What exactly does detonation or pre-ignition sound like?

[GGRider01]

I'm wondering if anyone's got a video of a bike detonating or pre-igniting. Can't find one on youtube.

Ever since I've had the 300, before I ever rebuilt it or changed the jetting, it has always had a low grumble or what I would call a sputter at low throttle openings.. but I've always been paranoid that is it the "marbles in engine" sound everyone describes when talking about detonation. I'm running 91 octane (highest available at pump, roughly 98 octane RON)/non-ethanol fuel. Never done a squish test and no idea what compression ratio the engine is running at.

Hopefully I'm just being paranoid, but would rather be safe than sorry. It is always at sustained throttle openings, except WOT.

 

[Rick]

Run some plug chops, your plug will tell the story.

I think there a "sticky" on measuring the squish.... based upon history that test should be the first thing any GasGas owner
should perform.

 

[barossi73]

Hmm hard to describe.sometimes referred to as pinking,as in rapid metallic pink,pink,pink.most noticeable when throttle cracked open suddenly from low revs.often followed by much worse metallic,destructive sounds,swearing,and empty bank account

 

[Capz85]

This is my current problem, sounds like a rattle ing around half throttle under load very noticeable

I've ruined a piston and cylinder and it's still happening l, so I can relate to the swearing and empty bank account

 

[RBrider]

This is my current problem, sounds like a rattle ing around half throttle under load very noticeable

I've ruined a piston and cylinder and it's still happening l, so I can relate to the swearing and empty bank account

Try raising the needle one notch (IE: lower the clip one notch) Doesn't cost anything and it can't hurt . It will richen up the mid throttle jetting.

RB

 

[Capz85]

Yes I richend the carb and will run 2 0.5 base gaskets this time, hopefully it will improve

 

[gasgasman]

The chain hitting the subframe can sound like detonation.

 

[GGRider01]

Hmm hard to describe.sometimes referred to as pinking,as in rapid metallic pink,pink,pink.most noticeable when throttle cracked open suddenly from low revs.often followed by much worse metallic,destructive sounds,swearing,and empty bank account

Well, rapid acceleration it sounds tits on. It could just be intermittent four-stroking which is prevalent, but not impossible to get rid of, with sustained partially opened throttle. I found a post floating around on the internet from Jakobi (he's everywhere) that suggests looking at the plug under a magnifying glass - metallic specks indicate detonation. Will have to take the tank off and check it out. Got my spark plug wrench in the mail but the freaking clip on the right radiator hose is too close to the plug to allow it to slip on - will have to slide it a bit.

 

[Jakobi]

Spark plug, piston, rings.. they'll all show signs of detonation if it has been occurring.

But as others have said.. there are a million noises coming from these machines at various throttle positions (on and off throttle). Chain slap can happen under load at lower rpms. Pipe can vibe against the spigots if the o-rings start to go. Plastics can vibe against the body if they have some slop in them. One of my rad braces on a particular bike would jiggle and dance at certain rpm - metalic sound to the max. The powervalve assembly has a certain amount of free play in it to allow it to operate as the carbon builds up on it. Some have had the PV arm vibe where it clears the cylinder. Others down deeper against the cases.

You can try to isolate certain things to see if they only happen under load, under decel, in gear, stationary. Apply pressure to particular areas (ie the pipe/plastics). Visually inspect. Probe, etc.. but generally I live with the bulk of the sounds.

Capz situation is different in that they have experienced cylinder coating failure and then rapid wear again since.

 

[motopsycho87]

From my experience of not cutting the head enough after doing my squish, revs hit a brick wall. The bike just sounded rich as hell, nothing really audible to be honest. The easiest way you can tell is take the head off and look for little bits missing from the head or piston. Or look through the exhaust or plug hole. It's a lot easier to tell pre ignition on a 4 stroke!