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Discussion Starter · #1 ·
For those of you that have viewed my M52-M54 engine build and swap forum you know I posted there that I was working on internal replacement parts for a cost effective and long term fix for the DISA self destruct syndrome. Here is what I posted there plus the CAD models of the new internal replacement parts.







The 1st pic is of the flapper valve and lever arm that rotates the flapper valve. As you can see the end of the flapper valve has a hex shaped hole in it. The section of the lever arm just past the pointed and slotted end has what's left of a hex shape O.D..

In my opinion, the reason these fail is due to the following:

> Because the 2 parts are injection molded they need draft (taper) in order to release from the mold.

> Because of the draft on the ID of the hex hole and the OD of the hex section of the lever; and the allowance for manufacturing dimensional tolerances, the 2 pieces have to be made with a clearance in their fit together.

> The code PA66 GF30 on the flapper valve means it's made of 30% glass filled nylon.

> The code PA66 on the lever arm means it's made of just nylon, without glass fill.

> Because there is clearance between the 2 parts in their assembled state, and because there are strong pressure pulses inside the intake manifold, these 2 pieces vibrate against each other during normal operation.

> Once the nylon starts to wear a little, the tiny glass fibers in the flapper valve start to become exposed. Since the lever arm is plain nylon, the exposed fibers in the flapper valve start to wear it away, then it's all down hill from there. The lever arm was most likely not made with glass fill because it would eat up the sleeve bearing and seal that it rides in. I have seen this same erosion in other parts where a glass filled plastic moves or vibrates against a non-glass filled plastic.

My solution will be to machine both pieces out of aluminum, then anodize them for wear resistance. They will be made in such a way that they lock solidly together once assembled, and indexed so that the flapper valve is slightly preloaded against the rubber sealing lip inside the housing when in its closed position to prevent vibration.


New aluminum parts view 1.


New aluminum parts view 2.


New aluminum parts cutaway view showing fitment of the pieces.

A few things to note about the new design:

1) The new aluminum parts will be stronger than the OEM plastic parts.

2) Since all the internal parts lock solidly together they cannot vibrate against each other and erode like the stock pieces.

3) Since a worn and freely flapping about flapper valve is the most likely cause of the internal supporting framework breaking; if a current DISA valve still has a solid internal support structure, there should be no reason for it to break in the future.

4) Since the flapper valve is screwed to the lever arm, and since the lever arm can't get pulled through it's support bushing, even if the internal support framework were to break the flapper valve would remain captive. No possibility of parts running amuck inside the engine.

5) Same concept applies to the pivot pin on top of the flapper valve; it will be screwed and thread locked to the valve. With the OEM design the stock steel pivot pin is just pushed into the plastic flapper valve and falls free in the event of failure.

I hope to machine the first set within the next week. If everything goes to schedule I hope to be able to offer a repair kit in about 2 weeks. The kit will include all parts shown plus detailed instructions, a new O-ring seal and a mini tube of red thread lock. This should be a very easy DIY repair.

All feedback welcome.
 

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Really nice work. Must be a bit slow in your shop to tie up a CNC on a project like this. Do you have an estimated cost?

Jerry
 

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Discussion Starter · #7 ·
Really nice work. Must be a bit slow in your shop to tie up a CNC on a project like this. Do you have an estimated cost?
Thanks, It's rare that I don't have at least one free machine. No cost estimate yet, I need to see how much machining time and manual time I end up having into them, I'm shooting for approx 1/3 the cost of a new DISA or less.
 

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DISA rebuild

BikesStillRule,

I'm very interested in your rebuild kit. My daughter's has apparently gone bad on her X3 2.5. I'm not sure yet if the vacuum diaphram is bad or not, as I haven't yet pulled it. Is there a part for that as well?

Please PM me when you have the kit available. I'll give it try and report back.

Eric
 

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Discussion Starter · #15 ·
I'm very interested in your rebuild kit. My daughter's has apparently gone bad on her X3 2.5. I'm not sure yet if the vacuum diaphram is bad or not, as I haven't yet pulled it. Is there a part for that as well?

Please PM me when you have the kit available. I'll give it try and report back.
Funny you should ask; I have just finished the 1st prototype parts and everything fits perfectly, so I hope to make a small first run over the weekend. The kit will include new aluminum flapper valve, aluminum bell crank actuating lever, custom titainium bolt/pivot pin, small packet of 262 loctite threadlock, a new silicone o-ring, a small packet of synthetic grease and complete instructions.

The DISA valve from my vehicle is the original with 120,000 miles on it, and even though the plastic bell crank lever and plastic flapper valve were completely worn out and starting to fracture, the main frame ass'y, vacuum pot, inner support bushing, outer support bushing and bell crank seal are all in perfect condition. This gives me a certain level of confidence that most used DISA's will be repairable. I'll keep everyone posted on expected shipment availability.


Exploded view of rev2 design.

The revision 2 design incorporates a very light weight custom titainium cap screw that both secures the assembly together and acts as the internal pivot pin. With this design everthing is secured together from outside the DISA/manifold assembly, meaning there is nothing to fall into the intake manifold that's small enough to make it to the engine, even if the main screw were to loosen and fall out.


Transparent view of rev2 design.
 

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Discussion Starter · #18 ·
Will your kit work with an '04 X3 2.5? I checked and the part # for the E39 is one number off, 805 vs 806.
I just searched applications by part number and there is a different part number for all the 2.5l engines (ending in 806) compared to the 3.0l versions (ending in 805).

The version I'm currently working on is the 3.0 liter version. As soon as I can I will try to get my hands on the other version and see what the internal differences are.
 

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Props to you BikesStillRule!!!!
I will post your efforts on the other board too, I am certain there are people interested in this. If you will start "mass"-producing the kit, at least let's increase the audience....

P.S.: I posted it on the other board here.
 
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