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Guest Message by DevFuse

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is it worth the time to polish rods and crank?

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5 replies to this topic

#1 JonOfScio



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Posted 10 June 2004 - 07:05 PM

is it worth my time to polish the piston rods, and the areas of the crank that touch oil (ie: not the bearing areas) to reduce friction in the oil?

because there is so much oil around and about the crank and rods in a flat 4, I was thinking this would have some good benefits.

Also, what about the insides of the block, I've seen small discussions on polishing and/or painting (high temp engine paint) to reduce tendancy of the oil to stick to the insides of the block. I think this might not necessarily be worth the time.

Thanks for any opinions.

#2 baccaruda



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Posted 10 June 2004 - 07:12 PM

I'd ask a VW shop what they think.

#3 The Scooby

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Posted 10 June 2004 - 07:49 PM

one word: yes

it works on otehr engine, why not try a subie now.

#4 All_talk


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Posted 10 June 2004 - 08:04 PM

I'm an old VW guy (and an Engineer). I doubt you would see measurable gain from polishing the crank and rods, there velocity alone will shed the oil quickly and I believe the subie engine has a good windage tray. RPM is a big factor in these kind of losses, and while 6000 isn't to bad its not the 12,000 that high end race engines run.

Polishing the case could cause some trouble (I know it can be disastrous for a air/oil cooled VW), as it will reduce heat transfer. Polished surfaces have much less surface area than the raw casting, the oil will hold more heat instead of passing it out through the case and to the water jacket. In fact, one of the important things that oil does is transferring heat from the friction producing areas to cooler places in the engine so if it spends a little clinging to the case its really not a bad thing, as long as its not so slow that you’re pumping the sump dry.


#5 Caboobaroo


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Posted 10 June 2004 - 09:27 PM

With the amount of work for such a little gain, it's not worth it IMO. To smooth the casting from the INSIDE of the block would be such a pain and VERY timely. If you keep the oil changed regularly like you do in the Legacy, you shouldn't have a problem with it:D

On another note, gimme a call this weekend. I'm gonna be over at Chris Kobernick's house and I'll have my phone on. Later Jon

#6 Nug


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Posted 10 June 2004 - 11:29 PM

Polishing metal parts removes rough edges, in turn removing stress risers. Stress risers are areas where cracks can form. Rods are often polished and shot-peened to make them tougher. Of course, they need to be balanced afterwards.

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