ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 3, 2018 6:36:13 GMT -5
so I just got my BBK and the top of the piston look like pebble beach. When I did my friends BBK, it was the same thing. Just wondering, do any of the BBK pistons have a smooth top? I wish I still had my lathe. I would take a light cut to clean that up. I have been working on bike engines for over 50 years, most of them hp racing engines, and have never seen piston tops like these. It refuse to belive that this is some super secret way to get better mixing of the fuel air that only works on GY6 50cc engines!
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Post by humanshield on Aug 3, 2018 11:43:24 GMT -5
None of my BBK's came with pistons that match your description. But a pic is worth 1000 words Would like to see a picture of this
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 4, 2018 8:41:49 GMT -5
 I notice if you look at a lot of the adds for other BBKs they also have rough tops |
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Post by mrkswthwrth on Aug 4, 2018 9:54:30 GMT -5
Chances are its a cheap cast chinesium piston, and they only machine the sides because the ring lands and od are the only surfaces that need to be precise. They do it yuppppp dance money.
Lol where did that come from? Meant to say "they do it to save money" but I'm leaving it
Look at a naraku or wiseco piston. Machined all 'round from quality material.
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Post by humanshield on Aug 4, 2018 11:22:21 GMT -5
Nice picture. Now we see exactly what you meant.
There are "some" schools of thought that might say having that rough surface could aid in vaporization of the mixture.
But I tend to agree with the post above. It's probably a cost saving step.
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Post by mrkswthwrth on Aug 4, 2018 11:26:01 GMT -5
As far as i know, that type of texture is great for intake runners and possibly intake ports. No clue about the effect on piston crown. But I'm no mechanical enginerd
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Post by gsx600racer on Aug 4, 2018 12:32:44 GMT -5
You pay for cheap, you get cheap parts.
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Post by jackrides on Aug 4, 2018 13:59:20 GMT -5
It'l collect carbon faster. Good or bad? Increased compression. Insulates piston from soaking up combustion heat? (Heat = combustion energy) Thoughts?
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Post by humanshield on Aug 4, 2018 14:58:39 GMT -5
It'l collect carbon faster. Good or bad? Increased compression. Insulates piston from soaking up combustion heat? (Heat = combustion energy) Thoughts?
Common thinking on carbon buildup is usually along the lines of "it's bad, so remove it".
But you make some good points imo.
Seems reasonable.
Sometimes you can get pre-ignition from carbon buildup though.
A.Tricoire et al [7] have experimentally studied 1 mm thick plasma sprayed 7Y 2 O 3 -ZrO 2 coating with a graded transition of NiCrA and A&S YSZ over the top of a serial piston for heavy-duty truck engines. They found that the insulated piston leads to an increase of NOx, soot, and BSFC.
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Post by 190mech on Aug 4, 2018 18:47:57 GMT -5
Sorry fellas,I crawled under the 2 stroke/4 stroke fence to give my reply,,A polished piston reflects heat better than a rough one,so get some sandpaper on that cobblestone road!OK,I'm going back to the other side,,Darn! the briers are thick in this narrow path!!
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Post by gsx600racer on Aug 4, 2018 18:53:51 GMT -5
Sorry fellas,I crawled under the 2 stroke/4 stroke fence to give my reply,,A polished piston reflects heat better than a rough one,so get some sandpaper on that cobblestone road!OK,I'm going back to the other side,,Darn! the briers are thick in this narrow path!! Give me 3 hub caps and I will say I never seen you here.  |
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Post by GrumpyUnk on Aug 6, 2018 13:54:40 GMT -5
That 'pebbled' version is all I have seen. I thought about making it smooth, but figured the material needed to be left alone for maximum strength. If you look from the underside, it appears there is not a lot of metal to make the piston thick. It's possible the surface helps suppress pinging or pre-ignition as the surface might be rough enough to inhibit a wild flame front from forming.
I figured it couldn't hurt, so left it alone. I did think about reducing the total mass of the BBK piston by machining, sanding or polishing, both 44mm and 47mm, but decided I'd sooner keep the thickness.
tom
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Post by dexameth on Aug 6, 2018 15:21:33 GMT -5
Most BBK's will come with a cast piston like that. Naraku is one that machines theirs down pretty nicely, as well as our Hoca pistons. Not only do the tops change from cast to machined, the compression height will change as well. I've seen some really nice machined down cast pistons, so don't be fooled when thinking of forged pistons.
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