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I think its about time i ask for some help. getting in over my comfort level. Bought used 2 yrs ago. Cant remember how man hours on it, but not many. invoice says 800km when i got it. maybe i have put several hundred more on it.very little use, easy trails. never sunk. stored under cover. mild climate. so pretty new condition with light use and not swamped.
Quad ran fine, parked at friends house, then no start. codes 51, 51. had previous wiring issues so checked all of the electrics. replace the TBAP harness with OTB harness (found 3 worn wires). at one point had a code 22. reset the computer. no codes now. Fuel pump runs and there is normal appearing fuel at the injectors (i dont have a pressure tester for the rail, and i cant get the cap off anyway). There is spark on both sides. Changed the plugs, no help. tps, tbap and cps all good to the wiring harness at the CDI plug. Checked, charged and jumped the battery charges to 12.6 or so and discharges to 11.6 or so under cranking. it turns over easily but does not burn the fuel i know is going into the cylinder even though i know there is spark. thinking it must be out of time i had a look at the flywheel/timing ring key way (woodruff) and appears ok - did not remove the flywheel off the crank (was missing a bolt for my puller)....so all of this done 3 hrs from where i live and ran out of time. I was thinking the timing must be off. but as far as i can figure it can only be changed by computer.
Now i have the quad at home. checked the compression and 190 on the left and 65 on the right. so now i am looking for a mechanical issue. Still no codes. Ok so i pull the head off thinking i might have a blown head gasket ( btw i did notice a slight drop in the coolant reservoir) oil still looks normal. there is some mild scoring on the rear side of the pistons - about 2-3x worse on the 190 side (left), but too mild to catch a finger nail on. looks like that was coming from the casting edge on the case - is rough. the scoring does not progress all the way up the piston and is not scored at or between the rings. the rings look normal not scored and move freely. there really does not appear to be any blow by. the scoring on walls of the cylinders are even more slight and also is not all the way to the top. so mild i really dont think honing will make any difference. there is really not much to see with the valves, they all appear to be moving, nothing looks excessively worn. the under side of one valve had some light rust again on the good side (190). i can see the cam through most of the rotation and it looks ok, but i don't really want to go deeper in. turns over nice and smooth, no click, crunch or grind. So ... now we get to some questions.

1. could it have just been the head or base gasket? and would i see evidence on the gasket? it looks normal to me.
2. if the scoring is worse on the side making 190 lbs, could the scoring on the 65 lbs side really be the problem? do i need to replace the cylinders, rings and pistons?
3. could this be a valve problem even though they are hydraulic? FWIW they were just very lightly ticking and sounded very normal to me when the bike was running. stuck open exhaust? i know i should have been watching closer when i took the head off. they appeared to be going up and down nicely and evenly.
4. what else can give me low compression?
5. is it surprising to not even get a cough or a sputter with all this. i would think the 190 side would fire and it would try to run? do i have 2 problems?

THANKS FOR READING! i will try to get some pics of the pistons, and valves
 

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These engines r pretty stout and there aren't many tare down questions on them but I do recall a couple of worn cam situations. We're the lobes just basically wore down to nothing. There is a engine remanufacture nFlow that supports the forum hopefully he chimes in.
 

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You can usually see where the head gasket is bad if you have a blown head gasket. Just because you do not have a lot of scoring on the lower compression side doesn't mean you do not have any damage there, you could have excessive ring end gap wear etc. You mentioned that there is a little rust on the valves, and excessive wear. In order to do it right I would installed a new top end, piston, rings cylinders. Install new valves and lifters. I would also check the connecting rods to make sure they are in good shape. We sell a complete cylinder kit for $495.00 That includes cylinder, two piston kits and a top end gasket kit. We also sell a complete remanufactured cylinder head with valves installed ready to go for $275.00. I hope this helps, if you have any questions we will be glad to help! www.nflowmotorsports.com
 
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