SFCK problem found, not rectified yet.

Ok im breaking my golden rule about not talking on the technical board, but i will throw my 2 cents worth in. 

My 3c is in a fairly high state of tune, fancy ross pistons high compression 10.5:1.  Biggest valves we could fit black diamond, ported to within an inch of its life, port angles changed, keihin cv carbs set up after a LOT of trial and error.  Cams are genuine axtell, b8es plugs, goes like a cut snake even dragging my fat arse around.  John Wilson spent a huge amount of time setting up the ignition, had my bike at his place for months.  First time i took it on a snowy rally, i got detonation, not pinking, but detonation.  Scared the crap out of me, not a hot day, not caning it, but just this huge rattle just as chris descibes.  Took some advance out of the ignition, problem solved.  Go to the next ignition just recently as the 18 year old Wilson ignition finally died.  The new ignitech supplied by Red is a very fancy bit of kit.  Red spent a hell of a lot of development time setting up the curve, and I thank you heaps Red.  However, first time out on a run, detonation again!  Took 3 degrees out of the curve and presto, we are back!  Thing is a weapon. 

Setting up the ignitech on the 6 plug racer was interesting, total guess work as the advance curve had to be made from scratch.  Will and I copied a twin plug curve from the sasche box and it went ok, no detonation, but pinging on my test hill.  Took 2 degrees out of the curve above 3500 and presto, bella machina!  I rode it and the torque is impressive.  Today was the first time Will had ridden it, did steering head bearings, wheel bearings and modified front suspension, and today we did wisemans ferry, mangrove mountain, laguna for brekky.  Will is as impressed as I am, the increase in torque is quite noticable, Vince you need to ride it again, it steers now! 

Anyway, my 2 cents worth, sorry for sticking my head in.

Marty
 
That roads a great suspension tester, how was the fork. If it steers well and doesn't deflect on the bomb holes out there its gota be good. You brave soul venturing into the tech crap. I wonder how similar your advance curve is to mine, done by some local bloke who we know. BTW 2 tapered bearings or the bottom one tapered and the top not tapered?
 
Tapered on the bottom ball bearing on top.  Will hit a big pothole under hard braking, full movement of the fork all good.my new thing just did everything superbly, how boring is that.  1999 suzuki gsf1200.  No chalenge at all, however it had been dyno tuned by motorcycle weaponry, mine used 4 litres more than rosses same bike on the same run.  Must have some big holes in the carbys.....
 
  Chris            and to Vince ,  Dave Ward  Moto Italia . Emu Plains ...quality technician Ducati Belt and Bevels and Aprilias.. was a go to person for Pantahs, told you about him at fest of speed .    but he has been slowing up, business was for sale ,  got rid of all his pantah stuff and racebikes .
 

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redax5 said:
try a set of B9ES plugs first, that is easy, should make the engine run slightly cooler and is what we changed to on the race engines
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So what plugs are you running now?? I have never run anything warmer than a B9ES in my SF, from when it was stock (originally std Bosch 260 T2) to when became virtually an SFC motor, running a measured (buretted) 10.25:1.  And I've never fouled a plug. If it's running B8s I'd be scared, quite frankly. SFs do NOT like warm plugs,

Hate to say it, but rather you than me trying to set up Dells for a motor like yours, Chris.

As for the noise, I'd certainly be playing with the ignition curve. Marty's experience shows how critical it can be.

I should also mention that I pulled my motor down because it developed a knock and I suspected either cam flanges or big ends. It turned out to be the toothed belt pulley I'd adapted to the original flange on the ND alternator I run.  :-\ :-\ :-\ End bolt had come loose and was allowing a tiny bit of backlash in the keyway!!! Funny how sometimes we suspect/expect the worst.

Red, do you know what the clearance swish to head at TDC is on Chris's motor?
 
try a set of B9ES plugs first, that is easy, should make the engine run slightly cooler and is what we changed to on the race engines

o
Click to expand...

  Hi Chris - The std SF's are  listed as running on N2 champions - the B9ES is the equivalent - apart from running around town etc - B8's are too risky IMHO. Used to run my Sf with 11.2:1 (true) comp and use B9EV - have used B10's in the past when Dynoing to avoid "plug fade" - not a common thing on todays accelerometer type dynos though.
  Just to change tack - a constant metallic noise is not that unusual on an SF between 3000-4000 RPM - hard to track down - can just be a cam chain resonance thing or even the rockers with too much end float on them. Plenty of owners have stripped motors down to find nothing obvious. - just my take - best of luck - Phil
 
I agree that mechanical sounds are easily misdiagnosed as engine when they are anything from a cracked numberplate to a bloody mirror or exhaust baffle.
However Chris has mentioned that the squishband on the piston has an odd texture, with an engineer mentioning "predetonation" evidence, which sounds like the detonation you have when you aren?t having detonation (sorry, a Claytons joke). To me either you either have or don?t have detonation, and if his sound is in fact detonation, then from my experience the simplest and least risky course is to retard the ignition a tad, so easily done with an Ignitech. Eh Marty. Fitting knock sensors and TPSs is great if you have a head full of knowledge and experience, otherwise you introduce a load of variables to navigate your way through. Modern carbs (like FCR) have mixture compensation for low throttle high rev (and full throttle low load), it could also be that your mixture is a scrap lean at high rev for small throttle openings. As Dells don?t have this facility, I?d be trying ignition advance. Your B8 plugs could be risky when you really use it hard but shouldn?t be a cause of detonation from my experience anyway.
 
To my understanding, detonation, or pre-detonation if you like, is an un-controlled combustion occurring before the incoming fuel charge is actually ignited by the sparkplug.  Heat and compression are enough to ignite the charge.  With the CR at 9.5:1, which is far from being OTT, it would seem to  be solely a heat-related issue.

It may be caused by glowing carbon build-up on piston crown, valves or combustion chamber, but this can be ruled out as Chris' engine is freshly put together.  Another possibility would be a glowing sparkplug tip, caused by incorrect heat range and thus acting like a glowplug as in a diesel engine.  First step would be to fit a colder plug and use higher octane fuel, if only to rule out the possibility of pinking.  I'd then look into enrichening the fuel delivery at the particular point where the detonation occurs (needle choice, slide cut-out maybe).

What I don't understand, is that such a condition should occur while trundling along at constant rpm without a great load, I'd expect it to happen when the engine is under load.  Without load, internal combustion engines aren't very fickle regarding fueling or ignition timing, it's when they're loaded and real heat and power is produced that all parametres need to be up to scratch.

piet
 
sfcpiet said:
[...]
What I don't understand, is that such a condition should occur while trundling along at constant rpm without a great load, I'd expect it to happen when the engine is under load.  [...]
Click to expand...

Not an uncommon thing on highly tuned 2-strokes with expansion chamber exhausts, Piet. On 4-strokes I had it once during my past days on the Alfa Romeo 2 litre DOHC. With the two double Webers well in tune, ignition spot-on as well, all fine under hard accleration and thottle wide open, but nasty detonations showed up when trundling along the highway at 120 kph, with the throttle barely opened. The notorious rubber flanges bolted between carbs and head  had developed cracks, and only at low throttle/high vacuum conditions reasonable amounts of air have been sucked through the cracks, leaning out the mixture, in consequence excessive combustion temperature and shortly after detonations. Replaced the rubbber flanges, problem gone.
 
martymoose said:
Ok im breaking my golden rule about not talking on the technical board, but i will throw my 2 cents worth in. 

My 3c is in a fairly high state of tune, fancy ross pistons high compression 10.5:1.  Biggest valves we could fit black diamond, ported to within an inch of its life, port angles changed, keihin cv carbs set up after a LOT of trial and error.  Cams are genuine axtell, b8es plugs, goes like a cut snake even dragging my fat arse around.  John Wilson spent a huge amount of time setting up the ignition, had my bike at his place for months.  First time i took it on a snowy rally, i got detonation, not pinking, but detonation.  Scared the crap out of me, not a hot day, not caning it, but just this huge rattle just as chris descibes.  Took some advance out of the ignition, problem solved.  Go to the next ignition just recently as the 18 year old Wilson ignition finally died.  The new ignitech supplied by Red is a very fancy bit of kit.  Red spent a hell of a lot of development time setting up the curve, and I thank you heaps Red.  However, first time out on a run, detonation again!  Took 3 degrees out of the curve and presto, we are back!  Thing is a weapon. 

Setting up the ignitech on the 6 plug racer was interesting, total guess work as the advance curve had to be made from scratch.  Will and I copied a twin plug curve from the sasche box and it went ok, no detonation, but pinging on my test hill.  Took 2 degrees out of the curve above 3500 and presto, bella machina!  I rode it and the torque is impressive.  Today was the first time Will had ridden it, did steering head bearings, wheel bearings and modified front suspension, and today we did wisemans ferry, mangrove mountain, laguna for brekky.  Will is as impressed as I am, the increase in torque is quite noticable, Vince you need to ride it again, it steers now! 

Anyway, my 2 cents worth, sorry for sticking my head in.

Marty
Click to expand...
 
martymoose said:
Ok im breaking my golden rule about not talking on the technical board, but i will throw my 2 cents worth in. 

My 3c is in a fairly high state of tune, fancy ross pistons high compression 10.5:1.  Biggest valves we could fit black diamond, ported to within an inch of its life, port angles changed, keihin cv carbs set up after a LOT of trial and error.  Cams are genuine axtell, b8es plugs, goes like a cut snake even dragging my fat arse around.  John Wilson spent a huge amount of time setting up the ignition, had my bike at his place for months.  First time i took it on a snowy rally, i got detonation, not pinking, but detonation.  Scared the crap out of me, not a hot day, not caning it, but just this huge rattle just as chris descibes.  Took some advance out of the ignition, problem solved.  Go to the next ignition just recently as the 18 year old Wilson ignition finally died.  The new ignitech supplied by Red is a very fancy bit of kit.  Red spent a hell of a lot of development time setting up the curve, and I thank you heaps Red.  However, first time out on a run, detonation again!  Took 3 degrees out of the curve and presto, we are back!  Thing is a weapon. 

Setting up the ignitech on the 6 plug racer was interesting, total guess work as the advance curve had to be made from scratch.  Will and I copied a twin plug curve from the sasche box and it went ok, no detonation, but pinging on my test hill.  Took 2 degrees out of the curve above 3500 and presto, bella machina!  I rode it and the torque is impressive.

Anyway, my 2 cents worth, sorry for sticking my head in.

Marty
Click to expand...

Don?t be sorry Marty, this is exactly the information I was looking for.

It?s all well and good to hypothesise, people throwing in theories and suggestions.

But your seat of the pants experience, same type of pistons and ignition, with the note, ? huge rattle just as Chris describes? nails it.

It?s one of the great things about this forum, there is so much experience here, the fact that you experienced the same thing and found the fix is so much easier than chasing our tails ?for ever and a day? until it is found. And, in the meantime fearing implosion every time it is taken out.

You guys may have noticed, after finding the intermittent misfire, I wrote on that thread that I rode it home above 4,500rpm, pulled a wheelie etc. The reason being was to keep it out of the clatter zone, something I didn?t want common knowledge at that stage.

Red recently said that some of his best fixes, have been from customer experience and feedback. This indeed is the same scenario.

Thanks to all who have had input, and I suppose, I?ll have to buy Marty a beer or two.

Let?s hope this helps someone else who experiences the same issue.

More power to the forum.



 
Gravelroad said:
Not an uncommon thing on highly tuned 2-strokes with expansion chamber exhausts, Piet. On 4-strokes I had it once during my past days on the Alfa Romeo 2 litre DOHC. With the two double Webers well in tune, ignition spot-on as well, all fine under hard accleration and thottle wide open, but nasty detonations showed up when trundling along the highway at 120 kph, with the throttle barely opened. The notorious rubber flanges bolted between carbs and head  had developed cracks, and only at low throttle/high vacuum conditions reasonable amounts of air have been sucked through the cracks, leaning out the mixture, in consequence excessive combustion temperature and shortly after detonations. Replaced the rubbber flanges, problem gone.
Click to expand...

Yes Stefan,

This can happen when something is amiss.  But Chris' motor has just been put together, probably rather meticulously I would imagine, so faults such as an air leak could safely be ruled out.  At least it wouldn't occur to me within this scenario.

Those stupid Alfa intake stubs have ruined quite a lot of nice motors.

piet
 
Seems to me that there's some confusion as to what causes pinging. I would be wary of taking advice from anyone using the term "predetonation". They're mixing up the terms "pre-ignition" and "detonation" to come up with a word that's at best ambiguous, and at worst, shows a level of ignorance about what's going on. (BTW, I'm not including Piet in that indictment. He was simply quoting an earlier use of the term).

Pre-ignition and detonation are different things. Here's a very basic explanation of the terms as I understand them.

Detonation (AKA knocking or pinging) always happens after the spark plug fires. It is an uncontrolled secondary ignition of the fuel mixture away from the normal flame front that radiates out from the spark plug. So you get two (or more) flame fronts, which causes pressure in the combustion chamber to rise much more rapidly than with normal flame propogation. When the spark ignites the mixture, the pressure in the combustion chamber starts to increase at a predictable rate as the flame front progresses. The pressure builds to a maximum at around 14? ATDC when the piston is beginning its power stroke. But under some conditions, the rise in pressure and temperature as the mixture burns can cause a pocket of unburnt mixture ahead of the flame front to spontaneously combust as in a Diesel engine. When that happens, the pressure in the combustion chamber rises very suddenly and way too early. It's this sharp increase in pressure that causes the pinging or knocking noise.

How does retarding the ignition fix it? In simple terms, retarding the ignition delays the point of maximum pressure until the piston is further down the cylinder on the power stroke, which reduces the peak pressure enough to stop the detonation.

Detonation is more likely to happen with a lean air fuel mixture, so tweaking the carbs to give a richer mixture can also fix the problem.

Pre-ignition, as the name implies, is ignition of the fuel mixture before the spark plug fires. It can happen any time from when the fresh fuel mixture enters the engine until the spark plug fires.  It's usually caused by a hot spot somewhere, like a glowing spark plug electrode or carbon deposits. It's damaging to the engine because you get gas pressure build up while the piston is still on the compression stroke, producing massive reverse torque forces. But there's no sudden pressure spike so it doesn't normally produce a pinging sound. No amount of tweaking the ignition timing will fix pre-ignition, unless the pre-ignition is actually caused by the spark itself being badly mis-timed.

"Pre-detonation" is not a thing. It's just a confusing word.


 
I had the later at one point, its also called a silent engine killer, no pinging with that just melted piston. You might find salt and pepper deposits on the end of a spark plug if you are lucky and see it before the engine dies, that's bits of melted piston flying about. Mine was a badly blended valve seat, the end of which acted as a glow plug setting the mix off at the wrong time. That was fixed by Reds brilliant welder mate.
 
Dellortoman said:
Seems to me that there's some confusion as to what causes pinging. I would be wary of taking advice from anyone using the term "predetonation". They're mixing up the terms "pre-ignition" and "detonation" to come up with a word that's at best ambiguous, and at worst, shows a level of ignorance about what's going on. (BTW, I'm not including Piet in that indictment. He was simply quoting an earlier use of the term).

Pre-ignition and detonation are different things. Here's a very basic explanation of the terms as I understand them.

Detonation (AKA knocking or pinging) always happens after the spark plug fires. It is an uncontrolled secondary ignition of the fuel mixture away from the normal flame front that radiates out from the spark plug. So you get two (or more) flame fronts, which causes pressure in the combustion chamber to rise much more rapidly than with normal flame propogation. When the spark ignites the mixture, the pressure in the combustion chamber starts to increase at a predictable rate as the flame front progresses. The pressure builds to a maximum at around 14? ATDC when the piston is beginning its power stroke. But under some conditions, the rise in pressure and temperature as the mixture burns can cause a pocket of unburnt mixture ahead of the flame front to spontaneously combust as in a Diesel engine. When that happens, the pressure in the combustion chamber rises very suddenly and way too early. It's this sharp increase in pressure that causes the pinging or knocking noise.

How does retarding the ignition fix it? In simple terms, retarding the ignition delays the point of maximum pressure until the piston is further down the cylinder on the power stroke, which reduces the peak pressure enough to stop the detonation.

Detonation is more likely to happen with a lean air fuel mixture, so tweaking the carbs to give a richer mixture can also fix the problem.

Pre-ignition, as the name implies, is ignition of the fuel mixture before the spark plug fires. It can happen any time from when the fresh fuel mixture enters the engine until the spark plug fires.  It's usually caused by a hot spot somewhere, like a glowing spark plug electrode or carbon deposits. It's damaging to the engine because you get gas pressure build up while the piston is still on the compression stroke, producing massive reverse torque forces. But there's no sudden pressure spike so it doesn't normally produce a pinging sound. No amount of tweaking the ignition timing will fix pre-ignition, unless the pre-ignition is actually caused by the spark itself being badly mis-timed.

"Pre-detonation" is not a thing. It's just a confusing word.
Click to expand...

Ooops, sorry, that was my fault, in my first post, my race car guy said "detonation" my terminology was pre-detonation, as I hadn't ever heard the term "detonation" ie. post ignition explosion before. 
 
And of course tell us if any changes rectify the problemo! You're right, Chris. It's Marty's hands-on that offers the best indicator for finding the fault and fixing it. Also interesting in all this is that you've always found your motor to be very rough/vibratey around those revs, even with your first set of pistones, which ultimately nipped up (probably for different reasons, but the roughness carries over to the new slugs - assuming same ignition curve?).

Classic pre-ignition is that thing that happens on old car engines where you turn the key to ;off' and the thing decides to keep running for an indeterminate amount of time!
 
Piranha Brother 2 said:
You're right, Chris. It's Marty's hands-on that offers the best indicator for finding the fault and fixing it.
Click to expand...

Agreed, but here's another spanner in the works I just remembered.
This first appeared on the Levo run, but not on Snowy run earlier, nothing was changed from one run to another ???

Levo and Brett will remember, in Gloucester I said I could hear a clatter every now and then, and wondered if it was the cam chain.
The only difference was the hot weather on the Levo run.
 
1.  lift the needle a notch or change the taper. Should be working on the needle jet when coasting at speed.

2.  cooler plug.
 
sfcpiet said:
What I don't understand, is that such a condition should occur while trundling along at constant rpm without a great load, I'd expect it to happen when the engine is under load.  Without load, internal combustion engines aren't very fickle regarding fueling or ignition timing, it's when they're loaded and real heat and power is produced that all parametres need to be up to scratch.

piet
Click to expand...

Maybe because of slow  flame speed, the end-gas is heated long enough to detonate, despite of the low initial pressure.
Happens to some V11 Guzzis at 4500-5000 RPM, part throttle, even with premium gas.
The solution is either to fit some high(er) compression pistons which better match the combustion chamber, creating a squish band or cut the advance a bit.

Angelo
 
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