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Rattle on start up

scam75

scam75

Well-known member
20 year old cars just keep surprising you don't they! When I started my car up yesterday I heard knocking coming from the top of the engine. I immediately thought it was coming from inside the dizzy cap. Took the cap off and all was fine. Car was parked on a slope as well (facing up the hill) don't know if this could affect anything. I revved it a few times and it stopped. I then took it a drive about 60 miles without sparing the horses and all was fine. Oil level was fine and pressure was good.

I started it up this morning and after idling for about 30 seconds the top end chatter started up. It went away after I started driving again.

I've heard talk of sticky valves before, any thoughts, and should I worry about it or is it fairly common?

Stuart
 
Sounds like the sticky valve thing, or possibly the injectors.
When you checked the dizzy did you also check the tightness of the rotor arm screw?
Mike
 
How recent is the oil? Could be that it all drained from the hydraulic tappets on the slope and is taking a while to fill up again.

Just thought - isn't there a valve to help stop the oil draining right out of the head when stopped? Maybe that valve is starting to fail
 
The screw was tight on the arm and also the oil is new after a recent service. Not sure what oil was put in, didn't ask.
 
Its the non-return valve in the head I would bet. If it it gunked up it will allow the oil to drain from the cambox over night.
 
Is this a concern or just a minor inconvenience? If it's the former what kind of job is it to sort out?

Stuart
 
To be honest I dont know if it would cause an issue, maybe long term. I had that issue with a 944 but the head gasket was a bit leaky and the startup rattle cleared as I cleaned everything when I replaced the gasket.
I have heard that some oil filters also drain overnight, causing clatter on startup. Not sure how true that was but swapping the oil filter is worth a go.
 
As James says there are types of filter which will fit that dont have the required one way valve, but I would have thought that a garage would know which one to fit. So if its draining out of the head, look at the pressure relief valve.
Mike
 
Its the one way valve in the head.

Its like a varicose vane in your leg that stops the blood draining down due to gravity. When the pump is stopped it loses pressure and the head pressure required takes time to build up.
 
Hi Paul
What happens to the valve? Does it stick or get crud in it?
Where exactly is it and how do you clean it?
Sorry lots of questions - not been that fsr in to it yet.

Mike
 
Good call guys but if its only since the last oil change it is worth checking the filter too. Some foolish local garage put a cheap white type filter on mine once:( replaced with proper Porsche part and trouble stopped :)
 
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