BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

Have to admit I'm not across the finish line yet, but am hobbling right along.

Finally after 2 years of research and plotting and searching, I got my low gear ratio parts for my trans.

I don't like the high 1st gear, and that 5th gear is a little too low for comfortable 2 lane cruising (for my personal tastes) besides getting my engine just in the bottom of the buzz rpm range at 60, and 6th is too tall for 60 mph except for 1 rider on flat road. And I do 90%+ of my riding on 2 lanes, mostly hilly. So with the low 1st & 6th gears, I'm also swapping in a 2.62 final drive to achieve my goal of a 5th gear that will run 52 to 65 mph between 3k & 3600 rpm, still have a 7% lower 1st gear, and will still run 75 (fast enuf for this old man when I do on occasion get on a freeway) at 3750 which, in 6th, is still just under the rpm where my engine starts to buzz. Even with foam handgrip sleeves and gloves, my hands won't take that very long at all before they start to tingle from the assault on my beat up old nerves.

Finally found out how to ID a genuine low gear trans by the code on the upper right of the bellhousing. Found out that RTP or GSA trans are not necessarily the low ratio units. Before I found that out, I bought an RTP trans and swapped it in, only to find out it was a standard ratio. Aaarrgghh! And, no, you do not have to point out I should have counted input & output revolutions in 1st to verify.

Anyway, found a genuine low ratio trans. When I got it, the front seal was leaking like a sieve and the input shaft had some spline wear, maybe 20% or so. (Got a partial refund becuz of that, so it cost me less than a new bare input shaft, and I've got a case 1/2 sold for nearly that figure.) I had figured on just swapping complete transmissions, but obviously not with worn splines and a leaky input seal.

Being good used input shaft assemblies are apparently made out of unobtanium, a kind and thoughtful soul on this forum suggested I transplant the low ratio parts (intermediate & output shaft assemblies) into my trans that's in the bike now. Input spline and seal problems solved!

Nice idea, but the labor $ !!! (and I'm laid off)

Well, I dug out my shop manual, my heat gun and IR thermometer, and went to work. First time inside a bike trans. Like several other things I've read about doing work on these bikes, that job is usually referred to as something definitely not for the faint of heart and usually best left to the experts. More so than any of the other complicated jobs that DIY's typically tackle.

Well, this old hot rodder with over 40 years of building performance engines and auto transmissions figured if somebody else could do it, so could I.

Here's my progress so far.

http://s719.photobucket.com/albums/ww20 ... ar%20Swap/

By swapping entire shaft assemblies, I don't have to press the bearings off and on (all my bearings are as smooth as butter and nice and tight) and fiddle with resetting overall assembly length.

Also my seals don't even seep, and this trans shifts smooth as silk, much nicer than the original trans I took out, even neutral to 1st. So am reusing the shifting components in this trans along with my input shaft with perfect splines. New clutch while I'm at it, and lubing splines with Honda moly 60, of course.

Just have to button the case back up and reinstall it in the bike. Really not that big of a deal. Actually, rather interesting.

Is there any need to shim the shafts as is necessary on the Airhead transmissions?

Glad it's going well and that you were able to get such good deals!

Finding the right gasket material was a little difficult. I ended up using Honda-Bond because I had it in my tool box. It's the correct material for this kind of application and it works great. The only down-side is that the stuff is gray and a thin bead can be seen on my black trans. No big deal tho.
My trans was apart for months while I tried to make a better input shaft and clutch hub. I was concerned that I wouldn't get it back together, but like you said, it only goes one way. BTDT with the shifter spring. .
After I had it all back together I took it for a quick test ride. All went well except for a fluid leak. Turned out I hadn't inserted the input shaft seal far enough. If you take the entire wheel to tranny assy out in one piece it can be out in under an hour. Wrestling it back into place is a bear tho.

DaveF wrote:Is there any need to shim the shafts as is necessary on the Airhead transmissions?

According to the manual - yes. I did not. The setup to measure the shaft length properly is not easy. Instead, I measured to make certain that the replacement shaft had the same dimensions as the old and re-used the existing shims.

Yes, I had looked at R & R the entire rear assembly, but discarded
that idea after I envisioned wrestling with reinstalling it.

I used to always try to avoid some steps in any mechanical job by
not taking some things apart, but over the years have learned that
it usually pays to spend a minute or two getting things out of the
way instead of going thru the frustration of wrestling with something.

As far as airhead shaft length, well, I don't have a clue about those
transmissions. This is my first BMW. Probly is similar tho.

I had thought about shaft disassembly but when I thought it out,
I reasoned that the shaft assemblies would be the correct length
as installed, so why go thru that. I had built myself a small hydraulic
press some years ago, and have all the pullers, etc, but still it's a
time consuming and difficult job. For measuring, I had snapped up
a set of mike's off ebay a couple years ago that have large enough
set-ups so I could mesure the outside lengths. But, again, why bother?
Besides, all the bearings rotate very smoothly without a sign of any
roughness, and are nice and tight with no wobbling, etc.

If a person did have to R & R an end bearing, all one would have to
do is compare the thickness of the new one with the old one and change
shim thickness accordingly if even needed, instead of having to go thru
measuring the entire assembly length.

The recommended Loctite 574 is described as an anerobic material
that will withstand up to 300 deg F and remains somewhat flexible
between the aluminum halves of the case to counteract any potential
leaks from expansion & contraction. 518 is about the same except
it stays more pliable. I had a tube of that from years ago and it is
a fantastic joint sealer in automotive applications. But neither were
available locally.

I found this during a search to learn more about the Permatex product
which I was able to find in a small quantity. Don't know if it's true or not.
Found a toothpaste sized tube (1.7 fluid ounces) locally for $17.

Permatex bought out Loctite and the new number for 518 is Permatex #51813

So I think it'll be OK.

macx wrote:If a person did have to R & R an end bearing, all one would have to
do is compare the thickness of the new one with the old one and change
shim thickness accordingly if even needed, instead of having to go thru
measuring the entire assembly length.

If I found that there was even a .001" difference between bearings I would be terribly upset. Bearing are made to very tight tolerances. I replaced the bearings on my input shaft not because they were bad, but I knew that I would be pulling them and that can be a little traumatic.

Successfully reassembled the case, ready to go in.

A little tricky getting what BMW calls the "lock pin" which
is attached in the rear case to go inbetween the 2 legs of
the torsion spring on the shifter mechanism when dropping
the rear half over the bearings and other shafts to mate
with the front half. Several things to go together and watch
at once. But I had it hot enough so once I was happy with
the alignment, it dropped right into place.

The BMW service manual specifies seal protectors to slip
over the input & output shafts, which of course I don't have.
I cleaned the shafts of grease / lube, wrapped tightly with
electrical tape continuing past the end of the shaft 1/2 a
tape width which formed a tapered cone beyond the end of
the shaft. Lubed with some gear lube, seemed to slip right
thru the seals with no problem. Have seen similar "seal
protectors" for the lip seals on the clutch pistons
while assembling automatic transmissions. Quite similar
in the way they work to
the tapered sleeve ring compressors.

Trial shifted thru the gears, seemed to shift OK, as good
as one can tell by hand with no lube in the trans and it
sitting on the bench.

The Permatex Anerobic Gasket Maker seemed to do a good job.
Very similar to the Loctite 518.

Got the clutch cleaned & loosely assembled and in place & the
disc centered with my homemade alignment tool.

Trans and the rest of the stuff goes on tomorrow.

Then the moment I've been anxiously awaiting for 2 years -
"the big test"

I love it when a plan comes together :-)