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.
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.