Ducati.ms - The Ultimate Ducati Forum banner

1 - 20 of 48 Posts

·
Registered
Joined
·
1,673 Posts
Discussion Starter #1
Got the endoscope today, not really sure what I was expecting to see.

The front piston appears filthy but normal looking, the back one had these marks on the surface, thoughts?

I suppose I should try to turn the pistons, the valves move easily enough on the front but I only turned it a quarter turn feeling the spring tension. The back one did not move as smoothly and I am not sure I could feel spring tension.

977169
 

·
Registered
Joined
·
4,912 Posts
without something else in the frame for size reference, that pic isn't useful. turn the cams to valves-closed position and turn the crank to put a piston somewhere below half-stroke and take another photo. repeat for the second piston. or, skip all that, install new belts and try turning the wheel by hand.
 

·
Registered
Joined
·
480 Posts
too me that pic does not look like a valve came into contact with the piston, I would normally expect to see more damage in basically a near perfect circle or 1/2 circle--I have never seen a bunch of little pits like what I see in that pic. --put a set of belts on--rotate the engine through by hand with the plugs out--if you find it binds and will not rotate all the way through smoothly then stop and take the top end off----Now if it does rotate smoothly all the way around then --Do a leak down test first-if a valve is damaged you will probably find it this way--if no leakdown then do a compression test.--if the compression & Leakdown test are good then you are probably good to go
 

·
Registered
Joined
·
5,911 Posts
I’d like to see the combustion chamber on the rear head. The exhaust valve and spark plug too, for that matter. Preignition is the first thing that comes to mind, but I’ve never seen it spread around the piston dome like that. A foreign object bouncing around, like a plug electrode, is also a possibility. Not enough information to make a good guess, at least for me.
 

·
Registered
Joined
·
1,725 Posts
too me that pic does not look like a valve came into contact with the piston, I would normally expect to see more damage in basically a near perfect circle or 1/2 circle--I have never seen a bunch of little pits like what I see in that pic. --put a set of belts on--rotate the engine through by hand with the plugs out--if you find it binds and will not rotate all the way through smoothly then stop and take the top end off----Now if it does rotate smoothly all the way around then --Do a leak down test first-if a valve is damaged you will probably find it this way--if no leakdown then do a compression test.--if the compression & Leakdown test are good then you are probably good to go
.. makes sense to me!!! ... (y)
 

·
Registered
Joined
·
1,673 Posts
Discussion Starter #7
It has had occaisional pre-ignition, the carb woes were another thing for quite a while.
I'm trying to figure out how to turn it, I guess by the clutch nut? I ordered the belts this morning, both belts were torn.
 

·
Registered
Joined
·
946 Posts
A foreign object bouncing around, like a plug electrode, is also a possibility. Not enough information to make a good guess, at least for me.
Yeah, that looks more like foreign object damage to me as well. Plug electrode or some small part capable of making it past the valve face and into the combustion chamber. Does not look like a dropped valve to me at all.

That said, I had a 53 series Detroit that snapped off a chunk of a valve face. The engine didn't even miss a beat. That chunk somehow made it past the exhaust valves and into the exhaust side turbo inlet where we found it.

It was our clue to remove the head and see how bad it was inside. The damage to the piston and roof of the combustion chamber looked quite a bit like the piston crown in the picture. Kinda like someone took an ice pick to them both. ....sean
 

·
Registered
Joined
·
5,911 Posts
Was there any spatter on the plugs, like tiny droplets of melted metal ? Another sign of preignition erosion. If it was an”FOD” , any idea what it could be ? If you don’t use air to blow the dirt from around the plugs stuff can fall in when you remove them.
 

·
Registered
Joined
·
1,673 Posts
Discussion Starter #12
Going out to examine now, the other chamber looks dirty, but none of these sparkly chips. I would say they are chips rather than blobs stuck on top. Hooking the endoscope to my laptop this time instead of the phone to get a better view.

Still a little unclear on how to rotate the pistons.
 

·
Registered
Joined
·
547 Posts
Those little white marks are nothing more than micro hot spots where the carbon has thermally decomposed at a higher temperature than the surrounding carbon. Normal when the carbon starts to build up in thickness on top of the piston. If the cylinders appear to look different internally you will find that one cylinder is running richer than the other for some reason. My bike had the needles in different positions front and rear to compensate for the standard, different length exhaust pipes but I also had an issue that the front cylinder valve guides were leaking oil down the side of both valve guides as well. Found out about the needle height when I first went to a tuned length 2-1 pipe and it ran like a bitch until I pulled the carbs apart and fitted a Factory Pro jetting kit. Found out from the previous owner that he had it tuned on a dyno which picked up on different fueling requirements for each cylinder.
 

·
Registered
Joined
·
1,530 Posts
not really sure what you're looking for here.

did the engine break a belt? title would indicate so, maybe i missed something.

if the cams turn freely the valve/s are generally not bent.

if the cams have drag, the valve/s are generally bent.

looking inside the cylinder is of no practical benefit in a broken belt repair. leakdown test will tell you if shit is bent. do it with both belts removed, cams on base circle.
 

·
Registered
Joined
·
1,673 Posts
Discussion Starter #16 (Edited)
The directions for changing the belts in the Haynes manual are not helpful in the condition my bike is in.

I cannot rotate the rear wheel in gear with no spark plugs in as I used to be able to when the belts were in place.

I have gotten a good look around the tops of both pistons with the endoscope and its 90 degree mirror, although I cannot move the pistons, and there are no semi circle marks. I cannot aim the camera to see the valves, I can, but it is so out of focus I can't see shit.

Both belts broke, probably the front one first which tangled and broke the back one, becoming wrapped 4 times around the big common gear at the bottom.

It did backfire into the air box once in the preceding 1/2 hour before the belt broke, I thought it was too rich/flooded when cold starting.

How do I move the bottom pulley gear and where do I move it to? Line up the dot? It almost is, just a smidge more.

How do I turn the valve gear pulleys? Do I line it up with their marks too? The front one moves about 4 teeth distance anticlockwise with smooth spring resistance but no further with my fingers.

The back one barely moves anticlockwise, one tooth distance, but smoothly. No extra noises, it is like something is stopping it. That piston appears to be further down in the cylinder, the front one appears to be at the top of its stroke or close to it.

I don't know what to do next since I cannot move anything and I wouldn't know where to move it to anyway.
 

·
Super Moderator
Joined
·
26,066 Posts
Yeah...she's all done buddy. Off with her heads! The bottom end isn't a concern at the moment...though it may become one.

May as well order up a top end gasket kit, and FFS get yourself a Desmotimes Desmodue manual. And a crank turning tool. It's rebuild time!
 

·
Registered
Joined
·
1,673 Posts
Discussion Starter #18
Well, I went to Motomfg dot com to order a crank turning tool and it turns out I already ordered one from them in January, better go find it.
 
1 - 20 of 48 Posts
Top