Holes in Pistons-Crank Seals?? - Page 3 - REV Chassis - Performance and Trail Models - DOOTalk Forums

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Holes in Pistons-Crank Seals??

600 SDI

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#31 Daag44


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Posted 02 January 2016 - 11:56 AM

What happened was I was on Oneida Lake just cruising along around 55MPH, wasn't racing or WOT when it backfired and died.  Engine temp was normal, maybe a tad bit high but nothing significant,  by the gauge and by hand.  At that moment I knew it wasn't good.  Pulled the plug and the end was burnt right off with no compression.  Meanwhile I'm alone.  Luckily 2 guys saw my side panels open and stopped.  They offer to tow me back.  I was like well I might be able to nurse it back on one cylinder.  Well I did and that didn't last long, that's why booth pistons have holes, and they towed me back.  
I too thought possible fuel issue etc, but was hoping this has been seen before to lead me to a successful repair. Due to the condition of this sled, I wouldn't be surprised if it's something with the injectors/fuel filter etc.  
How do I get the timing checked?  Is this something that is through the ECM or manual?

The backfire was pre-ignition from a glowing red hot ground electrode. My guess is it was running the hotter BR8 plugs and they got hot from a combination of engine running lean and exhaust temps shooting sky high with no protection from the muffler EGT sensor.
A consistent 55mph across a lake sound just right for the known Lean Hot Spot on the 2004 600 SDI calibration explained by BRP running 6900-7000 rpm @ 40-45% Throttle Opening. In this range the calibration does not take into account the muffler temperature (EGTS) to send it into a Limp Home Mode if needed. Had the rpm moved above this range for just a moment before the big bang, the sled would have dropped dramatically in power from a full on Limp Home Mode with the exhaust valves dropped. The problem was corrected in the MY2006 calibration file 420 665 199.


The eRAVE exhaust valve opening in this range is what I haven't confirmed. I know they are meant to open very late while cruising. On the 1K they can still be closed at 6,900 rpm with 40% throttle opening, and can open as late as 7,200 rpm under low throttle opening.
If you are the owner for the 5,000 miles, I would guess that you normally never ride this rpm constant. Perhaps you were following or someone else was riding it.
We don't hear of such failures often. In this rpm/load range the ECM isn't looking at the poor mans O2 sensor (muffler EGT) to realize it's running too lean and hot. Both pistons having holes on the crown is rare, but it makes sense seeing it was push through on only one cylinder.
The high speed injectors will need to be flow tested as those are activated above 6,500 rpm and are likely fouled. Also check the fuel filter and the two check valves for the fuel tank vent lines.
Fuel Injector Tester  
http://www.amazon.co...Injector tester
Notice that Bill didn't bother to mention the crank seals. With two seals on each side it becomes difficult to draw enough air from the end of the crankshaft to cause a lean/hot condition.

I would think the first one went down from injector failure then the other went do running it while one side was already gone once you don't have enough fuel for the motor to burn the spark plug will burn the hole do to high internal temps, just like it would with too hot spark plug range or too much timing. - Bill

Edited by Daag44, 08 March 2020 - 08:47 AM.

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