Questions on replacing pistons

[ducpainter]

I stuff a bit of rag in the case around the rods when putting in the pin clip, incase it drops inside engine.

a good idea whether in the chassis or not. 

[Howie]

None of the Ducs have a knock sensor. but your 4 valve is water cooled, has a different combustion chamber design, etc.  My friend's BMW 1100RS pings on anything less than 91 with 10.7:1 compression, and will even ping on that if oil temp gets a little on the hot side.

[ducpainter]

None of the Ducs have a knock sensor. but your 4 valve is water cooled, has a different combustion chamber design, etc.  My friend's BMW 1100RS pings on anything less than 91 with 10.7:1 compression, and will even ping on that if oil temp gets a little on the hot side.

I understand that chamber design and water cooling affect things.

Chamber design has a much larger overall effect I think.

[Ddan]

I don't think any Duc has a knock sensor...not even with the Siemans ecu.

What I was getting at was the motor was designed and set up with that compression, fueling and timing.  It's pretty standard the 900 motors with HC pistons need timing and fuel work to run right

[ducpainter]

What I was getting at was the motor was designed and set up with that compression, fueling and timing.  It's pretty standard the 900 motors with HC pistons need timing and fuel work to run right

I'm not disagreeing.

He probably will need to do something...

He's not running a 900 though. He has a 750 so the parameters are somewhat different.

Just like with my water cooled 4 valve.

[Ddan]

I'm not disagreeing.

He probably will need to do something...

He's not running a 900 though. He has a 750 so the parameters are somewhat different.

Just like with my water cooled 4 valve.

Just like   

[bond0087]

Thanks for all of the thoughts... I'll be stuffing a rag in there for sure, because spending an hour trying to find a dropped pin clip would just be classic me  Thanks for the tip!

The info on what does/doesn't ping is appreciated, and I'll add another data point to the "will it ping" discussion when I get done... hopefully not when trying to figure out how to fix my ruined engine! I've got no problem switching to the highest octane I can get my hands on, though.  Premium and 45mpg still beats the hell out of my car at 20mpg on regular, so I'll still be happy with the cost.

[brad black]

my stuff on hc 750 and ignition

http://www.bikeboy.org/brads750m.html
http://www.bikeboy.org/ducati2vignition.html

same crap chamber as  a 900, just smaller bore.  should ping.  altho mine is surprisingly resistant to pinging, but it does have 900 cams.  it has ferracci pistons, allegedly 12:1.  never checked it.  i remember years ago a guy emailed me who had bcm fit high comps to his 750.  it pinged, so they told him to fit 900 cams.  not sure if he did or not.

i always replace base gaskets, but they're cheap and i have to guarantee the work.  i think i left my std ones in, squish was ok at that.  use threebond 1215 or equiv.

a 4v motor should see 12.5:1 without pinging, altho 996 like a bit less timing at that.  but a 996 has about 3 - 4 more degrees at wot than a 916 even, so it's a bit of a apples to oranges thing unless you know the actual eprom and ignition mapping.  and the advance is digital, not a single step thing.  that's why the 2v ping.  12:1 makes a 900 go nuts.

i'd fit an ignitech unit, easier than pullig the alt cover and moving then regapping the pick ups.

[bond0087]

Thanks for the response, Brad.  I actually read those two articles (and most of your other 2V related ones) already, they are very informative.  Your 750 article made me want high compression pistons, but maybe that was the wrong conclusion to draw from the article. 

I makes sense that the Ignitech system would probably be the better way to go, but I've got way more time than money right now (being a grad student and all), so I think I'll try rotating and regapping the pickups first.  Plus my left side engine cover leaks, so I'm hoping to clean up the mating surface, use some fresh sealant, and hope that I kill two birds with one stone there.  The single step ignition advance that they do with the 2V doesn't seem like the greatest idea in the world; I'm not surprised that it causes trouble. 

Do you know what engine speeds are most prone to detonation?  I noticed that your ignition timing in general is less advanced at higher engine speeds, is that because those higher speeds are more likely to detonate?  Or is the low engine speed right around where the timing jumps to full advance the real problem area?

[bond0087]

Just wanted to say thanks again to everyone that responded! 

I put my new pistons in this weekend, and it all went reasonably well.  The job wasn't without difficulties, but when it was all said and done, I pressed the starter button and it roared to life first try!

I did the job in the frame (thanks ducpainter), and I would say that is certainly the right way to go.  The frame hardly ever got in the way, and removing the engine would have been a pain. I definitely dropped the wrist pin retaining ring down the crank case onto the rags that monsta suggested, so thanks again for that, saved me a lot of trouble.

I went ahead and retarded the timing all the way and filled her up with 93 octane.  I didn't hear any pinging, but it's hard to say for sure, because I only rode it about a mile, and not under much load (I finished at 2am, and my bike is not exactly quiet). 

I'll post some more details and useful pictures / information for others thinking of doing this job once I get a few miles on it and I can get a better impression of the difference before/after.