View Single Post
TurboKraft TurboKraft is offline
Registered User
 
TurboKraft's Avatar
 
Join Date: Mar 2005
Location: Phoenix, AZ
Posts: 2,534
Quote:
Originally Posted by WERK I View Post
The spring is a nice afterthought. Don't know who came up with the idea, but kudos to you!

The spring should be weak enough to allow oil pressure to the ball overcome spring pressure, but enough spring pressure to allow the ball to seat against the cup.
Thanks!

Not just for Garretts, and not trying to add restriction (a correctly sized restrictor fitting at the turbocharger is more effective and controllable). The spring is just there to add pressure on the ball and stop oiling after the crankcase oil pressure drops enough after shutoff.

Why?

That was actually a solution first concocted for a 1986-88 930 with a K27 hybrid (turbo from reputable builder) that smoked like crazy on startup, even after a complete remanufacturing. The problem was over-oiling on shutoff, similar to a 993 Turbo. If you disconnected the drip can, ran the engine a moment and shut it off, oil would drain out of the turbocharger for at least 5 minutes. It had a large drip can which was ventilated.
Got a dozen different springs, found a pressure that worked ideal, and the over-oiling problem disappeared. Shut off the idling engine and maybe 5 seconds of oil flow.
Next engine start up: no smoking.


A note about the hollow bolt in the photo:
Maybe it's that the bolt is turned 90deg, but I don't see the usual groove in the bottom of the bolt. The bolt looks too short, like it's been ground down or replaced with a standard 14mm hollow bolt.
That's a huge no-no.
The slot is there so that when the ball is pushed against the hollow bolt by oil pressure, oil can flow around the ball and through the slot to get out to the oil supply line to oil the turbocharger.
Use a standard hollow bolt, and the ball gets pushed up and almost seals against the bolt. Greatly reduced oil flow, if at all. Learned that the $$$ way.
__________________
Chris Carroll
TurboKraft, Inc.
Tel. 480.969.0911
email: info@turbokraft.com
http://www.facebook.com/TurboKraft - http://www.instagram.com/TurboKraft
Old 06-16-2011, 05:46 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #58 (permalink)