HEXHEAD Tech - R1200XX - Throttle Body Sync, all years

[deilenberger]

GOAL: This thread will discuss balancing or sync'ing the dual throttle bodies BMW uses on their opposed twin Hexhead motorcycles. It involves the use of some specific tools - and assumes some level of intelligence on the part of the reader.

The articles, posts and comments in this tech section are posted by individual members and reflect their personal thoughts and experiences with repairing, maintaining, and generally working on motorcycles. This information may require specific knowledge and skills, may or may not be correct or current to model.

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PLEASE PRINT AND READ ALL THE INSTRUCTIONS BEFORE BEGINNING! Make sure you understand what is being said, and what the concept is. If it's confusing, or I haven't explained something well - feel free to PM me, I'll try to clear it up, and it may help make the DIY better!

TOOLS NEEDED:

• TwinMax - Electronic differential balance tool - available from various vendors: http://www.google.com/search?sourcei...S221&q=twinmax - Approx. cost - a bit over $100.
• 2 x 10mm open-end wrenches.
• Large fan to use for cooling the engine while doing the adjustment.

TwinMax:

[deilenberger]

BIKE PREPARATION:

• In order to do the balance - or even the balance check, one must first be certain the valves are correctly adjusted. This is vital. Misadjusted valves will throw off the Throttle-Body sync/balance. If you haven't done the valve check/adjustment, please see:
  http://www.bmwmoa.org/forum/showthread.php?t=35445
  
  
• You also need to have access to the two throttle bodies. On some bikes they are easily accessible (R1200R, R1200GS), other bikes less so. On bikes like the R1200RT it makes sense to do this check/adjustment as part of the regular service where the plastic body panels will be removed. For removing the body panels on a Hexhead RT - see:
  http://www.bmwmoa.org/forum/showthread.php?t=35262
  
  
• The bike also must be warmed to normal operating temperatures. Since the bike will be run in a stationary position for a short period of time, it may be worthwhile to use a large fan to provide some cooling air over the engine.
  
  
• Place your fan where it will blow directly onto the engine/oil-cooler assembly. Since you'll be running the engine for a short time with the bike stationary - we need to have some air moving over it so it won't overheat.
  

Once again - I'll repeat - do NOT continue in this operation unless you are absolutely certain your valves are correctly adjusted!

[deilenberger]

TOOL PREPARATION:

Seems like not much to prepare - but - even though the TwinMax is a solid state device, there is a bit of learning to do to use it correctly.

First - check your TwinMax and see if it has short small diameter extensions to the primary hoses on it. If not - you're going to need these. The connections on the hexhead throttle bodies are smaller than the ID of the long tubing on the TwinMax. Some of the dealers who sell it - if it's being sold for use with a BMW - include reducing nipples and some short lengths of hose that will fit the BMW throttle-bodies.

If you don't have the reducing hoses - you might contact the vendor who sold you the TwinMax, or visit your local pet store. Turns out that fishtanks use tubing of all sizes to connect up various air operated accessories, and reducing nipples to connect different size hoses are quite common. You may also find these nipples at the big rotating "stuff" rack in your local autoparts store. What you want to end up with is tubing with an ID of about 1/8" - which will comfortably fit over and most importantly - seal to the Throttle-Body nipples.

Next - you want to make sure your TwinMax has a fresh battery in it and turn it on and calibrate it.

Calibrating the TwinMax:

1. Turn the SENSITIVITY knob fully counterclockwise (DOWN.
2. Turn the TwinMax on - and center the needle on the scale using the ZERO knob.
3. Walk away for a few minutes. Despite it being solid-state, there is some settling time on the TwinMax where it will tend to drift around for a minute or so. Give it a chance to stabilize.
4. Keeping the needle centered on "0" using the ZERO knob, start increasing the SENSITIVITY. You want to be able to turn the SENSITIVITY to max with the needle remaining at "0".
5. Once this is done, turn the SENSITIVITY fully counterclockwise again - leaving the TwinMax ON. Don't touch the ZERO adjustment!

You're now set to use the TwinMax!

[deilenberger]

The TwinMax with the reducing nipple (yellow box) and reduced diameter hoses (green box):

[deilenberger]

CONNECTING TO THE LEFT (clutch side) THROTTLE BODY:

The connection points on the throttle bodies are located on the top of each body. On the clutch side - you'll find a hose attached to the nipple. This hose goes to a purge valve that connects to the charcoal canister on your bike. It's shown in the photo below.

With the engine OFF

1. Remove the tubing*.
2. Connect one of the hoses from the TwinMax to this fitting.

* - if your bike is not a US model, it may not use the charcoal canister, or your US bike may have had it removed. In that case - there will be no factory hose connecting to this fitting - it will be capped just like the one on the throttle side.

[deilenberger]

CONNECTING TO THE RIGHT (throttle side) THROTTLE BODY:

Again, the fitting is easily located on the throttle body:

1. Remove the rubber cap - put it where you'll find it later (they do like to go missing.)
2. Connect the other hose from the TwinMax to this fitting.

[deilenberger]

INITIAL BALANCE CHECK:

Now you can make your first balance check:

• Turn on your fan so air is flowing over the engine and oil cooler.
• Check that the TwinMax (the SENSITIVITY is still at minimum) is at "0".
• Briefly turn the SENSITIVITY to max (clockwise) and make sure the reading is still "0" (if not - correct it using the ZERO knob.)
• Return the SENSITIVITY to minimum (counterclockwise.)
• Start your engine, and let it idle.
• Slowly increase the SENSITIVITY.

At idle - it is not abnormal for the balance to be slightly off - with the needle moving a bit to one side of "0" - this is NORMAL. Do not be concerned, we don't ride at idle, and there is no real adjustment for this.

• Slowly open the throttle to 2,000-2,500 RPM, and observe what the needle does.
  
  1. If it starts to move off-center quickly, you can return to idle, and then continue on the next step - adjusting the balance.
  2. If it goes to the center, and stays there, you can continue to increase the SENSITIVITY.
• If the needle remains at "0" when the TwinMax is at maximum sensitivity - at 2,000-2,500 RPM, slowly rev the engine to 4,000 RPM. If the needle continues to hold at "0" continue increasing the RPM until you reach 6,000 RPM.
  
• If the meter has remained at "0" through the entire range of RPM while at maximum sensitivity - you're done. Stop the engine, disconnect the TwinMax, replace the hose/cap on the TB fittings, and put any plastic you removed back in place. It's as good as it will get. Go for a ride!

If this isn't true - we'll address correcting the balance (ie - sync'ing) in the next few steps.

[deilenberger]

What do we man by "sync'ing" or "balancing" the Thottle-Bodies?

In order for the engine to run smoothly - it must be producing the same amount of energy from each cylinder. An imbalance in the opening of the two throttle bodies will cause one cylinder to produce more power than the other - which results in vibration due to the uneven force generated. A boxer engine is inherently balanced IF the firing forces are equal. Our goal in balancing the throttle bodies is to make the engine as smooth and vibration free as is possible. Getting it "just right" can be very satisfying!

[deilenberger]

WHAT WE ARE ADJUSTING:

This shows what you'll be adjusting - the cable adjustment going to the throttle body. This is ONLY DONE if the Balance Check shows the balance is off - and you're absolutely certain the valve adjustment is perfect. The adjustment is done by first loosening slightly the locknut on the adjuster, then turning the adjuster, finally tightening the locknut.

The adjustment is usually - by tradition - made to the right side throttle body (and that's what I'm showing here.)

It does not have to be done only to the right side TB - that's a hangover from early R11 days when the bikes used a single throttle cable that went first to one throttle-body, then over to the second throttle body. The adjustment was done on the right throttle since doing it on the left would offset both throttle bodies. (More history than you needed to know - but since the claim is often made you can ONLY adjust the right - figured I'd clear that up..)

[deilenberger]

What we are NOT to adjust!

There is one screw on the throttle-bodies that looks awfully tempting to adjust. Just don't do it. This setting is set at the factory, and marked with green/blue paint - BMW's universal mark for "don't touch this!"

My finger is pointing at it - and it's circled in lavender. Just leave it alone. BMW has no adjustment procedure for this screw - and if you do adjust it - BMW claims you must replace the throttle body (at a cost of about $340).

So - just leave it alone!

[deilenberger]

CHECKING FOR FREEPLAY:

Before you make any adjustment, you should make certain that both cables have a bit of freeplay in them. This is so adjusting the cable doesn't change the idle position of the butterfly in the throttle-body.

As can be seen in the photo below, I've moved the rubber boot over the end of the cable up out of the way. Do this on both sides.

[deilenberger]

CHECKING FOR FREE PLAY - II:

Now, reach in with your fingers and pull up on the cable in the direction of the arrow in the photo. You should feel a slight amount of free movement before resistance to moving it is felt. That means there is free play in the cable, which is vital to the correct operation of the bike. The free play isn't much - but it can be felt by doing this. To feel the difference of having free-play and not, while pulling up/down on one of the cables, slowly open the throttle using the throttle grip. You'll feel that you can no longer feel the slight but distinct feel of a tiny bit of freeplay.

As you make your adjustments, you should make certain that there is always some freeplay in the cables. This isn't a problem if you're screwing the cable IN. If you need to unscrew it - OUT - you may run out of freeplay. If you do - put the adjustment back where it was, and move to the other throttle-body - where the same adjustment effect will be gained by screwing the cable IN.

When you're done with the adjustment - you MUST have a bit of freeplay in each cable.

[deilenberger]

ADJUSTING THE BALANCE - Loosening the locknut

We will be doing the adjustment with the engine running. That means the exhaust will be HOT, and there is danger of burning yourself. If this seems risky to you, wearing some mechanics gloves might be a very good idea (available at most any auto-parts store - they are rugged thin gloves that protect you from things like hot exhausts and sharp edges.)

You'll note in the photo below, I'm now using the two 10mm open end wrenches. The bottom wrench is a bit special. It's very thin. I find this is helpful since the locknut is also somewhat thin, and this keeps the two wrenches from conflicting with each other.

First you must slightly loosen the locknut (bottom wrench.) Do this while keeping the threaded upper (threaded) part of the adjuster from turning by using your other 10mm (top) wrench. It isn't necessary (or desireable) to loosen the locknut a lot.. you'll just find the adjustment will be more difficult. Slightly loose so the adjuster can be turned without much force is what you're shooting for.

[deilenberger]

ADJUSTING THE BALANCE - checking Balance and making the adjustment:

We must once again - make sure the Twinmax is zero'd out and again use the TwinMax to monitor the balance. I won't repeat the process - it's outlined above.

Once the TwinMax is ready...

1. Start the fan to keep the engine from overheating.
2. Check the TwinMax is still zero'd out at max sensitivity, then return it to minimum sensitivity,
3. Start the engine, and allow it to come back to operating temperature,
4. Check that the imbalance still exists on the TwinMax at 2,000-2,500 RPM engine speed. If needed, increase the TwinMax sensitivity so it the imbalance is obvious,
5. Using the top wrench to move the adjuster while keeping the lock nut from turning using the bottom wrench - adjust the cable at the throttle body.
6. Check if the imbalance got better or worse (at 2,000-2,500 RPM.) This will tell you the direction you need to adjust in.
7. REMEMBER - you cannot eliminate all the freeplay from either cable. If you need to adjust the cable OUT - I'd strongly suggest locking it back down, and moving to the other throttle body cable adjustment - where you can achieve the balance now by screwing the adjuster IN.
8. Continue making the adjustment until you've achieved balance ("0" position on the TwinMax at max sensitivity) at 2,000-2,500 RPM. Then increase the speed and make sure the balance remains.
9. Now gently lock down the locknut while holding the adjusting wrench. This isn't a contest of strength - the nut requires very little force to lock the adjustment.
10. Chances are excellent that the action of locking the adjustment will throw it off just a bit, so you may have to repeat and compensate for the change in adjustment. It's fiddly, but once you're familiar with how it changes it's fairly easy to do the compensation before tightening the locknut.

Once the TwinMax stays at "0" from 2,000 - 5,000 RPM, at max sensitivity - your job is done.

It actually takes longer to write this up then to do the adjustment!