Finally something I can contribute, just a moment to thank the collective wisdom and especially the core experts for many little bits of knowledge over the years.

OK, flappy bearings are supposed to be INA F-957762, but HK10 10 bearings fit perfectly at about $3.00 per bearing. Now the caveats.

Actually: the bearings are HK10 12RS (Rubber Seal) and are commonly  available for 8$ or so (Theo)

The Porsche part has a seal incorporated into the bearing, the ones I used don't. There is a need for a seal of because since this is the intake manifold. BUT, vacuum leakage would be pretty minor since the shaft clearance is pretty small and on the top end the cap completely seals the hole anyway.

A better solution than the HK10 10 bearing might be the HK10 12RS (rubber seal) which has a seal and is 12 mm thick as is the original. Unfortunately the RS was not available from the local suppliers, the story I got was that it was something that was not in high volume so they built them once in a while, probably when a mega order came in, but in between builds you were just SOL.

Add a 10x2 O ring behind the HK10 10 and viola we have a seal again. The O ring probably is fine in Buta although I was trying to get Nitril, I can't actually remember what I put in I think Buta. The seals go in first then the bearing, the retention lip for the bearing in on the interior side of the intake manifold and the bearings press in from the outside. Be careful to only press the bearings into the flush level. In other words the O ring should be touching the lip and the bearing, but you don't want the bearing crushing the O ring.

I can't tell you about the long term reliability for sure, but I have been running this arrangement since February 2001 with no apparent problems. I was most worried about too much friction with the O ring instead of the seal, but after a little hand testing and then observation of the vacuum actuator at startup I am pretty sure that the O ring does not inhibit the flappy motion. I would guess that any leakage would show up as idle problems. I was suspecting leakage a while back and did the test of pressurizing the intake described in the manual and found no leakage.

Well, good luck, if someone else tries it, let us know how it goes, also let us know if the RS is available this year.
Ralph S. Smith


Where did your mechanic get the replacement flappy bearings?

I got mine from Motion Industries (  ), but you should be able to get them from any number of bearing suppliers. The part number you want is HK 1012 RS. Bearings like that are made by several manufacturers including INA, NTN, and others. They all use the same part number.

Mike Schmidt
'88 928S4 Auto Black/Black "PORSCHE" cloth


Bearing type:

HK10 12 RS  or like this: HK1012RS!

1992 928gts Midnight Blue
1988 928s4 Cherry Red (Sold in 2006)
The Netherlands

Schocki has written a report of high idle due to intake leaking. Turned out the bearings had been damaged (rubber seal) while sandblasting the intake before re-painting. Here is a photoshoot of the problem and the dremel solution to get the bearings out and fix it.


Check Schocki's thread search "flappy bearing removal"

1. Cut bearing with dremel using tool # 9901
2. With a cut in the bearing it will collapse
3. Push out

Good luck
David Lutz

when you install the new ones put the bearing in a freezer for about 30 mins heat the intake with a heat gun or the oven in your house 250 should do the bearings should go in pretty easily make sure that the new bearings also have the rubber seal facing to the outside of the intake they prevent unwanted air leaks and also keep out dirt from the bearings