Quote:
Originally Posted by JC919
My question is why have some throttle actuators failed on practically new cars and others on cars with considerable mileage? If it happens to a car that is very low mileage, that would probably mean a problem with the manufacturing of these throttle actuators, whereas the older ones could just wear out.
Either way, in my mind this is a design flaw with these BMW V8s and I am happy to at least not be paying for the parts because the quote I recieved for each bank was atrocious.
|
So, I've been looking into these quite a bit (I have the teardown thread on M5board) and have 5 dead actuators now sitting in my basement. Every one has worn teeth at the exact point the teeth align when the actuator throttle bodies are fully shut.
On the S85, the throttle actuator itself has a little more travel to its spring shut position that it can not make due to the linkage and the throttle body being fully shut. I expect this is for some margin for safety in case slop develops on the linkage. I do not know if the S65 is the same, but from the pictures, it looks like it could be. For the S85, when the throttle body is shut, the actuator linkage arm is at top dead center. Disconnect the linkage and the actuator arm will spring another 30 degrees or so.
Since the wear occurs at this point, I suspect that it all happens at very low throttle. On the S85, you can drive around at any RPM (even close to redline in 1st) with light throttle and only the idle actuators are open. Only when you get past about 30% pedal does the throttle actuator finally open. This makes me wonder if the engine vibrations on the motionless teeth in contact may be causing the wear.
If you open one up (5 torx screw), you'll see the middle gear shaft drops into a hole in the circuit board. There is no bearing surface (like a thrust bearing) on the circuit board), so that means the white gear must have some play. I've been wondering if it isn't moving back and forth on the shaft due to the vibration and wearing prematurely.
At any rate, I have a set of drawings out to a CNC gear shop and hope to have the first set to test soon. I redesigned the black output gear (the black one) to be made of brass so it will not wear again. That way all the wear occurs on the white gear and that is very easy to replace. Future repairs would likely be under $15. Whenever I get them back, I'll post here and let you guys know if it works or now.
On M5board, a few guys are trying an outfit in the UK called BBA Reman whe says the can refurbish them. No positive experience yet, but they quoted around $300.