rebuilding throttle bodies

[benzboy]

I know I saw a post awhile back on rebuilding throttle bodies. my car is a mfi 73 911e. im not sure if they need rebuilt. im doing a top end rebuild on it. so I thought, while im in there. I didn't realize what it costs to rebuild t.b's. wow!!
anyways any help would be great

[regency]

Get them to Matt Blast @ Eurometrics. He did mine and they are a work of art. I have his # at my office. PM me if you can't find it on the Interweb - machine.

Steve

73 911 T MFI Coupe, Aubergine

[benzboy]

I talked with him. hes booked til sept. also it will cost about 2 grand. I would like to not spend that much money on them. I would like to know how to rebuild them myself. if that is possible

[HawgRyder]

The basic idea is to overbore the throttle shaft bushing area of the bodies...and insert new bushings (chill bushings...heat body) and then ream to size for the shaft.
If the shaft is also in need of repair or replacement..it gets into the fun zone.
New shafts...or make them yourself...then reinstall all throttle plates etc.
The bore of the bodies may also need attention (overbore to get them to smooth...new plates..etc.).
All in all...lots of time and machine work.
If you need new plates...Holley has some that are close...they will need to be cut down a bit to fit in the cleaned up bores.
Hope this helps.
Bob

[1QuickS]

I can do 'em. Send an email for info/price/schedule: Performance Oriented

[BURN-BROS]

Originally Posted by benzboy

. I'm not sure if they need rebuilt.

You can qualify the throttle bodies with an air meter.

If you cannot achieve approx. 4 kg/hr with some adjustment left on the mixture screws then you need a rebuild.

Throttle plates and the bore wear to the point where air bypasses around them enough to lean out the mixture. New throttle plates and remachining of the bore is required to achieve the required air flow.

I have worked hard to get to a very high level of quality in regards to rebuilding Throttle bodies. They are time consuming and require precision machining to get long term performance. As a result I have had the honor of rebuilding Competition throttle bodies for the 911ST, RSR, as well as the mighty 935.

Bushings are a non standard dimensions...meaning that they are not readily available and have to be custom made. Other shops run Teflon lined or oilite bushing, which prove to be inappropriate.

Once you bore the throttle bodies you expose the magnesium to I'mmediate corrosion. I have the housings Chromated to ensure the level of protection is maintained...something that most other re-builders do not do.

The throttle bodies are then assembled and qualified on a flow bench both at idle and at part throttle. All you need to do is bolt them to your engine and perform minor adjustment to the mixture screws and pump...If you chased the tune due to worn t-bodies.

Average turnaround from me is 3-4 weeks,

Before


After

[1QuickS]

Just as Aaron said:

• bushings are custom made (mine are full length through the journal to provide the maximum shaft support; you can see the ends of the bearings if you look closely enough at my throttle bodies)
• throttle plates fitted after boring bodies
• 8mm ball studs replaced if worn
• flanges fly cut to true them up for better sealing and to minimize stresses
• throttle shafts shimmed to control axial play
• flows set at closed throttle (resting on throttle stops) and flowed with throttles just cracked so throttle plate links are timed
• chromate finish after machine work to protect the magnesium

These tasks are not difficult but experience is better than "on the job training".

[chris_seven]

Originally Posted by BURN-BROS

Bushings are a non standard dimensions...meaning that they are not readily available and have to be custom made. Other shops run Teflon lined or oilite bushing, which prove to be inappropriate.

Aaron,

I would be interested in your objections to Oilite as a bush material.

I had considered using a Glacier DP4B bush but I am not happy to ream these bushes once they are installed so I guess I need to use a semi-finished bush with a reaming allowance.

Thanks

[1QuickS]

Hi Chris,

My take on Aaron's comment is that if oilite bushings are remachined to fit the existing counterbore in the throttle bodies then their wall thickness is too thin to be safe from cracking. Oilite, as I am sure you know is a sintered bronze and not homogeneous like valve guide material is. I routinely use oilite bushes in all my projects and machine the throttle bodies to accept bushings of sufficient wall thickness to avoid this cracking issue. I do remachine the bushings to a non-standard OD for MFI throttle bodies. The benefit of installing bushings with a length through the wall of the throttle body is increased journal length over OEM design which reduces the bearing loading on the throttle shaft thereby extending operational life.

[BURN-BROS]

Originally Posted by chris_seven

Aaron,

I would be interested in your objections to Oilite as a bush material.

I had considered using a Glacier DP4B bush but I am not happy to ream these bushes once they are installed so I guess I need to use a semi-finished bush with a reaming allowance.

Thanks

Oilite bushings seem to be as soft as the 69-71 bushings. The originals exhibited more aggressive wear as opposed to the 72-73 bushings, which look like C954 if I were to guess.

Edit; I should not say that Oilite bushing are improper for the application as they most likely have a higher lifespan than what was in the originals.

[lwein]

Kurt at PartsKlassic does them, very fair price.