[xBhp Universal Thread]: What is "shaving the head"?

[Bibhu]

I have a small ity bity question. What is "shaving the head"?

[ken cool]

Query Approved

[Bibhu]

My thanks goes to Mr. Cool.

[Praful]

And I thought this is going to be thread about shaving the cylinder head...

[ttg]

You remove a little metal, maybe a couple of mm from the underside of the cylinder head bringing the combustion chamber roof lower & effectively reducing the combustion chamber volume & so increasing the compression ratio.
Higher comp translates to a few good things
For the methods and ohter finer details, wait for the pros.

err, Maybe going by MR vipin_s ' logic, you apply a little lather on the fins on top of the head and shave them off with some machine he's got. (Mods, pls.. couldn't resist)

[Bibhu]

Hum........ kind of hard to find hair on the head of my bike's engine.

So I shave the area near the head gasket? is it ok to do it on a P200 cylinder?

[vipin_s]

What is "shaving the cylinder head"?

@praful/bibhu : hope few had some laughs !!Thanks
ttg :

Bhibu : Shaving is just removing material from the flat 'butting' surface of the cylinder head on a milling machine. It's termed shaving as the amount of material removed is very less, normally in few millimeters.
Shaving of cylinder head is done to increase compression ratio of the engine and for other performance modification.

To remove fraction of millimeters, grinding of surface is done !!

[k_tornado_sj]

Hum........ kind of hard to find hair on the head of my bike's engine.

lol........

[Bibhu]

Ok, why I am asking this?

Reason: as posted in another thread I am planning to do some Mods to my 180cl to make it radical( by 180 standards.)

I have come with a plan to install a 200 cylinder on the cl gear box with some clutch mod. ( turbo is still on the cards but seems unlikely).

Will shaving the head help in increasing usable power?

[iorhld]

You remove a little metal, maybe a couple of mm from the underside of the cylinder head bringing the combustion chamber roof lower & effectively reducing the combustion chamber volume & so increasing the compression ratio.
Higher comp translates to a few good things

how does shaving increase the compression ratio?shaving will just increase the volume of the cylinder or the effective combustion chamber.how does shaving brings the roof lower? i thought the opposite was true or adding a layer of metal to the upper head will result in more squeezing of the air trapped in between the piston and the cylinder head thus increasing the compression ratio.

please enlighten me,i may be completely wrong or maybe i didn't get what you are actually trying to say.
also what is polishing the heads? is it same as shaving the head?

[ken cool]

how does shaving increase the compression ratio?shaving will just increase the volume of the cylinder or the effective combustion chamber.how does shaving brings the roof lower? i thought the opposite was true or adding a layer of metal to the upper head will result in more squeezing of the air trapped in between the piston and the cylinder head thus increasing the compression ratio.

please enlighten me,i may be completely wrong or maybe i didn't get what you are actually trying to say.
also what is polishing the heads? is it same as shaving the head?

I was also confused the same way you are. And I still am!

[Praful]

how does shaving increase the compression ratio?shaving will just increase the volume of the cylinder or the effective combustion chamber.how does shaving brings the roof lower? i thought the opposite was true or adding a layer of metal to the upper head will result in more squeezing of the air trapped in between the piston and the cylinder head thus increasing the compression ratio.

please enlighten me,i may be completely wrong or maybe i didn't get what you are actually trying to say.
also what is polishing the heads? is it same as shaving the head?

I was also confused the same way you are. And I still am!

Lol, even I had the same confusion till a few months back!

When we say that the head is being shaved, its not the internal portion of the head that is shaved, if that is done the volume will increase and thus cause a drop in compression.

Instead, the part where the head sits over the cylinder block is shaved. This reduces the internal volume by a bit and thus increases compression.

See the below image for a clearer understanding...




Hope this helps in clearing the confusion.

[iorhld]

thanx prafultripathy,that was a nice technical explaination with diagram.you are officially my hero for the day.

[ttg]

how does shaving increase the compression ratio?shaving will just increase the volume of the cylinder or the effective combustion chamber.how does shaving brings the roof lower? i thought the opposite was true or adding a layer of metal to the upper head will result in more squeezing of the air trapped in between the piston and the cylinder head thus increasing the compression ratio.

please enlighten me,i may be completely wrong or maybe i didn't get what you are actually trying to say.
also what is polishing the heads? is it same as shaving the head?

From your reply, I assume you might not be an expert. so here goes

& How do you figure shaving increase volume?
you keep the cylinder/ barrel intact and remove metal from base of the head; not inside the head. so if yu take the comb chamber to be a hemisphere on top of a cylinder(barrel), you keep the cylinder(displacement) intact and cut out a disc from the base of the hemisphere. reducing the comb chamber volume(smaller effective volume hemisphere).
This isn't as easliy done as it's said as some part you shave off might be from the squish band. ask a tuner for such stuff.


This is for 2 strokes as there's just the head and no cam chain / stuff. Dunno how it's done in 4strokes. prolly the way you mentioned.(due to problems adjusting the timing chain.)
I once wanted to increase comp in my 180 ug2 but my mech was not so eager. so I didn't push.

& for polishing, you literally polish the ports for better smoother airflow . Think that's just about it. dunno if it's done on the intake

well, I've never done this (ie shaving, porting, polishing, etc). I'm a great armchair tuner
you can read this until a expert reply (from those been there done it)come in.

I was also confused the same way you are. And I still am!

C'mon man, your jokin skills ain't too good.

EDIT: someone just beat me to the reply ! should I delete this?

[Andante]

Let me add to this:
The compression ratio is basically determined by which volume of air the cylinder has above it at bottom dead center squeezed into the space that the cylinder has above it at top dead center. So a 150cc with a compression ration of 9 would compress that volume to about 16.7cc at top dead center.

So by making the chamber above the piston smaller the compression rises. The higher compression means more power.