VALVE/TAPPET ADJUSTMENT REQUIRED ?
06-02-2011, 11:15 AM
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VALVE/TAPPET ADJUSTMENT REQUIRED ?
Service manual says tappet clearances should be checked every 12 000 miles
as it happens ,it is the same interval as for my land Rover Discovery 300tdi
in her early days ,i used to scrupulously check the clearances every12 000 miles ,but after a while ,as there was no adjustment to be made ,i stopped and only check every 40 or 50 000 miles
over the last 100 000 miles ,no adjustment has been necessay and the car is now 200 000 miles (BTW:always run on full synthetic)
Every year i "listen" to the noise the valves make by applying an iron bar to the head cylinder and then to the cover ,with my ear at the other end of the bar (watch out for belts and pulleys!!)
Any thought as to whether this could be applicable to our cherished 964's ?
as it happens ,it is the same interval as for my land Rover Discovery 300tdi
in her early days ,i used to scrupulously check the clearances every12 000 miles ,but after a while ,as there was no adjustment to be made ,i stopped and only check every 40 or 50 000 miles
over the last 100 000 miles ,no adjustment has been necessay and the car is now 200 000 miles (BTW:always run on full synthetic)
Every year i "listen" to the noise the valves make by applying an iron bar to the head cylinder and then to the cover ,with my ear at the other end of the bar (watch out for belts and pulleys!!)
Any thought as to whether this could be applicable to our cherished 964's ?
06-02-2011, 12:19 PM
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I have always adjusted/checked my valve clearances every 15K miles. Could you go with longer intervals? Maybe but I am not willing to risk it on my cars. As valves wear, they will get tighter so you can't use listening as a wear to tell when its needed. A tight valve will runs the risk of burning. This maintenance procedure has worked well with my cabrio. I've got over 230K miles without any rebuilds.
Ultimately, its your car and you can do what you want.
Ultimately, its your car and you can do what you want.
06-02-2011, 12:33 PM
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very impressive,230 k miles with non rebuilt engine !!congratulations !
maybe also ,when tappets and valves wear the amount of play increases and hence the increasing "ticking " noise
maybe also ,when tappets and valves wear the amount of play increases and hence the increasing "ticking " noise
06-03-2011, 05:43 AM
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Interesting question - mine last had its tappets done 13k miles ago. The spark plugs were changed at the service before that 21k miles ago.
The book says 12k miles to do both, specialists say modern spark plugs can do at least 25k miles.
Some specialists in my experience say 12k for the tappets, others say 15k, and I have heard there's not much point doing them any less than 24k miles. Two specialists said to me that the plugs can go beyond 25k miles, but that if they aren't removed every 4 years they risk getting "welded" in, although I have never seen/heard of this before.
So my plugs are due for renewal and I might as well do the tappets as well. I haven't done it before on this car. It's not a job I fancy either, because of difficulty I find jacking the rear of the car, putting it on stands, and then limited access underneath. I think I will have to let a garage do it, unless somebody can convince me I'm worrying about nothing and it is quite easy to do all this without a garage ramp!
In any case I wouldn't go beyond 25k without adjusting the tappets. One specialist told me you can still get a larger gap emerging with time without being able to hear the tappet noise getting louder. Another specialist told me if you can't hear the tappets then don't worry about it. I reckon 25k max is the best approach........
The book says 12k miles to do both, specialists say modern spark plugs can do at least 25k miles.
Some specialists in my experience say 12k for the tappets, others say 15k, and I have heard there's not much point doing them any less than 24k miles. Two specialists said to me that the plugs can go beyond 25k miles, but that if they aren't removed every 4 years they risk getting "welded" in, although I have never seen/heard of this before.
So my plugs are due for renewal and I might as well do the tappets as well. I haven't done it before on this car. It's not a job I fancy either, because of difficulty I find jacking the rear of the car, putting it on stands, and then limited access underneath. I think I will have to let a garage do it, unless somebody can convince me I'm worrying about nothing and it is quite easy to do all this without a garage ramp!
In any case I wouldn't go beyond 25k without adjusting the tappets. One specialist told me you can still get a larger gap emerging with time without being able to hear the tappet noise getting louder. Another specialist told me if you can't hear the tappets then don't worry about it. I reckon 25k max is the best approach........
06-03-2011, 05:52 AM
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also ,with modern plugs which have 4 tips instead of one ,they last longer (this is of course IF combustion is clean AND no oil contaminates the plug )
What would be intesting to have as info is :
-what sort of size of gap you had found when you did the adjustments
-whether you think the increased gap was due to wear OR due to the nut loosening OR poor adjustment made previously
What would be intesting to have as info is :
-what sort of size of gap you had found when you did the adjustments
-whether you think the increased gap was due to wear OR due to the nut loosening OR poor adjustment made previously
06-03-2011, 05:31 PM
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993 lifters are prone to fail completely. I'm not sure that was really an upgrade on Porsche's part.
I checked my valves after I put ~10k miles on the car and who knows how many miles the PO put on the car since they were done last. None of them were off. I think stretching to 20k miles wouldn't be outrageous. As Rob mentioned, the listening method doesn't work if any of them are too tight.
I checked my valves after I put ~10k miles on the car and who knows how many miles the PO put on the car since they were done last. None of them were off. I think stretching to 20k miles wouldn't be outrageous. As Rob mentioned, the listening method doesn't work if any of them are too tight.
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06-04-2011, 05:40 PM
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-out of sheer curiosity today ,I looked at my written records and i checked the tappets on my land rover : 130 000 miles without adjustment
clearance is 0.2mm for both inlet and exhaust .All tappets were ok ,none of them accepted the 0.3 mm gauge
-I completely agree that the "noise " diagnosis would not work if tappets were tight.But ,if you have checked them once and they are ok ,surely they could not get tight after that ? In my view ,they can only get looser ?
-most likely the rate of wear depends also on the way the engine is run .if racing ,the rate of wear must be exponentially accelerated .So ,if you drive in normal traffic conditions ,wear must be reduced
clearance is 0.2mm for both inlet and exhaust .All tappets were ok ,none of them accepted the 0.3 mm gauge
-I completely agree that the "noise " diagnosis would not work if tappets were tight.But ,if you have checked them once and they are ok ,surely they could not get tight after that ? In my view ,they can only get looser ?
-most likely the rate of wear depends also on the way the engine is run .if racing ,the rate of wear must be exponentially accelerated .So ,if you drive in normal traffic conditions ,wear must be reduced
