www.zxrworld.co.uk

Hi all
I have got ZXR 400 that i brought race ready etc,1st outing on it down mallory it went bang,piston completly shatterd,i took it a tuners to get it all rebuilt costing me £800,ive raced it 3 times at darley moor and today it has gone and done the exact same thing on me,any one got any suggestions as to what may cause it,there was oil in and water etc was checked before i went out, any help will be great
cheers Matt

out of interest, what does your tuner think happened?

Impossible to say without having a full picture and leaving mechanical failure aside - piston shattering sounds like overheating due to ignition advance- is it running highly tuned engine + race ignition?

Was it the same cylinder? Has the tuner seen bike on the dyno. My advise - after the rebuild would be to dyno the bike and check the exhaust header temperatures to see if running hot

I Havent yet spoke to the tuner i will bel him in the morning and take it from there,
its running 72 bhp it was dynod whebn rebuilt before i picked it up,not sure what ignition it has on tho but i will check it and see
i was a differnt cylinder that was used on the rebuild,

Never, ever heard of pison shattering

One thing that I know happens is cold siezures, this can happen at somewhere like Snetterton where the water in the rad cools too much, closes the thermostat, then when heats back up in slower bits lets cold water back in thus seizing the pistons, which is why ZXR normally have tape covering some of the rad as they are too efficient. Siezing could, I suppose, cause piston the shatter, but what do I know
Are they Kawasaki pistons? ie, not cheap aftermarket!

They are all genuine kawasaki parts that i had done when rebuilt,when i say the piston has shattered basically theres no top on it its comple gone
i did notice when i was on the start grid that it was slightly smokeing from the headers or steam but i didnt think anything of it as we had just solved a petrol leak so i just thought it was the fuel burning that leaked out,spoke to the tuner and he says it could be my mistake by when i change down the gearbox i could be going down 1 to many gears,thanks for all the help so far

Sounds like the top of the piston has disintigrated - cant see how changing down two gears would do it given that changing down coincides with heavy braking. The tuner sounds like he is covering himself.

Suggest you take the head off (if not already) and photo the piston - put it up on the site and see if anyone can throw a bit of light on it. The man to ask would be Roger (RMKD177)

Perhaps its not engine tune related and electrical? Missing a spark? Running lean? Maybe bad clearances causing piston to hit the head or valves?

Is it still the same crank and rods after the last piston let go? Ar things still straight and balanced?

tuner said there was plenty of clearence when it was done,crank and rods all replaced since last bang!!

If piston was hitting the head I would have thought that the rod would shear rather than the piston disintigrate.

However, when he says there is "plenty of clearance" and given that this engine is race tuned - has he machined round the edges of the piston to ensure clearance. If not and the engine is highly tuned (running high compression) then there is a possibility that the piston could make contact. But this all seems unlikely - a pic of the piston would help.

This is a wikipedia note on "Detonation" which is a bit long winded but might be a possible explanation

Normal combustion
Under ideal conditions the common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion. The combustion is started by the spark plug some 5 to 40 crankshaft degrees prior to top dead center (TDC), depending on engine speed and load. This ignition advance allows time for the combustion process to develop peak pressure at the ideal time for maximum recovery of work from the expanding gases.

The spark across the spark plug's electrodes forms a small kernel of flame approximately the size of the spark plug gap. As it grows in size its heat output increases allowing it to grow at an accelerating rate, expanding rapidly through the combustion chamber. This growth is due to the travel of the flame front through the combustible fuel air mix itself and due to turbulence rapidly stretching the burning zone into a complex of fingers of burning gas that have a much greater surface area than a simple spherical ball of flame would have. In normal combustion, this flame front moves throughout the fuel/air mixture at a rate characteristic for the fuel/air mixture. Pressure rises smoothly to a peak, as nearly all the available fuel is consumed, then pressure falls as the piston descends. Maximum cylinder pressure is achieved a few crankshaft degrees after the piston passes TDC, so that the increasing pressure can give the piston a hard push when its speed and mechanical advantage on the crank shaft gives the best recovery of force from the expanding gases.


[edit] Abnormal combustion (Detonation)
When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat and pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur. Detonation is characterized by an instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front. A local shockwave is created around each pocket and the cylinder pressure may rise sharply beyond its design limits. If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed. The simplest deleterious effects are typically particle wear caused by moderate knocking, which may further ensue through the engine's oil system and cause wear on other parts before being trapped by the oil filter. Severe knocking can lead to catastrophic failure in the form of physical holes punched through the piston or head (i.e., rupture of the combustion chamber), either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into the oil system.

Detonation can be prevented by any or all of the following techniques: the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder; reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear); decreasing the manifold pressure by reducing the throttle opening; or reducing the load on the engine. Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures at the engineering level by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system. As an aftermarket solution, a water injection system can be employed to reduce combustion chamber peak temperatures and thus suppress detonation

Check this thread - there are a couple of pictures of failed pistons - albeit from marine engines

http://www.marinesurveyor.com/boatpoker ... piston.pdf

i will try to get a pic uploaded 2moz of the engine and see if any 1 can shed some light on it,thanks every1 tho

Thanks for the reccomendation 'Davw'..
The 'top and bottom' of it is....its been rebuilt wrongly! regardless of what the tuner says! One failure yes...i would accept that....components failing ?!? but not two on the trot.
Squish-valve to piston clearance???? valve timing??? ect ect all relevant to rpm....something is causing the failure and i would put money on it that its' the way the engine is set up (internaly)
BUT 'matthew' wont contact me...because he is still ! bringing me an engine that he arranged to bring 3 months ago

Rodger i wish i had brought it to you now the reason why i didnt was that a local bloke was takeing his to a tuner thats only 15mins from us and he said he would have it ready in time for the 1st race(was 2weeks at the time) thats the only reason i took it there,
would you be interested in doing it now??
cheers Matt

I have taken pics today but i dont no how to upload them onto this site