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measuring installed valve heights?

PSH

PSH

PCGB Member
morning all

can anyone advise on this please...two questions.... Porsche as per usual state a special tool for this job...can a digital vernier do the same job or does Porsche's tool take the measurement from a difficult place? and this leads me to my second question....where is the measurement taken from? Yes I know we are measuring the compressed spring but from what points? Porsche give the sizes as 41 mm for the inlet and 40.5 mm for the exhaust with a tolerance of + - 0.5 mm for each. It's also stated that this is a critical measurement which is why I'm asking where to measure the spring from. At first glance you may think that measuring from the top edge of the installed spring down to the head casting would do but castings being what they are will vary greatly and there isn't a machined part here that can be reached, perhaps the measurement is taken for the top edge of the spring retaining washer or perhaps the Porsche tool fits inside the spring to take a measurement from the centre...see my problem...too many variables.

So can anyone answer this question for me please, perhaps the question has been raised by another member of perhaps a Porsche trained technician can point me in the right direction. I have sent and email to Jon but no reply yet.

cheers

Pete
 
You just install it in place of the spring in each valve location and shim as required to get the right height. I have one you can borrow if you are ever anywhere near Kingston :) It makes the job much easier so that even a ham fisted amateur mechanic like me can get the measurement right!
 
I used 41 and 40.5mm long sticks that I cut out of a plastic box. If your fingers are not skinny enough to hold them in place then hold them with pliers.
 
thanks for the input guys....I can make what ever is needed to measure the distance but I need to know what to measure...is it a simple case of from the head casting to the top of the spring when compressed or is it a little more involved. Reason I ask is if it needs to be within half a millimeter I don't see how that accuracy can be achieved if the lower point is the head casting around the spring seat? also is the measurement from there to the top of the spring itself or is it to the top of the spring retainer washer. hope that explains what I need...:p)

Pete
 
Looking at WSM 15-17 it shows the tool installed under the spring retainer and the text says to install with shims, spring retainer and collets (which retain the spring retainer). Therefore the tool goes between the shims and the retainer with instructions to adjust the height by adding or removing shims. I read this to mean the measured distance is from the seat that the shims sit on (the machined head) to the bottom of the spring retainer. This way adding or removing shims will get you a measurement - otherwise you would have to include the thickness of the valve retainer in the calculation of shims.

I may be wrong....but it doesn't make much sense any other way....
 
The procedure in the WSM is a bit odd in the way that it assumes springs will all be of the same stiffness, which may not be the case.
The way to proceed is to choose the stiffest spring as the reference and add the necessary shims on the other (softer) springs to reach for each valve the same installed stiffness as the reference spring. You do this twice obviously since inlet and outlet valves are not preloaded the same.
 
Thanks guys..

TTM that makes complete sense to my mind from an engineering point of view, I'll take a look over the weekend... no one answered my question regards what is actually measured so i'm going to assume that the measurement relates purely to the spring itself when compressed which is what should be measured, i just didn't know if this allowed for the tool itself, Porsche being what they are for keeping things unconventional, the belt tension er comes to mind...lol. I'll measure the depth of each retaining washer and add that to the distance that I can get too between the washer and the top of the spring, this I can do with the tools that I have rather than making something special.

cheers

Pete
 
Thanks everyone and a big thanks to Jon for the very comprehensive reply to my email...many thanks

Pete
 
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