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Thread: Abarth 500 Cylinder head failure!

  1. #11
    Senior Member aelfwyne's Avatar
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    Quote Originally Posted by HalfPint View Post
    To me that doesn't look like pre-ignition cylinder damage. Usually a burned exhaust valve is due to improper seating. Unless the valve seats it cannot transfer heat and it just gets hotter and hotter. Then hot gasses push through the gap, acting like a plasma cutter. It's a vicious cycle that doesn't last long. I'd be looking for why that valve did not seat - perhaps a problem with the hydraulic lash adjuster.
    The oil thinned out on my Abarth after 9000 miles, (no excuses, a lot of circumstances came together and I thought I'd done an oil change when I hadn't), and along with sparkly oil, and one of my exhaust valves did something nasty, the lifter bucket and roller rocker self destructed, sending shrapnel through the engine.

    Oil failure can indeed destroy an exhaust valve. I have a rusty hunk of metal that used to be an engine sitting in a field to prove it.
    2015 Rosso Abarth - MAD FIAT - 5 Speed - Phase 2
    2015 Granito Lucente 500T - Proyecto Estupido (Salvage) - Auto - OFT Stage 1

  2. #12
    Senior Member HalfPint's Avatar
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    Quote Originally Posted by aelfwyne View Post
    The oil thinned out on my Abarth after 9000 miles, (no excuses, a lot of circumstances came together and I thought I'd done an oil change when I hadn't), and along with sparkly oil, and one of my exhaust valves did something nasty, the lifter bucket and roller rocker self destructed, sending shrapnel through the engine.

    Oil failure can indeed destroy an exhaust valve. I have a rusty hunk of metal that used to be an engine sitting in a field to prove it.
    Sure, oil can cause failure - but was the exhaust valve actually burned at the seat like the one shown above, or some other kind of damage to it? Also, the lifter/hydraulic adjuster failure might have been the initial failure.

    I found the oil info above to be interesting and am researching that more now, but I'm unconvinced this burned valve is due to oil rather than simple poor seating.
    Completely stock 2016 500 Abarth, Rhino & Nero,
    2017 Jeep Renegade 1.4 Turbo, Anvil & Black
    2016 Ford Fiesta ST

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    Senior Member aelfwyne's Avatar
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    Quote Originally Posted by HalfPint View Post
    Sure, oil can cause failure - but was the exhaust valve actually burned at the seat like the one shown above, or some other kind of damage to it? Also, the lifter/hydraulic adjuster failure might have been the initial failure.

    I found the oil info above to be interesting and am researching that more now, but I'm unconvinced this burned valve is due to oil rather than simple poor seating.
    I wanted to dissect the engine. However the head is bolted with torx bolts, and when I went to remove the head bolts, it snapped off a hardened torx bit into the bolt head rendering it very difficult to remove. Drilling a bolt is one thing - drilling a bolt that's torqued tightly enough to snap a hardened torx bit off clean is yet another. I'm sure it could be done, but I was more focused on just getting the replacement engine in place at the time. Rebuilding the original engine wasn't on my agenda, as I don't trust an engine where the oil has glitter without a full rebuild. So I just tossed the engine to the side and moved on.
    2015 Rosso Abarth - MAD FIAT - 5 Speed - Phase 2
    2015 Granito Lucente 500T - Proyecto Estupido (Salvage) - Auto - OFT Stage 1

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    Quote Originally Posted by HalfPint View Post
    Sure, oil can cause failure - but was the exhaust valve actually burned at the seat like the one shown above, or some other kind of damage to it? Also, the lifter/hydraulic adjuster failure might have been the initial failure. I found the oil info above to be interesting and am researching that more now, but I'm unconvinced this burned valve is due to oil rather than simple poor seating.
    Correct me if I'm wrong, but I don't think he's saying it was oil fail that destroyed the valve, directly. The theory is thinned oil slipped past the rings and created the carbon build up. The carbon build up becomes a glow plug, pre-igniting the fuel air and the pounding broke the valve. I assume the pistons took some interesting damage as well. The problem could have been made worse if, detecting unburned O2 in the exhaust, the engine may have stepped up with extra fuel. I understand defective oil rings, bad injectors, bad spark and such could be other ways carbon can build. It's can be made worse by high compress in a turbo and if the owner ran low octane fuel (which detonates more easily).

    Before FI, this would probably be a car that would spit/sputter for a few seconds after the ignition was turned off, would be my guess.

  6. #15
    Senior Member HalfPint's Avatar
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    Quote Originally Posted by map View Post
    Correct me if I'm wrong, but I don't think he's saying it was oil fail that destroyed the valve, directly. The theory is thinned oil slipped past the rings and created the carbon build up. The carbon build up becomes a glow plug, pre-igniting the fuel air and the pounding broke the valve. I assume the pistons took some interesting damage as well. The problem could have been made worse if, detecting unburned O2 in the exhaust, the engine may have stepped up with extra fuel. I understand defective oil rings, bad injectors, bad spark and such could be other ways carbon can build. It's can be made worse by high compress in a turbo and if the owner ran low octane fuel (which detonates more easily).

    Before FI, this would probably be a car that would spit/sputter for a few seconds after the ignition was turned off, would be my guess.
    A typical burned valve is pretty easy to identify by how it is eroded along the edge from the hot gases blowing past. I can't tell from that picture if what kind of damage that is, but valves are pretty tough and don't crack off too easily. There isn't any mention of other damage, so I'm assuming it's a burned valve. Pre-ignition can create high temperatures and pressures, which could certainly contribute to a burned valve, but those pressures are not going to selectively damage just the valve. The steel alloy of the valve is must harder, tougher and had a much higher melting point than the aluminum of the cylinder head.

    You'd have to look under that carbon to see what the rest of the combustion chamber looked like. If it's only a burned seat I'd look elsewhere for the cause.
    Completely stock 2016 500 Abarth, Rhino & Nero,
    2017 Jeep Renegade 1.4 Turbo, Anvil & Black
    2016 Ford Fiesta ST

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