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Discussion Starter #1
Before last season the compression on my 2012 rush 600 was 90 psi on both cylinders. I decided to replace the pistons with prox rather than have it blow up on the trail. Had a little over 3000 miles on it. Also turned up the oil pump at that time. 60 miles into the first ride of the year, mag side cylinder lost compression. I tore the motor down, rings were stuck on the exhaust side, looked like it got hot. It was coated in oil so i assumed it to be a vacuum leak or lean condition rather than the lack of oil these engines are known for. There was some oil under the flywheel, so i figured that the crank seal was leaking and that was the cause of the failure, and the only thing keeping it alive before was the lack of power from low compression. I had the mag side connecting rod replaced on the crank because the big end bearing was bad, and the cylinder replated because it was scored. Injectors were cleaned and flow tested and fuel filter was replaced. Reed valves and throttle body boots all looked good. Rode it 130 miles last weekend and lost compression on the mag side again. Im at a loss for what happened. I followed the service manual (correct sealant, torque specs, piston to wall clearance, etc.) I'm at the point where i need to sell it as is and lose thousands of dollars or part it out even though i dont have the free time to do so and try to recoup some of my money. I cant see rebuilding it again and having it blow up on me again shortly after, so unless i can find out exactly what caused it im not wasting more time or money on it. Im just hoping someone here who has more experience than me can provide some insight. Thanks in advance

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If the rings stuck again I wold question the ring end gap and if they fit in the grooves smoothly. I don't know the piston to wall clearance on the Rush 600. I don't know if they run them loose like the old Fujis or if they run it tighter nowadays. If they are .002 -.003" you might have to be a little careful with break in. My buddy had a 600 Rush and had to rebuild it every 3k miles with Polaris pistons and always broke it in like he stole it. I would be curious what happened to the 2nd piston failure.
 

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Discussion Starter #3 (Edited)
Engine is out, and i can see the stuck rings through the exhaust port. I did gap the rings, and as far as i could tell, they fit well in the grooves. I had a machinist check piston to wall clearance per the specs i gave him from the service manual. Ive read that one of the issues with the 600 cfi was too much piston to wall clearance, causing the piston to rock and the ring lands to widen which is why I had 90psi of compression on both cylinders. Also certain years of pistons were more prone to cracking than others, although i didnt experience that. I plan on doing a leakdown test before I tear into it, and possibly have an expert look it over to see if theres something I did wrong or an underlying issue I overlooked

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Discussion Starter #4
The piston is melted badly on the front, to the point where i can see the rings from the top, and also burnt in the middle. The pto side piston looks good. I was told by someone who rebuilds these that the fuel pump is likely bad, and also the fuel map in the ecu on the 2012 isnt very good and i should get it reflashed at the dealer once i get it back together. Does anybody have any experiences with the fuel mapping being an issue and would a power commander also be a good idea? Im still worried that ill rebuild it again and have it blow up again. Why does it have an exhaust temp sensor if it doesnt give a code when it's lean? I would also consider putting an analog pyrometer on it as extra insurance, so i would be able to see when its lean.

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Discussion Starter #5
Failed piston and the other one for comparison.


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Did you have you fuel injectors flow tested and cleaned?
New fuel filter after rebuild?
How does the mag side crank seal look now that its apart?
 

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2020 Indy XCR 800 129", 2019 Indy 850 129", 2011 IQ Turbo 121"
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That isn't the fuel map. There is another problem (or problems) that need corrected. I agree that the injectors should be cleaned and flow tested or simply replaced. The fuel pickup in the tank should be replaced and the fuel pressure checked. It may be possible the fuel pump is dying. Having a plugged pickup can kill the pump over time. Verify the TPS setting also. Also question the detonation sensor. Clearly, there was serious detonation going on. Codes in the ECM?
 

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i will fourth the inj. on that side. det sens should have thrown the sled in limp mode. when you had the eng out the first time, did you remove the injectors? replace the fuel filter? its been a while since i have seen a piston do that that fast, but you are getting way to much air/not enough fuel on that side for sure. i have seen pin holes in the boots on these sleds that are very hard to find. causes all kinds of headaches
 

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Discussion Starter #9
Fuel injectors were cleaned and flow tested, fuel filter replaced, i looked at the fuel pickup and it looked good. Havent noticed any noises from the fuel pump, ive heard of people having a noticable whining from the fuel pump. My only question with the fuel delivery theory is that based off my research, it's a cfi 2+2 system which means it has 4 injectors, but over 5% throttle it only runs off the top ones, and the way the fuel rail is routed, the upper mag side (bad piston) gets fuel before the upper pto side (good piston). The pto side does look a bit lean, but no actual damage as far as i can tell. No codes at all, just lost power on one cylinder on a long straightaway, until it was only running on one. Mag side crank seal still looks good, and i pressurized the engine with about 5 psi and sprayed soap on the crank seals, case halves, base gaskets and reed cage/ throttle body boot and found nothing.

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I recently worked on a 2011 4 injector that had issues.It blew up and when I put it back together with cleaned injectors the plug was still white on one side.Hooked it up to digital wrench on the injector test mode to find that one case injector wasnt firing.Replaced the injector harness and problem solved.
 

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Discussion Starter #11
I recently worked on a 2011 4 injector that had issues.It blew up and when I put it back together with cleaned injectors the plug was still white on one side.Hooked it up to digital wrench on the injector test mode to find that one case injector wasnt firing.Replaced the injector harness and problem solved.
Did it have any error codes? I had dET on the gauge literally 5 seconds before the cylinder went down last year, far too late for me to do anything about it. The second time it blew up, nothing. Seems like theyres not much i can do myself in terms of diagnostics. I guess ill have to rebuild the motor again and bring the sled to a dealer and have them reflash the ecm and check for any issues.

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Discussion Starter #12
I was checking continuity on the stator, Dc chassis coil, which runs the fuel pump, reads 0.3 ohms, should be 0.2 ohms. Could my fuel pump have been getting low voltage due to this? And is that something the dealer could prove with digital wrench?

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it could, depending on if the stator is headed south, they will run great then fall flat, or give on/off voltage issues, and kill motors. just not that common. when i get home i can send you a pdf of the wiring diagram
 

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Discussion Starter #14
I appreciate all the help so far. I pulled the jugs off, pto side piston is cracked, lots of aluminum on the cylinder bore, probably need both cylinders replated, rod bearings seem okay, dont want to have to split the cases again if i dont have to.

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The sled I was working on never threw a code. I took a couple laps around my shop and checked plugs.One was white.Plugged into digital wrench and one injector wasnt firing,but that was a 4 injector engine.
If I were you I would plug it in and check for codes.It wont necessarily trip the light to throw codes.Iwould also have them perform the injector test on Digital wrench.Yours is lean as hell on that one cylinder.Im assuming that you checked your ypipe for cracks too.
 

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Very good suggestions. Hadn't thought about the y-pipe, but definitely have seen them crack. My '12 and '15 both had weld beads all over them by the time I sold the sleds - mostly underneath where it was very hard to see.
 

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Discussion Starter #17
Are you guys saying an exhaust leak from the y pipe could burn a piston like that? No cracks on the y pipe as far as i can tell, but there is a bit of oil around the outside of the flange, definitely a minor leak if any. Definitely a nice coating of aluminum on the inside.

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Are you guys saying an exhaust leak from the y pipe could burn a piston like that? No cracks on the y pipe as far as i can tell, but there is a bit of oil around the outside of the flange, definitely a minor leak if any. Definitely a nice coating of aluminum on the inside.

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Absolutely a y pipe leak will cause a burn down when leaking enough.
A 2 stroke needs a good sealing exhaust for proper back pressure. As the piston comes up, some of the gas mixture escapes out the exhaust port. The exhaust is tuned to have back pressure to force the escaping mixture back into the cylinder. A leak in the exhaust will cause low back pressure, plus some of the mixture will escape through the leak. Also extra oxygen will be added through the leak during back pressure. All wich will cause a lean mixture during combustion. Hope i explained myself good enough.
 

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Pro Ride Rush chassis 800s got a bad rap. A few minor issues that need addressed to make the reliable.
1- Turn up the oil pump.
2- Vent the oil tank or change to a different cap like the Cat or John Deere.
3- Clean the injectors, change the filter, and replace the sock in the tank.
4- Keep the engine cool! A Doo thermostat and scratchers works wonders.
5- A Power Commander Fuel Controller with the appropriate map for the year.
6- Make sure the TPS is set dead nuts

I rebuilt a 12 800 last year that previously went 80 miles on a shop rebuild. Guess what I found? Oil tank wouldn't feed, plugged MAG side injector, and a cracked Y pipe. A recipe for disaster on a two stroke!

Most of these apply to the 600s as well. The fuel mapping wasn't bad on the 600, but the rest applies.
 

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I also forgot to ask if you cleaned the ypipe and pipe really well . All too often that step is overlooked and the debris from the first blow up gets sucked right back into the engine.
 
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