Detonation Pre-Ignition

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Original Submission by T August 30th 2006;

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Blue 3.3 6 Cyl CF Bedford Engine. Note the white centre electrode which is normal for HEI in a properly tuned, maintained and operated red/blue/black 6 cylinder Holden Engine. The Engine that runs clean is much less likely to detonate. Photo by reppilF. Click to Enlargen.
 

Detonation and Pre-Ignition:


Pinging:

Blue 3.3 6 Cyl CF Bedford Engine. Petrol buring Engines can run equally clean if they are operated correctly. Photo by reppilF. Click to Enlargen.
  Pinging is a term that describes Detonation, Pre-Ignition, Excessive Advance or any combination of the three.
Carbon buildup will contribute heavily to Detonation and Pre-Ignition. Fixing the state of tune and using correct operating procedures are equally as important as setting the timing and maximum Spark Advance. See the PCV Page for the cause of carbon on this Engine. Click to Enlargen. Photo by Lovemyholden.

Detonation:

When the ignition occurs at the correct time but burns the mixture burns too rapidly.

Pre-Ignition:

Pre-ignition is when combustion is initiated prior to the spark occurring.

Excessive Advance:

The spark occurs earlier than the manufacturer's specification.

Causes of Detonation and Pre-Ignition:

One big factor in detonation and pre-ignition is combustion chamber deposits.
These are most easily formed when an engine has weak ignition, insufficient spark advance
and the engine doesn't see enough load.
Glowing deposits are the usual cause of the trouble and the trouble is
often mitigated by proper use of the engine in addition to having
any weak ignition or inappropriate spark setting cured. Proper use
would be cruise power for a sustained period.Faulty TVS causes pinging 

Combustion Chamber Deposits and Pinging:

An excerpt from LMH's PCV page submission.
Submitted by Lovemyholden on Fri, 23/12/2005 - 02:32.
... Or so I thought! Over several thousand K's I noticed my car started to ping under load. Strange, I checked timing, all ok! After a while it got so bad couldn't even do 100KPH without severe pinging. No alternative, take the head off and inspect combustion chambers. I found large sheets of thick carbon flaking off the pistons. I couldn't believe it. Motor is in good shape, good rings, guides etc, why is it burning so much oil.
End of LMH's PCV Page submission.See the PCV page for full details.

Clearing Combustion Chamber Deposits:

If the above items are properly set then combustion chamber deposits
will diminish and so will detonation and pre-ignition.
Light loads with weak ignition and poor advance also causes
the piston ring grooves to fill up with carbon. The piston rings
will then no longer gas pressurise.
A Piston that succumbed to excessive Pre-Ignition. Click to Enlargen. Photo by HPEngines.

Links:

HPEngines Shed

Terms:

Terms


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