knocking detonation?

[tyler]

Hi i have a pretty quiet knock when i accelerate not at high speeds but just at like 1500 to about 2500rpms i thought it might be a rod knocking but when i retard the timing the knocking goes away so im wondering if its possibly detonation, and what helps get rid of it, thanks

95 accord lx
A/T 4cyl

Topic

[Lorrin Barth]

Detonation is an irregular noncontinuous clicking (sorta) sound the comes in spasms during acceleration or when hill climbing. The noise is different than any other sound I’ve heard an engine produce.

One solution is higher octane fuel. You already know about backing off the timing. Carbon can build up in the combustion chamber raising the compression ratio. High speed long distance driving will burn some of this off.

[Andrew]

I agree with barneyb; most likely cause of knocking in an old engine is carbon deposits. These can also result in ‘running on’, where the engine runs for a short while after you switch the key off. Try Eric’s video on decarbonising your engine with water.

[tyler]

i have the timing backed as far as i can (while still in spec), which is 13 btdc i heard if i advance the mechanical timing and retard the ignition timing it can help with detonation/spark knock, any suggestions has anyone tried this? Cos its completely gone when i retard the timing like 3 or 4 degrees. I took my head off a few months ago and cleaned all the carbon out of the Combustion chamber and everywhere else also.
thanks i appreciate any answers

[Andrew]

[quote=”the_tensl” post=111538] I took my head off a few months ago and cleaned all the carbon out of the Combustion chamber and everywhere else also. [/quote]

… that would rule out carbon, then!

Did the knocking start after the head job or did you do it because of the knocking? I ask because if the head was skimmed and the gasket renewed the piston protrusion above the block could have altered, changing the compression ratio.

Wrong spark plug heat ratings?

Burned exhaust valves?

Lean mixture or hot-running engine?

[tyler]

yeah im pretty sure it was knocking before the job but im not 100% but like i said when i retard the timing the knocking goes away (but then my cars out of time and really lags) thats why i was asking maybe advance the mechanical timing and retard the ignition timing?
got the ngk plugs it says to get under the hood
the exhaust valves are more worn but there still in decent shape
the engine seems to be running normal temp

[Andrew]

If your car’s worn and out of time then I suppose the notion of retarding the timing to maximum spec is irrelevant, as the specs presume sound mechanical timing. You could then either file back the distributor notch to get more adjustment or, as you said, advance the mechanical timing. However, I can’t see your car running well with the mechanical timing messed with.

I think the correct answer would be to get a timing belt kit and re-time the car before setting the ignition timing to just eliminate knock, and perhaps running on higher octane stuff. It’s hard to be any more specific than that without a good look over the whole engine’s mechanical health. Best of luck!

[tyler]

yeah i just heard someone suggested to advance the mech. timing, its a brand new timing belt kit everything seems to be in time and running fine i just cant stand that little knocking noise, it doesnt affect the driving at all, what about if you time it with the crankshaft on the exhaust instead of compression cycle could that make a difference? just trying to rule out as much as possible thanks

[Bill]

I forget if your car has an EGR valve but if it does make sure it’s working. It allows the recirculation of exhaust gases back into the intake charge to cool combustion. If it’s not working or the passages in the system and cylinder head are plugged it can cause the noise you explain.

[tyler]

Yeah i cleaned out the valve and the ports

[Bill]

Try adding some vacuum to the valve with the engine idling. It should stumble and possibly stall.

[tyler]

Ok will try it, What will this tell me?

[Bill]

It will tell you if the EGR valve is capable of doing it’s job. You would have to “T” into the vacuum line with a vacuum gauge to see if it’s being commanded on however.

[Author]

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