what would cause this?
Cruiser
Joined: Feb 2014
Posts: 129
Likes: 11
From: NPR, FL
Detonation caused by running too lean, not enough octane, too much advance or a combination of all 3. Melted 3 pistons like that years ago on my Kaw. 14:1 CR build. Colder weather hit and I didn't richen it up. Since it only happened on the rear cylinder I'd say your running too lean.
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Joined: Jul 2012
Posts: 95
Likes: 1
From: Lincoln ne
Sorry I haven't updated my signature. I'm running a crane H290-2 cam (581 lift 240ish duration) went to carb as well. The pistons were 10.5:1
Head look splattered with garbage and a bent exhaust valve.
The plugs were reading rich when they were checked 450 miles earlier.
It wasn't the mechanic that put them in. Everything was checked three times before each piston went in. And it's not blow by, it's oil running down the piston. Sorry for the bad pic.
Would detonation make just the edge bust out? Could ethanol fuel help cause this?
Head look splattered with garbage and a bent exhaust valve.
The plugs were reading rich when they were checked 450 miles earlier.
It wasn't the mechanic that put them in. Everything was checked three times before each piston went in. And it's not blow by, it's oil running down the piston. Sorry for the bad pic.
Would detonation make just the edge bust out? Could ethanol fuel help cause this?
Outstanding HDF Member
Joined: Jul 2013
Posts: 2,874
Likes: 36
From: Houston, TX
How did you not hear the pinging? Must be that thunderheader!
That is odd... did you check the timing with a timing light? I haven't put a light on mine, but it's close... no problems in over 4k miles on the rebuild, but I am running stock compression pistons.
I wonder if your M&M EFI had more to do with this than anything.
That is odd... did you check the timing with a timing light? I haven't put a light on mine, but it's close... no problems in over 4k miles on the rebuild, but I am running stock compression pistons.
I wonder if your M&M EFI had more to do with this than anything.
Road Warrior
Joined: Apr 2007
Posts: 1,952
Likes: 15
From: Senoia, Ga., by way of Miami, Fl..
Its tough to tell in the pic, but that sure looks broke rather than burnt/melted.. There does appear to be aluminum splatter, but I'd have to wonder if it wasnt a broken piston that started the whole mess... Do a search online to see if you can relate yours to other pictures, the one's I've seen melted from detonation look worse..
Club Member
Joined: Apr 2011
Posts: 5,776
Likes: 7,811
From: SE Louisiana
That sure looks like classic detonation to me.
Quite a few things can cause detonation, or pre-ignition leading to detonation.
just a few that I can think of,
Ignition malfunction/too much timing, partially blocked carb jet, lugging, bad fuel/low octane, intake leak, even a loose spark plug(not dissapating heat and glowing), how about a fuel tank vent malfunction causing a lean condition?
Point is, finding the actual cause of detonation can be hard to pinpoint, and just rebuilding without knowing can lead to a repeat failure.
Quite a few things can cause detonation, or pre-ignition leading to detonation.
just a few that I can think of,
Ignition malfunction/too much timing, partially blocked carb jet, lugging, bad fuel/low octane, intake leak, even a loose spark plug(not dissapating heat and glowing), how about a fuel tank vent malfunction causing a lean condition?
Point is, finding the actual cause of detonation can be hard to pinpoint, and just rebuilding without knowing can lead to a repeat failure.
Outstanding HDF Member
Joined: Oct 2010
Posts: 2,706
Likes: 14
From: Near Frankenmuth, MI
Appreciate hearing further details and explanations.
Here's a link to their PDF on these pistons. There is an explicit warning to adjust the timing:
HYPEREUTECTIC PISTONS: The low thermal conductivity of this alloy requires engines running hypereutectic pistons to reduce total ignition timing 2 to 4 degrees. Final timing may vary with your application.
Hope that isn't the reason for the troubles.
Here's a link to their PDF on these pistons. There is an explicit warning to adjust the timing:
HYPEREUTECTIC PISTONS: The low thermal conductivity of this alloy requires engines running hypereutectic pistons to reduce total ignition timing 2 to 4 degrees. Final timing may vary with your application.
Hope that isn't the reason for the troubles.
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Road Warrior
Joined: Apr 2007
Posts: 1,952
Likes: 15
From: Senoia, Ga., by way of Miami, Fl..
I'd buy that... The crack would cause the edge, causing the hot spot, then the detonation..