[DeTomaso] WARNING: .050 may be the wrong kind of Bomb

[Dan Courtney]

I haven't picked up a borescope yet but I ran a compression test tonight and 
all 8 cylinders were consistent around 150 psi. Haven't done a leak-down 
test yet.
There were no rings on these AP 25 plugs and I noticed #8 is gapped at .045, 
pretty sure it was put in at .050. The other plugs are at .050.
Could impact from the domed piston to the plug tip crack the electrode 
without breaking the tip? Although #5 is missing 1/2 the tip, #6 has an 
intact tip but not much electrode. The other 6 plugs all look brand new.
I may convert to AP 32's, to lessen any potential detonation, and hopefully 
they come with rings.
I may check the intake gasket, to see if it shows sign of an intake leak. 
The intake bolts at the end by #5 & #6 are studs with nuts (to hold the 
throttle linkage I fabbed for the AirGap) and may have loosened.
Otherwise I can't think what could be potentially causing detonation.
I'm assuming the backfire I'm getting about 6 seconds after any significant 
deceleration is being caused by the collector donuts, as those locknuts keep 
getting loose, but maybe from an intake leak?
The secondary butterflies do not appear to be opening, but it seems like 
that would lead to a rich condition, rather than lean for detonation.
I'll try and find a borescope tommorrow, to see if anything is damaged.
If it looks good I'll try for a dyno tune appointment.

Dan

Dan F. Courtney

La Jolla, CA

(858) 551-5455 Phone
(858) 551-5456 Fax
----- Original Message ----- 
From: "P. Rimov" <rimov at charter.net>
To: "Dan Courtney" <dfcex at excaliburre.com>
Sent: Sunday, May 24, 2009 7:45 M
Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb


> Dan are you running domed pistons or have you had the heads milled to 
> increase the CR? If so you may need to add an extra ring or two on the 
> plugs of the offending cylinders. It is possible the extra gap on the plug 
> was just enough to result in contact with the piston. Plugs are great for 
> heat but not so good when they are dropped or bumped by a piston.  It is 
> possible the spark plug wire was loose or popped off at some time to cause 
> the #? to foul. I would not start worrying about pulling the heads just 
> yet. What ever pieces broke off in the cylinder are long gone through the 
> exhaust. I would be more concerned about any valve damage from the plug 
> remnants before or while they exited the exhaust valve. Valve damage can 
> easily be ruled out through a compression check and lead down check, but 
> again I don't think you have to start worrying just yet. One last thing I 
> would change your oil and make sure to filter it and check for any foreign 
> material.
>
> Cheers my friend
>
> Paul
> ----- Original Message ----- 
> From: "Dan Courtney" <dfcex at pacbell.net>
> To: <JDeRyke at aol.com>
> Cc: <detomaso at realbig.com>
> Sent: Sunday, May 24, 2009 7:12 AM
> Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb
>
>
>> Jack,
>>
>> I timed it at 12 deg @ idle, 32 deg total in around 2,800 rpms.
>> Fuel pressure is from an electric pump internally regulated at 6.5 psi.
>> The plugs in the same cylinders looked OK before switiching out after 600 
>> miles of highway and desert driving.
>> It's not just the ceramic part missing, also the electrode and, on #5, 
>> 1/2 the top of the tip.
>> It's seems strange that the other 5 plugs (except #2 / fouled) look new.
>> Where would I find this scope? I really don't want to pull the head.
>>
>> Thank You,
>> Dan
>> Dan F. Courtney
>>
>> La Jolla, CA
>>
>> (858) 551-5455 Phone
>> (858) 551-5456 Fax
>>  ----- Original Message ----- 
>>  From: JDeRyke at aol.com
>>  To: dfcex at pacbell.net ; detomaso at realbig.com
>>  Sent: Sunday, May 24, 2009 12:27 AM
>>  Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb
>>
>>
>>  In a message dated 5/24/09 12:10:59 AM, dfcex at pacbell.net writes:
>>
>>
>>    What worries me more is, where are the tips of the plugs? Are they 
>> sitting in the cylinders, about to punch through my brand new pistons? Or 
>> has that already happened?
>>    I'm also wondering if detonation could have played a role.
>>
>>
>>  Thats a sign of detonation. Check your total ignition advance and your 
>> fuel pressures. Normally, a plug gap will either fire, or not, so thats 
>> not the cause of your detonation. The piston crowns likely look 
>> shot-blasted but unless they made really deep pits, the pistons will be 
>> OK. Any extra pieces of ceramic are long gone out the tailpipe. A fiber 
>> optic borescope can look thru the plug hole and inspect the piston tops 
>> without pulling the heads. My best guess- J Deryke
>>
>>
>>  **************
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