M4x.75 Screw Source

[DSPTurtle]

Does anyone have a good source for the MFI butterfly replacement screws? The thread in the throttle rods is an M4x.75 and unfortunately the usual suspects for replacement metric hardware do not seem to carry them.

[JJ 911SC]

Might be faster to tap your own as nobody seem to carry them.

[cgarr]

Might try some gun shops, that's a pretty old German DIN standard

[Spenny_b]

I had a similar case with trying to source M8 fine thread fittings (to plug 4 ports on 2x Tial wastegates)....devils-own job trying to get them so bought a die and made my own. Ironically, the die was not difficult to source via eBay! Never a bad thing to add tools to the collection

[DSPTurtle]

The hard part about that is it being a pan head that fits down in the throttle shaft.

[chris_seven]

Unhappily there are more issues with the Throttle Plate Screws for the MFI Throttle Bodies than just thread pitch.

There are two different shafts depending on the age of the system:



The upper shaft is a from a 2.4/2.7 throttle body and the lower shaft is from a 2.0/2.2 litre throttle body.

As can be seen the 2.0/2.2 system uses a reduced section shaft and a countersunk throttle plate screw.

The head of the screw is a reduced diameter and the angle of the countersink is also not standard.

The later shaft also uses a non-standard head. An M4 Pan Head Screw has an 8mm diameter head and this doesn't fit into the shaft recess which is 6.5mm diameter.

The screw supplied looks as if it is a reduced head fillister style of screw but I am not totally sure that this is quite right.

The other issue is that both screws have a small recess at the ends to allow them to be staked into position.

I have been looking for the correct screws for about 2 years now but without success.

I have had quotes to re-manufacture but Minimum Quantities are 5000 pieces which is a real pain.

For the later shaft we have found a plated screw which is made from a very soft steel. It a reduced diameter Pan Head with a Pozidrive head of 6.25mm dia so it fits quite well into the shaft recess.

It has a 0.7 pitch but is a loose fit into a standard thread and does tighten into an MFI shaft without damaging the female thread.

The head is very slightly too tall but they do work.

[kennethg]

Lawson Products has M4 machine screws. Most are .7 pitch though.

[BURN-BROS]

Supertec just had both types made. They look very nice

[Charles Freeborn]

My usual go-to for that sort of thing is smallparts.com (now part of Amazon). But theirs is m4 .7 too.
I assume you've tried McMaster and so on?
-C

[Spenny_b]

Originally Posted by chris_seven

Lots of researched stuff

Now that's a comprehensive reply for such a seemingly insignificant part!! Can only be from the keyboard of chris_seven!

[DSPTurtle]

I can promise you that it is not an insignificant parts since you basically must destroy it in order to remove it (grinding off the peened edges) and reassembly is critical since these tiny pieces of metal sit directly above the intake valve
I will shoot Henry a message and see what he has in stock. Maybe my head studs are ready too

[chris_seven]

Originally Posted by Spenny_b

Now that's a comprehensive reply for such a seemingly insignificant part!! Can only be from the keyboard of chris_seven!

We have been drawing up new throttle shafts for Weber, Zenith, Solex and MFI systems and we are trying to standardise on a format of shaft design/throttle plate screw so we don't have to make too many different parts and the first thing we needed to do was produce a bit if a matrix of which part used which type of fitting.

We have decided to make the shafts with a cut away style similar to the Solex 40PI and the 2.0/2.2 MFI shafts



This results in a throttle plate screw with the following appearance:



The slot is designed to allow the screw to be mechanically locked with a screwdriver.

They should fit the early MFI and the Solex 40PI standard shaft without problem and I don't think the 0.5mm protrusion will have too adverse an effect on airflow.

We are making the shafts from 4340 Steel and they are being precision ground and surface treated.

We have made all of the correct end plate fittings from laser cuts which have been 'vibro'd' to deburr them, case hardened and zinc plated.

We have also purchased a used Taumel Orbital Riveter so we can attach these plates to the shafts in the correct manner.

We are just finishing a throttle plate jig so we can match throttle plates to carb bores.

We have also re-manufactured all of the gaskets for all of these carbs using Klinger Gasket materials, we have Viton B 'O' Rings being made and all of the springs needed are being made and should be ready by mid February.

We have manufactured the correct profile cheese head screws to assemble Zenith and Solex carbs and have ordered reduced AF hexagon nuts which are used in different parts of the carb/manifold assemblies.

We have made new idle mixture screws for Solexes and have plans for several other parts which are difficult to find.

We have a die being made for Solex Jet Carriers as an example and this should be completed in the next few weeks.

We have just taken delivery of a large AquaBlast cabinet so we can finish carb bodies to a high standard and hopefully be able to service and overhaul all 911 carbs correctly.

[Spenny_b]

Bloody 'ell!

Now I feel like some kind of Judas for going EFI [gets coat]

[Henry Schmidt]

Supertec does indeed have these rare little screws in stock.
We have perhaps the largest selection of MFI pumps, throttle bodies and ancillary parts in north America.

[designdesk]

Originally Posted by chris_seven

We have been drawing up new throttle shafts for Weber, Zenith, Solex and MFI systems and we are trying to standardise on a format of shaft design/throttle plate screw so we don't have to make too many different parts and the first thing we needed to do was produce a bit if a matrix of which part used which type of fitting.

We have decided to make the shafts with a cut away style similar to the Solex 40PI and the 2.0/2.2 MFI shafts



This results in a throttle plate screw with the following appearance:



The slot is designed to allow the screw to be mechanically locked with a screwdriver.

They should fit the early MFI and the Solex 40PI standard shaft without problem and I don't think the 0.5mm protrusion will have too adverse an effect on airflow.

What is your company Called? Are you still selling the screws?

[horizontallyopp]

Originally Posted by designdesk

What is your company Called? Are you still selling the screws?

Unfortunately, the user chris_seven is no longer with us as he passed away. His shop was Fenn Lane Motorsports in the UK, so you could look them up and contact them. However as noted above, Henry at Supertec might be your best resource.

[KTL]

Originally Posted by horizontallyopp

Unfortunately, the user chris_seven is no longer with us as he passed away. His shop was Fenn Lane Motorsports in the UK, so you could look them up and contact them. However as noted above, Henry at Supertec might be your best resource.

Thank you for sharing that unfortunate information. I noticed awhile back he had not posted since November of 2017 and hoped just this was not the reason. Chris had an INCREDIBLE amount of technical knowledge to contribute and that will be missed. That said, what he did contribute was always highly technical and very informative to us average Joes. Many people will continue to benefit from his willingness to share amazing knowledge with the forum that reads like we are reading from a textbook

RIP Chris.

[jpnovak]

Found these.

https://www.classicandexotic.com/store/p-2544-round-head-slotted-screw-m4-x-075.aspx

Not may other options. The tap and die sets seem to be easier to find if you want to make your own.