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Discussion Starter · #1 ·
I’ll try to keep it short. Last year, I had to fix worn valve guides and a minor cylinder score (vertical). I opted for 944 kit while at it. All done, and about 4000 miles later, I had badly scored cylinders (both). I found a good used cylinders and pistons, and new rings, and went back to stock bore. 200 miles later (still breaking it in), another scored cylinder (vertical). When I found the damage to 944 kit, my best assumption was that I screwed up the installation (I assumed that t rings were correct and didn’t measure them, stupid me). When I installed these used set, I went through the checklist meticulously, and I’m certain that parts and/or installation are not the issue. It was also running beautifully till I felt unusual vibration at about 3500rpm, at which point I promptly went back home). Anyway, I just can’t figure out what is causing it. It’s not the issues with the heads or cylinders. I didn’t put actual oil pressure gauge to it, but the oil pressure light operates normally. It never had any indication of overheating, so what could it be? I need to figure out what it needs, so I’d appreciate any input. Thanks,
 

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Discounting human error...it sounds environmental...you have something internal possibly breaking down producing an abrasive or an existing abrasive that never got flushed...send your oil in for analysis... anything foreign should be detected...just thinking aloud
 

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1991 Ducati 907ie, 1991 Ducati 900SS, 1991 Ducati 851 Strada
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could also be that you are running the motorcycle too lean----Lean is mean & fast---but does not last.---Are you running a stock air filter setup--( stock box, filter & top? )--Is the motorcycle timed correctly? or running too advanced? --when you converted to the 944 setup could you have installed an o-ring incorrectly or used sealant that may have clogged an oil passage? ---too many questions that need answers.
 

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Well damn that really sucks. My understanding is that the cylinder walls are just splash lubricated, so that should work regardless of oil pressure (and you'd have big end Conrod bearing issues first, if oil pressure was the issue). So assuming you had enough oil in there, and it wasn't olive oil, that shouldn't be the cause.

Is there any sign of heat damage or high temps anywhere, spark plug for starters?
 
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Discussion Starter · #6 ·
Thanks all for the comments. I'm really lost, so I really appreciate your thoughts -

Discounting human error...it sounds environmental...you have something internal possibly breaking down producing an abrasive or an existing abrasive that never got flushed...send your oil in for analysis... anything foreign should be detected...just thinking aloud
Oil, I didn't think about. Of course, oil was changed when the cylinders/pistons were installed. I may send sample in, just out of curiosity at this point.

could also be that you are running the motorcycle too lean----Lean is mean & fast---but does not last.---Are you running a stock air filter setup--( stock box, filter & top? )--Is the motorcycle timed correctly? or running too advanced? --when you converted to the 944 setup could you have installed an o-ring incorrectly or used sealant that may have clogged an oil passage? ---too many questions that need answers.
The carb setting - I was really conservative and I made sure that if anything, it's on the rich side. It's got stock everything. After going back to stock bore/piston, the timing also was set back to stock timing. I wondered if there could be a mistake like sealant in the oil passage and stuff like that, but the second time around, I was so meticulous about every step of it, so much so I'm pretty certain that isn't the cause (of course, there's always a chance that I screwed up somehow, my ability to cock things up is a mystical level). I haven't opened it yet, I just checked it with bore scope that I borrowed from work, so maybe there will be a discovery.

Well damn that really sucks. My understanding is that the cylinder walls are just splash lubricated, so that should work regardless of oil pressure (and you'd have big end Conrod bearing issues first, if oil pressure was the issue). So assuming you had enough oil in there, and it wasn't olive oil, that shouldn't be the cause.

Is there any sign of heat damage or high temps anywhere, spark plug for starters?
So every time I took it out, I remove the plugs and check the condition. Until the issue occurred, both horizontal and vertical plugs were just about as good as I could expect. When I took them out this time, the horizontal still looks almost textbook healthy, the vertical is black. Oil level is good. Heat damage - you mean, like a localized hot area? What should I look for?

what does it look like? lots of nikasil marks really aren't anything to worry about.
I haven't opened it yet, I just looked into it with bore scope. I think it can take a picture, so I'll try to take a picture and post it. I looks bad though, it does not look good.
 

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Scoring in the piston and cylinder some times is from debris in the oil, often a main bearing failure which could also be the vibration. Check the drain plug magnet for a fair amount of steel.
 

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Thanks all for the comments. I'm really lost, so I really appreciate your thoughts -



Oil, I didn't think about. Of course, oil was changed when the cylinders/pistons were installed. I may send sample in, just out of curiosity at this point.



The carb setting - I was really conservative and I made sure that if anything, it's on the rich side. It's got stock everything. After going back to stock bore/piston, the timing also was set back to stock timing. I wondered if there could be a mistake like sealant in the oil passage and stuff like that, but the second time around, I was so meticulous about every step of it, so much so I'm pretty certain that isn't the cause (of course, there's always a chance that I screwed up somehow, my ability to cock things up is a mystical level). I haven't opened it yet, I just checked it with bore scope that I borrowed from work, so maybe there will be a discovery.



So every time I took it out, I remove the plugs and check the condition. Until the issue occurred, both horizontal and vertical plugs were just about as good as I could expect. When I took them out this time, the horizontal still looks almost textbook healthy, the vertical is black. Oil level is good. Heat damage - you mean, like a localized hot area? What should I look for?
I meant, signs on the spark plug that could indicate hotter than usual combustion temps in that cylinder. You'd know, the plug would look all melty and blistered. Black probably just means oil, because of your scored cylinder. So that's probably not it. Not sure what I'd do at this point but I agree that sending an oil sample away is probably a good start. Labs like Blackstone will send you a little container in the mail to drain the oil into.
 
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Discussion Starter · #10 ·
I meant, signs on the spark plug that could indicate hotter than usual combustion temps in that cylinder. You'd know, the plug would look all melty and blistered. Black probably just means oil, because of your scored cylinder. So that's probably not it. Not sure what I'd do at this point but I agree that sending an oil sample away is probably a good start. Labs like Blackstone will send you a little container in the mail to drain the oil into.
Oh, thank you for that, I'll contact them.
 

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Discussion Starter · #11 ·
So here are the pictures of the bores. Both horizontal and vertical show scoring. The drain plug has no big bits of metal. I can't tell very well, so I'll look more closely, but I feel like there's some ground steel, but it's so little I can't even really tell.
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(the bottom picture is vertical cylinder.)
I really just don't understand what's causing it. It must be some to do with the bottom end, something down there is chewing up the cylinders.
 

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The key is if you can run your finger nail over the marks can you feel anything---if you can there is an issue if you cant I would still want to know what it is but as stated before the Nikasal lining is very hard and you almost have to try to damage it. --once removed I would run a flex hone through them just to break the glaze then clean them and check if you can feel the marks--plus I would measure the bores all around just to make sure.
Pull your filter screen out as well & see if there is an abnormal amount of metal on it.--
 

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did you check the piston ring end gap before installing on the pistons? file to specs? my guess is the end gap is binding when expanding-just a guess.change the oil after 30 minutes after the first start? did you use a breakin oil?oil pressure light ever flicker or illuminate while running -sign of a crank bearing going South as ducvet mentioned.
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looks pretty normal to me. i remember doing a hot up job on a 916sps back in the day that had 500km on it and it had a lot of those marks in the cylinders. i asked pete smith about it and (from memory) he said he thought it was silicon getting pulled out of the nikasil as the surface had settled. if it's not causing an issue leakdown wise i'd not worry about it.

if that is what you've been spending a heap of money "fixing" i'd say you've just been wasting it, unfortunately.
 

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Discussion Starter · #15 ·
did you check the piston ring end gap before installing on the pistons? file to specs? my guess is the end gap is binding when expanding-just a guess.change the oil after 30 minutes after the first start? did you use a breakin oil?oil pressure light ever flicker or illuminate while running -sign of a crank bearing going South as ducvet mentioned. View attachment 1039094
The ring gaps were meticulously measured this time (unlike the last time, ugh!), so I'm pretty confident I did that bit right. But no, I did not use the break-in oil, and I did not change oil after the first 30 minutes either. Ugh. Oil pressure light never flickered or came on while running, so I was just assuming all was well on that front - but now I'm not sure.
 

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Discussion Starter · #16 ·
looks pretty normal to me. i remember doing a hot up job on a 916sps back in the day that had 500km on it and it had a lot of those marks in the cylinders. i asked pete smith about it and (from memory) he said he thought it was silicon getting pulled out of the nikasil as the surface had settled. if it's not causing an issue leakdown wise i'd not worry about it.

if that is what you've been spending a heap of money "fixing" i'd say you've just been wasting it, unfortunately.
Mmmmm...so the 944 kit that I removed had much worse scoring than this, like when you run your fingers, it feels like it's sandpaper surface. And granted, those pictures were taken with the borescope, so I haven't felt it yet, maybe I'm over cautious but it sure looks like the beginning of the same damage. The compression test was still healthy, but the plug is definitely becoming blackAZzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz...sorry my cat just did that. I'll run the leakdown test and report back.
 

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leak down will help tell you if there's any bore or ring damage causing an issue as such. but sounds odd. over cautious is not a bad thing. i doubt oil would be an issue.
 
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