Topic: Polishing Piston Tops

[SD750F]

I have a question for any engine experts...  Okay when I was removing the carbon buildup off the top of my CB750 F3 pistons I was thinking, "What would happen to reduce the amount of carbon build up if I polished the top of my pistons?"

I am a strong believer in turbulence and how it will improve fuel burn. But I thought any roughness or lack of on the top of the piston would not make any difference inside the cylinder.

Awaiting any response...

Scott

[MRieck]

Polish them....it holds heat and removes sharp edges. I generally coat mine.

[rbmgf7]

it probably wouldn't hurt too much. if you decided to go all out and polished the entire chamber, you'll increase the chances of preignition. there is a reason why everything is left "rough" from the casting process.

[JAG]

I've thought about using a scotch-brite pad to atleast clean them up.

But when you say polishing, are you refering to using like what is used when polishing the covers?? If so I don't know if it would last all that long under those conditions..

Again, the only thing I've heard aside from getting new pistons is scrubbin them down with a scotch brite pad to clean up the carbon..

[Raul CB750K1]

it probably wouldn't hurt too much. if you decided to go all out and polished the entire chamber, you'll increase the chances of preignition. there is a reason why everything is left "rough" from the casting process.

I thought that one of the reasons for preignition are sharp edges and pikes, red hot, that ignite the mixture before it is fully compressed. A polished chamber and piston should avoid this.

I think that the only reason everything is left "rough" at the factory is to save on hand labour.

[scondon]

it probably wouldn't hurt too much. if you decided to go all out and polished the entire chamber, you'll increase the chances of preignition. there is a reason why everything is left "rough" from the casting process.

  Dammit Mike, you polished the crap out of my chambers. I want my money back

[martino1972]

just clean em,dont worry about polishing,and drive the piss out of the bike here and there to burn the carbon out..
automotive places(like me)sometimes get an car from an old lady(like 75 year old ladies)for as tune up..
first thing they(and me) do is take the car on the highway and give her hell...(the car that is,not the granny.. ),it burns all the carbon buid up out,and the car runs better already..
you can also get aditives for in the fuel that will help to keep it clean..

[oldbiker]

If you ever get a chance to see inside an F1 engine, you will find out that you could use their internals as a shaving mirror.
I think they know what they are doing.

[troppo]

just clean em,dont worry about polishing,and drive the piss out of the bike here and there to burn the carbon out..
automotive places(like me)sometimes get an car from an old lady(like 75 year old ladies)for as tune up..
first thing they(and me) do is take the car on the highway and give her hell...(the car that is,not the granny.. ),it burns all the carbon buid up out,and the car runs better already..
you can also get aditives for in the fuel that will help to keep it clean..

Yeah, gotta blow those cobwebs out every now and then

[Raul CB750K1]

Yeah, gotta blow those cobwebs out every now and then

You talking the car or the granny?   

[troppo]

You talking the car or the granny?   

I guess that depends on what turns you on, after all how often would granny get taken out for a long hard ride

[SD750F]

When I said polished, I was thinking nothing more that a fine abrasive such as a Scotchbright pad followed by buffing with a aluminum rouge and a wheel. Just the tops mind you.

Scott

[chippyfive50]

polish like a Polish pole polisher polishes his Polish pole  

[Raul CB750K1]

Whne I said polished, I was thinking nothing more that a fine abrasive such as a Scotchbright pad followed by buffing with a aluminum rouge and a wheel. Just the tops mind you.

Scott

If I'm reusing the pistons, I just use a wire wheel to remove the carbon build up, not sanding nor polishing.

[MRieck]

When I said polished, I was thinking nothing more that a fine abrasive such as a Scotchbright pad followed by buffing with a aluminum rouge and a wheel. Just the tops mind you.

Scott

Right....just the tops. Be careful with the buffing wheel....it can grab the piston and yank it right out of your hand.

[mystic_1]

Right....just the tops. Be careful with the buffing wheel....it can grab the piston and yank it right out of your hand.

My understanding is that oil doesn't cling very well to highly-polished surfaces, so this is why one wouldn't want to polish the hell out of everything inside the engine, yes?

mystic_1

[Raul CB750K1]

My understanding is that oil doesn't cling very well to highly-polished surfaces, so this is why one wouldn't want to polish the hell out of everything inside the engine, yes?

mystic_1

You want rubbing parts as polished as you can. Otherwise the oil would get into the microscopic "craters" and would not create the film you want. If parts are well polished, the oil will create a film that will avoid the metal getting in contact. Obviously, the more flat the surface is, the less oil it will retain. But that's why you want a pump to supply oil without interruption.

[rbmgf7]

it probably wouldn't hurt too much. if you decided to go all out and polished the entire chamber, you'll increase the chances of preignition. there is a reason why everything is left "rough" from the casting process.

I thought that one of the reasons for preignition are sharp edges and pikes, red hot, that ignite the mixture before it is fully compressed. A polished chamber and piston should avoid this.

I think that the only reason everything is left "rough" at the factory is to save on hand labour.

yeah, you're right. i had it backwards, duh 

[mystic_1]

My understanding is that oil doesn't cling very well to highly-polished surfaces, so this is why one wouldn't want to polish the hell out of everything inside the engine, yes?

mystic_1

You want rubbing parts as polished as you can. Otherwise the oil would get into the microscopic "craters" and would not create the film you want. If parts are well polished, the oil will create a film that will avoid the metal getting in contact. Obviously, the more flat the surface is, the less oil it will retain. But that's why you want a pump to supply oil without interruption.

Why, then, are crankshaft journals (for example) not polished to a mirror finish?

mystic_1

[scondon]

My understanding is that oil doesn't cling very well to highly-polished surfaces, so this is why one wouldn't want to polish the hell out of everything inside the engine, yes?

mystic_1

You want rubbing parts as polished as you can. Otherwise the oil would get into the microscopic "craters" and would not create the film you want. If parts are well polished, the oil will create a film that will avoid the metal getting in contact. Obviously, the more flat the surface is, the less oil it will retain. But that's why you want a pump to supply oil without interruption.

Why, then, are crankshaft journals (for example) not polished to a mirror finish?

mystic_1

   They are, aren't yours   Now I'm going to have to send my crank back to APE for a refund. I hate this thread

[mystic_1]

All the crankshafts I've seen have had a satin finish to the journals, not a reflective mirror-like finish.  Granted that may be my own inexperience talking, never been inside a true high-performance motor before.

I've wondered about polishing other internal motor parts like the shift drum journals, shift forks and shaft, transmission shaft splines, and so forth, but I've never heard anyone recommend this.

mystic_1

[martino1972]

crankshaft journals are forced oil fed,so they can be mirror polished...
cylinder walls are splash oil fed and should not be polished to a mirror finish,you need those little craters and what not to keep the oil film present on the walls and pistons.

[mystic_1]

Makes sense, martino.  Thanks.

mystic_1

[scondon]

All the crankshafts I've seen have had a satin finish to the journals, not a reflective mirror-like finish.  Granted that may be my own inexperience talking, never been inside a true high-performance motor before.

   I've never seen my reflection in a journal either Glad you joined up, Mystic. Keep them posts a'comin

I had a hard time removing the Kreem using just the POR product.  I ended up using a couple of gallons of Acetone and that worked quite well.  I would quarter fill the tank with Acetone and let it sit and periodically swish it around.  You can then filter the big chunks of Kreem in a spaghetti strainer or similar and put the acetone back in.  It was a pain in the butt, but the POR-15 came out really nice.  Also, the Acetone will just eat the paint off your tank, so if you intend to keep the original paint, be careful.

 But did you polish the Kreem or leave it rough

[bunghole]

Whoops!  I had two thread windows open and posted to the wrong one.

I do have a related question though.  I just got some new crankshaft bearings.  I noticed that they have a satin finish to them.  Is there any benefit to giving them a light polish?  I read something about "prepping bearing inserts" somewhere and it seems like there is some controversy surrounding it.

[martino1972]

i wouldnt polish them,let the crank settle itself in the way it wants too,just use lots of assembly grease on the journals...

[scondon]

 Bearings have a coating on them to prevent wear during installation/ initial start-up. Leave 'em be is my guess.

[rbmgf7]

i figured the bearings were left satin-like to create a no slip boundary between the layer of oil and crankshaft. looking at the crankshaft, the "races" (not sure of a correct term) are polished to almost a mirror like finish which helps glide across the layer of oil. IMO

[heffay]

I've never specifically polished piston tops or cylinder domes to a hi gloss... only to remove excess carbon buildup.
as soon as those plugs start firing again i know its all over for those highly polished surfaces.   

now, if i was building a bike for a single drag race... i would polish the crap out of the domes, piston tops and my skull.   

heres the extent of my usual work that i consider to be in the "tune up" category... i think it just makes for a sudden revival to the motor's spunk...

3 before and 1 after


after


1 piston top partially cleaned and 1 complete


hey Gordon... what does Manuelle say?