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Thread: Detonation incident ???

  1. #1
    b's sanger
    I had an incident where bad gas caused my #8 cylinder to detonate in my BBF. This collapsed my plug electrode and I had to limp in. I later did a compression check which showed about 130psi with the rest of the cylinders showing between 130 and 135psi. I ran the boat a couple of weeks later and it ran fine. My question is should I be looking any deeper for possible damage to this cylinder, and if so what should I be looking for.
    Any help would be great Thanx.

  2. #2
    Hotcrusader76
    One cylinder was 130psi and the others were between 130-135psi?
    I don't see any problem with those numbers. Did you do a leak down at all?

  3. #3
    gnarley
    2 years ago I had a similar thing happen to 3 holes. One was a little low but I don't know what it was to start since I bought it used. I got all things sorted out and later in the year the comp was within 8-10 on all holes and checked it after every trip and still seemed fine. Then a year and a half after the detonation I had to pull the heads and was able to inspect the heads & pistons and all was fine.
    I'd say keep an eye on it but I bet you'll be fine. If you really need you could always get a bore scope and pull a plug and take a look if it makes you feel better.

  4. #4
    b's sanger
    Thanks for the replies, and no I have not yet done a leak down, mostly because it ran good the next time out. I did have a few specks of alloy after I pulled the plug the first time, which likely came of the edge of the pistion. And yeah all the holes are between 130 and 135, which is where they were before the problem occured. The threads on the #8 plug had a bit of oil on it, I am hoping this was not related.

  5. #5
    LakesOnly
    b'sanger (BANGER),
    What brand and part number pistons are you running? What heads are you running?
    You saw peppering on the plug, eh? Hell yes you need to do further investigation. Exactly what and how far depends on a few things.
    LO

  6. #6
    LakesOnly
    Originally posted by gnarley
    If you really need you could always get a bore scope and pull a plug and take a look if it makes you feel better.
    GNARLEY hit the nail on the head. Based on the extent of your observations, I was going to recommend a borescope inspection through the spark plug hole.
    I just put ten hours on my new BBF and intend to perform this inspection as part of the 1st service.
    LO

  7. #7
    b's sanger
    I'm not sure about the pistons except that thet are about 2/3 dished or so, kind of in a "D" shape. The pistons came installed used when I bought the boat. And the heads are C-9's gasket matched intake port and opened exhaust port with 2.125 intake valves and 1.75 exhaust valves.

  8. #8
    Mopar426
    Had a similar problem, one of the spark plug insulators broke off during a detonation attack. The engine quit firing on that cylinder. I took it back to camp and pulled the plugs and found the damaged plug. I took my mini shop vac to that cylinder via spark plug hole and sure enough a chunk or chunks of ceramic flew out. The engine ran great for two more years until I tore it down and saw the damage. The piston top was hammered with pits and the combustion chamber was pitted also and that was only from running the engine less than a minute after the failure. I was glad my buddy towed me in. I would do a visual just to make sure. My engine also ran great with the hammered piston.

  9. #9
    b's sanger
    Anyone know where to pick-up a borescope for a reasonable price in the LA/OC area. I just need something with the flexible optic and maybe a place to rent one if possible.
    Thanx.

  10. #10
    LakesOnly
    Originally posted by b's sanger
    I'm not sure about the pistons except that thet are about 2/3 dished or so, kind of in a "D" shape. The pistons came installed used when I bought the boat. And the heads are C-9's gasket matched intake port and opened exhaust port with 2.125 intake valves and 1.75 exhaust valves.
    Sounds like you have a D-Cup piston with C9VE-A heads. The piston dish mirrors the combustion chamber of the cylinder head. This is a good design as it maintains the squish area of the quench pad.
    Assuming you have the 11 cc dished pistons and a stock 460 stroke, your c/r is around 10.30:1. Comes close for 92 octane pump gas...might want to consider blending fuel.
    My concern about your detonation was due to a different piston that has a very narrow ring land between the crown and top compression ring. Chances are you're okay as far as the detonation goes; not a bad idea to check with a borescope if possible.
    LO

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