I have a chinese 150cc 4-stroke in my buggy. I have put a pipe and new intake which really woke it up, I need more power though so I am going to mil the head.

Anyway, I have access to a cnc router which I can setup to shave the head down. However, it will leave tiny little lines in it from the bit, can I just sand the head on a piece of glass with 600-1000 grit sandpaper? Should I just leave it to the professionals? Yes, I am a tightwad.

I have been advised to take about .050 off, does this sound good?

this is the same basic engine used on all the 150cc chinese quads that you see everywhere.
compression ratio is around 9to1 right now.
thanks in advance,
kell

 

Milling too far will cause you the need to use higher octane fuel to avoid spark knock. I wouldn't sand it by hand because you would never get it exactly even. Having your cylinder head sit un-even can leave you with a world of trouble. My advice is to leave the head alone. For the amount of time and money the gain is hardly even noticiable.

 

Depending on how thick of a head gasket it has on it right now, make another one out of soft copper and spray it with the copper coat or something equivalent. A lot of times you can gain anywhere from .020-.050 by doing this and not having to touch the head.

 

Yes, you can "lap" the head flat using 600 grit paper, and a pane of glass, or better yet, a granite plate. Hopefully the shop has one of those (granite plates) if it has a milling machine. Use a light weight oil when doing so though such as WD-40. Use figure 8 patterns while doing so, and try to make sure the head does not rock back and forth, or it will not be completely flat.

You may (as mentioned) have to bump up the octane if you shave too much off the head, so be careful. Also, the squish band may be affected by shaving the head. It is the squish band that is responsible (in part) for keeping the piston cooled.
There is more to head work than simply just shaving off .050"

 

thanks,
thats what I was looking for.

kell

 

Here is a clear picture of the exact kind of head I will be working on:

150cc head

2fun, can you tell by the picture if the squish band will be affected?
(obviously I don't know anything about squish bands)
This is just a fun little engine to try and make faster!
Kell

forgot to mention, these engines where originally produced as 125cc scooter engines, they are a yamaha design licensed to chinese manufacturers.

 

I dont think 2fun realized that the motor was a 4-stroke. You dont have a squish band on a 4-stroke motor to worry about, only piston to valve clearance.

 

Bubba, you are correct. I was not thinking it was a 4-stroke. However, yes, 4-strokes have squish bands too. I will include a few articles proving so.
It is usually the 2-strokes that are the object of discussion when talking about squish band, but yes, virtually all heads incorporate one. The squish band does more than simply cool the piston, it also is a way to make the air/fuel mixture turbulent, thereby increasing power.

Please see the following articles for some good info on squish band. [img]i/expressions/face-icon-small-wink.gif[/img]

Squish and car motors



Squish band explained

Squish band showing a valved motor

Squish bands on Harleys

 

Sorry Kell, but I am unable to tell if you would be ok with that head or not.

Generally what people with 4-strokes do to increase the power, is to get a higher comp piston, however, that would probably cost you more than you had planned (if one is even available).

The problem you would have to worry about (as Bubba mentioned) is the piston to valve clearance.
You may be able to get away with shaving a few thousandths off (as this is probably a low compression motor), but if it were me, I wouldn't chance it.

I have no experience in shaving 4-stroke heads, so i am not going to try to give you advice on it.

Sorry. Just my 2 cents

 

You'll have to excuse me, it's been a few years since dealing with the drag car motors. The term for the squish band in a 4-stroke is the "quench area".

The high dollar aluminum air flow research heads were always set up according to our needs as far as cc'ing, angle milling,etc, hence the only thing we needed to be sure of was piston to valve clearance.

I dont believe Kell will incorporate any problems with the little 150cc motor by bumping up the compression a little. After all we're not talking about a drag buggy here, just a slight gain.