Questions about engine detonation....

jan9898

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Apr 3, 2010
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What are some common causes of detonation?

Can detonation be caused from a failed fuel pump?

Can detonation be caused from a failed or failing carburetor?

Can detonation cause damage to the threaded part of a spark plug and the igniter?
 

Aloysius

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Re: Questions about engine detonation....

Detonation is the violent spontaneous explosion of the air/fuel charge, as opposed to a normal controlled burn. It results in extreme temperatures and pressures that melt pistons and plugs, and damage the lower end from the shock load. too much ignition advance or a lean condition under load causes it. Detonation can destroy an engine in seconds.

"Pinging", the audible noise often heard during low speed conditions, is NOT detonation.
 

ChrisCraftJohnny

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Re: Questions about engine detonation....

What are some common causes of detonation?

Can detonation be caused from a failed fuel pump?

Can detonation be caused from a failed or failing carburetor?

Can detonation cause damage to the threaded part of a spark plug and the igniter?

What are some common causes of detonation?

Poor octane rating of gas - Bad ignition timing - Bad plugs/ignition parts - Engine running too hot - Carbon build-up on piston head leading to over compressing air/fuel mixture


Can detonation be caused from a failed fuel pump?

Fuel starvation from a faulty pump does not point at detonation. Points more stalling and runability problems.


Can detonation be caused from a failed or failing carburetor
Same as above

Can detonation cause damage to the threaded part of a spark plug and the igniter?

YES

Hope this helps,

Johnny
 

86 century

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Re: Questions about engine detonation....

Any thing that can cause a cylinder to go lean can cause detonation. Also carbon build up will do a good job of it as well.

About the plugs if it is bad enough you will see damage.

The main cause of detonation is heat ever had an engine over heat and not shut down when you turn the key off.
 

Bondo

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Re: Questions about engine detonation....

What are some common causes of detonation?

Can detonation be caused from a failed fuel pump? Ayuh,... Absolutely...

Can detonation be caused from a failed or failing carburetor? Ayuh,... Sure can...
Can detonation cause damage to the threaded part of a spark plug and the igniter? Ayuh,.... Sure do...

A lean condition, for Whatever reason, is probably the #1 cause of detonation...
 

jan9898

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Messages
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Re: Questions about engine detonation....

Brand new not rebuilt engine 30 hours past the break-in time. 450 HP 454 Bravo One. Obviously not a stock engine.

From day one had carb. problems and the carb. was re-built.

Was running last saturday around 4,000 RPM and heard a noise like the engine was spuddering down and was losing RPM's and speed. Immediatley cut it off. Check the dipstick and it was 5" past the full line and the oil was thin, smelled like gas. I later turned the key to the second inginition position to check the gauges and the oil pressure did not move at all, ther was none.

Got towed in. The mechanic pulled the plugs today, plug on cyllinder 5 looked like it was seared off and was told there was also water in the oil pan.

Pulling the engine to investigate further. He thinks its from detonation. He's a good mechanic, good guy and I trust him but I have no warranty on this engine and in my head I'm watchin the $$$ sings roll. He is telling me it could have been from bad gas.

I just have a hard time beleiving that this motor that had all these extra beefy good parts, could be shot already from some low octane gas and detonation. We never heard any knocking or pinging in this engine.

Any thoughts or reccomendations are greatley appreciated. Put all my savings up for this motor, got no warranty and 4 months out of it.
 

Aloysius

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484
Re: Questions about engine detonation....

Fuel pump diaphragm failure. How else would that much fuel get in the oil?

The absolute, bottom line tell is 5" of extra oil level and "smells like gas".

Are you SURE this guy is a professional?
 

Evinrude Boater

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1,143
Re: Questions about engine detonation....

Is a lean pop really detonation. I had an alternator belt get chewed up in a rusty pulley and the rubber dust plugged the spark arrestor leading to a pop. I wonder if that's when I damaged my engine?
 

Aloysius

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Re: Questions about engine detonation....

You don't usually hear detonation...so, no, a "lean pop" isn't detonation. "Pinging" isn't detonation.
 

Don S

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Re: Questions about engine detonation....

Here is some information on Pre-Ignition and Detonation from a Mercruiser training manual.

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Alpheus

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Re: Questions about engine detonation....

Pulling the engine to investigate further. He thinks its from detonation. He's a good mechanic, good guy and I trust him but I have no warranty on this engine and in my head I'm watchin the $$$ sings roll. He is telling me it could have been from bad gas.

He may be a nice guy, but if this is what he actually said to you, he is not a good mechanic. Sounds like he was just throwing words and phrases at you that he hoped you wouldn't understand.

If water was in your oil, it would be a chocolate milkshake. Not thin and smells like gas.

You should get a second opinion. It couldn't hurt...
 

maxum_man

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Re: Questions about engine detonation....

I'm no professional, but looking at the above info...Fuel pump gave way and leaked into oil pan. Air/Fuel mixture was lean and caused detonation. Possible.
 

jan9898

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Messages
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Re: Questions about engine detonation....

MY ORIGINAL POST

Brand new not rebuilt engine 30 hours past the break-in time. 450 HP 454 Bravo One. Obviously not a stock engine.

From day one had carb. problems and the carb. was re-built.

Was running last saturday around 4,000 RPM and heard a noise like the engine was spuddering down and was losing RPM's and speed. Immediatley cut it off. Check the dipstick and it was 5" past the full line and the oil was thin, smelled like gas. I later turned the key to the second inginition position to check the gauges and the oil pressure did not move at all, ther was none.

Got towed in. The mechanic pulled the plugs today, plug on cyllinder 5 looked like it was seared off and was told there was also water in the oil pan.

Pulling the engine to investigate further. He thinks its from detonation. He's a good mechanic, good guy and I trust him but I have no warranty on this engine and in my head I'm watchin the $$$ sings roll. He is telling me it could have been from bad gas.

I just have a hard time beleiving that this motor that had all these extra beefy good parts, could be shot already from some low octane gas and detonation. We never heard any knocking or pinging in this engine.

Any thoughts or reccomendations are greatley appreciated. Put all my savings up for this motor, got no warranty and 4 months out of it.

MY FOLLOW-UP POST


Thanks for the resposnes everyone.

Consider this the follow-up, I made a visit to the mechanics shop today.

The engine was pulled and the exhast manifolds removed.

The first item I noticed was the valve in the #5 cylinder that was sheared off. This is of course the same cylinder that I first noticed the spark plug that looked like it was taken to a grinder.

I saw the top of the piston as well, it is hard to say whether it looks like one of the pistons in the picture from Don S's post. Although I saw things that may look like what is pictured, the piston was severley dimpled and beaten from something. If this is even possible, the valve was sheared where it tapers thin and the piston looked like this thing peice of the valve that was still attached was beating the top of the piston.

I checked the dipstick again during this visit and this time the oil looked like a milkshake and the level was still 5" over the full level. I noticed no water in the oil when the boat first broke down.

How can I tell if the fuel diaphragm went bad??

Could a fuel diaphragm going bad cause all of these problems, sheared spark plug broken, sheared valve, possibly a blown head gasket becasue now I see water in the oil?
 

jan9898

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Re: Questions about engine detonation....

I meant thin peice of the valve in my post.
 

Aloysius

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484
Re: Questions about engine detonation....

1) not a head gasket leak
2) detonation doesn't break valves
 

coheej

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Re: Questions about engine detonation....

With the head of the valve loose in the cylinder, you very well may have cracked the cylinder head or split the cylinder wall. This could be where water came in that did not show up earlier when you checked the oil. Unlikely, but it's also possible the valve failed. What were the spring pressures and quality of the valves. With 450 HP was this a roller lifter motor? There are a lot of things to look for when you tear it down, including the fuel smell in the oil.
 

JustJason

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5,319
Re: Questions about engine detonation....

jan9898 said:
I just have a hard time beleiving that this motor that had all these extra beefy good parts, could be shot already from some low octane gas and detonation. We never heard any knocking or pinging in this engine.

Well... believe it, now you have first hand proof of it. Im not saying you had detonation, but it certainly will destroy even the best, most expensive of parts.
You more than likely will not hear it knock, especially if it's high speed detonation.

aloysis said:
2) detonation doesn't break valves

Sure it does. Especially if the detonation is causing temps to rise, but your not holding it at wot. If your on and off the throttle, causing temps to go up and down... valves get brittle awefully fast.

Jan... any chance you can post pictures of your damage? I'd like to see the piston, the clyinder walls, the underside of the head (valve area and combustion chamber) and the spark plug.

If you had detonation, it will show up. Discoloring of 1 side of the piston or combustion chamber vs the other side (it's the exhaust side your looking for). Is the plug just broken or does it look like it melted? Color of the insulator?
How's the valve seat look, is it beat into the head? Where the heads new or used? Valves new or used. Where the valves fitted to the guides by a competent machinist or mechanic?
It's impossible to say without seeing the engine. You could have had detonation or pre-ignition. Especially if you ran the engine with a known carb problem.

You may have had a defective valve from the get to. Improper assembly and fitting. The engine may have injested something, a nut or bolt, especially if ran it without the flame arrester off. I've seen screws that come out of throttle blades on carbs because somebody thought it was a good idea to grind the peen over to pull the shafts and they throw the screws back in... they fall out that way.

Lot's of variables on this. Where'd you get the motor? Why no warranty? Long block or short block? Who put it together, installed it, test ran it?
 

jan9898

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Messages
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Re: Questions about engine detonation....

Thanks for the repsosnes, I'll get pictures and keep this updated..

For right now can anyone anwser this question---How can I tell if the fuel diaphragm went bad??
 

Aloysius

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Messages
484
Re: Questions about engine detonation....

Detonation doesn't cause valves to fail, especially if there's no other indicator. Are those 2 piece exhaust valves?

Let's look at temps. Exhaust temperatures are often 1200 degrees or more..I've seen exhausts glow red. However, aluminum melts at what..1300 degrees? It's highly unlikely that an exhaust valve got too hot if there's no piston crown damage.

UNLESS..with that many revs and stock springs, the valves may not be following the cam and/or seating properly. Failure to seat properly prevents the valve from rejecting heat to the seat, and cooling properly. Failure to follow the cam properly allows the valve to slam closed, further stressing the valve. Loose valve stem clearances also reduce heat transfer and allow the valve to strike the seat at an angle..I just broke a stuck exhaust valve yesterday by bending it slightly.

I'd suspect a simple case of too many revs with faulty valvetrain.
 

JustJason

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5,319
Re: Questions about engine detonation....

you can pull the pump apart and look at it. You can install the fuel pump on another engine and run part of a boat side system test written here...
http://forums.iboats.com/showthread.php?t=283269

You'd jump to the section of the pumps ability to create a vacuum.

Other than that, there's not much you can do.
 
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