F650 Counter Balance (c/b) Seal Failure FAQ

compiled & edited by Kristian #562
By Flash #412, Elroy#825, John Douglas (UK) & Stephen (Oz), 21/11/01
Thanks to Richard #230, Hombre Sin Nombre
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 21 April 2006

• Introduction
  • What is the Counterbalance, or "Compensating" Shaft?
• C/B Seal Failure
  • Typical Symptoms
  • Causes
  • What you should not do
  • What you should do before you go to the Mechanic or try and fix it

For other related FAQs:

• Engine Misc. FAQ

This FAQ concerns a problem which manifests itself in high mileage F650’s and has causedconsiderable concern to those whose bikes have fallen victim to the particular seal failure, not least because the problem has been particularly difficult to identify. Hopefully this will help you or your mechanic quickly resolve what it is that needs repair. This FAQ does not (at present) give a detailed how-to about repairing the problem itself, because it means a pretty severe engine teardown, but it does give pointers on which Parts need replacing.

• The compensating shaft is essentially a counterweight that "throws" (i.e. i own angular momentum) opposite the piston & crankshaft, to smooth out the motor.

Typical Symptoms

• In all known cases there have been large quantities of oil observed in the air filter, up to a quart of oil after every trip. Here are some testimonies of symptoms:

  "I've recently replaced the engine side cases on my F650 due to salt corrosion, and ever since have had a lot of engine oil ending up in the airbox. Bike is five years old - done 50,000 miles and until now never missed a beat - no major probs or dramas. This oil is coming in through the crankcase breather tube, in rather alarming quantities. I first suspected worn rings causing crankcase over pressure - but a compression test came up normal. Oil level is ok, in fact a little low if anything. The oil filter has been changed recently (after the problem started - in case it was blocked) and the problem continues. In taking the right side engine cover off to look at the breather tube from the inside, there's a small (5mm) port which disappears into the engine, this port connects to the crankcase breather, and is *FULL* of oil. I'm assuming this is not normal, and that possibly the problem lies deeper in the engine somewhere."

  "I was TOLD we had a club member here whose counter-balance shaft was destroyed by a blocked oil-way (symptom was oil in air filter) and it wasn't replaceable - according to the local dealer. The TRUTH turns out to be that due to what appears to be a sloppy c/b shaft/bearing fit, the associated seal died. Now, as anyone with experience of the old British iron will recall, the return oil pump (scavenge pump) has to be able to outperform the supply pump to keep the sump from filling up with oil, but it won't be able to cope if something like this happens. I've now learned that on newer models particularly there often appears a small tear in the r/s engine gasket which allows the alternator to fill with oil, which then overcomes the scavenge pump. This clearly is the most likely situation with John's since it began when he had taken this cover off. For other people who develop this symptom unrelated to any maintenance work it's more likely to be the previous problem (blown seal on c/b shaft). In two cases I know of now, the dealer's done a top-end job for nothing when this happens. I'll let you know (if you're interested) whether BMW eventually 'comes to the party' or not as our member is now facing an ADDITIONAL $2,500 repair bill on TOP of the top-end job, to replace a part which they originally said was just not available, and which was almost certainly defective since the beginning."

  "This one is worth wrench-of-the-week award, if solved. We are dealing with an 1996 F, with 137k km on the clock. After each trip, the airbox overflow on the right deposits a puddle of oil. We can verify we do NOT have too much oil in the bike. Both oil pumps work. Piston rings have been replaced since the problem was identified. This did not solve it. The very competent BMW wrench is stumped."

  "I posted last week about a high-mileage bike that piddled a puddle of oil after long trips. Just to confirm the outcome of the saga: The balancing shaft seal had worn out, allowing oil to get from the engine casing to the alternator enclosure. From there, it made its way into the breathing circuit, ending up in the air box. Midway Motors was able to completely disassemble and reassemble the motor to get to the offending seal, we rode about 350km on the weekend and, no oil leak! When we arrived at the destination, my cell phone rang (about 6:30 PM). Alan Matthews from Midway Motors wanted to know how the trip went. Now THAT's service! Maybe he could teach some of those BMWNA people how to treat a customer. OBTW, he had no spare parts left over at the end! Thanks to Chris, Flash & Richard, who contributed in hunting this one down. Special thanks to the SPCA for donating a replacement seal."

• After each trip, the airbox overflow on the right side of the bike deposits a puddle of oil on the pavement.
• A number of owners have replaced the rings, checked the compression, verified the valves, guides and stem seals are O.K.
• The Mileage of affected bikes has been in the range 60,000 - 137,000 kms.

Causes

• Failure of Counterbalance Seal. This Parts Drawing #1 shows Two Seals, #13 and #15.

  Part #13 is the seal for the c/b Shaft. It's called the "WELLENDICHTRING AN AUSGLEICHSWELLE Part# 11 11 2 343 019 13 and is a 15X24X7 Seal.

  A Wellendichtring is a Shaft Seal and "Ausgleich" means "balance"

  Part #15 is the "WELLENDICHTRING AN ABTRIEBSWELLE" or the Driving (Countershaft) Seal which is Part# 11 11 2 343 018 15 and is a  25X40X7 seal. You do not need this part.

• The oil probably got from the alternator housing into the airbox, through the breather system. The compensating shaft passes from the oil-filled part of the engine to the alternator housing. The rubber seal on the bearing at that junction fails, letting oil into the alternator housing.
• Another possibly damaged part, due to lack of oil is part #8, the c/b bearing on this Parts Drawing #2. The counterbalance itself is part #1. The bearing supports the compensating (counter-balance) shaft.
• Also, there is a possibility an internal oil-way supplying the counter-balance shaft plugs up, forcing the oil out the breather. This could eventually cause the seal to fail, so look at the oil-ways feeding the c/b shaft, particularly if you've had some mechani who may have left a bit of rag or gasket in the system, do some work on your bike recently.
• Crankcase pressure, which may be forcing oil IN the Alternator Cavity out the breather is caused by several things:
  1. Blow-by (fuel-air mixture leaking past rings).
  2. Compression effect of the piston descending in the bore. Normally the latter is a very transitory effect since the piston goes up as much as down, but the former indicates worn rings.
  3. There is one OTHER way that pressure gets into the crankcase (in theory at least), which could be forcing oil out the breather pipe. Worn rings OR WORN VALVE-GUIDES can produce excess crankcase pressure. The latter is usually not a problem, probably because long before worn valve-guides (and related seals) let products of combustion into the valve-gear cavity (and thence to the crankcase) the motor's ready for at least a top-end job. Perhaps if rings were done on the cheap and no-one checked the condition of the valves/guides/seals then this could result though.

What you should not do

• You shouldn't continue to just fill up the oil and ride the bike, because apart from the other parts of the engine that need oil, the c/b shaft itself can be wrecked.

What you should do before you go to the Mechanic or try and fix it

• Verify the leaking oil is it's definitely in the Airbox and not from the Oil Pressure Sensor.
• Carry out a blow-by test to check the Condition of the Rings.
• Verify you do NOT have too much oil in the bike.
• Verify both oil pumps work. There is a pump to fill the oil tank and another to feed the engine working parts. These are located in the centre of the crank case and driven by plastic gears visible behind the clutch.
• Check the breather mechanisms. A big single pumps a lot of air that needs to go somewhere and the breather system had better be working properly.
• Check how good the cover gaskets seal. It is possible that you have an air leak and are just sucking air into one of the covers, and eventually through the crankcase vent into the air filter housing. Or through a cracked vent hose near the side covers you replaced.

Luckily, so far this is not a common failure, but it might be worth keeping in mind as our collective kilometres accumulate.