K12RS Transmission Overhaul Photos

[matanuska]

While everyone else was out riding, this is how I spent my weekend

 

I replaced the old transmission input shaft with damaged splines with the new one. Reinstalled all new transmission seals. Used my test fixture to align the engine output and transmission input shafts to better than 0.0005” indicated runout and bolted the two housings together. Then mounted the whole thing up on my Bridgeport and re-bored and reamed the original locating pin holes to the new alignment. I used two 3/8” ID drill-jig bushings from McMaster as the new locating pins. The bushings are precision ground with an OD of 0.5015” (the original BMW ones are 0.4535” (11.51mm) OD). I reamed the holes in the intermediate flange with a 0.501” reamer to allow a slight press fit and reamed the holes in the transmission with a 0.502” reamer to allow a slip fit for disassembly.

 

After cleaning everything up, pressing in the new bushings and reassembly, I measured total runout between the engine output and transmission input shafts to be just a tad over 0.0005”. Since the consensus for runout on these type of splines seems to be less than 0.003” (remember I found them off by about 0.011"), I feel pretty good about this repair.

 

All that’s left is to reassemble everything and hope the bike will start again!

 

Transmission before opening;

 

 

 

Initial opening. Everything looks good, just covered with a light grey dust of very fine metal particles;

 

 

 

 

Shifting components removed, gear cluster ready for removal. Requires heating of the aluminum cover to 80-100C;

 

Old input shaft;

 

Old and new shafts compared;

 

 

Newly reassembled input shaft;

 

 

Rechecking final compressed length of the shaft. Only different by 0.0005” but still well within spec.

 

Gear cluster reinstalled;

 

Shift components reinstalled;

 

Everything cleaned up and ready to go;

 

Cover reinstalled;

 

New splines ready to go!

 

Re-boring the locating holes;

 

 

New pin installed;

 

 

Transmission / bell-housing reassembled showing resultant offset;

 

[Firefight911]

Wow! That is impressive!

 

Nice work and awesome photos of a job well done.

 

Can't wait to hear how she runs once all buttoned up.

 

[KMG_365]

 

 

 

 

 

 

. . . but . . .

 

 

 

 

 

 

 

 

. . . but . . .

 

 

 

[/speechlessness! ]

[SWB]

Outstanding job. I could not do this. Well, I could, but my bike wouldn't run or shift afterwards.

 

That's one heck of a professional job. I don't know what you do for a living, but you could corner the market on rebuilding damaged (and defective) BMW transmissions.

 

But then I guess your Beemer wouldn't be a "fun hobby" anymore.

 

I'll be watching for your road test results, every 1000 miles or so.

[Dennis Andress]

Uh, may I be so bold as to bring up the thought of a tech day (in your garage)??

 

 

Dennis

[ESokoloff]

What Jamie said

 

 

 

I think

[Marty Hill]

Uh...WOW!

[Endobob]

Every time I think I may take on a major repair job I read a post like yours and realize I am not in the same league!

 

You obviously have the talent, tools and patients it takes for this type of precision work. Nice Report!

[bmwmick]

Derek,

OUTSTANDING pics!! 5 tenthousandths should be OK.

I'll bet the factory doesn't use the precision equipment you just did.(obviously they didn't on YOUR bike)

Good luck on the final assembly.

Mick

[Spinner]

Derek!

Impressive to take on a complex job such as this, measure, machine and refit to precission tolerances, reassemble, and, take pictures along the way.

 

Very nice job. And thank you for the effort to share it with us

[Tacky]

These photos are very interesting matanuska they show the part of the casing that was ripped off my K1200GT maybe I could buy one and replace that single part. was it easy to split the casing in half from the main casing that holds the gears and are special tools needed?

Regards Tacky.

[matanuska]

...but you could corner the market on rebuilding damaged (and defective) BMW transmissions.

Well, I figure either I fixed the problem once and for all, or just royally f***’ed up my bike! Only time will tell. Until then, I’d be hesitant to try my experimental “surgery” on someone else’s MC.

 

At some point though I’ll have to reopen the clutch to inspect everything. What a PITA! I’m almost thinking about mounting a cheapo blue tooth webcam or something inside the clutch housing to keep an eye on things!

[matanuska]

These photos are very interesting matanuska they show the part of the casing that was ripped off my K1200GT maybe I could buy one and replace that single part. was it easy to split the casing in half from the main casing that holds the gears and are special tools needed?

Regards Tacky.

I guess it all depends on your confidence to take on that type of work but no, I don’t think it is all too difficult to open up the tranny. Since you wouldn’t actually be messing with any of the gears or shafts from the front cover that would make things even easier.

 

Looks like Chicago BMW lists the trans casing for your bike at $397.60 US (23112330130), so that might be a viable alternative if you can’t find a complete used tranny for a decent price. You’ll also need to install all new shaft seals in the back casing, probably another $50 or so.

 

The BMW service manual shows a special fixture for holding the front cover while removing the rear, but you can probably rig up something of your own like I did. You need to heat the area of the bearing pockets with a heat gun to make removal easier. BMW also has custom sized drifts for pressing in each seal, but I just went to my tool drawer and found an appropriate sized socket the same diameter as each seal to press them in.

 

You could also just take the tranny with the new housing to a local BMW dealer and have them do the work. Shouldn’t take more than about 2 hrs labor. Of course, the big job is actually removing the tranny in the first place. That requires quite a bit of disassembly.

[RFW]

Derek,

OUTSTANDING pics!! 5 tenthousandths should be OK.

I'll bet the factory doesn't use the precision equipment you just did.(obviously they didn't on YOUR bike)

Good luck on the final assembly.

Mick

Not to take away from the excellent workmanship here, but I guarantee that Getrag uses tools a hell of a lot more fancy than a general purpose Bridgeport milling machine with a digital position readout accessory.

 

Bob.

[RFW]

These photos are very interesting matanuska they show the part of the casing that was ripped off my K1200GT maybe I could buy one and replace that single part. was it easy to split the casing in half from the main casing that holds the gears and are special tools needed?

Regards Tacky.

While remachining the casing takes skill, experience and decent tools, disassembling and reassembling the transmission is pretty straightforward and requires no special mechanical skills. I did it on my old K100RT just to see what was inside and verify all was well in there after I bought it (used).

 

Bob.

[DEF]

Only one criticism.....the ream you used is too long and could produce some minor offset.

 

Other than that, I would sure like to have a nice Bridgeport in MY garage....I would like a three axis version please...oh and a nice NC machining center, while you're at it....

[matanuska]

...While remachining the casing takes skill, experience and decent tools, disassembling and reassembling the transmission is pretty straightforward and requires no special mechanical skills...

Yes, it is relatively easy to accurately move a couple of ½” holes using a Bridgeport and a good DRO. It’s also fairly easy to open up the tranny and reassemble everything as long as you’re not making any design configuration changes. Just need to be careful and pay attention to details. But you would be hard pressed to manufacture any of these components to the required accuracy on something as crude as a Bridgeport.

 

...but I guarantee that Getrag uses tools a hell of a lot more fancy than a general purpose Bridgeport milling machine with a digital position readout accessory...

I believe these spline alignment problems demonstrate a weakness in the QC system. However I can’t tell if the problem is on the BMW side (engine bell-housing) or Getrag (transmission casing). Somewhere, on one of the two manufacturing lines, about one part in every 5,000 or so must not correctly locate in a CNC machining center resulting in alignment/mounting holes bored a few thousandths off.

[matanuska]

Only one criticism.....the ream you used is too long and could produce some minor offset...

Yup! If you look at the transmission casing though, the bolt holes are so close to the casing sides (particularly the back one) that there is no way to get a drill chuck or collet in there down close to the hole. I even had to buy a special 12" long 31/64 drill bit to do the initial rough boring, then hold the reamer out at the very end of the shank to get down in there.

 

No doubt the manufacturer drilled and bored the holes from the front side of the tranny flange with the bell-housing separate, but since I wanted to do the whole thing as one assembly, I had to work-around the long reach requirement from the back side.

 

DR

[Laney]

Speechless, huh Jamie? Not me!

 

I don't know if you'd want a tech day in a nice garage like that, but would you consider a trade? I'll give you my garage, with a workbench, the 10 ft. tall Craftsman toolbox, and the used oil, and you give me yours.

 

I'll even throw in the cat. (Not really, Cat stays with me.)

 

Seriously, beautiful garage, pictures, and not that I'm all that knowledgeable about it, but the work looks great too.

 

I hope it's all together soon and working better than when it was new.