Power valve hitting piston

[shakenbake]

Hi
Stripped the top end today after the bike starting making funny noises and looks like the power valve has been hitting the piston.

I can fix this with new piston etc but just wondered if anyone had any idea why this had happend.i have not tinkered or adjusted the power valve in any way, previous to it going bang i had slight loss of power. Then crunch.

The bore and everything else seems ok though, just the piston that is knackered and the power valve has grooves on it where it has connected with the piston.

Any help would be appreciated.

Thankyou

Jay

[knackeredMk1]

Should never happen and is impossible if a rebore is done correctly. There is no way without some kind of catastrophic failure that this should happen,

viewtopic.php?f=20&t=5267

Pistons can suffer severe wear on the exhaust port side due to poor maintenance or partial seizure without hitting the power valve.

[shakenbake]

Looks like I've had a catastrophic failure somewhere then as the power valve has the same markings on it as the piston

[shakenbake]

And its all standard. With regular maintenance. Although I must admit, I haven't played with the power valve cables much, perhaps the cables have stretched causing the valve to move slightly?

[knackeredMk1]

The power valve should never hit the piston - No matter what position the PV or piston are in. PERIOD.

Two really far fetched options I can think of -

With truly terrible maintenance the piston and rings could perhaps become so loose in the bore that they caught the PV but that is almost unbelievable.

For some reason (and I can't think what) the PV shaft could get unseated or bent. This could cause the PV to move into the piston.

Much more likely that due to wear, poor maintenance, or some kind of oil/jetting failure the piston has partially seized and the aluminium scrapings from the side of the piston have deposited on the PV.

[shakenbake]

Ok
Mate

Thanks for the reply I'll check it out.

Thanks again

[shakenbake]

So just a bit of an update and some help required if possible.

Turns out my cdi/ecu was knakkered so sent it to 2stroke lab to get repaired which I received back yesterday (great service and comms by the way)

Fitted the cdi, started the bike, the power valve instantly moved to the closed position I think (right hand side lifted up to the max) I revved the bike and tried setting off then the bike cut off.


I adjusted the power valve cables so that the points align as it says to in the workshop manual, but now when I start the bike, the power valve doesn't move and then when I try to set off it just cuts out... Confused.com, I'm just hoping I haven't knakkered the ecu/cdi again somehow as the power valve seems to have stopped moving when revving he bike??? The servo doesn't seem to be trying to move at all..... Could I have Nik naked the cdi/pgm again???

Thanks in advance

Jamie

[gregorious77]

the valve turns anticlockwise to open. so right hand side up is opening.
Did you check the valve was free to move from one end of its travel to the other? you should be able to move it with ease from one stop to the other. Are the cables well oiled and free moving? did you connect the cables the right way round? if it was opening all the way on tickover it may be the cables are backwards! Is this an AR? the cables cross over as they pass across so front of servo goes to back of valve and vice versa. mine were on backwards and it killed my PGM after it had been repaired by Nick.

[shakenbake]

Hi

I'm sure the cables were the right way round but I shall re check, if I have to send it away again that's what I'll have to do. I took lots of pictures and put it back the way it started I'm sure but I will double check, the power valve moves freely and all cables are clear for movement and well lubed. Thanks for the response, I shall investigate further.

Cheers

[jm38]

check your rectifier if it goes it buggers the pgm powervalve circuit