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Discussion Starter · #1 ·
1997 900SS CR. I had the engine out, and had the heads off and the cylinders off, replaced the pistons, and then put it all back together. After some initial problems (see earlier thread "Runs on one cylinder, Sometimes") it seems to be running properly now, for about 40 miles. So far so good. But.

After a 25 mile or so test run, looking for oil leaks around the engine, etc., found a small o-ring on the case, right side, behind the vertical cylinder, right in front of the oil breather. I looked on the parts fiche, and I can see there is an o-ring that its there between the cylinder barrel and the case right in front of where I found it. I looked at a video "Ducati 600SS Full Restoration, EP3" and it shows the restorer installing the o-ring at 18:37 in the video. Appears to be for one of the oil passages. [BTW, If you are like me and have never taken a Ducati apart, these video on the 600SS are a pretty good guide on how to do it.)

Of course, I can't tell if the mystery o-ring I found came from there without pulling the head and the cylinder, which I can't do unless I take the motor out, which means taking the back end of the motorcycle off. As you all know.

If this is where it came from, is there any danger in just leaving it as is? So far I haven't seen any oil leaking out from that area. Or, do I need to suck it up and just take it all apart, because I could be not getting oil where it needs to be.

I'm retired, so I have the time to do this, but it is a lot of work for an amateur like me, if I don't have to do it.

On the other hand: when all my passion was working on boats, there was a saying, "God doesn't count against you the time you spend working on your boat." I'm hoping he has the same attitude toward working on your motorcycle.

Bob Ross
 

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Did you take any pictures of your cases with the cylinders off?
I will guess you have oil cooled cylinders on a 97 900ss us model but know that later motors eliminated this o-ring (and often leaked). Did you use base gasket sealer or assemble a dry base gasket?

It is possible that the head feed o-ring is the one you found it sits tight in front of the breather on the right side. If you used sealer on the base you may be fine but probably temporary, it would be a high pressure leak if it happens and will puddle in this area. The 97 should have had a base gasket that surrounds the o-ring in the pocket so you may not be able to see it but I would look very carefully before pulling it all down.

As belter said what size o-ring? post a picture with measurements and we can see if it is even the correct one for that point. Only other o-rings are the oil feed pin (small) and oil return (fat) o-rings. Those are at the cylinder to head.
 

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Discussion Starter · #4 ·
The o-ring is one of the small ones. The parts fiche doesn't list an actual size but labels it as 750. Guessing it means 7.5 mm. I measured the ID as between 7 and 8 mm. Of the two sizes of o-rings that are used between the cylinder barrel and the head, this is like the smaller of the two.

My memory of what I did in reassembling this particular part is vague. The metal base gasket between the case and the cylinder barrel was coated with sealant on both sides. If the o-ring was located as I referenced in the video of the 600SS restoration, the o-ring is located outside of the gasket and would not have had any sealant around it. But, I don't know if there is any difference in this minute aspect between the 600SS and the 900SS.

Don't know much about the oiling system, but was hoping that maybe this was a gravity drain back into the case and not a pressurized feed going up into the cylinders. If the latter, can't imagine it isn't going to leak sooner or later, and I probably should just man up and fix it. Also, if this is a pressurized feed going up to oil the cylinder, probably not good to have the o-ring gone, possibly losing pressure?

Anybody got a picture of the bare 900ss case, or the gasket itself? May give a clue about whether this is inside or outside the gasket.
 

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I must have typed 5 different responses to this, but each time after looking at what I typed on the page I realized the only support I could give you is for taking it apart and putting that damm oring back in if you are 100% sure you didn't buy another one and use it instead. Yeah, that sucks, I feel your pain.

When I took mine apart, that oring fell exactly where you found yours, as I was looking other places when I lifted the head up I did not notice it - I found it later.
 

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If you take a picture of the o-ring sitting on a ruled scale, That would probably allow Belter, Ducvet or others to identify it exactly--Then you could get a real good answer--short of that everything is a guess--a picture is worth a 1000 words
 
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part #5?
Ducati O-ring 9.25 x 1.78; Viton O’Ring used for the rear head oil gallery on 2V & 4V heads, also used on the oil pump



RefPart NumberDescription# On DiagramPrice Per ItemQTY In BasketDetails
188641181AC O-RINGx2$0.75
288641211AC O-RINGx3$1.70
312110051AA PISTON PINx2$53.15
412020141BB VERTICAL CYLINDER-PISTON ASSYx1$1285.70
5938232037C O-RINGx1$0.75
678610471AB GASKET, CYLINDERx1$8.85
7080517125C BUSHx2$3.80
888641331AC O-RINGx2$1.10
9707806516C ALLEN SCREW M6X16x6$0.95
1024710171AA COVERx2$91.05
1179120031AC HEAD-CYLINDER GASKETS SETx1$66.80
1278110111AA BOLT, SPECIAL TE M10X1x4$14.20
1385250241AC WASHER 10X14X1x8$0.40
1493310012BA PIPEx1$87.40
1593310022BB PIPEx1$58.05
1678610391A**Dead ->78610392Ax1$8.40
78610471AB GASKET, CYLINDERx1$8.85
1712020151BB HORIZONTAL CYLINDER WITH PISTONx1$1248.25
1888440111AC CIRCLIP, PISTON PINx4$1.25
1912120141AB PISTON RING SETx2$357.30
2012220081AA PISTON ASSYx2$993.10
Ducati Spare Parts
 

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if it's small it's #1. is it new, as in the one you tried to fit fell out, or used, as in the one that was replaced? it's not a very big puzzle.
 

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Discussion Starter · #9 ·
I took a picture of the mystery o-ring.
IMG_20200302_130434998 (1).jpg

Unable to deal with the uncertainty of it all, I decided to dive and resolve the mystery. Was this from the oil passage in front of the oil breather and between the vertical barrel and the case? Took everything apart and discovered it wasn't from there. There was an o-ring in that spot.

Relieved, I guess. Still don't know why the mystery one appeared. Meanwhile, putting it all back together.
 

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At least you are not alone.
I was modding a 821 hyperstrada clutch and when I opened it up I found ... this.

980940


Funny someone at the factory dropped a o-ring into the threads and did not notice?
I do not even see that size o-ring anywhere under the cover on that model.

The base gasket o-ring is about 12mm od the oil returns are more like 15-16mm od. I jus measured a oil feed pin o-ring that sits on the outside of the feed pin between the head and cylinder and it is about 11mm od with a wire size of 1.6mm. this is the closest to your mystery o-ring.
 

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Thats just nuckin futz, but still not as funny as the 2 cigarette butts I saw in the bottom end of a Ducati engine when it was taken apart at around 1000 miles
 

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That looks like the o-ring that goes between the primary cover and pump that feeds the oil pressure sender on my 900SS. Do they still use it there on the newer bikes? Mine wouldn't build pressure to the sender and ultimately illuminated the oil light once the oil got warm and thin.

I had to pull the clutch in it's entirety (for the second time that day) to put it back into place.

I can't be the first to have forgotten it.



At least you are not alone.
I was modding a 821 hyperstrada clutch and when I opened it up I found ... this.

View attachment 980940

Funny someone at the factory dropped a o-ring into the threads and did not notice?
I do not even see that size o-ring anywhere under the cover on that model.

The base gasket o-ring is about 12mm od the oil returns are more like 15-16mm od. I jus measured a oil feed pin o-ring that sits on the outside of the feed pin between the head and cylinder and it is about 11mm od with a wire size of 1.6mm. this is the closest to your mystery o-ring.
 
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