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      10-16-2022, 07:04 PM   #1
grannyknot's Avatar

Drives: 2008 Z4M coupe
Join Date: Oct 2021
Location: toronto

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Overhauling S54 throttle bodies

This my fourth set of these throttle bodies that I've overhauled now and I think I have figured out the dos and don'ts, so I hoping this will help others get theirs back into shape.
About the only replaceable thing that sometimes wears out on these TBs is the plastic pull rod or #11 on the diagram. The delicate stuff, Stainless Steel shims, Butterfly valves, Butterfly shafts, Butterfly brass screws, return springs, you can't get any of it so you have to take care of what you have.

I refer to it as overhauling but what you are really doing is a through cleaning but I don't just mean for aesthetic reasons, the real reason these TBs need to be dismantled are the 15 roller or needle bearings.
12 supporting the Throttle or Butterfly valve shaft and 3 supporting the TBs and linkage.

Every set I've taken apart regardless how much mileage is on the car shows all of the needle bearings are seized with hard packed grease and dirt, to the point where the needles are no longer turning.
The throttle shaft is made of brass with a thin layer of chrome over it, the needle bearings are hardened steel so the shaft takes the wear and that's not good.
A set of S38 TBs I took apart were so worn into the brass that they were starting to leak unmetered air through the bearings.

The set of TBs in these photos have 91,000mi on them and I think I got to them just in time.
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What a mess.
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Here you can see on either side of the flat area in the middle is where the chrome has worn through and it has gone down to the brass underneath.
Once it is into the brass it starts to wear quickly.
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I would encourage you to take MANY photos from every angle, you will need them. Remove one TB at a time, disassemble, keep all the parts in a bag that is labled just for that TB, also it's a good idea to scratch the number of the TB on the bottom, 1-6, they are not all the same.
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Just before there first bath with a lye based industrial degreaser.
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That's better.
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I wish I had taken a photo of the hardened grease, these next 2 photos are of the cleaned needle bearings, brake cleaner, a dental pic and compressed air will get them moving again.
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If you are going to media blast the TBs then some tight tubing in the needle bearings will help keep the grit out.
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The Butterfly valves have a front and a back, don't mix them up, mark the back side of the Butterfly with the number of the TB.
You'll need a T10 star socket to remove the brass screws, the back end of those screws have been mushroomed out to make a thread lock but the brass is very soft and backing the screws out is not difficult, put them safely in the bag. Rotate the throttle shaft 90 degrees and pull the Butterfly out.
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When you reinstall the Butterfly be very slow and patient! This is an operation that can gouge the soft aluminum or brass so easily.
Take your time and line up the holes and gently let the throttle close untill you have a perfect fit with no light showing around the edges.
Don't let the spring on the shaft snap it closed, it will jam and damage the edges.
I made a tool out of and old punch to help mushroom the the threads back but you can also use a screw driver to bend them back down.
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Everything ready for assembly, rebuild one at a time, you don't want any parts left in the assembly tray when you are done
Refer to your photos, it's good to start with #1 then you can install it on the main linkage shaft, pay attention to where and in what direction the operating lever points, #15 on the diagram.
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I used bearing grease in the past but I tried sticky liquid assembly lube this time hoping that it will stay soft and fluid longer.
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The SS washers on the end of the throttle shaft act as a seal to keep dirt out of the needle bearings so make sure you grease it well to help that.
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Also, do yourself a favour and do not touch this black cap or the nut behind it, that is the throttle stop, it was set at the factory and none of those settings will have changed when you bolt it back on to the intake side of the head, you've been warned
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Fully assembled and ready to go back to work.
You can tighten the bolt on the #1 operating lever but don't fully tighten the rest until all of the TBs are fully torqued to the head, the #1 operating lever, (Editing this next bit for a change in procedure) has already been tightened so move on to #2 TB and push that lever down while tightening then #3 and continue on utill all the levers are bolted down.
Now when you push the central lever down all six butterflys should open exactly at the same time, if they don't you need to go back to that TB, loosen the bolt and push the lever closed while tightening. See last pic, the index finger of my left hand is pushing the lever down fully while tightening.

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2008 E86 M coupe

Last edited by grannyknot; 12-01-2022 at 04:18 PM..
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      10-16-2022, 08:16 PM   #2

Drives: E86 Z4MC
Join Date: Jul 2012
Location: Detroit, MI

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Thanks for sharing. Mine were not as dirty but you made me want to check on them.
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