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Discussion Starter #1
for measuring squish the cylinder are torqued.
I guess you have to measure squish with one set of cylinder gaskets and then use a new set of gaskets after you made sure everything is alright. Or am I being paranoid about the use of the gaskets ?
 

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Discussion Starter #3
forgotten info

I am changing to High comp pistons so I am a bit paranoid about the squish / crush
will buy second set of gaskets
 

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Hi,

You should use the new gasketts. The motor seals the first time it is run, so as long as you don't start the motor you can use the gaskett again. Gasketts can vary in manufature and this will also effect the squish.

I have built alot of motors and have never had one leak. (well, ok, there was one 1500cc GSXR that fought me a bit but that had more to do with the fire rings and the fact that the head gaskett was 2mm thick)

Gray
 

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Discussion Starter #6
squish measured

put everything together and measured the squish.
at the moment everything is around 1.2 mm. (some are 1.18 and some are about 1.28)
My base gasket is 0.3 mm.
I think the recommended amount is 1 mm. 20 percent more sounds like a lot too me.

Do you think this is too big of a gap ?
I am running carrillo rods (don't know if they will stretch) and JE high compression pistons and bored up cylinders.
I am not looking for max performance, I just wonder if this is too big to run normally/efficiently.
I would be actually happy to use a little bit less compression in the hope I can use normal fuel instead of high octane but that is also a minor detail. :rolleyes:
 

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The 'base gaskets' are actually shims which normally means you can re-use them. I did on mine yesterday.
 

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put everything together and measured the squish.
at the moment everything is around 1.2 mm. (some are 1.18 and some are about 1.28)
My base gasket is 0.3 mm.
I think the recommended amount is 1 mm. 20 percent more sounds like a lot too me.

Do you think this is too big of a gap ?
I am running carrillo rods (don't know if they will stretch) and JE high compression pistons and bored up cylinders.
I am not looking for max performance, I just wonder if this is too big to run normally/efficiently.
I would be actually happy to use a little bit less compression in the hope I can use normal fuel instead of high octane but that is also a minor detail. :rolleyes:
1.2mm is a perfectly acceptable number for the "squish" clearance (more properly known as "deck height", by the way). 1.2mm will still provide the desire "squish" affect and will not materialy lower compression when compared to 1mm deck height.

There is a real danger in too much deck height, but "too much" is going to be over 1.5mm, maybe closer to 2mm, depending on combustion chamber and piston dome shapes. As a rule of thumb, flatter piston tops, shallower combustion chambers, and narrower squish bands will tolerate wider gaps.

The idea is to generate a violent enough "squishing" action to force all of the air/fuel charge out of the squish band area and into the center of the combustion chamber. The higher the piston dome, the deeper the combustion chamber, and the wider the squish band, the more violent this action has to be to evacuate the charge from that area. The danger lies in leaving too much of the combustable charge out there; it will detonate (ignite under compression, like a diesel) due to the high localized compression in the squish area. Higher domes in deeper chambers block this area off better than flatter domes and shallower chambers.

Fortunately for us, our air cooled two valve Ducatis have relatively shallow combustion chambers, and can therefor achieve high compression with relatively low piston domes. These factors render render "squish" to be somewhat less critical than in, say, an old-school hemi head with deep spherical combustion chambers.

Anyway, that's kind of a long-winded way of saying "you are fine", with hopefully just enough explanation to support that assertion.
 

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Discussion Starter #9
thank you

thanks for the explanation, very much appreciated.

I am using JE pistons with higher domes than (the pretty flat) standard pistons.
I ll leave everything like it is then and assemble it like it is now.
 

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i'd pull the base gaskets. 0.90 is nice. with std pistons the chamber taper is more than the piston taper so the tightest point should be at the outer edge anyway. i don't recall how the je taper compares to the chamber taper. pretty sure it's still the outer edge.

the lesser the squish distance the more resistant the motor becomes to detonation. it will make around 0.3 difference to the compression ratio.

i also machine 3mm off the je piston crowns to lower their comp too. drops them to 10.8 or so.

it will also retard the cams 2 or so degrees and reduce the piston to valve clearance so you can't run as much advance as before (as i always do), but with je it shouldn't be an issue as they have deeper cut outs. with std pistons it gets that way.

as it happens i wrote a piece about it recently.

Brad The Bike Boy: Setting squish and cam timing implications; 900SS Carb model
 

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Hi,

I am going to agree with Brad 100%. Check your mesurements the tightest point should be a the outer edge of the piston.

I am not a big fan of JE pistons I would rather use Pistal or Weisco. Maching the piston I would say was completely optional. I, myself, am using 11:1 Weiscos.

Higgy, I have never set the squish on a Motorcycle motor at more than .040" or 1mm... I have also set motors at a alot less than .040". You can set a 600cc 4 cylinder pretty tight and not worry about contact.

Gray
 

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Discussion Starter #12
machining parts

I read the piece about the squish settings and cam timing.

thank you for all your input but I am in Japan :( and asking anything out of the absolutely normal is almost impossible. Finding a shop that can machine 3 mm or the domes is going to be way too much trouble. I know it is trivial work but trust me when I say that I know what I am talking about. I asked around a lot for boring up of my cylinders. lightning crankshaft, getting a second hole to install a second spark plug and up till now I had to send my parts overseas (US) to get the work done. Even cutting holes in my clutch cover is going to be a problem. When I find someone who "might" be able to do the work it is ridiculously expensive and without any guaranty that the work will be withing tolerances/specifications hence the sending to US of my parts.
This has made this build a very frustrating exercise and I am close to giving up so I am just going to install everything the way it is.

thanks again for all the help.
 

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Hi,

I am going to agree with Brad 100%. Check your mesurements the tightest point should be a the outer edge of the piston.

I am not a big fan of JE pistons I would rather use Pistal or Weisco. Maching the piston I would say was completely optional. I, myself, am using 11:1 Weiscos.

Higgy, I have never set the squish on a Motorcycle motor at more than .040" or 1mm... I have also set motors at a alot less than .040". You can set a 600cc 4 cylinder pretty tight and not worry about contact.

Gray
I like 1mm as a minimum for just about any road going, air cooled engine, but I have set race motors a bit tighter. Water cooling (like in the 600cc fours you mention) allows less clearance, since we don't see the wild swings in head and upper cylinder temps that air cooled motors suffer.

Oh, and I'm using Cosworths in my Ducati (not listed, but they will make anything you want), but I would not hesitate to run JE's.

JE, unfortunately, earned a bit of a bad rap years ago with their pistons for air cooled applications. They were having trouble finding an alloy that would match the CTE's of the various motors for which they were selling pistons. They have done an awful lot of work since then, however, and we now run them by choice in both race a street motors. They are now a fantastic piston, right up there with Mahles, Cosworths, etc.

All of that said, in the end, 1.2mm will work just fine for Anatak. I've built many an air cooled motor with that deck height (street engines, mind you) with perfect satisfaction. As a matter of fact, some folks who understand what this means will even ask for it.

So, Anatak - carry on; you have absolutely nothing to worry about. If I had those parts I would put them together as-is and not lose a moment's sleep over it.
 
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