Originally Posted by APIDavid
(Post 8261167)
It's one of those words that companies use to make something sound good like they do with womens cosmetics. You know, ' It has hyaluronic betones' OR ' co-ordinated enzymes' That sort of crap - that makes you feel good, but is no better than anything else.
Right. So because the block happens to expand at the the same rate as these pistons, you don't have to allow for any extra clearance within the bore (other than the absolute accepted minimum)? Does this mean that 'normal' pistons expand more, so extra clearance has to be allowed for, so as to stop them from seizing in the bores? |
Originally Posted by APIDavid
(Post 8261107)
Version 8 are hyper-eutectic. repeat after me........
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[quote=joz8968;8261187]A bit like L'Oreal 'Replumper' :lol1:
Right. So because the block happens to expand at the the same rate as these pistons, you don't have to allow for any extra clearance within the bore (other than the absolute accepted minimum)? Does this mean that 'normal' pistons expand more, so extra clearance has to allowed for, so as to stop them from seizing in the bores?[/quote] That would be my take on it, David |
Originally Posted by jd5217
(Post 8261436)
I would if the same was being said by everyone.
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Originally Posted by APIDavid
(Post 8261522)
that would be my take on it,
David And what is it for 'normal' ones? |
I can confirm that the V5 and V6 do have forged pistons.
These are easy to identify from cast pistons too. The cast pistons have casting marks underneath the pistons and will display a criss cross pattern on them. Forged Pistons have a very smooth underneath. Here is a set of V5 forged STI pistons (which are for sale btw) as you will see the underside of the pistons is smooth. http://www.scoob.co.uk/forsale/pistons2.jpg |
Originally Posted by dazdavies
(Post 8261553)
I can confirm that the V5 and V6 do have forged pistons.
These are easy to identify from cast pistons too. The cast pistons have casting marks underneath the pistons and will display a criss cross pattern on them. Forged Pistons have a very smooth underneath. Here is a set of V5 forged STI pistons (which are for sale btw) as you will see the underside of the pistons is smooth. http://www.scoob.co.uk/forsale/pistons2.jpg Nice sales pitch Daz, wish I'd thought of that :p David AND regarding ring gaps and clearances I have no idea, as we don't use the B/S pistons. BUT generally, 3 thou per inch of bore. David APi |
Originally Posted by APIDavid
(Post 8261592)
regarding ring gaps and clearances I have no idea, as we don't use the B/S pistons.
BUT generally, 3 thou per inch of bore. David APi So, for example, taking the std bore's diameter of 92mm (c. 3.6"), then you have to allow about 0.011" (0.28mm) of clearance (i.e. 3.6 x 0.003)? |
Originally Posted by joz8968
(Post 8261641)
Right.
So, for example, taking the std bore's diameter of 92mm (c. 3.6"), then you have to allow about 0.011" (0.28mm) of clearance (i.e. 3.6 x 0.003)? David |
Originally Posted by APIDavid
(Post 8261662)
Yeah about that for a top ring.
David Are they called: 1) 'Top ring' 2) 'Compression ring' 3) 'Oil control ring' What are they technically called and what is each one's 'job'? :wonder: |
V8 Euro STI engines have forged pistons.
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Originally Posted by joz8968
(Post 8261680)
How many rings does the Impreza piston have: 2 or 3?
Are they called: 1) 'Top ring' 2) 'Compression ring' 3) 'Oil control ring' What are they technically called and what is each one's 'job'? :wonder: |
The other two are self-explanatory but what is the 'Top ring's' job :wonder:
Also, did I get the order correct? |
The order is right and the top ring is a compression ring also.
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Cheers
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Top ring - Compression control ring + takes most of the heat from the combustion process. Most top rings are coated eg moly/chrome/gas nitrided to reduce wear and improve the durability in the harsh environment they work in.
Second Ring - Compression control and oil control, they provide a secondary seal and help dissipate heat. Most have a Tapered lower edge to scrape the oil from the cylinder wall to prevent it getting into the combustion chamber. Oil Control Ring - Does what it says on the Tin. This is a good bit of high speed camera work YouTube - From Inside a Working Petrol Engine Mick |
Wow. That's fascinating and rather beautiful (gayer :lol1:).
Really illustrates the flame front's controlled burn when the spark plug fires. I'd love to see footage of an engine detting or pre-igniting! :p |
Originally Posted by Pavlo
(Post 8261884)
V8 Euro STI engines have forged pistons.
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