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Let's talk about Throttle Assembly rebuilding (DIY content inside)

664 Views 10 Replies 5 Participants Last post by  dbenkert
It got cold, time to address the things that nag me with the car. The wiper sprayer quit spraying so I was going to dig into that, popped the hood and smelled gas (ut-oh) and traced it to a failed injector o-ring. With that story out of the way I was staring at the dirty, slightly grimy throttle assemblies. After going back and forth I decided to go ahead and pull them for a full-teardown and refresh. Why? There's a thought-line out there I see time-to-time that resistance in the assembly is/can be a contributor to TA wear and failure. After 110k miles, assemblies so mechanical in nature surely need and would benefit from cleaning, inspection and re-assembly.

At least that's how I talked myself into it, so now that I'm here let's talk about what I found and what I'm doing.

7-10-11 mm sockets
1/4" drive and wobble and 11mm socket will get to half of the nuts holding down the throttle bodies
For the other half I took an 11mm wrench and hammered a 45 degree bend on the neck of one end, that got all but one last nut.
For that last booger, very back left (cylinder 10), I had to run to harbor freight and get S-bend wrenches.
Magnet, pliers, the regular I'm digging in stuff.
Snap ring pliers (for the recessed butterfly rod that feeds into the throttle position sensor)
Torx T-10

  1. Pull the hvac covers and plastic, remove intake plenums.
  2. Remove injector assemblies
  3. Remove throttle assemblies
    1. I found it beneficial to remove the nylon tie rods that connect each lever arm to the butterfly.
  4. Using a nylon sand-mallet I gently persuaded each throttle body from the cylinder head until I could lift the entire unit, as an assembly, and transfer it to my inside work area.
  5. Once you have the assembly at your workspace it's easy to remove each lock-nut, and with light mallet taps to "break free" each lever arm and slide it off the connecting rod. I've kept each piece seperate, bagged together with any other parts labeled with the cylinder it feeds on the motor.
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Let's take a moment to discuss what I found at this point. These are highly designed assemblies, a work of art really. Each throttle body is cast in aluminum and very light, the rod the ties everything together is heavy, perfectly machined steel and each lever arm not only has a through-bolt but also clamps the arm against the rod when tightened. The steel rod rides on needle bearings in each throttle body (where I expected to find bronze bushings) as shown below. I think it's going to have been an important and useful endeavor to to clean and re-lubricate each of these needle-bearings with fresh grease, with the level of design that went in it was surprising to find no rubber seals or washers to keep them clean, over time I can't see how they wouldn't become contaminated and gritty.

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From this point I disassembled each butterfly assembly which was quite straight-forward.
  1. Remove the two T-10 screws holding the throttle plate, open the throttle valve and slide the plate out.
  2. Remove the c-clip securing the throttle rod in place and slide the assembly out, there will be two metal washers, a c-clip, a throttle spring and and a "wavy washer" to keep track of.
    1. This was another moment where I discovered something worth mentioning, each throttle body had a set-screw for equalizing spring-tension between independent units which I find fascinating. I find it interesting, as a joined assembly with single rod to open/close all throttle bodies, that they went to this level of detail with spring tension to need to account for the manufacturing differences. I've thought about finding some type of tension meter (maybe even a fishing scale) to find average tension then equalize each re-assembled unit but undecided if I'll go to that length or not yet.
  3. I noticed that when releasing the spring tension the throttle rod turned 180 degrees and the spring wasn't "wound up", important to understand for proper re-assembly.
    1. As with the rod between each throttle body, the rod rotating the throttle butterfly sits on similar needle bearings that looked equally as dirty.
The units didn't look terribly caked with carbon buildup considering the 16 years and 110k miles of travel and EGR system, but there is some to see and remove:

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  1. With everything disassembled it's time to clean, I've used a toothbrush, wire brush and different towels with a citrus-based cleaner/degreaser. For the soft metal of the butterfly I wet-sanded using degreaser and 2500 grit to minimize the marring of the surface/metal. In fact I'm going as far as to polish them with compound and a light towel (un-necessary) because why not.

Once clean I noticed that these units were nicely bored at either end, but the casting surface was as-casted in the bend portion of the throttle body. I started reading from this point as to any benefit there may be to smoothing out the runner and if so, to what degree I should do it - and I'll be interested to hear opinions of other board members. From my research this "gritty surface" will create a boundary-layer of air as causes a small amount of turbulence to the flow. You need this down-stream from the injector as it helps keep the fuel mixture atomized and if that boundary layer doesn't exist you can have the fuel stick to the outer walls and begin a washing effect.

That's not required here, the injector squirts at the base of the intake runner and the atomized mixture goes straight into the head portion of the intake path so I've concluded that smoothing runners could provide some benefit to airflow into the motor. This isn't "porting" as I know these are already precise channels with good flow, more of a polishing process to provide that last amount of benefit to the intake path. I'm not expecting "gains" so-to-say, but it's something I think is fun and wanted to take on as part of the overall project that will provide some benefit to the motor.

I'm using a Dremel with a 120 grit flap wheel to level down the surface being extremely careful not to re-shape the bump above the injector or the split-channel below where airflow is separated to feed each valve. Once leveled I'm giving it a quick finish with 400 grit, wet, and finally a run with a gray scotch-brite. I'm not taking these to a mirror finish as I want to retain a lesser, but existent boundary layer of air as there is a benefit to flow speed having that.

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Very little material removed, just leveling off the surface, but there was more work in the tighter sections where there was a rough "hill" where it looks like two halves are joined during the process of casting (not sure how the manufacturing process created these but they were obviously not part of the engineered design.

I haven't reassembled a finished throttle body yet, but for greasing the needle bearings after cleaning I'll be using LiquiMoly 2003 Mos2 Long-Life grease I have on-hand:

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A couple of years ago I found that my throttle bodies were a bit squeaky and sounding like the tin man.

Some say to avoid oils because of trapping dust, I gave mine a very light spritz of WD rust formula and then a bit of silicone spray after wiping the moving parts clean of WD overspray.

It was effective at least at getting rid of the wizard of oz tin man effect, but I often wondered about a complete teardown.

Looking forward to seeing the results of your endeavor!
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