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Detecting Spark Knock/Pinging


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I read Rob Siegel’s column in a recent issue of the Hagerty Driver’s Club magazine responding to someone writing in about their MG TD. An interesting point that Rob made was that with lower compression engines, detonation can’t always be heard. He suggested that feeling vibrations through the shifter can be a better indication of detonation than listening to the engine. I pulled a couple degrees of timing out and lo and behold, my shifter stopped acting like it had too much coffee. 

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17 minutes ago, paulyg said:

I pulled a couple degrees of timing out and lo and behold, my shifter stopped acting like it had too much coffee. 


At which rpm were you feeling the vibration?

How much total advance do you have now?
How much does that leave at idle?

Do you see any evidence of pre ignition on your spark plugs?

   

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Detonation (or "pinging") can be caused by too low octane and/or too much spark advance (or the combination of both), and is especially noticeable when the engine is under load at low rpm--like trying to climb a hill in too high a gear.  It's always sounded to me like small pebbles in a coffee can--a tinny rattle.  

 

It does not do your engine any good!

 

Most new(er) cars have knock sensors that will retard the spark to prevent detonation--although E30s don't, and I have listen carefully to my M42 motor and not lug it like I can my '02.  M42s do not like to be lugged and will ping insistently until you downshift.

 

mike

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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I have a 123 distributor that was matched to a stock curve. I was running 35 degrees mechanical advance and using the vacuum advance feature as well, 36 degrees total timing with WOT. Back to about 33-34 now. Advance is 18 degrees at idle- this is including 8 degrees of vacuum advance. 

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23 minutes ago, paulyg said:

Back to about 33-34 now. Advance is 18 degrees at idle- this is including 8 degrees of vacuum advance. 

 

So you took 1-2 degrees off the top and left the rest of the curve the same?

You were feeling the vibration at full advance?

 

18 at idle is quite a bit.  How many degrees between 2-3K rpm?  That's where mine tends to ping.

   

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42 minutes ago, paulyg said:

Advance is 18 degrees at idle- this is including 8 degrees of vacuum advance. 

So, your vacuum advance is connected to manifold vacuum ... not ported. 

This is how it should be with a vac advance dizzy.

This works best on my car...so critics be damned! 😁 

 

 

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1 hour ago, paulyg said:

IMG_4942.thumb.jpeg.a8d33cf10d5cd6141547b737fdf67ca1.jpeg

The visibility of the ground strap is not the best, but the strap should show a color change in the bend with proper timing.

 

From the plug reading information I have, 

 

"Too much timing and the color change will be very close to the threaded body of the plug, too little and it'll be closer to the tip.  Ideally we want it right in the apex or center of the 90 bend on the ground strap. "

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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On 3/2/2024 at 1:50 PM, John76 said:

So, your vacuum advance is connected to manifold vacuum ... not ported. 

This is how it should be with a vac advance dizzy.

This works best on my car...so critics be damned! 😁 

 

 

That is interesting, I use ported vacuum as that is how the manual shows it is connected and I have it that way on both my NK and e9.

Edited by HBChris

HBChris

`73 3.0CS Chamonix, `69 2000 NK Atlantik

`70 2800 Polaris, `79 528i Chamonix

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Either way works if the proper curve for each method is used.

  • Like 2

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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That.^

 

It totally depends on what the distributor wants to see.

 

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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