Spark knock

[underpowered]

what are all the cause of Spark knock, detonation, pinging, pre-ignition or whatever you want to call it?

my bike, mods in sig, has developed spark knock over the last few months. it is not due to octane as i am using Klotz 113 race fuel. other causes other than lack of octane?

[SHADETREE101]

if you are real lean it could cause this, also head gasket leaking.

[underpowered]

jetting is spot on. hedgasket is not leaking, no oil showing at least.

[sixer3]

slight off-set in timing?..a tooth advanced?

[underpowered]

replaced teh timing chain a week ago. the pinging was one fo the reasons for doing it. it is in time, and it was doing it before with the old stretch chain, which was retarted(timing) if anything.

[GPracer2500]

I explained what detonation is in THIS THREAD (http://www.exriders.com/vbb/showthread.php?s=&threadid=227662). "Pinging" and "knocking" are descriptive labels for detonation stemming from the fact the detonation often sounds like a pinging or knocking sound. Pre-ignition is a separate phenemonon. You usually don't know that pre-ignition has happened until after the engine destroys itself.

I'm not sure what would cause detonation to start happening when it wasn't happening before. Carbon build up on the piston and valves could promote the occurence of detonation. The build up raises compression and can cause localized hot-spots in the combustion chamber. If you have a timing light it might be worth checking to be sure the ignition timing isn't abnormally advanced for some reason. The two "hash marks" on the flywheel (not the "T" or "F" mark) indicate where in the crank's rotation the spark should occur at full advance. Too much ignition advance will cause detonation.

[underpowered]

Originally posted by GPracer2500
......."Pinging" and "knocking" are descriptive labels for detonation stemming from the fact the detonation often sounds like a pinging or knocking sound. Pre-ignition is a separate phenemonon. You usually don't know that pre-ignition has happened until after the engine destroys itself.

I'm not sure what would cause detonation to start happening when it wasn't happening before. Carbon build up on the piston and valves could promote the occurence of detonation. The build up raises compression and can cause localized hot-spots in the combustion chamber......


well, i have pre-det and still dont know what is causing it. Carbon build up? not a chance since it did not start till after i installed a new cam, at the time i did so i cleaned the carbon off both the piston and the head. timing? not that either, as i said new cam chain and everything else check fine. nothing irregular in the electrical system or the valvetrain. the Pinging got slowly worse the more i rode it after i installed the new cam. teh first few days it was fine, then is slowly started doing it and now it is loud and does it anytime under a load. i am stumped:confused: . I guess i will tear it down next week just to see if tehre is anything internal i am not seeing from the outside.

[GPracer2500]

Originally posted by underpowered
....timing? not that either, as i said new cam chain and everything else check fine....

The timing I was talking about is the ignition timing, not the valve timing.

Maybe the new cam is yielding a different amount of compression--if the new cam has less valve overlap than the dynamic compression of the engine goes up. Maybe you didn't notice the knocking right away but now that you're focusing on it you're able to detect it more easily?? Just a thought.

BTW, pre-detonation is not a term. It's just detonation.

Good luck...hopefully there will be somthing obvious when you open it up.

[underpowered]

yes, i know what you meant about the timing. like i said, all electronics check fine, it sparks when it should. and compression should not matter, as i am running 113 klotz race fuel. i should be able to run much higher compression than i already am. it is only 11:1, so race fuel should not be needed at all.

ANd where i come from, Pre-det is when the air/fuel mixture combust before it is supposed to. in your thread you state "Detonation ALWAYS occurs after the spark plug fires" well Pre-det is causing my Pinging, or so i thought. my motor is for some reason combusting the fuel mixture before it is supposed to.