930 throttle body rebuild

[reclino]

Seen a few posts about these, how the throttle shafts seals leak, and the bearings cause wear to the shaft, have not seen anyone offer a rebuild solution. My brother suggested ignoring this potential time suck, gently clean it and bolt it on the car. I was unable to follow this advice.
So let's jump in with both feet and try not to get.lost down another dead end rabbit hole.






I thought this looked odd before removing the screw, looks like someone missed when setting up to stake the backside of the screw.









I thought the screws were secured with Loctite, I was mistaken.
Pro tip, grind off the stake on back of screw before removing the screw.

[reclino]

There is some wear in the shaft, and the bearing seals are toast. Let's have some fun and develop a kit for this repair. Unless someone knows of a kit already available.

[reclino]

Shaft appears to be hard chrome plated, and the bearings have worn through this plating.







If I were to replace the original needle bearings with bushings this wear would likely stop and this shaft could be saved.
It's possible that cleaning, replacing the O-rings and grease could also be a viable repair, but I don't think it would last as long as bushings unless I replace the shaft or have it grind down the shaft, chrome plate and grind back to size. Grind plate grind
= pretty spendy on such a little part.

[reclino]

And once again the quality manager throws on the brakes just when we were getting up a head of steam.

[Mustangkev]

following along with this. I did a smoke test on my car and the only leak on the intake was both side of the throttle shaft.

[reclino]

This has to be the worst designed and built part I have looked at on the 930 thus far.


They decided to mill the radial O-ring groove where it plugs into the bypass valve. The NC machine likely had worn X Y half nuts with excessive backlash.... This surface should be 16 RMS surface finish to be air tight it probably measures 300+ RMS it's like waves in the ocean. This is a divot in the O-ring gland at least .008" deep and these marks go all the way across, a perfect leak path. It would fail a smoke test when new .



WTF the idle air screw is designed without an O-ring seal, just lots of fine threads. Will lube this with some Teflon loaded grease. Was probably installed with grease when new, but that's long gone.

[reclino]

My car is pretty low miles, but the age has taken its toll, these are sealed needle bearing, and the seals came out as little crumbling bits, I have determined O-rings that will work, but there not perfect. This throttle shaft bearing seal arrangement is similar to the 944 turbo. There used to be seal kits available for them, but looks.like there NLA.

[reclino]

You know that kit of O-rings you buy, then they never seems to fit whatever it is you have apart???



Well found one that will fit and function.....
Probably going to make a drawing of the shaft, and shop it around see what it costs to make quantity 50, buy the correct needle bearings and screws I had to destroy to get out.
Likely every 930 on the road needs this rebuild kit.
EngiNerding

[908/930]

Looks like fun, what diameter do you thing the rollers were in the bearings? I'm thinking polish the shaft back up and swap out the steel rollers for some made out of torlon, likely some dirt will always find a way in there. Not sure if bushings would last long in there. WOW that is horrible machining on that O ring groove.

Replacement O rings should probably be viton or silicone to deal with the heat.

[reclino]

8mm ID 12mm OD and (12mm depth?) Getting the caged needle bearing out will require a bit of tooling and some finesse. Yes Torlon might be good here, I was thinking of Rulon a fiber reinforced PTFE, but I would not want to give up the O-rings so would need to either find a 8mm ID 12mm OD lip seal, or a cage to hold in an O-ring. Max temp of this part will be on shutdown with heat soak, during operation post intercooler temps should be below 120 deg F?

[reclino]

Well, I have decided the best, quickest way forward is to put new double sealed needle bearings in with the original worn shaft.
The shaft wear is very minimal, basically worn through the hard chrome. I suspect with proper grease inside it will last for years.
I did some surfing and these sealed needle bearings seem to be on all cars of this vintage, BMW, Chrysler to name just a few. Failure mode seems the same, seals crumble and fall out, resulting in vacuum leaks and wear to the throttle shaft.

Bearing I am planning to use is an INA HK0812-2RS.
Grease will the Porsche extreme pressure grease I got for the clutch pilot bearing.





These are in the housing tight, without heat I doubt this puller would have worked.



Screws for the throttle plate seem to be 4mm x 0.7 x 8mm long? Not yet verified this but likely I am going to have a box of 50 of these once I double check the dimensions

Feels strange sometimes coming on this site and giving away free tech data. Honeywell or Lockheed-Martin would charge quite a bit for this type of teardown instruction.

[908/930]

Do you have any high temp grease without silicone around or Krytox grease? The seals on those bearings is really a weak spot, not really intended to be used as a seal against pressure and vac, the high temp after shutdown really does not help. Yup, give the shaft a quick clean up with some 400 grit in your portable lathe (cordless drill) and should be good.

[reclino]

Yes do have some Krytox grease, it's white extremely high temp and loaded with Hexagon Boron Nitride, at least I think that's what's in there. Not sure I need that extreme high temp, but will look into it.

[reclino]

Box of 100 oval head screws.....

[Rich76_911s]

Yeah my car is in desperate need of this as well.

[reclino]

I ordered 12 different size O-rings, X-rings and lip seals, I may find a seal solution that may work rather than replacing the bearings. I also ordered a couple Teflon lined bronze bushings, but would need to turn some little cups to hold the seals in place. Have not made a drawing of the shaft yet, but I think a new shaft is going to be required to fix many of these the correct way.

[fourblades]

Looking forward to seeing your solution.

A lot of people will want these if they can be DIY installed.

John

[reclino]

It's so tempting to just pull the trigger on the parts shotgun, and not very satisfying when it's a miss.
12 different sizes of O-rings, x-rings, v-seals, and a few lip seals, quantity purchased 244 or so.....
None of them are perfect, some are close.
Even the oval head screws are not exactly correct, head diameter is too large and I think the angle on the back is 82 deg on the factory screw, metric screws have a 90 deg countersink angle....

[fourblades]

Frustrating! That is a good close-up photo.

Maybe a buddy can turn them down for you since you only need a couple?

John

[908/930]

I think what you need is a 60 deg metric FHCS.