P500 p500 timing drift?

[BLZI]

hey.. i could use some help if yall can.. was pulling on a talon to get it out of some mud then right after i started hearing my p500 making a different noise from the exhaust or so i thought.. down hill from there.. got worse then wouldnt run at all.. i get it home then it ran for about 2-3 min then started making that same noise.. just a change in tone of the engine not a knock or anything like that.. died and no start.. noticed pressure coming back into the airbox and the throttle body pulsating.. shot a little starting fluid in the intake and wouldnt fire off.. later i tried to start it and it would start and run fine then again died and no start.. i noticed that when it would start the throttle body wouldnt pulsate.. i pulled the head and noticed the piston had kissed the intake valve.. almost seems like the timing is moving.. fine one second then off to the point that im losing compression back into the air filter the next.. is this possible? with the shot of starting fluid not working kinda rules out fuel in my mind. seems like the timing wouldnt move back and forth if it jumped. thanks in advance for any assistance.. i did purchase the service manual but its only going to help if i already know whats going on

 

[pappyo]

If the piston hit the valve.( valve is most likely bent )
On the compression stroke intake should be closed.
Bend intake valve will allow compression back into the airbox as you describe.
With the head off put a couple spoons of gas in the intake port see if it leaks out around the valve.
On other method pull the valve out of the head Chuck the valve in a drill or drill press you'll see wobble.

 

[BLZI]

i did put the valve in a drill and it seemed perfect.. seat and all.. has me confused. didnt notice any wear on the shaft either

 

[NTCPrezJB]

Cam chain?

 

[906UP]

If the valve "kissed" the piston it's junk whether you can see a wobble or not. They're cheap, just replace it but you need to figure out what caused it in the first place. Since you think it's intermittent I would inspect the rocker shaft to see it it's binding, other possible causes could be a broken or weak valve spring, a lifter bucket hanging up and not allowing the pushrod to go back down......a few other things that are possible but unlikely if it's intermittent are a bad camshaft, collapsed chain tensioner, stretched cam chain, broken cam hold down, stripped cam drive sprocket on the crank.

The whole system is really quite simple, if you can post some pictures we may be able to help you a little more.

 

[pappyo]

A little more info on the cause may help.
What gear & RPM. when pulling on that talon?
Questions:
What year, miles ,hours , maint frequency & oil used?
Does it get hard use vary often? ( on offence ment here) do you drive like a old man ( me ) or like you stole to it just trying to track down all possible causes.
Find the problem ,--find the cause -- it's needed to determan the Final Cure & cost.
So far you have a piston & valve needing replacement BUT WHY & what else?