Author Topic: Engine damage during dyno run (428 CJ Resto build cont.)  (Read 6799 times)

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aj

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Engine damage during dyno run (428 CJ Resto build cont.)
« on: April 14, 2019, 11:02:42 AM »
After dyno sheet showed lean condition during 2 pulls (A/F in 15-16 range), I decided to borescope at Brent's suggestions...which then led to pulling heads off.  I'll deal with shop that ran dyno'ed with lean condition (yes, inexcusable).

After removing heads,  I saw odd, bad, and truly ugly things.  :'(.   I've posted a few photos and would appreciate thoughts/comments from experienced folks on the following:

The Odd:
First thing I noticed was sticky dark oil residue on tops of all pistons and back side of all intake valve.  Also could see on tops of piston oil pattern where it bulk oil was migrating across top of piston much like water on a windshield.  That led to investigation of PCV tubes and fitting (stock CJ resto stuff) where I found evidence of oil.  Oil baffles had been from the stock CJ cast valve covers to clear the rockers.  My understanding if IF motor was inhaling large volume of oil, that would greatly increase chance of detonation. 

The Bad:
Signs of detonation.  I'm no expert of forensics but it appears the detonation was extensive enough to escape the past the head gaskets and leave combustion residue including the sticky dark oil residue on the block-to-head mating surface beyond the metal ring of the head gasket.     

The Truly Ugly:
Two fairly deep scratches in #8 from two small pieces of debris that embedded into side of piston just above top ring.  I don't know if the debris could have been caused by detonation or lean condition.  (Side Note:  When new valve guides were installed, it broke/chipped bits of the head's guide boss as the guide was pressed in. I've always been leary a small chunk of the guide boss could further crack off  and get inhaled.  But I would have expected to see a bigger piece of loose guide boss than the very small pieces of debris that caused scratch.)
 
Pulled the number 8 rod/piston and bearing and crank look fine.
 
At first it appeared I could simply clean up the oily residue and address the PCV issue and retry on dyno  (obviously at different shop) using higher octane, richer carb setting, etc.   But upon discovery of the scratches,  looks like ill need bore job and bigger pistons.

I don't know if the lean condition and detonation caused the debris that led to scratches...of if they're separate and unrelated. 

So I suspect I'll be boring as needed and new pistons.   Dadgum it.       


 
Adrian Jacobs
Weatherford, TX
1970 Shelby GT500 
1970 Boss 302

jayb

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #1 on: April 14, 2019, 11:51:53 AM »
Well, that sucks, sorry to see all that.  A couple of comments.  If the oil on the deck is sneaking by the head gasket seal around each cylinder, probably its from detonation lifting the head or gasket a bit to allow that.  If I had to guess, oil in the cylinder and on the valves is probably from an intake gasket leak.  Those two problems are easily fixed.  The big deal is the damage to #8, those scratches look pretty deep.  But you could just bore and/or power hone that one cylinder and go a step bigger on the one piston.  One piston that's 0.010" or 0.015" oversize won't be enough to affect the balance, and the engine will never know the difference.  Also, do your best to determine where the debris that caused the scratches in the cylinder wall came from; best bet is something obvious, like left over material from porting on the heads and/or intake that didn't get completely removed.

It really makes me mad when I hear of incompetent dyno work.  It's not that hard to take care of an engine on the dyno.  The A/F numbers are a big red flag, and you always want to run race gas on the dyno, because even if you do run lean, you won't hurt the engine if you're running 110+ octane.  Sounds like your dyno operator didn't know what he was doing...

Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

wowens

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #2 on: April 14, 2019, 05:06:50 PM »
Ouch ! All that on a stokish build is hard to understand.
Woody

My427stang

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #3 on: April 15, 2019, 06:23:25 AM »
Check ring land dimensions, you may find those piston are beat up worse than they look

Sorry to hear about it. I think you may have had more than a jetting issue the way it went hard lean, maybe fuel supply?  Float level? PV too small a number and closed? Combined with DCR too high? Regardless Dyno operator should have shut it down, but recommend some deep thought before the next one
« Last Edit: April 15, 2019, 09:22:59 AM by My427stang »
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Ross
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Falcon67

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #4 on: April 15, 2019, 12:55:06 PM »
Agree - scratches that deep would be more likely from debris than detonation.  Piston tops and valves don't really look as bad as they could.   Also agree that getting a measure of ring clearance should be part of forensics. 

FElony

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #5 on: April 15, 2019, 09:05:56 PM »
Can that A/F happen from secondaries not opening up? We don't talk about 2V's here, but what happens when you WOT a big engine with one, and it hits a point of no more acceleration? Does it go lean?

Drew Pojedinec

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #6 on: April 15, 2019, 09:16:57 PM »
Can that A/F happen from secondaries not opening up? We don't talk about 2V's here, but what happens when you WOT a big engine with one, and it hits a point of no more acceleration? Does it go lean?


LOL!

FElony

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #7 on: April 15, 2019, 10:06:43 PM »
Can that A/F happen from secondaries not opening up? We don't talk about 2V's here, but what happens when you WOT a big engine with one, and it hits a point of no more acceleration? Does it go lean?


LOL!

Evidently, you don't know either.

Barry_R

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #8 on: April 15, 2019, 10:40:07 PM »
They tend to roll rich when secondary opening is delayed.  If you get to a point where vacuum from too small a carb exceeds power valve settings you can pull back lean, but we do not see that often - except on oval track race cars in those "two barrel" classes.

This just looks to be dead lean.  Possibly a serious and repeated supply problem or a float stuck "closed"?  I have had engines run out of fuel in the middle of a dyno pull and not seen that level of damage.  You can clearly hear an issue when something goes wrong - and abort the pull in an instant.

Drew Pojedinec

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #9 on: April 15, 2019, 11:13:10 PM »
They tend to roll rich when secondary opening is delayed.  If you get to a point where vacuum from too small a carb exceeds power valve settings you can pull back lean, but we do not see that often - except on oval track race cars in those "two barrel" classes.

Oval track carbs, especially 390's are going to do that anyway as they have a .130 HSAB.  They come pre-jacked up in order to work for their intended purpose, no doubt why oval track is truly it's own branch with highly specialized folks working there.

Quote
Evidently, you don't know either.
Sure......

How does an engine pull fuel from a carburetor?

FElony

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #10 on: April 15, 2019, 11:53:31 PM »
How does an engine pull fuel from a carburetor?

It totally sucks?

Falcon67

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #11 on: April 16, 2019, 08:20:13 AM »
How does an engine pull fuel from a carburetor?

It totally sucks?

Wrong!  :lol:  Now he'll go into "depression", maybe because we put too low pressure on him.  Can't stroke everyone's ego.   

e philpott

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #12 on: April 16, 2019, 10:16:58 AM »
How does an engine pull fuel from a carburetor?

It totally sucks?

Wrong!  :lol:  Now he'll go into "depression", maybe because we put too low pressure on him.  Can't stroke everyone's ego.

if it doesn't suck , please explain how Idle circuit works ? lol

BigBlueIron

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #13 on: April 16, 2019, 11:31:05 AM »
Pressure differential.

FElony

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Re: Engine damage during dyno run (428 CJ Resto build cont.)
« Reply #14 on: April 16, 2019, 11:50:26 AM »
How does an engine pull fuel from a carburetor?

It totally sucks?

Wrong!  :lol:  Now he'll go into "depression", maybe because we put too low pressure on him.  Can't stroke everyone's ego.

Hey, what did I ever do to you? The only thing that depresses me about this forum is the ever-dwindling lack of humor too many members exhibit. I guess there is truth behind the old fart crotchety meme.

It's good to have an ego. It keeps you grounded, aware, and forward-focused. Just ask Jay.