final drive rebuild how-to?

[cookie]

starting this morning. can't finish as i only have some of the bits.

not looking forward to getting the bearing off without the proper puller, but hey ho.

i'll report back how it goes

 

[MattW]

starting this morning. can't finish as i only have some of the bits.

not looking forward to getting the bearing off without the proper puller, but hey ho.

i'll report back how it goes

Brill

 

[Steptoe]

Is that really true? I would have expected bearing manufacturers to work to pretty tight, internationally recognised tolerances. Tighter tolerances than those used to make a motorbike final drive (hence the shims). But hey, what do I know....

Mick

livin' the dream

"Hence the shims".
The shims are so the internals can be fitted within spec. That's how the cases are made. Purposely oversized so a wide range and type of bearings can be fitted anywhere in the world and to take into account backlash and differences in the crownwheel and input helicol gears, which need shimming to adjust backlash... Thats why the shims are needed. Not just to pad out the bearing.

 

[warmshed]

I believe that reputable make bearings have a tolerance less that one, 10thousanths of an inch and engineers are known to use them as a standard to calibrate their micrometers if the calibrated piece has been mislaid.

 

[Steptoe]

I believe that reputable make bearings have a tolerance less that one, 10thousanths of an inch and wont play any part in the required shimming.

I wonder why final drives ever need reshimming.

 

[buellzebub]

I wonder why final drives ever need reshimming.

My belief would be that it's because the final drives are not that accurate. Look at it from a financial point of view, it would cost BMW an absolute arm and a leg in tooling, casting, machining and quality control costs to set set up a production line more accurate and repeatable than a bearing manufacturer. I'd like to think BMW were that conscientious but unfortunately I doubt it.

Mick

livin' the dream

 

[Ian J Hartley]

My belief would be that it's because the final drives are not that accurate. Look at it from a financial point of view, it would cost BMW an absolute arm and a leg in tooling, casting, machining and quality control costs to set set up a production line more accurate and repeatable than a bearing manufacturer. I'd like to think BMW were that conscientious but unfortunately I doubt it.

Mick

livin' the dream

True, but he's on about re-shimming following a bearing change. Not original shimming at factory.

 

[buellzebub]

True, but he's on about re-shimming following a bearing change. Not original shimming at factory.

Hmm, good point. The FD dimensions aren't going to change, the bearings should also be of consistent dimensions (I believe), so one would assume that re-shimming might need to be done once to correct any inaccuracies in the initial factory build up. After all I guess the factory aren't going to spend as long or take as much care as someone like steptoe working on a customer's bike or an owner rebuilding his own bike, taking multiple measurements to ensure it's as correct as can be.
That's my theory anyway
Mick

livin' the dream

 

[Ian J Hartley]

Hmm, good point. The FD dimensions aren't going to change, the bearings should also be of consistent dimensions (I believe), so one would assume that re-shimming might need to be done once to correct any inaccuracies in the initial factory build up. After all I guess the factory aren't going to spend as long or take as much care as someone like steptoe working on a customer's bike or an owner rebuilding his own bike, taking multiple measurements to ensure it's as correct as can be.
That's my theory anyway
Mick

livin' the dream

Agreed.

The way I read this, is that if the original bearing and shim were close to the top/bottom of the tollerance range then a slightly thicker/thinner bearing would take it to over/under tollerance requiring a re-shim.

Also the backlash will have to be addressed through re-shimming to take out some of the wear.

Also. As you say,the factory were probably not as diligent with the preload.

 

[MattW]

I like to think that because my 1100 is a very early '94 and a new flagship bike for BMW, the transmissions were assembled by fastidious white coated German technicians who cared deeply about their work (and not minimum wage Mexicans who couldn't give a monkeys as long as it was close enough)

 

[Nobby]

Done mine Wednesday night old bearing mic'd up at 707 thou and the new one was bang on the same..got from bmw so just suck it in..and what a difference it makes to the ride its unreal..

 

[Paul G (BHT)]

.... not looking forward to getting the bearing off without the proper puller, but hey ho.

if you haven't done it already, the secret is little taps either side..... if you give it a huge belt the bearing will not go anywhere and will tend to lock.

Heating the bearing also helps

 

[warmshed]

Agreed.

The way I read this, is that if the original bearing and shim were close to the top/bottom of the tollerance range then a slightly thicker/thinner bearing would take it to over/under tollerance requiring a re-shim.

Also the backlash will have to be addressed through re-shimming to take out some of the wear.

Also. As you say,the factory were probably not as diligent with the preload.

But as the bearing tolerance is less than one tenthousanth of an inch it just never comes into the equation.

 

[cookie]

all done.

there is quite a gap between the bearing and crown wheel, in fact my bolster was too thin for the job, so i switched to a better shaped cold chisel. that just pushed the outer race which sprung back as soon as the chisel was removed.

then we used the bolster on one side to take up the slack, while the chisel went in from the other side. one of us held the crown wheel and located the business end of the chisel while the other applied a judicious dose of snap~on's finest dead blow hammer. the holder also spotted for the gap closing between chisel and crown wheel to avoid damage.

after swapping sides a few times, it started to move. by adding various bits of scrap steel behind the bolster to fill the expanding gap it got big enough to get my puller in, which spun it off straight away.

if i do the job again i will grind down the feet of the puller so it fits from the off

i miced up the bearings and my crappy old micrometer made them within a fraction of a gnat's cock the same size. certainly less than a tad of a bee's wing anyway using the British Standard Insect Scale.

shim went back in as was

this was Springer's GSA and the work was done as the output seal was leaking. also springer complained of a thrumming noise from the area.this was only changed 2000 miles previously and bearing failure was the suspect. no wheel play was evident and there was no real roughness when turning the wheel, just some very slight unevenness that i put down to the UJs.

on removal of the seal, the bearing looked fine, but we decided to remove the cover to check it better. again, seemed okish, vaguest hint of roughness maybe, but as we had a new bearing and associated bits lying around* we changed it anyway.

when it was all back together, there was absolutely no hint of roughness when turning the wheel and was smooth as a very smooth thing. no idea about the thrumming yet, as i've not heard back from springer. he may be awaiting the breakdown truck as i right


*thanks to Pikey Dave for leaving a box of bits here years ago, i'll sort you out for them later

 

[MattW]

all done....

Excellent - good to hear how it went