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Detnoation Problems
What exactly causes detonation? If detonation is sufficent to cause rod bearings to fail with just minimal run time on motor, will there alsways be signs left on the pistons?
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Re: Detnoation Problems
don't know how to explain exactly the cause (bad gas, bad timing), but I had melted sparkplugs, or also the ceramic part of the spark plug coming out of it's base, leaving the piston to throw the compression out of the engine with a funny noise with it, also had melted valves, with holes in the valves (compression = 0) and broken/melted pistons. the top rings were also kind of spotted. things that make you go, umhhh...
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Re: Detnoation Problems
Dean, I don't know who you are but the next time i'm up there I have to shake your hand. You've got worse luck with boats than I do, just ask Hoghead!
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Re: Detnoation Problems
Originally Posted by kennyo
Dean, I don't know who you are but the next time i'm up there I have to shake your hand. You've got worse luck with boats than I do, just ask Hoghead!
This is how bad it is... My wife is encouraging me to get a harley so I will quit obsesing over this boat...... :( Think about it........ :mad: So anyway, I am getting ready to order one..... :D One of the boat shop owners this weekend told me "Man, you know WAY to much about this stuff to be a CPA"..... I told him the education was not cheap.... |
Re: Detnoation Problems
Originally Posted by jeff32
don't know how to explain exactly the cause (bad gas, bad timing), but I had melted sparkplugs, or also the ceramic part of the spark plug coming out of it's base, leaving the piston to throw the compression out of the engine with a funny noise with it, also had melted valves, with holes in the valves (compression = 0) and broken/melted pistons. the top rings were also kind of spotted. things that make you go, umhhh...
I sent a motor back to the place I got it from, it lasted about an hour, rod bearings on #5 and 6 destroyed. Pistons show no sign of detonation, but the shop says it has to be detonation, otherwise the bearings would not come apart. They have not gotten the motor back yet, but I can see where this is headed, and I need enough ammo to re-direct if the conversation needs it. So far the place I got the motors has been straight, but they have not had to send a new motor yet either......... :rolleyes: |
Re: Detnoation Problems
Some quotes:
Detonation (also called "spark knock") is an erratic form of combustion that can cause head gasket failure as well as other engine damage. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading. Detonation can be caused by: Lean fuel mixture Fuel octane too low Improper ignition timing Lugging Carbon deposits Excessive milling of heads or block, which will increase compression ratio. Pre-ignition, as the term suggests, is the ignition of the fuel-air mixture before the regular ignition spark from the spark plug. If the regular spark occurs shortly after the pre-ignition, the colliding of the two flame fronts will cause a pinging noise. Preignition causes loss of engine power and can cause severe damage to pistons, rings and valves. Detonation and pre-ignition are so closely related that it is en difficult to distinguish one from the other by sound. Each can lead to the other and either condition can cause extensive engine damage. |
Re: Detnoation Problems
Forgot to add:
Pre-ignition can be caused by: Carbon deposits that remain incandescent Spark plugs too hot a heat range Spark plugs not firmly seated against gasket Detonation or the condition leading to it Sharp edges in combustion chamber Valves operating at higher than normal temperature because of excessive guide clearance or improper seal with valve seats. Overheating Ignition crossfiring. Induced voltage in spark plug wires that run parallel to each other for long distances |
Re: Detnoation Problems
Detonation severe enough to quickly damage rod bearings would also do serious damage to pistons and valves. It also is not likely isolated to two cylinders (unless fuel injected). Since 5 and 6 share a journal on the crank the failure of even 1 half of a bearing set can blitz all 4 halves on 2 rods.
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Re: Detnoation Problems
Could it be the crank on that jurnal be bad?[big] to tight? etc. I would think if it detinated enough to get the rod bearing that it would show up in the spark plug first. Also the rod could be on the small side ,ck it with a AG gage.
I know on my nitrous motors it takes out the plug first :( |
Re: Detnoation Problems
That is what I thought, so thanks for confirming that, now I do not feel like I am loosing it or something........
plugs, pistons, and head gasket all look good......... I kept thinking something of the magnatude to destroy rod bearings by compressing them would most assuradely show up somewhere else too.... I hope the conversation with the motor guy goes well tomorrow.... |
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