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Thread: DISA 0 Ring
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Old 03-20-2011, 02:11 PM
rdl rdl is offline
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Location: Ontario, Canada
Join Date: Jun 2010
Posts: 1,768
Mein Auto: 530i 2003
I replaced the original DISA seal with an O-ring today. The vacuum leak is gone.

I've never had much luck with the brake cleaner test method. I use a length of 1/8" plastic tube, one end in the ear, other end at the suspected leak. When checking for suspected leaks, one will hear a soft hissing sound around small orifices even when the seal is tight. For instance if you place the tube next to a good tight ICV or throttle body you will hear hissing, same for the CCV distribution piece connections to the inlet manifold. A vacuum leak has a higher pitch, sometimes even a slight whistle, and the volume and pitch will change as you move to or from the precise point of the leak. It's a bit of an aquired skill. Rumour has it that musicians are expert vacuum leak detectors, leaks are high C while good joints are a middle C (joke)

I tried to save the original seal "just in case" but found it pretty firmly stuck to the DISA groove. As you can see in the picture, I didn't succeed.
It took me about 45 minutes to remove the old seal and then clean up the groove with an Exacto knife, jeweller's screwdrive, dental picks & an old toothbrush. If I were to do it again, I'd just gouge out the old seal & save 15 minutes. It is important to get the groove clean & smooth so the the O-ring can seal properly.

I used a size #140 O-ring in Nitrile. It was the best size I could find in common standard size ranges:
ID 2.237 inch, 56.8 mm, Section 3/32 nominal, 0.103 inch, 2.62 mm
Price was under $1. Viton would have been ~$3.50. Both trivial compared to a new DISA. Nitrile has better low temperature (winter) properties & I judged Viton's advantage in oil resistance & high temp to be irrelevant for this application.

I used a thin smear of engine oil on the O-ring and the manifold bore. It was a firm push to insert the DISA into the manifold, SWAG maybe 5 lb force. Defintely more than with my original old seal, but not so much to roll the O-ring, I hope. Never the less, I think I'll try to find a 56 x 2.0 or 56 x 2.5 which are std metric sizes & give those a try. The compression with the #140 works out to ~30% which is OK but I'd be happier with a lower number in case (more likely when) I have to R&R the DISA in the future. This application doesn't require high contact pressures for an adequate seal.

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