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Gary jp4

Polished Combustion Chamber/Head. Good Idea?

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I just polished the head on my 250 SX. Thought I would share.

IMG_0583.jpgIMG_0582.jpg

Everyone has always told me you need to polish the head. It had some scratches and pretty bad machine cutter marks, especially up in the dome around the spark plug, from manufacturing I guess. I have another head that doesn't have as much machine marks but has a lot of pitting. I should have taken a before and after shot of this one.

I got carried away and took it to almost a mirror finish. Took the machine marks out with 360# "wet or dry" and water, then took the sanding scratches out with progressive grits 500#, 1000#, 1500# and then polished with MET-ALL aluminum polish and a cloth. It went pretty quick by hand and the jump from 1500# to polish was quick and easy. metallpolish.jpg

Do you think I will see any difference in the way it runs? Power?

What are the advantages in polishing the head?

Deposits don't stick as easily?

How much is good or enough? Like a mirror or stop at some certain grit?

Gary

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looks good, but im not sure how it will run, ive heard differant takes about this, if its smooth, fuel will aptomise on it/stick/it will kinda be like sweat on a cold can of pop on a hot day,and some people say the smoother the better. now im not sure which is true but it does look good. id say ur fine tho and might not notice any dramastic changes either way, but may be wrong.

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Hahah that's nice but I really doubt it changes anything performance wise. If you want some bling you should polish the outside instead :thumbsup:

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It'll definitely clean up easier- I did it too. From what I remember reading it helps to reflect the heat of combustion back into the gas charge.

Yah, like I'm gonna notice 0.05% more power :banana:

It was satisfying to do though, warn't it?

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Yeah it was.

It helps to be OCD and ADD and do things like that when you are supposed to be doing other things. :banana:

I'll do the top of the piston to accessorize and take pictures together.

It will be a shame to have them tarnish. When it does, I guess I'll call it patina.

Gary

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Dare I muddy the waters?

Oh, go ahead.

The idea is to combine air (oxygen) and fuel (hydrocarbons) and create heat (expanding the trapped air above the piston) and pushing down on the top of the piston,, which turns the crank, which eventually turns the rear wheel and makes the bike go.

Any heat lost from the combustion process is wasted energy. (heating the piston crown and combustion chamber is wasted heat)

So,  in reality, you'd rather have a nice thin layer of insulating carbon coating the piston crown and combustion chamber for that 1% power difference.

But polish looks bitchin!

Chopped chicken liver

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Do those tiny marks do anything once a small layer of carbon is on the head ? Most likely not ,do they do anything anyway ? No proof they do ....head is totally different shape and compression ratio to STD ,STD is often around 170 psi on a 250 and these are closer to 210 by owners measuring ,but it's the gooves ! Groovey man !

Shape you head to the same as that one in the picture ,bet it works just as good or possibly better ,snake oil in a head ?

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34 minutes ago, mog said:

Do those tiny marks do anything once a small layer of carbon is on the head ? Most likely not ,do they do anything anyway ? No proof they do ....head is totally different shape and compression ratio to STD ,STD is often around 170 psi on a 250 and these are closer to 210 by owners measuring ,but it's the gooves ! Groovey man !

Shape you head to the same as that one in the picture ,bet it works just as good or possibly better ,snake oil in a head ?

Dont know. Not pimping. Just posted because its not polished. Not my head. Not my argument. 

It is pretty though. 

I remember guys putting dimples in chambers in the 80s.

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Yes most people who are interested have done it, but few bothered to carry on ,no one bothered to patent it you know ? Till recently

Lots of history on Google of this type of modification, it's been around for ages ,nothing new at all .

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20 hours ago, seer said:

Dont know. Not pimping. Just posted because its not polished. Not my head. Not my argument. 

It is pretty though. 

I remember guys putting dimples in chambers in the 80s.

That's the RK Tek Head's inner cone.  Put one on my 300 XCW 1-2 months ago and its like night-day difference.  Total beast-mode.

RK_Head.jpg

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If you are chasing performance polish the intake and exhaust porting.  Be sure to round any corners that are not a mating surface.  You want laminar flow and sharp corners promote turbulence. The inside surface of the head, and sometimes the top of the piston, will build a layer of carbon deposits that will quickly eliminate any gain you received from the polish.

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2 hours ago, arc2arc said:

If you are chasing performance polish the intake and exhaust porting.  Be sure to round any corners that are not a mating surface.  You want laminar flow and sharp corners promote turbulence. The inside surface of the head, and sometimes the top of the piston, will build a layer of carbon deposits that will quickly eliminate any gain you received from the polish.

I would agree on polishing the exhaust port, however, I would strongly suggest not polishing the intake tract.  You need some turbulence in the intake charge to properly atomize the air fuel mixture before combustion, but not so much as to cause a restriction.

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I've read up a fair bit in surface texture ,the tests seem to say at most you see 2% change from say a really polished intake ( bad ) to a rough texture ( says to be good ) the difference was almost too small to measure ,so your basically wasting your time if you make it rough or smooth

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58 minutes ago, mog said:

I've read up a fair bit in surface texture ,the tests seem to say at most you see 2% change from say a really polished intake ( bad ) to a rough texture ( says to be good ) the difference was almost too small to measure ,so your basically wasting your time if you make it rough or smooth

While not confirming your number I note that to those with an absolute need for speed 2% is worth pursuit.  Advances in understanding are always obtained at the edge of what's known. The exhaust gases are much hotter than on the intake side so the volume and thus velocity are higher.  That might lend credence to polishing the exhaust side as a priority.  I point out that the properties of gas flow is not a linear phenomenon so be careful when reaching for conclusions.  Without the proper instrumentation to test the results polishing the ports can be a feel-good exercise based on what your mentor has passed down to you. Most riders will improve their performance by a larger amount if they get well-fitted underwear! If you are interested in this topic,  I suggest you look up gas flow through an orifice as a function of the radius at the edge of the opening.  Small differences can make for very large swings in flow rates.  

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The 2% was from the best to worst results ,if the surface isn't bad ( ie not polished )the results were smaller , this is in the area where the Dyno can't even show it ,each run can vary by more than that ,based on how hot the engine is. I know your agreeing I'm just adding extra content

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On 3/11/2010 at 4:23 PM, Gary jp4 said:

Yeah it was.

It helps to be OCD and ADD and do things like that when you are supposed to be doing other things. :banana:

I'll do the top of the piston to accessorize and take pictures together.

It will be a shame to have them tarnish. When it does, I guess I'll call it patina.

Gary

So it looks shiny and cool. :thumbsup: The cool thing is you’ll feel good about your bike and maybe you’ll just hold the throttle open a little longer into the turn or you are just a little bit more enthusiastic while riding. :smirk::ride:

My phathead dome head was shiny like that on my 01 cr 250. It worked great. I also have an RK head similar to the one showing on my Beta 300 rr with that textured dome. That works good too.  :excuseme: it’s good either way.

Edited by hawaiidirtrider

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