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mingmong's Avatar
 
Join Date: Dec 2004
Location: london
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Correct Valve height?

Just got my heads back from the machine shop and now I'm a little worried/confused. According to all the manuals the height of the valve stem (measurement 'D' in the pics) should be 46.0mm +/- 0.3. I've measured all my intakes and they are within this range. The Exhausts however are a bit out. Ranging from 45.4mm (at worst) to 45.6mm (at best). My question is...why is this measurement important? Or should I get the machine shop to re-do these?

Cheers Mark
Old 07-11-2005, 11:31 PM
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Mark

They are shorter and therefore not a problem, (Explaination is the seat, they have been replaced?). Factory specs apply to factory work/materials, -0.1--03 mm can easily be explained by man tolerances of vales and seats, focus on installed spring length

HTH

Neven
Old 07-12-2005, 12:53 AM
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Thanks Neven (sleepless nights over!). My thinking was that because they're sorter then the only thing that changes is the exhaust won't open quite as much as it would if it was 0.3mm longer. I'm assuming this doesn't really matter. I'm pretty sure the seats are original but the machine shop skimmed a few atoms off them to seat the valves nicely.
Mark
Old 07-12-2005, 06:27 AM
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I think this affects the seat pressure and associated static spring shimming as the heads are reassm.. right?
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1989 3.2 coupe, DIY top end at 77k, now 112k
Old 07-12-2005, 07:00 AM
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Mark

No the opening distance is dictated via the cam, This is just a setup tolerance, but if you have replaced the valves then the head of the valve may have more 'meat' so it will sit lower in the head, The important settting is the installed spring height (also put them in the right way up!). In the worst case you won't be able to get set the springs to their minimum height but I doubt this as usually they have 2-4 shims and I think each one is .25mm?

HTH
Neven
Old 07-12-2005, 12:34 PM
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Many thanks Neven. I'm in the process of getting new springs. The one's I had where some aftermarket unknown and didn't have any shims under them. Don't suppose anyone knows how many shims I'll be needing to buy?
Mark
Old 07-12-2005, 11:57 PM
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I'd budget on 3 per valve, but they don't cost a lot (0.55c from pelican) but they are one of those things that don't wear out so a porsche shop may have them chesper 2nd hand (36 will cost 19.80 USD of the top of my head)

HTh

Neven
Old 07-13-2005, 02:01 AM
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