Setting squish on a 02 MS4

[Ddan]

You can degree your cams to Brad Black's specs:
http://www.bikeboy.org/camtime4v.html

Likely you'll need to adjust mixture a bit, so that may make a difference.

Narrower squish leads to more combustion chamber turbulence, so mixture is less likely to detonate.
And if it's narrow enough, the mixture there won't burn 'til well after TDC, as the piston and head absorb heat from the thin layer.

If it's wide, it takes a long time for the flame front to fill the combustion chamber and then get to the edge of the squish.
During that time, the pressure is rising, and it may get high enough for the mixture in the squish to ignite on it's own (detonation).

Thanks   

[mahoneygod]

been dragging my feet getting this done but im checkin my squish and on both horizontal and vertical im around .39-.48 mm on all sides except the intake side. both are mearsuring at .72-.77 mm is there a reason for this? ive rechecked 3 times with the same measurements. am i doing something wrong?

[ducatiz]

When I replace the retaining clips for the pistons do I need a specific kind or will the ones from Lowes do the job?

I use D472 spec circlips.  You can use the POS wire clip that comes with the piston, but I never have. Circlips are easier to install and if you get the right size, they sit tighter.  I bought a box of 100 from mdmetric a long time ago for $30 and they are worth it.  They come out easily with a tool and never come out at all otherwise.

When I'd build drag VW engines, that is what we'd use.  I saw more than one instance of a factory type popping out.  No thanks.

[mahoneygod]

thanks ducatiz ill check it out

[ducatiz]

Cometic makes head and base gaskets, tho they don't show different thicknesses.


AFAIK, 916SBK base gaskets would be the same pattern, typically the SBK's had different thicknesses available from Ducati.

The thicknesses are listed on the first page -- in inch...?

Available thickness:
.027”, .030”, .036”, .040”, .045”, .051”, .056”, .060”, .066”, .070”,
.075”, .080”, .084” .086”, .089”, .092”, .095”, .098”, 120”, .140”

[alibaba]

Perhaps I have been under a misapprehension all this time.  Any discussion I have seen or heard tuners discuss re squish did not deal with the top of the piston to head clearance but with the "squish band".

This was always defined as an area machined to create a thin band around the outer circumference of the piston and was measured to the bottom of the combustion chamber above it.  The theory being that this "squish band" would compress the fuel charge in the area furthest from the spark plug abd "squish" it upwards creating turbulence at the plug.

And, it does seem to me that a 'squish' in this area would be more effective than at the top of the piston.  Any squish I have heard measured referred to the height in this area between the piston and the head.  Often a corresponding flat band is machined in the head right above this band on the circumference of the piston to create maximum squish.

For example, the measurements I use in a 600cc Gold Star are .025" minimum clearance needed (due to rod growth'),  .030 ideal, .050 is OK, .060 is just getting to large to give any benefit.

[ducatiz]

it all has to do with chamber volume at TDC

squish refers to the volume

a squish band is just one tweak of it.  i believe they reduce squish which forces the burn mixture into the pocket.

i don't know how i feel about that, it sounds hokey off the cuff.

but if you're going to talk about a squish band, you better understand squish first.

[mahoneygod]

OK with of of that said. I'm using some solder in four places on the top of the piston in a nsew pattern right against the the cylinder wall. torque it all down turn the engine a few times take it apart and measure the thickness of the solder. Is this a measurement of the squish or the squish band?

thanks for your input guys

[ducatiz]

Turns out "squish band" is just the area of squish, as viewed from the side 2-dimensionally.

http://www.ducatitech.com/2v/maint/rebuild/headwork.html

scroll down

[mahoneygod]

Ok that explains squish quite well. My question still remains why are my numbers so far off?

[mahoneygod]

So Ive double checked my measurements and they are off. Has anyone had their cylinders machined? Is it usually expensive?