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the SS 900 has got 68 x 92mm stroke / bore, while the SS1000 has got
a 71.5mm crankshaft and 94mm pistons.

94mm pistons take the SS900 engine to 944cc, the most common upgrade
i'd say, that will fit the SS900 crankcase with no issues nor extra work, the
cylinder spigots of the 944cc kit are thinner but have got the same outside
diameter.

cheers.
 

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Discussion Starter #3
Thanks a bunch, I was thinking of just buying a set of 1000DS pistons, boring the 900 cylinders all said and done.
 

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hm, the cylinders are nikasil plated, and that plating needs to be taken off
first, then they are bored to 94mm and re-plated.
there are lots of 94mm piston kits available for the SS900, if the stock
cylinders are in good shape, i would consider high comp. 92mm ones
that drop right in, and have some other work done for the rest of the
money, like cams or carbs.

cheers.
 

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If you go through all that work to bore and plate your jugs and THEN put in stock pistons, have someone slap you in the head. The stock pistons will weigh 2-3X any aftermarket pistons, and have lower compression. Look into a set of JE, weisco, or pistal 94mm kits.

Look at the pic of my 92mm stock vs. Mahle pistons. Stock comp on the carb bikes was 9.2:1 vs. 11.5:1. You really need the compression bump. A 944 with low compression would probably be less of a gain vs. stock bore with higher compression. (dyno would tell you the difference)
 

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Discussion Starter #6 (Edited)
Good points indeed. Are the 1000 pistons higher compression than the 900? I was thinking the 1000's were 10:1 as opposed to 9:1 for the 900.

It seems like it wouldn't be worth my time...
 

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that is true, the SS1000DS is listed with 10:1,
so the pistons should give 10:1, in conjuntion with
the SS1000DS heads that is.
I would skip that idea but get me some drop in 92mm
ones if needed.
 

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hm, the cylinders are nikasil plated, and that plating needs to be taken off
first, then they are bored to 94mm and re-plated.
there are lots of 94mm piston kits available for the SS900, if the stock
cylinders are in good shape, i would consider high comp. 92mm ones
that drop right in, and have some other work done for the rest of the
money, like cams or carbs.

cheers.
amen :cool:
 

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Discussion Starter #9
Thanks guys, pulled the trigger on a set of JE 92mm 11:5:1. $250 bucks.. not bad I'd say. Read some good things about the JE's, however most mentioned to retard timing a few degrees to offset for detonation.

I will think about adding an extra plug to the heads however, depending on the cost.
 

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I would be willing to bet the 1000DS has a different rod length, piston pin location in the piston, or both to allow for the longer stroke without having to use taller cylinders. If that's the case, simply putting 1000DS pistons on 900SS rods, on a 900SS crank, will result in either drastically increased or reduced compression. Deck height will also be affected, possibly to the point of the pistons hitting the heads. The only way to solve these issues is with a custom rod length. Lots of fussing about to determine that length. You made the right choice.

I've run JE's in nickasil barrels on 911 motors. Fantastic pistons. I wouldn't hesitate to use them in my 900SS.
 

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Discussion Starter #11
Thanks again, yes I went and did some further research and concluded that valve angles are different between the motors, and a lot of dry work would be needed to make this work. ie not worth it.

Anyway, I have a set of 1000 pistons around if anyone needs some for a project. Check the Classifieds....
 

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I would be willing to bet the 1000DS has a different rod length...
i think SS900 i.e. and SS1000DS got the same rods installed, and
the cylinders of the SS1000DS should be ~1.75mm longer then.

i won't bet this time as i am not 100% sure.

:)
 

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Leo,
When you get your JE's, check the CR - when I measured mine during rebuild, the actual CR was 13+:1, rather than the 11:1 it said on the box. Machined the crowns down to give (measured) 11.2:1. Initially retarded ignition by 2 deg, but after a day on the dyno, am back to standard settings (although now accurate, as timing marks on flywheel were out), with no pinking at all on pump gas.
 

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Discussion Starter #14
Leo,
When you get your JE's, check the CR - when I measured mine during rebuild, the actual CR was 13+:1, rather than the 11:1 it said on the box. Machined the crowns down to give (measured) 11.2:1. Initially retarded ignition by 2 deg, but after a day on the dyno, am back to standard settings (although now accurate, as timing marks on flywheel were out), with no pinking at all on pump gas.


will do, I'll have my mechanic take a look at em, unless there is an easy way to measure them then I'll do it....
 

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will do, I'll have my mechanic take a look at em, unless there is an easy way to measure them then I'll do it....
Measuring the actuall compression ratio achieved is a bit tricky. You need to be able to measure or calculate actual combustion chamber volume at TDC, and total cylinder + combustion chamber volume at BDC.

The most accurate way is the "beaker test". The high level overview is that we use a calibrated beaker full of liquid to first accurately measure combustion chamber volume with the piston at TDC, then drop the piston to BDC and measure the resultant combustion chamber volume + cylinder volume.

I use a little valve with a hose on it that I made that screws into the spark plug hole to control the flow of liquid into the chamber. The hose goes to a beaker with an outlet on the bottom of it, like an IV drip or something. I used the mondo turkey baster from hell for mine.

To do this, we need to assemble one cylinder, piston, and head to the motor. Leave the cam out of the head, but it needs the valves. Put some heavy grease on the rings so they seal the liquid that you will be filling things up with. I use ATF, but any oil will do.

The next part is easiest if the motor can be positioned with the spark plug hole up. Screw the valve into the spark plug hole, connect the hose, and hang the beaker. Fill the beaker enough that there is enough liquid to fill the whole cylinder, and then some. Write down the fluid level. With the piston at TDC, crack the valve and let it fill up. When it quits bubbling, and the fluid in the beaker settles to its new, lower level, the difference is your actual chamber volume. Write this down. The difference between the two measurements is the chamber volume.

From there, rotate the piston to BDC with the valve open, allowing the cylinder to fill. Take note of the volume of remaining fluid in the beaker. The difference between this lowest volume and the original volume in the beaker, the first number you wrote down before you filled the combustion chamber at TDC, is the combined volume. Write this down. A lot of guys get confused here, and use the difference from the second measured volume (after filling the chamber) - this is a mistake. This is the displacement, which we already know.

Combined volume / chamber volume = CR. And now you have one hell of a mess to clean up. It's easiest if the motor is on a stand that allows it to be rotated so the spark plug hole is down.
 

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Discussion Starter #16
Sounds a bit tricky, but great method nonetheless.

With regard to ping/detonation. I plan on upgrading the coils to get a fatter spark in there. Retard the timing as well? Or what's a better compression ratio to use on the street? 11:1 ? 10.8?
 

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+1 on Higgy's response, although probably takes longer to write than do!
I'm running my SL on the road on ordinary fuel with a measured 11.2:1 CR. After trying numerous ignition settings on the dyno (have an Ignitech unit fitted) found that standard settings give best results - no need to retard, but had to reset the pickups, as the timing marks on the flywheel were inaccurate
 

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You should be fine with whatever CR the JEs work out to as long as your squish is properly set to no less than .040" but not over .050". That's achieved with different thicknesses of your base gasket (Chris Kelley sells these). These are not exactly radical changes to make to an SS and tons are out there running fine most without even checking the squish. For comfort, once it's broken in, measure the compression. You expect between 17 - 20 times CR as a compression reading so something around 200 psi is fine with the JEs.

At $250 for the 92mm hi comp JEs, you are probably getting the best performance bang for the buck, assuming you're doing the wrenching. The dual plugs....not so much. At least not with a mostly stock engine. Here's Doug's view of it. http://www.visi.com/~moperfserv/2plug.htm
 

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Agreed on the dual plug assessment - the 900 SS motor isn't going to benefit much, if at all. The single plug is not all that far off center, and even higher compression piston domes don't create a "blind spot", or an area in the combustion chamber that cannot "see" the plug.

Dual plugs shine in applications where the original single plug is well offset from center and the piston dome blocks off the far side of the combustion chamber. It allows the flame front to start from two sides and meet in the middle, which allows the timing to be backed way off while still achieving complete combustion. Think old style hemi head, with big valves that almost touch, with the plug way off to one side in the crotch formed by those valves, like these:
 

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Discussion Starter #20
Great, thanks again, I will be doing most of the wrenching myself.

However, I'm concerned after talking to a local shop. They are recommending a replate of the cylinders even though they haven't seen them yet.

I have the standard drop in kit 92mm, and I'm no professional when it comes to assessing cylinder condition, but I was hoping to just do a hone and drop them in. What do you guys think? anything I should be concerned about. They look OK to me, still see cross hatching however there a few scores here and there. Keep in mind the motor did not smoke at all with previous pistons. The bike has 25k on it.
 
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