Thanks Lee Agreed. More than likely the big ends. ufff. one thought though also, regarding the clac gap. it much mor intermittent than that. more of a clac gap clac gap gap gap clac clac gap clac .etc. hehehe very intermittent. And its strange that the vertical doesn't seem to fire properly too. But yes looks like i've gotta get the engine out. Pfff the movement in the clutch basket is still a concern, probably not that that's clacking against the engine casing? wish it was. Also like you suggested. maybe the bottom shell has a flat spot. It would explain why the compression is one bar higher. piston travels higher?
Even if a big end shell has worn out at an early stage it would only mean a movement of four or five fag papers at the most which wouldn't be enough to alter the compression reading. If A main had totally failed then play could be considerably more but I think you'd be aware of that.
I had the same noise when I knocked the bottom end out on my 996 at Knockhill. The engine was quiet at tickover but you could hear a rattle as it was gently revved. The noise was the piston kissing the cylinder head.... Same happened with a BMW V8 engine. Apart from the bottom end shell and rods on the 996, and the pin on the V8, the pistons/valves/heads were not damaged, and the only marks on the piston was were the carbon had been removed by touching the head.
I don't have a picture of the 996 piston, but this is from the V8 and you can see the clean area where the piston touched the head
Here's my therory on how the noise is more intermittent , if the shells are damaged the locating 'nidges' ride over in the rod this allows the pair of shells to spin in the rod aswell as spinning on the journal , if one shell has more meat than the other this is where you get a clip then miss a few .... a more uneven noise as the shells rotate . Chris..... just looking at where you say about doing a cylinder leakage test , when looking for cylinder faults , I do 3 tests Compression test Cylinder leakage tests And a dynamic compression test , just out of interest does anyone do dynamic compression tests and understand the diagnostic value , not trying to be a know it all here by the way , I work on cars in the diagnostic field so it what I do most days
Never needed to do third option but am fully aware of procedure . Can be of benefit if you have a persistent mystery problem. Leakage test is my favourite, thoroughly enjoy checking an engine out this way.
Thanks people, awesome info. Nobody likes the inevitability of an engine removal, I guess its the next motion. I was trying to avoid that. but ok. I like the mechanics. just don't have an in door workshop here in Spain at the moment. But I will get on it I guess. good job I'm a MotoGP and wsbk photographer I might be able to borrow some of the special tools. uff. I have pics here in my albums for everyone to enjoy including pics of mechanical work with ducati.. Nick Little | Facebook shame the cant give me an engine.. jjjj when I decide to strip my bike I will do a photoshoot.. and post it here. anymore excellent advise is welcome. or a cheap engine. thanks N
Commiserations Nick, I think deep down you knew it was major But don't blame you for ruling out all possibilities first
I had issues where leakage test shows no leakage , cranking compression good but cylinder contribution counter kept flagging engine management light on saying cylinder 3 was low performance , long story short the exhaust lobe was very worn so cylinder emptying was poor , the dynamic test is the good one for these type of issues because it shows the ability of the cylinder to flow as appose to seal . Its also good for diesels with coked up inlet valves or where swirl flaps have come adrift of the actuator bar , or petrols with variable inlet runners , not ducati related mind but is of diagnostic use . Try it sometime just for the hell of it , it may surprise you , I take the Schrider valve out of the compression tester , but it's better if the compression tester guage is oil filled to damp the cylinder pulses
Yes, interesting as it was something external that was affecting the running. I remember somebody diagnosing a rust patch partway down a cylinder which would only show up on a dynamic test. The rust was quite dry so hardly affected running but had created a void so sealing dropped off as the rings passed it.
Now I don't think for a minute that this has anything to do with your problem. But while riding I had an intermittent clack and judder when I had an inside link of a chain snap. As outside link bent the broken piece would occasionally catch on the frame. Hope you get to the bottom of your trouble soon.
I hadn't thought of it before but everyone talking about random 'clacking' has reminded me, and I think you are right - that is the sound that a spun big-end shell makes which also means crank and conrod badly worn and often scrap apart from re-metalling which just isn't worth it unless it's irreplaceable. It only takes momentary oil starvation if at high revs (or that pesky crank coreplug unscrewing) for this to happen.
Ufff so in principal it probably not worth reparing? in that case anyone got a 996 engine for sale.. shippable to spain?
Of course it's worth repairing Nick, the minimum you might need is the crankshaft, a conrod and obviously bearings and gaskets. When a crankshaft journal is worn enough for a shell to spin then (as said) it is possible that piston has kissed the cylinder head/valves but hopefully not. If you could get a whole engine from a trusted source that is of course one alternative.
