Sleeve Gear Bush Clearance

Cowboy Don said:

Sooooo, um, 0.002"?

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I wonder what Stan, Jack and Inspector Blakey and there ilk did when their gearbox failed... Pull it out fit a new part and away you go. All on the ironing board..

So in N with rear not up on center stand, 1st and 3rd still turn to carry up some oil, yet if not idling on side stand but level the picked up oil is some distance from bush seam entry/exit, with main shaft turning inside, so likely heating thin bronze more tha thick shaft, so as bush OD bumps into less heat expanded shaft, only room left for the extra vibrations of atoms/molecules is to crinkle the roundness of bush thickness as it also swells inward closing its bore. Ugh. I'd say shoot for .0025" and let running in fight it out from there. I ain't got cog and shaft and bush rotations down but about only way i can think of for any active gathering in of oil might be angled drillings that kind of scoop it up or just let some oil drool straight into the bushes. Mainly I think its just that these dis-similar metals tend not to ionically attract to point of galling, [as say SS in aluminum] till temps get so high there's local melt pockets that alloy together that precipitate out as much higher melt & harder ceramic like grit. Manx don't have the torque of big twins so stay in hi rev's low gears longer, so if not holding hi load hi rpms we know sleeve bushes can last 10's 1000 of miles, at least the chain gang can. I class AMC bushes with tires and speedo drives and chains. Also getting on throttle torque AMC wasn't designed for tends to put a box in the shafts which also takes up sleeve bush tolerance. After 3 sleeve bushes grooved and ran DextronII, the paper thin 1st gear bush
worn out or even broke up twice the rate of sleeve bushes dissolving. I was a very bad boy to Peel but don't want to go through that with Trixie which I baby, compared. This is many decades long issue so would of thought by now bush kits would come all ready to fit.

My point was that the bush expands due to high speed difference between shaft an bush but it is trapped inside the cooler so not expanding sleeve gear so in expands into the clearance space and the CLEARANCE SPACE REDUCES LEADING TO FRICTION .

I made the point about the chain being still just for clarity sake.

According to Mickey Hemmings if warming your bike up put it on center stand or paddock stand an in first gear. He also says that second gear is a weak point as you have noticed Al and that the later modified tooth form seems to ware just as badly as the earlier type.

NorComCycles said:

The new GENUINE mainshaft I have here measures 0.8101.

According to the factory manual, the minimum ID of the High gear bush when FITTED is 0.8120. That makes a min clearance of 0.0019.
The maximum ID of the bush fitted is listed at 0.8133, which would make for 0.0032 clearance.

I do not see those as service wear limits, but rather as the normal running range.

This info, from the HD shovel manual, gives a similar view.

Main drive gear bushing on mainshaft (loose) 0.0018-0.0032.

With a service wear limit of 0.0018-0.004.

Same application from 2 different manufacturers, with essentially the same spec.

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Thanks NorCom!

toppy said:

My point was that the bush expands due to high speed difference between shaft an bush.....

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I thought you said it expands due to loading/friction - but your now saying it expands because of speed differential? :? How does speed differential heat up the assembly?

toppy said:

....but it is trapped inside the cooler so not expanding sleeve gear....

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There will be heat transference to the sleeve gear so it will expand proportionally with temperature increase.

toppy said:

so in expands into the clearance space and the CLEARANCE SPACE REDUCES LEADING TO FRICTION .

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The bush will not "expand into the clearance space". If it ever gets to the temperatures you are assuming the only significant expansion would occur in the length of the bush, not the diameter and it definitely would not "expand into the clearance space". Therefore "CLEARANCE SPACE REDUCES LEADING TO FRICTION" does not occur.

The only component in the engine where dimension change occurs on the magnitude which you are stating occurs in the sleeve gear bush, is the piston. Aluminium alloy has a greater coefficient of expansion than bronze. Also the piston diameter is approx. 3.75 times greater than the sleeve gear bush and continuously heated to approx. 250 deg C (possibly more) yet only expands by approx. 0.004" . If the sleeve gear bush was subjected to the same conditions and made of aluminium alloy it would only expand by max. 0.001" diametrically. Notice I say expand - not contract. I'll leave you to your theories.

I did not realize I would have to be word perfect in my explanations of my explanations. I have been making bush bearing from all kinds of material for 25 year in my job an the reasons for their failure are all well known engineering facts clearance an material expansion rates can be found in a number of reference books.
The speed difference leads to fictions this generates heat this expands the bush causing it to bind an create more friction and so on.
If you like call Mick Hemmings an ask him about main shaft failure dew to sleeve bush seizing on it he has seen this happen.

toppy said:

I did not realize I would have to be word perfect in my explanations of my explanations. I have been making bush bearing from all kinds of material for 25 year in my job an the reasons for their failure are all well known engineering facts clearance an material expansion rates can be found in a number of reference books.
The speed difference leads to fictions this generates heat this expands the bush causing it to bind an create more friction and so on.
If you like call Mick Hemmings an ask him about main shaft failure dew to sleeve bush seizing on it he has seen this happen.

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Whatever you say.

Well what is your information based on and what is your engineering back ground??
If you expect me or others to except your views on what sound engineering practise then we should have some idea of your credentials surely AL ?

toppy said:

Well what is your information based on and what is your engineering back ground??
If you expect me or others to except your views on what sound engineering practise then we should have some idea of your credentials surely AL ?

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Engineering is based on logic and the laws of nature, so anyone with a degree of 'commonsense' should be able to understand the fundamentals. In addition to this, my argument is based on properties of materials and specifically coefficient of expansion. I have studied engineering to degree level and also completed practical engineering courses as well as working in engineering environments. I've covered approx. 130,000 miles on my Mk3 and have carried out all my maintenance and implemented improvements where I've thought necessary. Precision engine machining has been carried out by appropriately equipped machine shops, although not always satisfactorily.

I do recognise knowledge and experience can be gained in many ways, qualifications are only part of learning, but it is vital to be able understand and clearly communicate engineering fundamentals. Your argument is incorrect regarding behaviour of materials subject to change in temp., heat transfer between materials, expected operating temperature of components, and behaviour of oil molecules under pressure.

To be honest, I couldn't give a monkeys whether people whose opening sentence to an explanation starts, "I've worked in engineering for xx years....." believe a word I say or not. Typically they choose to ignore a logical argument which disagrees with their opinion.

I can see your point but mine is that there is far more than just simple heat expansion.The hole start of this seemed to be when I said not to be tempted to make the bush to close a fit as it will cause problems. As for not all engineering firms being up to scratch this is sadly a fact of life but I machine the center shafts of jet engines for a little firm you my have heard of Rolls Royce they like us to know what we are doing and be good at it an they are quite keen on thermal expansion as planes falling from the sky is bad for business

NorComCycles said:

The new GENUINE mainshaft I have here measures 0.8101.

According to the factory manual, the minimum ID of the High gear bush when FITTED is 0.8120. That makes a min clearance of 0.0019.
The maximum ID of the bush fitted is listed at 0.8133, which would make for 0.0032 clearance.

I do not see those as service wear limits, but rather as the normal running range.

This info, from the HD shovel manual, gives a similar view.

Main drive gear bushing on mainshaft (loose) 0.0018-0.0032.

With a service wear limit of 0.0018-0.004.

Same application from 2 different manufacturers, with essentially the same spec.

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Thanks for actually answering the question.

toppy said:

I can see your point but mine is that there is far more than just simple heat expansion.The hole start of this seemed to be when I said not to be tempted to make the bush to close a fit as it will cause problems. As for not all engineering firms being up to scratch this is sadly a fact of life but I machine the center shafts of jet engines for a little firm you my have heard of Rolls Royce they like us to know what we are doing and be good at it an they are quite keen on thermal expansion as planes falling from the sky is bad for business

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Like I say, Toppy, I'm not disputing what you do, just your understanding.

:roll: :roll: :roll:

"I argue very well. Ask any of my remaining friends. I can win an argument on any topic, against any opponent. People know this, and steer clear of me at parties. Often, as a sign of their great respect, they don't even invite me."

--Dave Barry

olChris said:

:roll: :roll: :roll:

"I argue very well. Ask any of my remaining friends. I can win an argument on any topic, against any opponent. People know this, and steer clear of me at parties. Often, as a sign of their great respect, they don't even invite me."

--Dave Barry

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Why not just stick to facts instead of making implications about things you have no idea about. It's a typical political tactic - if you can't win an argument using facts then make things up. Some of my comments are in reply to postings from people like yourself - if my opinions upset you then try thinking about what you've written before clicking 'submit' :wink:

I don't expect to agree with, or like, everyone who happens to ride the same brand of motorcycle as myself - I've come across some scum of the earth, mother fucking racists at Norton 'social' occasions, but at least with engineering the discussion is, or should be, objective not subjective.

If it comes across that I I'm upset by what you say then it is not ment to . I asked about your back ground purely to see on what you base your side of this discussion an told you my back ground so that you also may understand that my side of the discussion comes for working with these metals an learning the hard way what works and by being tort by those who have done the job since (quote) "before you wer born lad"
an just as you say because we have a similar liking for a motorcycle does not mean we have to agree on all things how dull would that be.
May you have a good year this year riding an I hope your bike runs well.we may not agree on some points but this is life

toppy said:

If it comes across that I I'm upset by what you say then it is not ment to . I asked about your back ground purely to see on what you base your side of this discussion an told you my back ground so that you also may understand that my side of the discussion comes for working with these metals an learning the hard way what works and by being tort by those who have done the job since (quote) "before you wer born lad"
an just as you say because we have a similar liking for a motorcycle does not mean we have to agree on all things how dull would that be.
May you have a good year this year riding an I hope your bike runs well.we may not agree on some points but this is life

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Thankyou, and enjoy life and your bike.

I heated up an old sleeve gear, with two bushings in it, on my shop wood stove. Temperatures were measured with an IR thermometer. ID was measured with a dial vernier caliper. I made three pairs of measurements. The first line of the initial conditions goes with the first line of the final conditions. Second with the second, etc. Measurements 1 and 2 were made in line with the 6 stamped on the end of the gear. Third measurement was made at 90 degrees to the first two.

Initial conditions:
temp ID outer ID inner
46F (8C) 0.817" 0.824"
42F 0.817" 0.824"
39F 0.817" 0.8235"

final conditions
192F (88C) 0.816" 0.823"
180F 0.816" 0.823"
170F 0.816" 0.823"

Someone should repeat these measurements.

Greg

Thanks for the info Greg,

A few variables to consider. Measurements ideally should have taken an average of the I.D as it's impossible to measure in exactly in the same spot and bearing in mind there may be non uniform wear on the bush I.D. A bore gauge would have been preferable to a dial caliper for the I.D measurements.

Your experiment suggests a change in dimension (contraction) of approx. 0.001" over a temp difference of 90 deg C which is not what the coefficient of expansion for the material would theoretically suggest.

If your measurements are accurate then the contraction in I.D must be due to greater force on the outer surface area of the bush due to a differential of expansion of the two components (bush and sleeve gear). In practice the temperature change would be approx half of the experimental temp. change therefore the contraction would be approx. 0.0005". Although expansion of the mainshaft would have to be considered regarding cold clearance.

The above indicates a contraction, not an expansion as I theorised, so apologies to Toppy and anybody else I contradicted - every days a school day .

AL this does show what I was trying to explain and also if you imagine that if the heat is caused by friction between the shaft an bush it can build up very quickly and that can lead to problems. I except your point that as the hole gearbox assembly heats up the clearances will remain but I was just trying to warn that if there was not enough clearance it could also lead to problems.
I agree at using a vernier to measure such small changes is also very difficult at best.
I think also that what is actually happening inside the sleeve gear at any given moment in time is affected by many factors an far more complex than it many at first appear (as with many other things to) an that in some instances you may be correct in others I may be correct an that sometimes we may both be wrong or right.
Thing are so often like that I find.

I had a similar thought to that ludwig but the lathe I have access to is at work an its 50 feet long so its a bit to big an I don't think my manager is that interested in old bike gearboxs to let me use it for that.

I have seen many failed bushes of all sizes due to this kind of thing. The best way I could try to explain it is that the metal is trying to expand in all directions but because it is within the sleeve gear which has more surface area an so is being cooled by air and oil better than the bush which can only real lose heat thru its contact with the gear the bush heat fast and therefore as the pressure of pushing on the sleeve gear bore is to great the path of least resistance is to expand to the clearance. This combine with the heat be generated forces out the small amount of oil there is so leading to more friction and heat in a vicious circle .
If this is allowed to go on long enough something must fail be hopefully you may have changed gear or something to reduce the load an give the heat chance to disperse before to much damage is done.