MFI throttle plate screw size?

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I apologize if its been posted before, but I'll be darned if I could find it. I had to tear down my 2.4E throttle bodies to clean them up and now I need replacement throttle plate screws. Near as I've been able to determine they are M4 with a 0.75 thread pitch, but I've only been able to find screws w/ a 0.70 pitch. Am I on the right track? Sure would appreciate it if someone could point me to a source for these screws.

chris_seven · 06-05-2012, 10:37 PM

The standard 'Coarse' size for an M4 Metric Thread is a 0.7mm pitch.

You may be able to find a Metric Fine at a 0.5mm pitch but I have never seen a 0.75.

The MFI Butterfly screw is generally a 0.7mm pitch.

The next issue will be to find the correct oval head size as the countersink dimension is smaller than the stock CSK head size which will cause too much of the head to stick into the air stream.

I have some Solex Throttle plate screws in brass that are very similar.

1QuickS · 06-06-2012, 05:54 AM

The guys at 356 Carb Rescue in Sedona, Arizona make their own M4x.75 pitch screws, slotted, countersunk with domed heads like those used on Solex carbs.

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Thanks Paul, I'll contact them and get some on order.

chris_seven · 06-06-2012, 08:40 AM

Guys I am sad to say that the thread in the MFI throttle shaft is M4 x 0.7

The above photograph shows a standard M4 x 0.7 screw protruding through the shaft and a Solex 40Pl butterfly screw alongside.

The next photo shows the difference in head size from above.

If anyone is making an M4 x 0.75 they will chew up the shaft or the screw.

1QuickS · 06-06-2012, 11:42 AM

Interesting; thread in the 73 MFI shaft I just pulled is M4x.7 but the screw is a pan head profile and not countersunk.

You can get some M4x.7 screws and machine the countersink onto the screws you get assuming you select an appropriate donor head profile.

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How did you check the thread size and pitch? Perhaps that is my problem. I ran a tap into the hole and ran into resistance with a 0.70 pitch and no resistance with 0.75 so I concluded 0.75 was right. Maybe I have a bad shaft?

1QuickS · 06-06-2012, 05:08 PM

I'm reversing my opinion; I just matched what threads there are on the MFI screw to both .7 and .75 pitch screws and the .75 pitch is dead-on while there is obvious mis-match with the .7 pitch.

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Talked to Candace at 356 Carb Rescue and indeed they are having these screws manufactured for their Solex carburetor repairs. 12 of them are in the mail and on their way to me. I'll post how they work after I receive them.

Thanks for the lead Paul.

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Well, unfortunately these don't work. The thread pitch is correct but the head is a tapered head, but the MFI needs a flat head screw.

The hunt goes on.

1QuickS · 06-25-2012, 09:13 PM

Try Matt Blast at Eurometrix

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Talked to Matt a couple of weeks ago. When I find a source for these screws he wants to know. They are salvaging damaged throttles for replacement screws.

Candace at 356 Carb Rescue gave me contact information for the machine shop they have making screws for their Solex carb restorations, but minimum purchase qty is 1,000. Anyone need 9,988 M4x0.75 screws?