserting simultaneously) may not be the best plan.

NDIY, since the bush being inserted displaces the bush being ejected at exactly the same rate, wouldn't it remain constant at once the force required? (Ignoring all the other variables.)

George B.

Constant – yes (well maybe, but dependent on the force required for each separate operation being identical), The same – no. Total Work Done would be the same, but all in one operation. Same Displacement, so Force must be increased (WD = F x D).

Edited By not done it yet on 07/02/2021 07:00:43

I haven't done the maths and could yet be caught out by something I haven't thought of, but this is the way I see it:

I would expect the extracting force to be F = Fmax at displacement D = 0, with a straight line reduction to F = 0 at D = Dmax. (Again, ignoring all other variables). If we plot a graph of displacement versus force, then the work done would be the area under the straight line.

Similarly, the insertion force would be F = 0 at D = 0 and would increase linearly to F = Fmax at D = Dmax. Again, the work done would be the areaa under the line.

At any value of displacement D = Dx the total force Fx = F extraction + F insertion = Fmax and total work done is Fmax x Dmax.

So I don't see how the force could ever exceed Fmax, which is the force required to start the extraction.

George B.

[not done it yetParticipant @notdoneityet]

Sorry, if you can’t see, I can't help you any further. Perhaps others might.

[patgasParticipant @patgas]

I know this is an old post, I have replaced the oilite bushes, new shaft arrived but it’s extremly tight, and tips to allow the shaft to fit.

[Martin of WickParticipant @martinofwick]

If you cant get the shaft in at all, see my post Feb 2021 a  few posts back on this thread. You might need to squeeze the bearing internals slightly by pulling through a slightly oversize olive based on the carefully measured id of the bearing. Go carefully as it easy to overdo it an make the bearing too loose.

If you can wrangle the shaft in one side or other, fit a pully or something to get a good grip and rotate by hand and try to get all the way through both bearings. Otherwise try rotating shaft into each bearing individually until they start to free up a little. Then see if you can get the shaft through both bearings and cautiously run in on machine with lots of oil at low revs, checking with your hand for increased temperature. When it gets ‘bath hot’ stop, allow to cool and then repeat until you can run for an extended period with only modest heating.

[DiogenesParticipant @diogenes]

Fitting instructions here – ‘Imperial Range’ notes towards bottom;

https://hpcgears.com/pdf_c33/4.27-4.40.pdf#:~:text=Before%20fitting%20make%20sure%20that%20all%20sharp%20edges,Always%20use%20steady%20pressure%20to%20insert%20the%20bearing.

[patgasParticipant @patgas]

I can only get the shaft in around 20mm one side, bearings went in true and square. My next option was to run a reemer through ? Or will this make them too large ?

Thanks

[noel shelleyParticipant @noelshelley55608]

DO NOT ream an oillite bush iŧ will smear the material and ruin it. Try using an undersize bit of bar to spread or stretch it. Check that in fitting it it has shrunk, gone in off square or burred. Noel.

[Martin of WickParticipant @martinofwick]

Reamers, meh!, if you have a really good quality sharp one and you can set it up on a lathe  to be perfectly normal to the bore axis, then maybe.

How did you fit, with a full length fitting pin?. There are several issues that can cause problems:

That the bearings get squeezed to slightly undersize with a short pin

That even when a full pin is removed the bearing continues to deform slightly to undersize from the pressure of the housing.

or there is a slight misalignment of the bearings due to an imperceptible twist to the countershaft bracket and the shaft will fit one or other of the bearings individually, but not go through both.

Do you get the same tightness when you attempt to push the shaft into the other bearing? If so you may need to squeeze them to shape. You can attempt this by working the existing shaft in gradually by hand.

Or if you have some really good measuring equipment, make up some steel olives at shaft diameter, shaft diameter +0.0005in  and ditto + 0.001 thread to match whatever threaded rod you have, round and polish ends and pull through bearing using the kit you made to take the bearings out.

Start with the smallest, do one side at a time and check fit pass the same size olive through several times before moving up a size. Best to er on tight side and check you can get into each bearing individually with the shaft without bursting a blood vessel. When you can do this, attempt to feed the shaft into both bearings. If it tightens up dramatically there is an alignment problem.

Don’t despair, I had exactly this problem on my 7 and worked the shaft through by brute force. I could barely turn it and couldn’t move it in or out. It was left in the conservatory for about a week or so while I tried to think what I was going to do. When I went back to it for another wrangling session, I was utterly amazed to find it was almost free, tight yes but turnable by hand and moveable back and forth. Popped it back on the machine and ran it.

No such luck on my S7 and had to slightly oversize one bearing by .001in to get the shaft to run. Although not a tolerance fit, there is no detectable play, but it does weep oil slightly.

 

 

 

[duncan webster 1Participant @duncanwebster1]

Instead of Martin’s olives, if you can get an accurate ball bearing that should do it

 

[HopperParticipant @hopper]

Oilite’s literature says you can ream their bushings as long as the reamer is sharp  . I posted a copy of it on this forum several times before, somewhere.

I reamed my ML7 countershaft bushings with an adjustable reamer about 7 years ago and no problems to date. Installation was done with a large bolt and nut and flat washers. No problems.

 

[patgasParticipant @patgas]

Yes this is what I’m going to do do I think, just clean them out by hand, reem them very very lightly with a couple of passes. The pressed in perfectly, I assume the have shrunk a little.

[HopperParticipant @hopper]

Link to that Oilite PDF saying reaming with a sharp reamer is OK.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.bearing.co.il/OILITE.pdf&ved=2ahUKEwiw-sfJstuIAxU9sVYBHchSDf0QFnoECCoQAQ&usg=AOvVaw0OBJVhhKYH4KIippu8UofA

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