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Mr.NightHawk


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MACK E7, We are having a wooshing sound from exhaust only on #6 cylinder.. we have compression checked all 6 are 380-390#s with no leakdown, new nozzle, new rack on 4-6, ran overhead, does sound better but still puffing on #6 only, verified cam and rollers are all good, new E up and lines... Cracked one at a time only #6 doesn't change the rest it was obvious stumbling more ? I'm stumped 🤔

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3 minutes ago, terry said:

Exhaust valve seat loose?

That's what we were thinking but the compression test and leak down were solid 390 we repeated the test several times.. we even did a 5/6 at same time to see if we were swapping compression but no luck there either

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2 hours ago, Mr.NightHawk79 said:

That's what we were thinking but the compression test and leak down were solid 390 we repeated the test several times.. we even did a 5/6 at same time to see if we were swapping compression but no luck there either

But with the exhaust valve closed, would that seal up the seat?

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33 minutes ago, Onyx610 said:

Why did you change all those parts? This started after the install?

It came back from a run " concrete truck" running bad, we found two eups that were weak, it ran better but #6 still woofing... So we figured ok maybe#6 is weak too no change, then ok maybe it was the nozzle.. nada, tried another eup just in case we got a bum unit... Nothing... So we did notice alot of oil pumping from #6 rocker and went out on a limb and thought what if the dip/spike that rocker is pumping out is causing a spike and cracking a Jake ... Nothing changed after the rear rack was replaced and properly adjusted... So I think we're gonna be pulling the head tomorrow cause it makes sense

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I would re-run the rack..... Start on #1, and DO NOT deviate from the way Mack lays it out...  Did you set the bridges to .010"?  do you have an engine brake?  lash on that will be .017" or .021" if it was updated... jojo

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I was gonna say make sure the injector line/nozzle was installed and torqued correctly. But looks like you guys got right to it. Sucks a simple mistake can cost a lot of money and work. 

Edited by Onyx610
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You just described exactly what happens when somebody tries to run racing gas or aviation gas in a gas engine that does not have enough compression to cause proper ignition.  The mixture is still burning as it goes out the exhaust port.  This leads to burnt exhaust valves and other issues.  Never thought about it doing something similar in a diesel, but your explanation draws a great picture.

Old race car mechanic I knew summed up the too-high octane problem like this: "Make sure you have enough 'squish' to make it go 'pop'".

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"Eagles may soar, but weasels don't get sucked into jet engines."

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