Head change

[W8TSON]

When replacing the piston for a brand new item does the head need to be changed also?

[roostafish]

No..... I wonder why you thought that though. Why would you think you need to change the head? If anything, while it's off, you could check the squish with the new piston in and do the squish band mod. It made a huge difference in my bikes jetting and performance.

[jostby]

I'm thinking kind of a strange question so I am going to give a couple answers in case friends are "telling you what to do"....

No, the head does not ever have to be replaced unless it is damaged or you change from say a 250 to a 350.

Some people may elect to not even remove the head. If you have room you can remove the cylinder from the engine case to access the piston without unbolting the head from the cylinder. But for the cost of 2 o-rings that would be unwise. Remove the head so that you can easily remove and clean the power valve at the same time.

If you have a 4-stoke it is probably wise to remove the head and disassemble it to inspect the valves, valve seats, cam, etc. (actually you have to remove it on 4T to access the piston).

Good luck!

[W8TSON]

I lent my bike out to my mate the other day at our local track only for him to come back with a seized kick, The bike still moves and selects gear,

I phoned someone today local about getting the bike booked in for getting it fixed, he said it sounds like the piston had gone, got too hot ect.

Im 99% sure he said head or poss could have been cylinder

[jostby]

possibly head if a 4-stroke. If a 2-stroke then if you are lucky the piston is stuck but won't be the head. Whip it apart, only takes a few minutes.

[W8TSON]

Its a 2-stroke, Im not that very keen on taking the bike apart as i wont have a clue where to start

anyone know if theres a manual online or that?

[roostafish]

I believe there is a motor manual here on this site. No worries though. If you're at all mechanically inclined, it's such a cinch. It's tougher to take the fuel cell, exhaust, coil, and coolant lines off than it is to do a top end rebuild...... no joke. The starboard side of the bike has a cover for the power valve acuator, which needs to be removed and disconnect the PV actuator, it's obvious once the cover is off. Then take off the four nuts holding the cylinder down (like mentioned earlier, there truly is no need to remove the head, you may want to to inspect it, and for peace of mind). You may need to whack the bottom of the cylinder with a dead blow hammer to free the base gasket, then simply lift it off. The piston is held by a pin and circlips, stuff a couple of rags under the piston in the crank area to keep junk (and stray piston clips) out of the bottom end, push the pin out and remove the piston.

Look closely at the cylinder bore for damage (most likely it's okay if the bike was running, honestly, the coating it pretty tough). Reverse process for reinstallation.

While it's off, check the rod for verticle play, any at all means replacing the rod is in order. Take the ignition cover off and grab the flywheel, pull up and down on it to check for crank bearing play, again, any at all means it's time to crack the cases open. This is also a fairly simple job, and is intimidating if you've never done it before, but not as bad as most people make it out to be.

I hope this helps, and I hope you don't have expensive problems to fix. Keep us posted.

[roostafish]

Another thought has come to mind. Is the bike siezed? Is it running? If so, do you just feel it is time to replace the piston? That's a good thought actually. Is there any strange sounds? If you're trying to fix a noise, it may help to listen carefully. A classic crank bearing noise would be a "white noise" type sound. A worn piston generally makes a slapping sound. If you're worried about smoke, not noise, that usually is a jetting, or soaked muffler, two strokes make smoke. I suppose an inefficient running two stroke smokes more, but again, likely jetting, not worn parts.

[W8TSON]

You make things sounds so easy roostafish The bike isnt running the kick wont wove theres no play in it what so ever I can still move the bike about back wheel isnt locked on and i can still select gears ok.

Think i have found the right manual so hopefully that will help me abit

Replacing the piston the only things i would need is gaskets and piston kit correct?

Thanks mate

[jostby]

If the piston is seized you may have to send the cylinder out to be repaired. The Nickasil coating inside the cylinder is very thin and if scratched off must be repaired. Take it to a bike shop and have them look at it if you are unsure.

You say the kickstart will not move and is locked up. If you put the bike in gear can you move it? Like to coast start it? Pull the spark plug out, put it in gear up on a stand and try to rotate the back tire. That should verify that it is either a kickstart issue or engine issue. If the cylinder comes off easily then the piston isn't seized, the problem is lower (crank bearings most likely)My bike locked up once and it was a crank bearing issue. What year and size is your bike?