Hydraulic Tappets

Paul Anderson · Oct 18, 2004

Anyone have any experience of 'backing off' the hydraulic cam followers ? I've recently had the head skimmed on my '95 9000 lpt ( Corroded core plug = overheating = head gasket ) and had the valves re cut while they were at it. ( 236k miles )
On re build I now find that the engine starts fairly easily but only runs on three cylinders ( No 3 is down ) and gets rougher as it warms up. My guess is that the ecu via the lambda sensor recognises the unburnt fuel from No 3 and weakens the mixture till the other three won't run. If I leave it to cool for 10 minutes or so then it starts OK.
I think that the recessing of the valves means that one or more of the valves in No3 is not closing fully and so I need to let some of the oil out of the cam follower to allow this to happen. Is it just a case of whipping off the camshafts and removing the buckets ? Is there a 'valve' that can be depressed in the hydraulic tappet whilst maintaining pressure on the tappet ? Haynes as per usual is blank on this.
Paul@Kippen.

AlanG · Oct 18, 2004

Paul
AFAIK hydraulic tappets are self adjusting. They have a port open to the oil distribution when the cam is 'up'. As the cam turns the tappet is pushed down, closing the port and turning the tappet into a solid unit (oil being incompressible). As the cam turns back to the 'up' position the valve spring brings the valve up and the tappet port is open to the pressurised oil system again.
Sorry, don't know the answer to your problem, unless the tappet is stuck or leaking and not driving the valve properly.

Paul Anderson · Oct 18, 2004

AlanG,

Yes, this is my problem. As oil is incompressible the hydraulic follower is now too'big' for my reground valves. I need a way to release some of the oil so that the valve will seat properly. Effectively the valve stem protrudes through the head further, by the amount recut and reground off the face. Other hydraulic systems I have worked with ( e.g. Vauxhall ) have a visible ball valve that is spring loaded that, when depressed allows the hydraulic unit to be 'collapsed'.
Is there a similar facility with the SAAB ones.

Paul@Kippen

djtaylor · Nov 2, 2004

I came across something the other day on one of the other saab sites that mentioned that if the valve seats are recut, that the valves should have an appropriate amount ground off the top (a precise amount - so don't go at it with the angle grinder!).

Hydraulic Tappets

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