Cylinder scuffing

[Ddan]

This is the vert cylinder from a '92 900 SS with JE high comp. pistons, standard bore.  It's been used on the track only for the last few years but the motor has just been run for diagnostic reasons since the last tear-down when it got valve guides.  I've got low compression on both cylinders, 180psi on the hor, and 150psi vert.  Leak down on both is 10%.  I haven't measured the bore for taper but I checked the ring end gap at the top, middle and bottom of the cylinder and got a max. difference of .04 mm.  So, what am I looking at?

[Howie]

I don't know what your readings should be with the high comp pistons and 10% leak down isn't awful but I would be concerned with the difference between the two cylinders.  Is all ring gap below 1mm.?  I have never seen a Ducati spec on taper, but typical would be 1-2mm.  Great photos, but I can't tell if the cylinders are actually scored.  I hope what we are seeing is piston material deposited onto the cylinder walls.  Maybe let Eric look at the cylinders?

[Ddan]

I've already talked to Eric and I am planning on bringing them down to him.  The cylinder isn't really scored but you can feel the different texture with your fingernail.  End gap ranged from .44mm to .48mm, within JE spec

[Howie]

Wow, I screwed up my decimal points, probably because I was one dose short on caffeine.  I will go back and changed them.  What do the piston skirts look like?  I'm thinking (hoping) what looks like scoring on the cylinders is an insignificant amount of material from the pistons nicely distributed by the rings.

[Speeddog]

Pictures of the piston(s)?

When you did the leakdown, where was most of the air going?

From your description, it sounds like the engine hasn't been run in a while?

[Ddan]

I'll get pics of the pistons.  

Up until this year the bike saw 6-8 trackdays per season, it's not been run this past summer.  

Hot, the air was going by the rings, cold it was rings an a bit by the exhaust valves.

I feel better now Howie   

[brad black]

those marks appear to be consistant with what you generally see in these cylinders.  I've seen them in cylinders 500km old.

[Ddan]

First, thanks for all the responses.  I've finally got the piston pics, and while they show a little abrasion it doesn't seem that bad, and also doesn't seem to line up with the marks in the cylinders

[Speeddog]

From those pics, I'd zip it up and run it.

Get new pin clips, don't re-use.

[Ddan]

Even with the big difference in compression between the two cylinders?

[ducpainter]

Even with the big difference in compression between the two cylinders?

I'm not sure you've run it enough to really seat the rings...

[Ddan]

I'm not sure you've run it enough to really seat the rings...

Well, I hadn't looked at it that way...   Should I put in new rings?  They're cheap enough

[ducpainter]

Well, I hadn't looked at it that way...   Should I put in new rings?  They're cheap enough

That would be your call, but they're basically brand new now.

The old girl needs a flogging I think.

You can replace them next winter when you're bored.

[Ddan]

That would be your call, but they're basically brand new now.

The old girl needs a flogging I think.

You can replace them next winter when you're bored.

I'm bored    

and it wouldn't break my heart to not have to take the motor out for a few years

FWIW, the motor has 5 seasons on it, maybe 30-35 track days

[ducpainter]

I'm bored    

and it wouldn't break my heart to not have to take the motor out for a few years

FWIW, the motor has 5 seasons on it, maybe 30-35 track days

New rings won't stop you from needing to possibly take the motor out for a different reason.

Isn't that the motor that came with that bike that had been so carefully looked after?

You'll be bored next winter too.