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Hello,
When reaming the sleeve gear bushes to accept the mainshaft, what clearance am I aiming for?
When reaming the sleeve gear bushes to accept the mainshaft, what clearance am I aiming for?
Sleeve Gear Bush Clearance
- Thread starter Cowboy Don
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Hello,
Welll... IMO... and im a rough barsket (cos i was born and breed in Adelaide
) and also being a DIYer would aim at "minimal" cos its a gearbox with heavy oil.. .002+ish thou i would think.. If it is a gearbox that your going to race or attempt landspeed record, disregard my comments and do further research... Or just disregard it anyway..
Welll... IMO... and im a rough barsket (cos i was born and breed in Adelaide
) and also being a DIYer would aim at "minimal" cos its a gearbox with heavy oil.. .002+ish thou i would think.. If it is a gearbox that your going to race or attempt landspeed record, disregard my comments and do further research... Or just disregard it anyway..
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Snug sliding fit when I knocked in my 2 (slightly longer each than the originals I knocked out-good...) new frozen bushes. One was a tad stubborn and had mushroomed the slightest bit from the socket head tapping impacts so the shaft wouldn't enter the bore so simply round-filed the inner bore a tad to help shaft enter no probs. Was thinking might have to ream this out but was only that. Went well ,soaked bushes in gearbox oil before final assembly and scrolled a small groove ala Hobot advice too, stopping well before exit point to primary. Happiness.
I have a new genuine main shaft that measures 0.809" in the area where sleeve gear bushes fit. Also two new genuine long type sleeve gear bushes which have not yet been pressed in an measure 0.912" in the bore. I have measured them with a digital veneer but it may not be totally accurate as has not been calibrated in a long time. I tried a 0.002" feeler gauge between shaft an bush an it does slide nicely though. I have worded for 25 years as a turner in toolroom an have made an fitted thousands of bushes it that time an my advice would be not to go less than 0.003" clearance as when bushes heat up with loading in use they expand very quickly leading to lose of clearance an more expansion till they seize. My own bushes are being replaced as they have expanded an damaged the main shaft which to needs replacing.
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Keith1069 said:
The mainshaft won't go in, so they gotta be reamed.
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Normally Norton bushings do not need to be reamed. Mick Hemmings Video of the Gearbox Servicing during his rebuild also states this.Cowboy Don said:
Are the gears AN Norton or Pattern?
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hobot said:
Steve,
I have also looked at this with an oil groove. I have heard of using a Triumph (dare I mention It) Bushing 571370, which has an oil groove but needs to be lathed down on the O/D. to fit. They are about 2.55” in length and have a scroll oil groove that starts at one end and goes to about 0.750” to the other end. The I/D fits the Norton Main shaft nice. I am still looking at making a mandrel to turn them down. I can’t give real road time testing until I do. I have a few but I have yet to experiment.
CNN
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After I saw how dry it gets in sleeve bushes I used a dremal ball bit and made mine own one spiral groove and smoothed the groove edges. There is nothing to prevent oil from exiting the outer bush seam, so I stopped groove short of the end of the outer bush in case in the few short intervals there might ever be oil enough to weep. It occurred to me angled drilings might pump some oil splash inward in lower gears but don't know and quite the lower gear use habit much as practical non lugging. Main shaft is below resting oil level and lower gears spin to sling oil out and prevent rentry so only time it gets some oil over it is in 4th so they stop spining with oil thrown over them. A detail 1' belt runners should be concerned with.
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toppy said:
This dosen't make sense. When an internal diameter i.e hole, gets heated the I.D gets bigger - not smaller. That's why we're able to fit bearings in alloy cases after the casing is heated. Even with two components of the same material, a housing I.D will expand more than a fitted O.D (shaft) because there is more material.
If the bush is heating up with 'loading' - do you mean friction? then method of lubrication needs to be looked at, but still wont lose clearance unless there is insufficient allowance for shaft expansion where the shaft is subjected to higher temperatures than the bush e.g exhaust valve stem clearance to valve guide.
On a pre-unit gearbox temperature will only be around 40 degC anyhow, unless you've got serious shaft/gear misalignment or lubrication problems, so any expansion will be insignificant. I'm pretty sure the sleeve gear bushes are porous so only sliding fit required. Funny how some people claiming ##years experience come out with incorrect theories.
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The bronze don't expand as much as the steel shaft and only lube system is a dry sump pump down when these things are spinning so the local heat can melt metal while the whole tranny temps may not get very high. Mainly its the different metals allowing more burnishing than galling away, for a time.
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Just to be clear, this is not to fit the bushes in the sleeve gear, it is to fit the mainshaft through the bushes. Also, the bushes are Andover.
Before I pressed the bushes in to the sleeve gear, they fit over the mainshaft easily and spun freely. After pressing them in however, I couldn't get the mainshaft to go through.
I have reamed them just enough so that the mainshaft will slide in, but it is a snug fit. The sleeve gear will not spin freely on the mainshaft, although I can turn it by hand.
Two people so far have given answers to my question, 0.002". Toppy, you mentioned 0.002 but then said not to go less than 0.003.
Before I pressed the bushes in to the sleeve gear, they fit over the mainshaft easily and spun freely. After pressing them in however, I couldn't get the mainshaft to go through.
I have reamed them just enough so that the mainshaft will slide in, but it is a snug fit. The sleeve gear will not spin freely on the mainshaft, although I can turn it by hand.
Two people so far have given answers to my question, 0.002". Toppy, you mentioned 0.002 but then said not to go less than 0.003.
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hobot said:
No, you're wrong. Don't know which book you're referring to ref. coefficient of expansion; Bronze (CuSn 6) 17.5 x 10(-6)/K; Steel (low alloy) 11.5 x 10(-6)/K. Therefore bronze expands at a greater rate than steel, therefore the clearance increases with temperature. Oil from splash will make it's way between bushes and shaft due to capillary action. If friction between the sleeve gear bushes and mainshaft generates heat to melt metal I think the whole thing would seize first.
A free sliding fit between the sleeve gear and shaft is fine. If it does not spin freely then you need to remove metal until it does.
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olChris said:
Why not? Some people on here are looking for answers to problems. I would never claim to know everything about anything, but giving advice based on fundamentally incorrect information will only mislead and possibly cause premature mechanical failure. See other gems on this subject relating to properties of materials. Everybody's entitled to make mistakes but when posting on forums a bit of research before advising is prudent.
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Oh ok I didn't look it up, only went by bronze compared to alloy expansion such as removing kicker shaft blind bush. So shoot for almost interference fit then eh. I disagree about the capillary action when these are still in relation to each other but not when it really matters spinning under load. The engine can easy over come the galling melting friction so no siezure just accelerated opening of clearances till clutch wobbles, again.
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gjr said:
The sleeve gear will expand at the same rate as the shaft but by a greater amount as the internal circumference of the sleeve gear is greater than the outer circumference of the shaft. This allows the bushes to expand as well. Clearance between the shaft and bushes is not a problem due to the low running temperature of the gearbox. If you ream the bushes to get a sliding fit on the shaft at ambient temp. of 0 degC, then at 40 degC the shaft will expand by approx. 0.0000003". I'd be surprised if this caused a problem even if there was no expansion of the bushes.
If my calculations are wrong I'd welcome anybody putting me right.
It is not as simple as the expansion rate of one type of metal verses another. As the bush runs on the shaft an the oil separating the two is forced out then the load will generate friction this will generate localized heat in the bush causing it to expand independently for any heat related expansion of the rest of the gearbox. This will now start a vicious circle as the expansion reduces clearance as the bush is trapped by the gear so more friction is generated leading to more heat an expansion an so on.
Mick Hemmings says on his gearbox rebuild dvd that he has seen the main shaft snap as a race bike warmed it engine in the paddock in neutral so no oil was being flung around inside the box. My own shaft show signs of localized heat damage from over tight chain by previous owner
Mick Hemmings says on his gearbox rebuild dvd that he has seen the main shaft snap as a race bike warmed it engine in the paddock in neutral so no oil was being flung around inside the box. My own shaft show signs of localized heat damage from over tight chain by previous owner
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