Ducati Monster Forum

Just double checking the squish I should be shooting for is 1.00 mm?

That's the generally accepted number, yes.

Squish? You mean sag?

Quote from: memper on May 25, 2012, 03:30:18 PM
Squish? You mean sag?

Nope...he means squish...

the distance between the piston and head at TDC.

Quote from: memper on May 25, 2012, 03:30:18 PM
Squish? You mean sag?

No, squish is the distance between the top of the piston and the bottom of the cylinder head at TDC.

Excuse my ignorance but how do you "set" that?

Quote from: lazyjinglin717 on May 25, 2012, 04:46:53 PM
Excuse my ignorance but how do you "set" that?

Typically with base gasket thickness.

If things were past adjustable tolerances you could machine a surface.

Speaking of base gasket thickness where does one acquire different thicknesses?

Cometic makes head and base gaskets, tho they don't show different thicknesses.
http://www.cometic.com/catalogs/powersports.pdf (http://www.cometic.com/catalogs/powersports.pdf)

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

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

Quote from: mahoneygod on May 29, 2012, 08:54:08 PM
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've never, and wouldn't, use clips from Lowes.

Get them from Ducati or whoever manufactured the pistons.

Brad Black just blogged about setting squish - this was about a carbed 900, but it's probably worth a read none the less:

http://bradthebikeboy.blogspot.com.au/2012/05/setting-squish-and-cam-timing.html (http://bradthebikeboy.blogspot.com.au/2012/05/setting-squish-and-cam-timing.html)

big

Good read. If my squish is good at 1.00mm do I need to advance my cams?

Interesting read, but I'm curious about his comment that looser squish could lead to detonation.  Anyone got any insight?

Quote from: mahoneygod on May 30, 2012, 11:28:01 AM
Good read. If my squish is good at 1.00mm do I need to advance my cams?

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

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

Quote from: Peggy on May 30, 2012, 12:17:40 PM
Interesting read, but I'm curious about his comment that looser squish could lead to detonation.  Anyone got any insight?

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).

Quote from: Speeddog on May 30, 2012, 01:03:07 PM
You can degree your cams to Brad Black's specs:
http://www.bikeboy.org/camtime4v.html (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   [thumbsup]

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?

Quote from: mahoneygod on May 29, 2012, 08:54:08 PM
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.

thanks ducatiz ill check it out

Quote from: Speeddog on May 28, 2012, 12:05:50 PM
Cometic makes head and base gaskets, tho they don't show different thicknesses.
http://www.cometic.com/catalogs/powersports.pdf (http://www.cometic.com/catalogs/powersports.pdf)

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...?

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

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.

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.

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

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

scroll down

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

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