Chamber Destruction

Discussion in 'InsideTopAlcohol.com Tech Questions' started by Bjs344, Oct 30, 2019.

  1. Bjs344

    Bjs344 Member

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    Roots MFI BBC set up on about 1800 hp. Right side head is annhiated. Every quench pad is caved in as if hit with a sledgehammer and 3 of the 4 quench pads have nickel sized holes opposite the spark plug.

    I’ve run this basic tuneup for years, have made a few passes that were way more aggressive (10-15 numbers leaner on the main for the same air occasionally with 1 more degree of timing). Worst I’ve ever seen is a little bearing squish. One time I took about .030 material off a couple straps on a 1/4 mile pass.

    This was an 1/8 pass. Set to shift at 8200. It’s been about 8400 before without issue. Shook in low gear which knocked the wires off the shifter. I realized it wasn’t shifting but it nosed over while I was reaching for the handle. Hit the handle thinking it would start pulling again but it didn’t so finally lifted about 550’. According to the grid it nosed at 8300 so it was already hurting itself at this point.

    Only 2 things I can think of are: it shook the shutoff closed despite the over center spring, or the grid somehow jacked a bunch of timing in.

    Does the chambers being beat in point to a timing problem?
     
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  2. Dave Koehler

    Dave Koehler Member

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    Just guessing that you will find that the chamber crashing started at the bottom end.
     
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  3. Bjs344

    Bjs344 Member

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    Pistons appear to be fine. Short block seems fine although I expect the bearings will be best to death when I get to them. Actually still kind of ran next time I tried to fire it except that it was shooting flames out of the water pump hole (wet block run dry)
     
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  4. Bjs344

    Bjs344 Member

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    To clarify, chambers aren’t “dinged up” like dropping a valve or something. More like you put a body dolly on the quench pad and then took a giant swing with a 10 lb sledge
     
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  5. TOL

    TOL Active Member

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    How do your head gaskets look?.......
     
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  6. Bjs344

    Bjs344 Member

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    Pushed out the orings and tried to extrude the gasket. Outside of the gasket stayed clamped though.

    I’ll try to post a link to pictures.
     
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  7. Bjs344

    Bjs344 Member

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  8. Bjs344

    Bjs344 Member

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    I forgot to mention, I didn’t know it was hurt until at home the next weekend when I tried to fire it up. I hadn’t looked at the grid and was still assuming it had just got unhappy due to the late shift and then was spinning the tires after I hit the handle

    I had already checked, as routine maintenance, valves and springs. On first attempt When it kind of fired but something was obviously wrong, I checked timing and distributor phase which were both spot on. So if it’s was a timing problem it was intermittent.

    It actually ran long enough on the left bank that it should have been on the pump but kinda sounded like it was still just on the squirt bottle so fuel pump is a suspect.
     
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  9. rb0804

    rb0804 Active Member

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    How’s the crankshaft itself is it broke?
     
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  10. Mike Canter

    Mike Canter Top Dragster
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    Do you have a fuel flow meter on it? Do you tape your fuel shutoff open? What do all the plugs look like?
     
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  11. Dave Koehler

    Dave Koehler Member

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    Pictures are not high resolution but are those holes something that was previously welded/fixed?

    I thought you were describing pistons hitting heads but this is a meltdown.
     
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  12. MaineAlkyFan

    MaineAlkyFan Active Member

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    What Dave said about previous weld/fixed areas? The holes are all opposite a water jacket & the heat signature on #4 looks like it was about to burn through. Are your nozzle lines all off a common manifold? Could the right side distribution be blocked or restricted?
    It would be good to see the other side & the piston faces.

    Chris Saulnier - Team Tigges
    Mechanic Falls, Maine
     
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  13. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    I would rule out the Grid putting timing in it.
     
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  14. Bjs344

    Bjs344 Member

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    Distribution feeds both sides.

    Two chambers on this set of heads was fixed previously. Pretty sure the one that DIDNT burn through had a previous repair. Definetely not he root cause as I haven’t hurt that many chambers in the past.

    Yes, the fuse was lit on #4 as well. Quench is caved in like the rest. I think it was probably thicker because it had been repaired.

    I can hear the eye rolls already, but the plugs looked fine. I have pulled way more aggressive plugs out of this motor 20 passes ago and it didn’t care.


    I totally f’d he tuneup about 5 passes ago (with nasty old warmup plugs still in it else they would have probably been the worst plugs I ever pulled out) so bad it rattled the intake loose. Air had come in over 1000’ while sitting In the lanes and i was swinging for the fence to start with. Didn’t care.

    No tape on shutoff. Just an over center spring from good vibes.

    No fuel meter.

    Not sure about crank or other side of the motor. I’ll get back on ITV this weekend
     
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  15. Mike Canter

    Mike Canter Top Dragster
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    While I agree that the Grid cannot suddenly advance the ignition you can get RFI picked up on the cranktrigger cable that will add pulses that will randomly fire the spark plugs and will look like pre-ignition damage and cause stuff like that. Have you looked at the Grid internal data acquisition on Ignition In to see if there was any extra cranktrigger pulses added?
     
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  16. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    How long has it been since the pump was flowed? Could be a pump going away.
     
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  17. Mike Canter

    Mike Canter Top Dragster
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    The pump going away would have been seen in the plugs
     
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  18. TOL

    TOL Active Member

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    If the pistons look fine, and the valves are not significantly tuliped, and the plugs are not screwed up, then my guess is it went really super lean in a hurry for some reason quickly.

    Also, looks like maybe the chamber roofs might not be so thick in those affected areas?

    Serious detonation would leave behind various trace evidence on the plugs/chambers/pistons. Pre-ignition on the other hand might not, and might in fact leave you with exactly what you are seeing.

    I am suspecting either a gross sudden lean-out condition, or a timing misphase/mistime issue, but that’s just my 2 cents. Rotor phasing? Grid issue? Crank trigger issue? Who knows......
     
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  19. TOL

    TOL Active Member

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    One further comment........ If you are seeing multiple cylinders all affected to one degree or another (5 by your information as near as I can follow) then you are looking at some sort of global engine-wide influence. Only two potential sources for that. Fuel flow or timing.
     
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  20. Mike Canter

    Mike Canter Top Dragster
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    Fuel and timing will show on the plugs. Pre-ignition caused by RFI interference randomly firing the sparkplugs will do it in a flash. Have seen this so many times.
     
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