Coating of the piston skirts

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Coating of the piston skirts

Postby joeleoni » April 16th, 2014, 7:06 pm

I am at a point of rebuilding for this spring.
Is the coating of the piston skirts good? Is it allowed for vintage racing?
1200 cc Predator

Joe
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Re: Coating of the piston skirts

Postby FV80 » April 20th, 2014, 7:50 am

Joe,
Coating of any of the internal engine parts or transmission parts is NOT ALLOWED in the SCCA FV rules. I would think the same would be true of most vintage organizations.
Hope this helps,
Steve, FV80
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Re: Coating of the piston skirts

Postby brian » April 20th, 2014, 2:09 pm

Geez, I saw some A&A chinese pistons with their skirts coated. Are these illegal as well? How about cutting a new top ring land? In the rule, C.4.b it specifies a distance from the wrist pin for the top ring land. Can I cut a new land as long as it meets this rule? Just wondering.
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Re: Coating of the piston skirts

Postby hardingfv32-1 » April 21st, 2014, 11:29 am

1) I had a 40 HP German brand cylinder set about 15 years ago with Moly coated piston skirts. Moly is really to reduce startup wear.

2) What makes you guys think you can cut your own grooves and get the right surface finish on the ring lands?

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Re: Coating of the piston skirts

Postby joeleoni » April 21st, 2014, 6:49 pm

Thanks Brian,
There was 2 choices for the coating, one the moly as you describd for start up,
and another more expensive for long running.
I will go with the moly for the break in.
Diggin moly was my last job (AMAX) here in Colorado.
Gotta use the stuff.
Thanks.
Joe
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Re: Coating of the piston skirts

Postby FV80 » April 21st, 2014, 9:14 pm

I believe that Moly would be considered a lubricant/protectant - similar to cosmoline. I was thinking in terms of the 'super' (expensive) hi temp coatings being applied in quite a number of other classes these days. Those coatings become a part of the part and (supposedly) do not dissolve or wear off quickly (like in minutes).

As for cutting your own ring lands, I can't think of any rule that would prohibit that .. as long as the resultant ring grooves meet the rules. I believe the rules allow machining of any previously machined surface.

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Re: Coating of the piston skirts

Postby hardingfv32-1 » April 22nd, 2014, 12:13 pm

Brownell's Teflon/Moly coat is the hot set up for DIY guys.

Moly is most commonly applied with bonding or PVD. Bonding contains about 60% moly and must be cured at about 350°F. PVD application is pure Moly and has an application temp of 350-500°F. Both should be considered permanent and not allowed by the rules.

Moly reduces the coefficient of friction of an oil covered surface by about 50%. So, if the CoF is .10 normally, then it will be .05 with Moly. Does that sound like a big difference?

Your are wasting your time on an engine that will be started so infrequently.

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Re: Coating of the piston skirts

Postby brian » April 30th, 2014, 2:47 pm

I guess my issue is in regard to how dimensional identical is interpreted. The Chinese 2mm lands were allowed specifically by the rule, but a 4th, 1mm ring land cut at the maximum dimension at the top of the piston is illegal in my book. Hell, if we can go cutting our own ring lands, why not open up the rules completely to allow any ring lands? It would save a ton on spacers.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
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Re: Coating of the piston skirts

Postby Dietmar » April 30th, 2014, 5:02 pm

Brian:

we probably should change the topic as we have gone from piston coatings to ring lands.

The GCR may not be specific enough for some, however : no component of the engine shall be altered, modified,...unless specifically authorized.

Adding material to a piston skirt is a modification and I stand with Steven D and believe this to be illegal, vintage or not.

As for adding an additional ring land, whether one can make it work or not is also illegal as it modifies the component.

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Re: Coating of the piston skirts

Postby brian » April 30th, 2014, 11:47 pm

thanks Dietmar, that's my thinking as well.
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