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1994 900SS CR, 2002 998 Trackbike
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Discussion Starter #1
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I just pulled the plugs out of my 900 to investigate a new oil consumption issue. What I found was something that looks like signs of detonation / pre ignition to me. Pictures are from an endoscope camera through the plug hole and maybe hard to interpret, but I see little aluminum balls on the pistons, about equal on both cylinders. Photos of the plugs to follow, I think there is a tiny piece blown off one of the insulators but I'm not an expert as may be obvious by now

I have 11:1 pistons and FCR41 with a TPS (ignitech TCIP4) and have been running like this all summer.
I last looked in there maybe 1000 miles ago, when I dialed in the cam timing to 109° centerlines. I thought my ignition map was on the conservative side with no pinging felt or heard, and the pistons were clean last time.

Guess the more advanced cams have pushed cylinder pressure up enough to cause this? Since the properly dialled cams made the motor way smoother at low RPM, I may have also abused the 2500-3500RPM range a bit too much since then?

Anyway, not sure what to do next. Is this damage concerning enough to warrant opening the engine? Guess the bike should really go on a dyno, but the nearest is 6 hours and a ferry ride away from me. I'm obviously gonna pull a few degrees of timing out of that map.
 

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time on a dyno may be well spent $ and time. No guessing about A/F ratio or ignition timing.....

Fred
 

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1994 900SS CR, 2002 998 Trackbike
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267 Posts
Discussion Starter #4
time on a dyno may be well spent $ and time. No guessing about A/F ratio or ignition timing.....

Fred
Absolutely, but it's basically a two day operation to get this bike on a constant speed dyno and back from where I live, so I couldn't bring myself to it so far.
 

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1994 900SS CR, 2002 998 Trackbike
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Discussion Starter #6
does it look like the plugs have aluminium on them?
I tried to take some pictures through a magnifying glass here, not sure what I'm looking at though. The surface looks rough and speckled but I can't tell if that is aluminum or burnt oil deposits. I can see through the camera that my horizontal exhaust valve guide is leaking oil. But both plugs look very similar to me at least. In the first picture it looks like a piece of the deposits or ceramic (left of the center electrode in the picture) has come off
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That looks like a bit of build up came off the insulator. I would say light detonation causing those flakes to come off the piston and insulator. If it was mine, I’d drop the timing back to where you had it before, replace the plugs, and ride it where you may cause detonation, like an area with some long uphill runs. Beat on it and check the plugs again. There is not enough going on there to make me pull it down.
 
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that plug does look a bit aluminiumy. pulling the horizontal is easy, i'd start there. look to see if it has started eating away at the top ring land.

that's a lot of oil on top of the pistons. is that a clean band around the outer edge?
 

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1994 900SS CR, 2002 998 Trackbike
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Discussion Starter #10
Yes the squish band looks very clean. I already stuck a piece of solder in there and turned the engine through TDC, I do have at least 1.6mm squish clearance according to that test, and I don't have thicker solder. So it must be oil washing it?

I cleaned the pistons some 3000 miles ago I think, when I had the heads off to replace the valve guide seals because of leakage. I didn't do new guides like I probably should have. Now I have oil leaking past the horizontal exhaust valve again. Not sure where the oil in the vertical is coming from.

On the endoscope ($11 usb endoscope from eBay...) I can't see any damage to the piston crown but I don't really know what it would look like either. Am I looking for erosion right at the corner? If you think it's worth it I can definitely pull the head
 

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if it does have 1.6mm, that's way too much and could cause pinging itself, but if the outer is that clean i'd be surprised. if there is that much oil in there that is also likely to make it detonate too. pull it apart to fix the oil and you might find the cause of the detonation, if there is one.

getting the guides k-lined is much easier than replacing them. new stem seals and away you go.
 

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Looks like fuel additive deposits on the plugs to me. What fuel you running? Any octane boosters or other OTC additives? You may need a step cooler plugs due to the likely increased cylinder pressure/temp.
 

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1994 900SS CR, 2002 998 Trackbike
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Discussion Starter #13
So I probably have excessive squish, and oil in both pots that needs to be addressed.. hmm.

Right now I have new plugs installed, and a few degrees of timing pulled throughout the map. I'm thinking I'll do a few test runs to check for pinging and to see what the plugs look like at full throttle. Then pull the front head this weekend like you suggested, to have a look at the damage, if any.

Then there is about a month of riding left here before winter weather takes over anyway. At which point I'll pull the motor out, get the guides lined, new valve seals, and address a few other things that have been bothering me on the motor. Then get it on a dyno with a competent operator before the spring, and set everything up right, like I should've done two years ago when I first had it out of the frame.
 
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