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Old 04-27-2013, 04:59 AM   #1
Johnny Locks OP
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Everything there is to know about Ping

OK, despite my post title, I don't have any answers. I have a lot of questions and I bet others here can help paint a good picture for a full understanding of the problem of pinging, which is what I need. My '92 R100GS seems to suffer from pinging. At least I think that's what it is. I noticed that earlier this spring when the temp was in the thirties it did not make this particular sound or vibration. When it's warmer I get it especially when I get to about mid-throttle trying to accelerate, especially around or under 4000 RPM. This bike is dual plugged, which I though was supposed to help reduce or eliminate pinging.

What I would like is to get a full understanding of what pinging actually IS. What exactly is the process that causes this phenomenon. The way I understand it now (which may or may not have any relation to fact) is that pinging is "pre-detonation" caused by the air-gar mixture igniting before it's optimal point. And that this is frequently caused by carbon build up that develops a hot spot so that during compression the air/gas charge will ignite before the spark plug fires. Is this basically correct? What else can cause pinging?

I think I saw somewhere that with dual plugs the timing advance should be different that single plug. That it should not be advanced as much. Is this correct? I have never set the timing on this bike, could my timing being off be causing my pinging?
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Old 04-27-2013, 06:28 AM   #2
DoktorT
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Quote:
Originally Posted by Johnny Locks View Post
I think I saw somewhere that with dual plugs the timing advance should be different that single plug. That it should not be advanced as much. Is this correct? I have never set the timing on this bike, could my timing being off be causing my pinging?
Go here: http://bmwmotorcycletech.info/index.html

Find the tech articles. You will find all info needed. Lots of info on the dual plug setup.

Yes, you need to retard spark at full advance around 3 dgrees for the dual plug setup. Other things that cause or add to ping. Gas octane too low. Use premium. Air leaks at collars between carbs and heads or throttle shafts or enricher gaskets. Carbon build up in combustion chamber.

Wrong jets/needles. That era was typically setup very lean, so a bit larger main and/or needles jets and/or needles may well be needed.

I had ping issues with my 79RS. Improved considerably by precise tuning. Set the timing retared 2 degrees and the mixture at higher spec limit. This is a single plug (stock) machine with 9.5cr.
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Old 04-27-2013, 06:36 AM   #3
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A R100GS shouldn't need premium with a CR of 8.5:1. You've got something wrong, either with timing, mixture, carbon build-up, or a combination of any of those. Clogged (or too lean) jets, overly advanced timing, crankcase breather blowing a bunch of oil into the intake and causing carbon build-up. All possibilities. My money's on your timing not being set correctly for dual plugs. Got a timing light?
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Old 04-27-2013, 07:22 AM   #4
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My 1977 R100/7 used to ping alot if I grabbed alot of throttle with the RPM's down in 4th and 5th gear, I figured that it was a result of having higher compression than later models.
I recently rebuilt my Bings and now it hardly pings at all.
I think it was pinging because I had a ripped diaphragm which made one cylinder do too much work.
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Old 04-27-2013, 08:16 AM   #5
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I'm with AW on this....check your timing. I'm dual plugged, on an R80, never run anything in the bike but regular and never have I ever pinged. I'm a 3 degrees retarded at full advance.
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Old 04-27-2013, 09:24 AM   #6
190e
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Ping and Pre-ignition

My understanding of Ping or detonation is that it is abnormal combustion that occurs after normal combustion has already been initiated by the spark. If the combustion pressure rises to early or too fast, spontaneous combustion occurs in some parts of the combustion chamber before the normal flame front has managed to get there. On an airhead detonation doesn’t sound anything like a bearing knock. The noise you hear is a pinging metallic resonance of the cylinder affected and it is characteristic of the noise that unlike a bearing knock it sounds to be at a faster frequency than the cylinder firing frequency. The reason for this is there can be more than one instance of detonation occurring in different parts of the combustion chamber on each cycle. Detonation can be destructive but it is not instantly destructive and an engine might run for a very long time with occasional periods of mild low speed detonation. Pinging can be useful as an indicator of optimum ignition timing. If an engine doesn’t ping under the gross provocation of high load and low RPM then the ignition timing may be too retarded. All modern mapped engines use knock sensors that detect the onset of detonation as a means of controlling ignition timing.

Ping should not be confused with Pre-Ignition which is abnormal combustion that occurs before the normal ignition spark. In fact it can be a long way before perhaps not that much past BDC. Pre-ignition is initiated by glowing carbon or a spark plug that is too hot. Because the mixture is ignited far too early it builds pressure for most of the compression stroke and so can be very destructive melting plugs and holing pistons quickly if not instantly. I don’t personally know or ever want to know what pre-ignition sounds like as I believe if you can hear it then it may be too late to save the engine.

To reduce or eliminate pinging you either need to retard the ignition or slow down the combustion process by using higher octane fuel or lower compression.

190e screwed with this post 04-27-2013 at 09:41 AM
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Old 04-27-2013, 09:55 AM   #7
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Regardless of what triggers the event, the pinging noise is the result of too much pressure within the combustion chamber before the piston has reached TDC.

Excess pressure is usually the result of mixture being ignited too soon.

Rich mixture burn slower than lean mixtures.

Mixture takes time to burn, this is why we have advance curves.

The more pressure the faster the burn, which in turn creates more pressure and speeds up the burn even more.

I know of five ways to reduce pinging in a Boxer motor.

1) retard the spark so the combustion process starts later.
2) richen up the mixture to cool everything in the combustion chamber down.
3)reduce the load on the motor by changing gears
4) longer duration camshafts that tend to allow more mixture to escape from the combustion chamber at low to midrange rpm's
5)lower compression ratio

If you have dual sparked heads the combustion process will be accelerated due to two starting points and will not require as much of a 'head start' (advance) to achieve optimal combustion as a single spark combustion chamber.
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Old 04-27-2013, 10:45 AM   #8
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http://en.wikipedia.org/wiki/Engine_knocking
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Old 04-27-2013, 11:17 AM   #9
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Good explanation 190e. Pinging can be caused by a lot of things. 9 out of 10 times in my experience working on airheads professionally, is ether timing and/or carb sync. Carb sync is a major influence. When one cylinder works harder, it is much more likely to ping. I would check those two things out first JL.

Twin plugs should be timed on the S mark at idle and around four degrees retarded at full advance. Most recommend 28 degrees full advanced and stock is 32. Although snobum has improved his dual plug timing article recently, it is still confusing and sometimes wrong at the same time.

190e, I just reread your post and I wanted to go over one thing: 'Slowing down the combustion process by using higher octane [rated] fuel." That statement is often understood as the slowing down the burn rate or flame front. For the most part, octane ratings do not change the speed of the flame front as it progresses from the spark plug. What it does is change what the unburned fuel IN FRONT of the flame front does. Higher octane rated fuel is a lot less likely to explode before it is consumed by the flame front. The combustion process at and behind the flame front goes on at ruffly the same speed regardless of octane rating.

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Old 04-27-2013, 11:47 AM   #10
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What about the squash band of our combustion chambers ?
Most of the airheads that changed the squash band can run much higher compression without the pinging and still use single plugged heads.
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Old 04-27-2013, 11:54 AM   #11
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What about the squash band of our combustion chambers ?
Most of the airheads that changed the squash band can run much higher compression without the pinging and still use single plugged heads.
That takes pistons and/or machine work. Besides, as I understand it, all this squish band buzz is about matching squish bands more than changing them. If people have found a magical squish band angle and edge other than actually matching the late model setup, what is it!
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Old 04-27-2013, 12:12 PM   #12
190e
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Quote:
Originally Posted by supershaft;21280388me.

190e, I just reread your post and I wanted to go over one thing: 'Slowing down the combustion process by using higher octane [rated] fuel." That statement is often understood as the slowing down the burn rate or flame front. For the most part, octane ratings do not change the speed of the flame front as it progresses from the spark plug. What it does is change what the unburned fuel IN FRONT of the flame front does. Higher octane rated fuel is a lot less likely to explode before it is consumed by the flame front. The combustion process at and behind the flame front goes on at ruffly the same speed regardless of octane rating.

Fair point supershaft. I guess I thought I knew the effect of octane but that's a better explanation that rings true.
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Old 04-27-2013, 12:15 PM   #13
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Originally Posted by supershaft View Post
That takes pistons and/or machine work. Besides, as I understand it, all this squish band buzz is about matching squish bands more than changing them. If people have found a magical squish band angle and edge other than actually matching the late model setup, what is it!

My bikes with the siebenrock power kits have a lot more problems with the pinging. And I do think its a squish band thing with the 1000 pistons made to fit into the 800 heads.
It will be one of the next things on my list of things to change
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Old 04-27-2013, 12:35 PM   #14
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My bikes with the siebenrock power kits have a lot more problems with the pinging. And I do think its a squish band thing with the 1000 pistons made to fit into the 800 heads.
It will be one of the next things on my list of things to change
I have always suspected that setup would ping. Most report no problems but I have seen that phenomenon play out countless times.

Supposedly Moorespeed's matching works. We know he isn't changing the head. It sure would be nice if someone buying the pistons would check how they match the head with some solder. Is the squish band constant from edge to edge? Does the squish decrease as it gets closer to center? How much? How does the piston match the radius at the end of the squish band?
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Old 04-27-2013, 12:47 PM   #15
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Quote:
Originally Posted by supershaft View Post
I have always suspected that setup would ping. Most report no problems but I have seen that phenomenon play out countless times.

Supposedly Moorespeed's matching works. We know he isn't changing the head. It sure would be nice if someone buying the pistons would check how they match the head with some solder. Is the squish band constant from edge to edge? Does the squish decrease as it gets closer to center? How much? How does the piston match the radius at the end of the squish band?
When I start on the heads I will try to make some detailed pictures. But it might take a while before I will take it apart.
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