Final drive rebuild?

[Big Lee]

Is there anyone out there rebuilding 12GS final drives yet?

Mine hasn`t gone but I was wondering if any little engineering firm has jumped onto what could be a lucrative market.

 

[RickG]

Having just rebuilt mine I reckon the economics of it could put off anyone wanting to do it commercialy.

There are 4 bearings, 2 for the pinion shaft, 2 for the wheel. Luckily mine had 'only' eaten the pinion bearings which I replaced along with a few seals for just over a hundred quid but it's a total s*d of a job and needs some very serious effort and time. The bigger problem is if the axle bearings are shot (wheel wobbling side to side at rim) since one of them bears directly on the crown wheel. If the track is worn you'll need to buy a new crown gear and probably a new pinion shaft too - unless it could be built up and reground to size. That won't be cheap and only sets the scene for the job of getting the alignment and mesh right which requires time, skill and a bunch of shims to hand. I'm given to believe BMW don't rebuild them but simply fit a new drive, which costs about a grand. I doubt an independently rebuilt box would come in at much less if all the parts and labour were taken into account.

Having said all that, if just the pinion bearings were gone a rebuild is probably going to be economic.

I think Steptoe may have been talking about the idea of a re-con' scheme in a post some time back but I may have imagined it.

 

[Big Lee]

What a pity that is, before long if one goes the bike will be uneconomic to repair

Best of luck to anyone who tries to re con them

 

[Panzer Patrol]

Done mine twice.

Once at 24k and just recently at 38k. The second time may have been due to a dramatic puncture episode and the resulting "banging about" it got.
It is as straighforward to rebuild as the 1150s, but with one or two bits that need a different approach. Mainly the wheel carrier, which is alloy and is an interference fit on the shaft. This needs careful heat to sweat it off at the same time as using a press to seperate the bits. It needs to be heated and shrunk back on so that there is no play at all on the splines after rebuild. BE CAREFUL, the carrier is £140 ish.

The large wheel side bearing is the same as in the 1150 (I think - need to double check). The smaller outer one is a roller and is a doodle to remove compared the the 1150 which is a taper roller down a blind hole and can be a complete twat to get out. So all it needs is to give the case a bit of warming with a heat gun and a gentle tap at the appropriate time and kerplonk!

Hopefully this is all that is needed if you have caught it in time and no damage has occured on the pinion bearings. You need a press and an engineer who knows what he is doing, or nerves of steel. As the assembly is quite lightweight compared to BMs of old ( yea, I know....yada yada yada) the assembly can be easily wrecked in the press if heat is not applied correctly.

From memory (which is shot to pieces) big bearing about £30, seals about £20 smaller bearing about £30 and a friendly engineers time about an hour labour for the rebuild. If you are anywhere near handy with a set of spanners you can get the assembly out and on the bench in 20 minutes.

It actually works out cheaper than putting a chain and sprocket set on one of those "soopa-doopa-mega-dega-wopa-dopa-double-triple-death-rockets.

Hope that helps..toodles!

 

[Bear]

This is not the first thread on the subject:- http://www.ukgser.com/forums/showthread.php?t=166875

 

[Big Lee]

Done mine twice.

Once at 24k and just recently at 38k. The second time may have been due to a dramatic puncture episode and the resulting "banging about" it got.
It is as straighforward to rebuild as the 1150s, but with one or two bits that need a different approach. Mainly the wheel carrier, which is alloy and is an interference fit on the shaft. This needs careful heat to sweat it off at the same time as using a press to seperate the bits. It needs to be heated and shrunk back on so that there is no play at all on the splines after rebuild. BE CAREFUL, the carrier is £140 ish.

The large wheel side bearing is the same as in the 1150 (I think - need to double check). The smaller outer one is a roller and is a doodle to remove compared the the 1150 which is a taper roller down a blind hole and can be a complete twat to get out. So all it needs is to give the case a bit of warming with a heat gun and a gentle tap at the appropriate time and kerplonk!

Hopefully this is all that is needed if you have caught it in time and no damage has occured on the pinion bearings. You need a press and an engineer who knows what he is doing, or nerves of steel. As the assembly is quite lightweight compared to BMs of old ( yea, I know....yada yada yada) the assembly can be easily wrecked in the press if heat is not applied correctly.

From memory (which is shot to pieces) big bearing about £30, seals about £20 smaller bearing about £30 and a friendly engineers time about an hour labour for the rebuild. If you are anywhere near handy with a set of spanners you can get the assembly out and on the bench in 20 minutes.

It actually works out cheaper than putting a chain and sprocket set on one of those "soopa-doopa-mega-dega-wopa-dopa-double-triple-death-rockets.

Hope that helps..toodles!

Great, thanks!

This is not the first thread on the subject:- http://www.ukgser.com/forums/showthread.php?t=166875

I posted on that thread too but theres been no postings of any places that were doing rebuilds so I thought I`d ask.

 

[RickG]

Panzer patrol is right about changing the two axle bearings, it's not too difficult or expensive - provided the inner race on the crown wheel isn't worn.

The pinion bearings are a s*d to change by comparison, mostly due to the set-up required to hold the final drive while you swing on the end of a long pole trying to unscrew the collar that holds the bearings in place. The bearings (as far as I could make out) are specials made for BMW, the larger is the same as fitted to 1150's.

The alloy wheel carrier will drop back on in one go provided it's heated in the oven to about 120'C with the rest of the assemply cooled in the freezer to -20'C. I'd recommend putting the bits in plastic bags first unless you want to incurr the wrath of SWSBO and have your chips tasting of gear oil.

The thread by patzx12 is an excellent guide to doing the job and shows exactly whats involved.

http://www.ukgser.com/forums/showthread.php?t=166875

As my bike is pre-drain hole I drilled and tapped a drain hole in the bottom of the housing whne it was apart as from now I'll be changing the oil regularly.

 

[Panzer Patrol]

Hi Lee,
I spotted a bike shop on fleabay who were offering exchange units at about £300. May be worth trawling to see if they still offer the service. Dont know if you know but, they change the ABS ring, which is forged into the crownwheel, in September 06 (I think) so there are two types out there. You can see the difference by looking at the ABS doofy through the sensor hole.
Cheers

 

[RickG]

You can see the difference by looking at the ABS doofy through the sensor hole.
Cheers

Think it's the same time they put the drain plug on

 

[Big Lee]

I timed that well didn`t I? Today after a run out, not really hanging about either , the back wheel rim is covered in a slight misting of oil and brake dust Ever so slight play at the rear wheel when the fd is hot but non when cold. It doesn`t seem to be coming out of the outer seal but the one nearest the brake disc.
I was looking at a 54 plate Yam R1 today which might have something to do with it

I`ve had it 5 years, is it gods way of telling me I need a change?

 

[RickG]

I`ve had it 5 years, is it gods way of telling me I need a change?

That or he's telling ya to get your hands mucky and sort it.

 

[Big Lee]

Could be I just had a close inspection and it appears that the oil isn`t coming from the fd but down the drive shaft and out through the casting hole underneath the fd.

 

[ed4554]

As my bike is pre-drain hole I drilled and tapped a drain hole in the bottom of the housing whne it was apart as from now I'll be changing the oil regularly.[/QUOTE]

Good idea however could it be drilled and tapped without stripping it down first? ie. drilled and tapped in situ?

 

[smartbear]

no difference!

As my bike is pre-drain hole I drilled and tapped a drain hole in the bottom of the housing whne it was apart as from now I'll be changing the oil regularly.

Good idea however could it be drilled and tapped without stripping it down first? ie. drilled and tapped in situ?[/QUOTE]

should be ok,after all any muck you creat will only join the rest of the swarf/grinding paste thats already inside the final drive

 

[Owen Snell]

Good idea however could it be drilled and tapped without stripping it down first? ie. drilled and tapped in situ?

Unless you strip it down first, there is a good chance that some swarf will get into the FD when you drill and tap the casing to make a drain hole. Given that the FD is simple to drain anyway and does not need changing that frequently, there is no need to take the risk.

 

[RickG]

Given that the FD is simple to drain anyway and does not need changing that frequently, there is no need to take the risk.

The reason I drilled the hole and fitted the plug was a) it was stripped anyway and it's only a 5 min job but mostly b) I intend to change the oil much more frequently in the hope that the nice new bearings will last longer. Given I do 25k a year this will constitute frequent changing so anything to make my life easier is a bonus.

if you were v. careful it may be possible to drill a hole and tap it (using grease on the tap) to minimise the amount of ally that was left to get inside the drive box. However, I reckon actually drilling the hole square and neat would be a s*d even if the bike was laid flat on it's side