Turbo - Setting-up the Wastegate

Wastegate mechanism setup Garret T2

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While the turbo is on bench, the wastegate poppet valve can be checked. Drop off the actuating arm from the solenoid and look under the circular valve in the exhaust outlet chamber. Are the seats of the valve and wastegate port it mates with in reasoanble condition. Does it look like it has been running open at all (heavy carbon on faces). Does it look like it would seal? This doesn't have to be the same standard as an exhaust or inlet valve seat, but a quick lapping with some medium valve grinding paste will take out a fair bit of damage quite quickly. Leave the poppet valve on the pivot arm and rotate back and forth manually (spinning valves with electric drills to lap them in is not a good practice). If you have to change any of the wastegate's parts or alignment, you can re-check the initial boost pressure that triggers exhaust dumping (bypassing the turbine). First the actuating rod's length should be such that the valve is just held closed. Connect a foot pump with built-in gauge to the solenoid nozzle (barb), and watching the actuator for the first signs of opening, slowly press down on the pump. Note the pressure. By also allowing it to bleed down, you should find it closes at a similar point, but there will be a bit of overlap (intended by VW). These VW diesel wastegates are usually setup for 0.5 bar, about 7.5 psi. This sets the maximum boost, or is intended to - of course can be modified using bleed valves in the line, or better still, Grainger style valves that actually allow an accurate max boost pressure to be set. 4 or 5 psi can be added without too much concern, above that the fuelling of a diesel would normally need to be looked at. Once you get to 15 psi an EGT and boost gauge to monitor for reliability is recommended. You will need to block off the BOV to get above about 10 psi (the safety Blow Off Valve in the inlet manifold) NB. Don't mess with petrol engine boosts unless you really do know what you are doing! Make sure you fit the wastegate pressure feed line with good fittings, don't use small jubilee/hose clips to secure it, they distort at that size and create leaks, use the original light fittings or swaged fuel-pipe style clamps. Can test the solenoid end connection easily enough for leaks, but not inlet boost side connection.

NB. Lapping the wastegate valve and seat on a KKK 14 turbo is a different job altogether. More difficult, but can be done though (coming later)

Harry