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Discussion Starter #1
Rzr has 970 miles on it with just a stage 5 trinity exhaust and canned Pvcx trinity tune. I’ve been working with Mike at Aftermarket Assassins to make a few improvements. Ended up purchasing 2018 head gasket, new head bolts, from OEM vendor, did DIY oil cooler mod, and RZRjoes’ BOV done right mod. Purchased 2017 injectors, low temp spark plugs, and tunes 3, 3.5, 4 and s3 clutch kit with performance helix from Mike. 3 being safe pump gas tune, 3.5 being possible with good pump gas but on the edge and 4 98-100 octane.

Not looking to bash anyone with this thread but looking to find answers and see what failed. I have experience building motors for turbo’d tuned import street cars. I have also rebuilt my old 2014 XP1000 at 1,900 mile with no problems. I don’t take shortcuts and used OEM manual for head work and everything torques to spec. Before work began everything was cleaned and bed was removed. Any pause in work and everything was covered and protected form FOD and was reinspected before it went back together. Project went smooth nothing was rushed and no leftover parts.

Replaced head gasket, bolts, injectors, spark plugs, clutch kit. Installed oil cooler and BOV, verified timing twice. Loaded stage 3 (pump gas) tune (This is the only tune I have loaded so far). Put clutch kit to recommended weights for tune and 32s. Did vacuum test on BOV mine was .375 instead of rzrJoes' .400. Bled coolant and oil systems, verified BOV/diverter was working correctly, insured clutch was performing correctly at idle.

Did a couple of pulls to insure clutching was working properly and engine temps were stable. Clutching was close Ran it 20 miles on dirt and paved roads, then checking timing again along with coolant and oil levels. Clutch was still running a little hot but that was the case before work was done, it was staying cooler than before, just not where i thought it should be yet. Car was running good, felt a little slower then previous tune and clutch off the line but then would pull strong, figure this was due to not dialing in the clutch yet. Only did one Wide open pull on a road, rest of it was pretty tame between 20-50mph making sure everything was working properly.

Took the car out for another 20 mile run on dirt and paved roads. Driving about 40mph and boom pssssss and died. Wasn’t sure what was wrong at this point, and called my wife for a tow. Got it home and have broken spark plug, ruined head, damaged cylinder walls, broken piston. I have not taken it apart yet as I was waiting to see what Mike wanted me to do, damage has been verified with a cheap borescope.

No leaks through this entire process, head bolts and gaskets are still fine with no leaks. No increase in temps at any point and no crazy boost spikes, no miss fires, no hard starting, no engine stumbling, verified timing again and still in.

Open to any ideas and requests for additional pictures to help determine cause.


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Subscribing for pics. Forensics are impossible without data. You didn't possibly drop that plug before installing it did you? Did you notice any signs of detonation when scoping it?
 

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This is terrible to hear. The carnage sounds exactly like detonation to me, but someone who clearly knows what they are doing, I just can't imagine you didn't hear it pinging if it was actually detonation.



You mention the car felt a little slower than the previous tune, but at the top you said you only had one tune loaded? Am I misunderstanding? I wonder if the damage was done previously and the piston let go later. Can you see any stress cracks in the piston leading away from the hole? I had a blown ranger blow a hole in a piston on a cold start, found out after the fact that it had been run with a tune way to lean previously, even though my tune was on the money. Engine builder said he was surprised it lasted as long as it did.


Good luck man.
 

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Discussion Starter #5
Fordtruckman. The car was originally on trinity tune and felt good, then did head gasket injectors and the rest of the stuff. Then installed The new aa tune seemed good but clutching was not dialed in. No noise before blew just poofff and coasted to a stop. Plugs were put in with a spark plug socket to insure no closing of the gap. I’ll get more photos when I have the head off.


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My guess is detonation. Everything else came after.
 

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I'll third the dropped valve, curious about the spring too.


Would lean conditions cause valve drop ? Just curious because the plugs look brand new. No fuel on them.


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No, usually the spring will break and let it fall in or if it's an interference engine overevving can cause valve float and it hits the piston. Could also be overheating causing the valve to stick in the guide.

If you had lean/detonation you would see signs like spots of melted metal on the piston, spots on the plug even. Of course it's so beat up you can't see much.

What does the spring look like?

More pics?

Oh, saw the head just break off the valve right after a 6 second run on a methanol fueled dragster not long ago. The crew was cranking it over by hand when it locked up. They pulled the head and no damage! The valve head must have just popped off after it was shut down. Owner got lucky on that one!
 

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EE
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The springs sure look OK from the picture. Looking back through again at the first pictures you posted, it sure doesn't look like any case of detonation induced failure I have seen, but I am also not a seasoned expert, just a shade tree mechanic.



Based on the views of the undamaged cylinder side, there doesn't appear to be any signs of detonation there. This would mean to me that whatever caused this, is more likely to be exclusive to the cylinder side that failed. Possibly a bad injector on that side? Or just bad luck with a defect on that valve stem strength from the factory? I'm curious to see the valve guide on the inside and see if it is damaged or worn severely.



But then again, there are no signs of pitting due to detonation on the bad cylinder side either; the valves would likely have pitting, and none of them that I can see anyway, exhibit this. The more I talk through this the more I think this was caused by the valve only, not detonation.



I feel like we can rule out float as the cause though right? You were just cruising and not at high RPMs? And the spring/retainer assembly appears to be OK. It seems to me maybe the valve got stuck on the way back up and then the piston hit and broke it off the stem. The rest from there is the damage you see in front of you. The question is why did it stick?





I hope I am not steering you down the wrong path; again I am just a novice. If anything maybe someone who knows more can point out errors in my theory and it will help identify the cause by process of elimination.
 

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Interesting pics,

1 - Are those the OEM pistons?
2 - What did you mean by "very close"?
3 - You would need to remove the plug shell to properly read the insulator but the timing mark on the strap looks long.
4 - Clearly the valve failed but whether it was heat transfer related or heat load related would require a metalurgic cut and not worth the time.
5 - I personally think you stuck that valve due to to heat load and then impacted it causing the carnage. It almost ALWAYS happens during the "shut down" as there is no additional cooling charge coming in and thats also when the valve temps spike. When I was involved with the SB-2 program the drivers had to VERY careful with the throttle after some hero laps....in a boosted deal its magnified x2!

- Scott @ MCB
 

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Discussion Starter #20
Interesting pics,

1 - Are those the OEM pistons?
2 - What did you mean by "very close"?
3 - You would need to remove the plug shell to properly read the insulator but the timing mark on the strap looks long.
4 - Clearly the valve failed but whether it was heat transfer related or heat load related would require a metalurgic cut and not worth the time.
5 - I personally think you stuck that valve due to to heat load and then impacted it causing the carnage. It almost ALWAYS happens during the "shut down" as there is no additional cooling charge coming in and thats also when the valve temps spike. When I was involved with the SB-2 program the drivers had to VERY careful with the throttle after some hero laps....in a boosted deal its magnified x2!

- Scott @ MCB


Scott,
Thank you for your input! what I mean by very close is that it was 0.01 from the spec sheet, and it wasn’t that one that failed. As far as I know factory pistons. With this amount of damage would you replace block as well? Or rebuild/ pistons, mid deck, head ?


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