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Gears grinding when trying to shift up or down

tboooe
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Re: Gears grinding when trying to shift up or down

Post by tboooe »

wa1nca wrote:
Tue Sep 27, 2022 9:10 am
I had to replace the rubber drive shaft boot yesterday so I removed the transmission by tilting the engine
My shifting bolt has the nut also on the bottom so it was a good time install it with nut on top

I did have to drive it out with a punch and hammer !!

Tommy
Yeah this seems to be bit more involved than I was hoping. I will wait until I have some more significant work to do on the bike before trying to reverse the pin. I would be curious to hear from you about the impact reversing the pin has. At least for me, my shift lever and nut doesnt hit the exhaust header when down shifting so I am not sure what reversing the pin would do.
Last edited by tboooe on Wed Sep 28, 2022 8:57 am, edited 1 time in total.
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Tommy
1967 R69s + a bunch of Ducatis

Daves79x
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Re: Gears grinding when trying to shift up or down

Post by Daves79x »

If your shifter hits nothing when you shift, don't worry about it. Thanks to Chuck here, and other research, I've discovered that BMW installed all shift pins from the top at the factory. As things wear, and shifters are removed and replaced several times, the shifter gradually gets rotated too far downward on many bikes and it will hit either the pipe or the frame when down shifting. This could also be a function of the header pipes not being exact reproductions of the BMW parts. In any case, I don't think you will find a transmission rebuilder that installs the pins down through these days because it's just not worth the risk that the shifter won't hit something. It's just too hard to change once installed.

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wa1nca
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Re: Gears grinding when trying to shift up or down

Post by wa1nca »

Well stated
I only changed mine because I already removed my transmission to remove and replace the drive shaft boot
Tommy
Tommy Byrnes
54 R51/3, 55 R50/Velorex 560 sidecar, 64 R27, 68 R69US, 75 R75/6
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tboooe
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Post by tboooe »

Just a little update on my shifting issues. First, thank you for the advice to wait a few seconds after pulling in the clutch and rolling off the gas. That definitely helped. Today I changed the transmission oil. I used the recommended 10w30 (Castrol fully synthetic). That further improved things. Now shifting the gears engage with a "clunk" instead of grinding.

Question...why does this bike require waiting a few seconds after pulling in the clutch before shifting? What causes the gear to grind when I dont wait?
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Tommy
1967 R69s + a bunch of Ducatis

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Re: Gears grinding when trying to shift up or down

Post by jwonder »

Tommy,

These are what I grew up calling “dog ring” gearboxes and as long as the dogs match up they go together very smooth. A good explanation of how this works is here https://jalopnik.com/heres-how-dog-box- ... 1828194393. Remember that you are matching the speed of the engine (input shaft) to the speed of the rotating gear on the output shaft in order to slip the dogs together.

For upshifting:

The “waiting 2 seconds” is not a hard rule. I find that with any of the BMW gearboxes there are sweet spots for each individual motorcycle at which rpm they like to shift.

A perfect example of this would be to try to short shift the motor and you should find that it will go in up and down very easily. Rev the motor to 2,000 and shift. Remember you idle at 750-1,000 so it’s not very much. You should find the gear just slips in.

I have also found that with BMW gearboxes they have two spots they love to shift at, mine typically like short shifting or revving close to the red line and then shifting. I think on up shifts you will find the same thing. Each motor and gearbox is different and you will need to find where yours likes to shift.

Basically I think the BMW engineers designed the box to shift at “old man” and “sport” riding styles on upshift without grinding.

Downshifting:

Downshifting is actually easier! Brake with the front brake and “blip” the throttle to match revs with the palm of your hand. Practice braking and blipping. You need to match the revs of the motor to how fast or slow you are going.

So, if you are “sporty” riding you need to rev the motor much more to match the revs.

If you are taking it easy (“old man riding”) then you still need to blip it more than you would think. The gear should just “click” in.

I hope this helps the explanation on why it happens and what you are doing.
James Wonder
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Flx48
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Re: Gears grinding when trying to shift up or down

Post by Flx48 »

Question...why does this bike require waiting a few seconds after pulling in the clutch before shifting? What causes the gear to grind when I dont wait?
I like James' explanation of what's going on in the trans.
I would just add that one might also bear in mind that the Earles fork BMWs were designed as a dualsport bike.

They were designed to be both a solo bike and a sidecar tug, and while time has proven the bike a success in fulfilling its design mandates, it was not all that was hoped for as a successful business model.
These bikes were introduced in 1955, which coincidentally was the peak year for sidecar sales in postwar Europe; the economy had improved enough by then, so that people were starting to buy cheap cars instead of having to use sidecars for basic transportation.
I think Steib postwar production was up to something like 10-15,000 sidecars a year by 1955, but in six short years dropped like a stone to zero by 1961.
So BMW's vision of bike production for both solo and sidecar use was a few years late, and/or the postwar economic recovery was much earlier than expected. (go Marshall Plan!)
That was good for the everyday people, but bad for the likes BMW and Steib.
Earles bike production similarly dropped off to under 20 bikes a day by their last year.

Anyway, the point is that the drivetrain was designed around dual purpose, and specifically I'm thinking of the heavy flywheel.
The heavy flywheel is ideal for the rig having to drag around 2-4 times the weight moved by the solo machine, as well as easier starting with a magneto ignition; mags produce less spark at slower rpms, and so a heavy flywheel, with more roll-on to push against the compression than a lighter flywheel, gives more opportunity to spark the plugs.
And the heavy flywheel also allows that nice low idle that always brings a smile.
But a heavy flywheel is not so good for quick acceleration or quick shifts; heavy flywheel roll-on is slower to rev up, and slower to rev down.
Those who wished for a more go-fast approach used to opt for an aftermarket aluminum flywheel, (which I believe was just one third the weight of stock) though sometimes with mixed results.

To me, the sedate shifting has simply always been an integral part of the character of the Earles bikes, so when I want quick shifts, I get on a different bike.
Best-
George

tboooe
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Re: Gears grinding when trying to shift up or down

Post by tboooe »

Thank you guys. Maybe I am totally dense but I still dont understand why the gears grind when I try to shift my normal way (almost simultaneous shifting after pulling in the clutch and rolling off the throttle). Why does waiting a bit after pulling in the clutch prevent the grinding? I understand how motorcycle transmissions work but maybe I am missing something.
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Re: Gears grinding when trying to shift up or down

Post by jwonder »

Tommy, it’s all about matching the input and output speeds to get a clean shifts.
James Wonder
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Long Island, New York

tboooe
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Re: Gears grinding when trying to shift up or down

Post by tboooe »

jwonder wrote:
Sun Oct 09, 2022 10:03 pm
Tommy, it’s all about matching the input and output speeds to get a clean shifts.
So why haven't I ever had this problem with any other bike I have ever owned/ridden over the last 20 years? What is unique about the R69s that is causing this? Apologies for all the questions...I just need to understand why this is happening so I can make sense of why waiting between shifts alleviates the gear grinding issues I was having. Its a sickness....
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1967 R69s + a bunch of Ducatis

Daves79x
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Re: Gears grinding when trying to shift up or down

Post by Daves79x »

Basically it’s because of the Flintstone pre-war technology. BMW didn’t get transmission technology to modern standards until pretty late in the /6-/7 era. It’s maddening until you just admit defeat and learn to shift as others have described. I felt exactly as you do a few years ago, but it’s now second nature and just a character thing.

Dave
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