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Discussion Starter #1
Well the valve seals did not take care of oil burning so I am going to do the pistons and guides. Doing just quick search on the web for pistons the only two companies I saw were FBF (fast by ferracci) and JE piston. Some say the JE's are heavy don't know. Both are drop-ins piston. I really hoping I would not have to deal with the squish. The valve guides I found 2 different materials they are made of aluminum/bronze and manganese/bronze not sure which is better


any suggestions or comments on pistons and guides
 

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Looks like the Mahles only come in 91 or 95mm, where the JE's come in 92 and 94mm. Direct replacement requires 92mm, so that kind of narrows the field. Mahle makes great stuff; I run their P&C's in two Porsche 911 motors right now. My third, and the most powerful and hardest used of the three, runs JE's (because they offer a greater variety of compression ratios and diameters). I've been nothing but happy with the JE's, and I'm starting to think they at least match the Mahles for quality. I wouldn't hesitate to put them in my bike.

I'm running 92mm Cosworths in my bike right now. It might be worth an email to them to see what they have. The can mine came in is marked "11.0-12.0:1", which I find kind of odd. It has to be one or the other...

Either way, you will have to "deal with the squish". It's not that difficult, especially with pistons like ours. Their flat "squish band" around their top periphery makes it really, really easy. No more torquing a head in place and crushing clay or solder to measure "squish" (more accurately known as "deck height"). You can simply use a depth plunger on a 6" dial caliper to measure this.

Deck height is a critical measurement. Too much can be as bad as too little, but for different reasons. Too little, and it's obvious what can happen - Mr. Piston meets Mr. Cylinder Head, breaking one or the other or both. That's bad. Too much deck height is more subtle - it will actually cause detonation.

This "squish band" idea, to work, requires that there be minimal clearance between top of the piston and the bottom of the combustion chamber around the outer periphery, or "squish" area. The idea is to force the fuel/air charge out from between the two, back in towards the center of the combustion chamber, thereby creating a great deal of turbulence. If it doesn't do this, because the clearance is too great, it will actually trap that fuel/air charge out there, and detonate it under compression, just like a diesel. This is really bad... This will eventually collapse the top ring groove, trapping the ring, and possibly even bind up the whole works, ripping the wrist pin right out the bottom.

Anyway, whichever pistons you choose, check that deck height. It's easy, it's free, and you will sleep better at night.
 

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Anyway, whichever pistons you choose, check that deck height. It's easy, it's free, and you will sleep better at night.
thanks for pointing that out, i was thinking about
it but couldn't find the time to do a little write up here.
i like to add that a 1-2° difference between the
angles of the piston and head is used on our two
stroke bikes to force the gases towards the combus-
tion chamber during the compression stroke.
Squish band in the head has a bigger angle than
the piston, it is "opening" towards the chamber.

Mahle pistons have a great reputation, i have
good experience with JE piston in my 95 cu.in.
big twin harley.

i have nice pics higgy, check the super G with stack.

:)





 

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Discussion Starter #6 (Edited)
It looks like I will be going JE pistons I found a 92mm drop-in kit for $250. My next decision is the guides in the head. I was told by a couple of people that the guides are only good for about 18k maybe that explains why this will be the third set at 45k. I contacted MILLENIUM TECHNOLGIES they use kibble/white valve guides made of nickle-bronze. The other guides I found were aluminum-bronze and manganese(silicone)-bronze. I think the nickle/bronze should have better wear resistance properties than the silicone or aluminum so that it may prolong this maintenance interval for 40k instead of 18k-20. At 20k I had them replaced at the dealer with the updated ducati guide not sure what they are made of. They made it 25k. What is a good squish number for the JE's ina 91 900ss


any suggestions
 

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If you are interested I have a brand new set of JE Drop in pistons for the 900 engine PN 157597. That I will sell you for $220.00 Shipped. I bought them to put in my engine before I decided to upgrade to a 1000DS.
 

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Discussion Starter #8
Sorry, I already purchased the piston. $220 that's a great deal I would have save $30. DAM !!! every little bit counts with this economy. I need to find some info on the different thickness cylinder base to adjust the squish like a place to purchase or part # and available thickness
 

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Chilehead
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That's what my ST2 and LeMans are set to, in both cases I simply removed the base gasket to get the correct squish (lucky, I guess).

Tom
 

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Discussion Starter #11 (Edited)
is a rebalance of the crank necessary when replacing the pistons to JE 11:1
some have said you can lighten the JE pistons to the stock weight or close to it
 

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i suggest do drill a big hole right through the top of the piston,
that will solve any compression issues at the same time, with
reducing actual compression to 0 : 1

:)

come on duc dude, how about if you start using your own
brain for some thinking now ?
where do you think that a piston can be made somewhat
lighter without weakening its structure and without altering
the compression ratio ??

:think:
 

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Aren't there different base gasket thicknesses available? That's how we set deck height on everything else with removeable cylinders, from Harleys (nice old Pan you have there, Muschi!) to Porsches to VW's. I haven't rebuilt a Duc motor (yet), but I would hope they are available.

The only way to lighten pistons without losing compression is to face off the bosses near the wrist pins on the bottom side. This is only done to match weights in a set; there just isn't enough there to lighten them significantly.

The only other way is to remove some of the dome. JE uses the same forging for all compression ratios of any given piston application, merely machining the top flat on the dome lower for less compression. There is a minimum thickness, but by the time you reach that, you won't have enough compression for anything other than a forced induction application.

In other words, you're stuck with the additional weight. This will not affect the balance of the motor, so long as both are the same. The counterwights on the crank balance the crank; they do not balance the piston/rod/wrist pin assemblies. The weights of those two assemblies offset each other on a 90 degree (or a 180 degree) crankshaft.
 

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Yes the base gaskets come in thicknesses. .2and.3 if I remember correctly. Unless you are racing the bike the difference in piston weight won't be a problem.Go with the Kibblewhite nickel/bronze guides, They are very well made and will last a long time.A squish figure of 1.0to1.5mm is what you should shoot for and measure at the pin axis so piston to wall clearance won't affect your measurement.
 

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Discussion Starter #15 (Edited)
i suggest do drill a big hole right through the top of the piston,
that will solve any compression issues at the same time, with
reducing actual compression to 0 : 1

:)

come on duc dude, how about if you start using your own
brain for some thinking now ?
where do you think that a piston can be made somewhat
lighter without weakening its structure and without altering
the compression ratio ??

:think:
The compression it's the issue here. There are spots you can remove material. Directly under the dome (pop up style dome only )of the piston for a SMALL amount of lighting & balancing if done correctly (removing to much material is not good) it is the thickest area of the piston basically the same result as machining the dome to reduce compression but from the bottom of the piston in a very small area with out compromising structure or strength. HIGGY"s way is the most common and easiest to match piston weights for balance. If the extra weight of the piston is NOT going create a balance issues I will match pistons and leave crank balance alone
HIGGY & WDIETZ186 thanks for the info
 

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JE Pistons are said to have the same weight as the stock ducati pistons,
so matching their weight will be your first priority here.

there is no thing like a balanced crank assembly in a stock ducati supersport,
and the stock configuration can be rather bad is what i got to read in a very
sophisticated thread we had running about this matter on the german board.

stress on the components like bearings and casings could be pretty tough then,
a well balanced crank is considered an essential if you are going to raise
the engine's power and rpm i'd say.


In other words, you're stuck with the additional weight. This will not affect the balance of the motor, so long as both are the same. The counterwights on the crank balance the crank; they do not balance the piston/rod/wrist pin assemblies. The weights of those two assemblies offset each other on a 90 degree (or a 180 degree) crankshaft.
and i do not agree to the fact the counterweights on the crankshaft do
balance the crank on a 90° L-twin, they are there to balance the whole
crankshaft assembly including pistons, pins and conrods.
why would there be used someting like a masterweight otherwise if you
have your crankshaft trued dynamically ?

anyway, what parts ( and how much of them basicly ) are added to get
the correct masterweight for crankshaft balancing is the important part of
it.

:think:

HIGGY & WDIETZ186 thanks for the info
you can thank me also my friend, i am trying to help you here.

:cool:
 

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Chilehead
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Pistons are reciprocating mass, and thus do not enter into the balance question, nor do the wrist pins and the small end of the rod. The big-end does, however, and the rod itself as both reciprocating and rotating mass, so it also has an effect on the balance, albeit variable.

Tom
 

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Pistons are reciprocating mass, and thus do not enter into the balance question, nor do the wrist pins and the small end of the rod. The big-end does, however, and the rod itself as both reciprocating and rotating mass, so it also has an effect on the balance, albeit variable.

Tom
Thanks Tom, that's another way to put it. There is simply not enough mass, and it is too close to center, for the counterweights on the crank to "balance" the piston/pin/rod assembly. Yes, the big end of the rod adds two components to the equation, but the added weight of one big end is still offset by the added weight of the other in both of these components.

Sorry Muschi, but we balance crankshafts all the time. They are balanced bare, all by themselves. Actually, there are two different kinds of cranks - "internally" or "externally" balanced. In the former, just the bare crank gets balanced to itself. In the latter, the flywheel is attached when balancing, and must forever remain matched with that crank.

We run some racing cranks with no counterweights at all. Kind of the extreme example of the lightened flywheel approach, it's an effort to reduce reciprocating mass. Surprisingly, vibration does not increase noticeably at all. A flat crank (boxer twins, VW fours, Porsche sixes) or a 90 degree crank (like ours) is surprisingly well balanced even with no counterweights. Stock Beetle motors have never had them.

Now look at our 45 degree Harley cranks. You simply cannot hang enough counterweight on the crank to offset the weight of those piston/pin/rod assemblies separated by only 45 degrees. They must balance each other - the crank simply cannot. Neither can the crank ever balance a single - look what BMW did with theirs, with the false piston to counterbalance the real one.

The dynamics of this are complicated. There are dozens of engineering papers explaining the nuts and bolts details of cylinder angle vs. balance. In a nutshell, we can achieve a "zero" primary balance at 90 and 180 degrees. This is with a single cylinder as a baseline "100%" shaker. A 45 degree twin becomes about an 80-some-odd percent shaker, 60 degrees takes a massive drop to well below 50%, and the "sweet spot" is hit at 90 degrees and again at 180 degrees. The piston/pin/rod assemblies are entirely responsible for the mass contributing to this vibration; remove them, and all of these cranks should be at "zero" balance.
 

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Discussion Starter #19
The crankshaft weight are to help with the firing stroke to smooth out the pulses yes there are cranks that have no balance weights usually resulting in more feel of firing stroke there are counter weighted cranks also called perfect circle cranks (the kind you can roll a crossed the floor)found in two strokes and performance vw's that help in offsetting firing forces and cutting through the oil they seem to run the smoothest we all know a well balance crank and rod big & small end & matched pistons w/pins & flywheels & gears etc. will run the smoothest but how good is the ducati stock balance it seems there is aways a better balance then stock but how far off are the two I've seen cranks where the balance marks were vertically nothing and other where they added a heavy slug for balancing I guess its up to the factory spec how good it is my bike is not a commuter just a weekend worrier stock motor arrow exhaust bmc filter fp-jetkit it has the typical 8k run off. Has anyone seen or hear of someone loosing the bottom end prematurely because of the stock balance
 
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