Polaris sportsman backfiring.... any help appreciated!! STUMPED

[whitegold]

So this is a polaris 2013 sportsman 800 efi, it started out running on one cylinder, we performed a compression test, 180 psi on pto side, 30 psi on mag side, so we disassembled the engine and found camshaft to be worn off and 2 lifters to be totally collapsed, but the crankshaft and connecting rods were in good condition. The pistons were also in good shape but the rings were questionable so they were replaced.

We put in a new aftermarket camshaft, new lifters, new water pump, new magneto/stator, new fuel pump ( not the regulator as it is holding at 39 psi), used cps and it was good, new tps, new map sensor, new coil, new spark plug wires, new ECU, new injectors. The flywheel key way is intact, not sheered, all the gears are timed properly, new plugs, adjusted the tps, checked intake boot for cracks, checked ETC, and checked wiring. We checked the oil pressure and at idle 3 to 5 psi, and then at 3500 to 5000 rpms we get 40 to 55 psi. The rocker assembly and valve movements seem to be good. We checked the exhaust for obstructions and it was clear.

The computer is not sending out any codes, not communicating with the scanner.

The engine will run now but it backfires from the throttle body.

STUMPED!!! Any ideas out there as to what could be causing this?????



https://www.youtube.com/watch?v=BM5jz1az4q8&feature=youtu.be

 

[sirkdev]

Bad valve seats? Or cracked seats?

 

[Teth-Air]

Timing chain has jumped in my opinion.

 

[Teth-Air]

If it the timing chain it usually happens after a over-rev condition. You may be able to reposition it and tighten the spring on the adjuster and be good to go. Depends if it is worn out or not and if any valves got hit.

 

[Lund]

You have a valve timing issue, when you assembled it it is possible that you miss installed the chain and have the valves not quite closed.
I would pull some covers and recheck the gear timing and reset the gears and chain. You will most likely find they are off one tooth.

 

[neilsleder]

My brute force did the same. Timing chain jumped

 

[whitegold]

There is no timing chain on this quad, it's gear timed.... all the timing marks are right on.

 

[Lund]

There is no timing chain on this quad, it's gear timed.... all the timing marks are right on.

I should of read the first post more carefully but yes the 800 sportman is a push rod motor so no timing chain.
Not that this post helps you any but it is a timing issue.

 

[whitegold]

agree, so we ordered a new OEM polaris cam and see if the aftermarket cam isn't lining up quiet right....