Kz650 compression after rebuild

I would start with removing the cams then turning the engine over by hand just to eliminate the cams as your problem. If you still have resistance then pull the head and cylinder then check clearances. Do not forget to check the ring gaps they just might be the problem too.
When I assemble an engine I will manually rotate it during the build process just to make sure everything is turning smoothly. For instance when I finish installing the crank I will rotate the engine by hand if that is smooth I will go to the next step. After installing the pistons and cylinder I will rotate the engine if it is smooth then I move onto the head, and so on. If something is not smooth I will stop and figure out why, fix it then move on.

Did that process too

Everything was moving smoothly step by step

Everything turns smoothly also now everytime the engine is cold

The problem occurs only when the engine is hot

I am reclutant to take things off like cams, head and cylinders when the engine is hot

I didn't mean take it apart while it is hot I was simply telling you how I do things. If everything went together smoothly and you have this problem now when it gets warm your left with one choice at this point. Taking the top end apart one piece at a time until you find the problem. Now I am assuming this problem was not present before putting in the piston kit. If not then it is something that was introduced when adding it. Most aftermarket piston kits need a larger piston to cylinder wall clearance since the pistons are forged, not cast, they have different expansion rates. If the machine shop set the clearance to the stock piston specs then problems will come up, I have had shops do that.

I said i should take it apart when hot because it is the only moment when the problem occurs

When the engine is cold everything was smooth during rebuild and everything is still smooth now when the engine is cold

I think at this point i should speak with people who worked on my cylinder block to fit the wiseco pistons

I know the problem only comes up when it's hot but the piston to cylinder wall clearances are checked cold. That is a good idea to check with the machine shop, get the specs they used from them and see. The wiseco specs are usually on the side of the box or inside the box on a spec sheet.

I would not take anything apart yet.

You might want to remove the spark plugs and turn the engine over with a wrench on the end of the crank. It should turn reasonably easily. Do it both hot and cold to tell if you can notice a difference.

If the piston to cylinder clearance is too tight the engine will stick. I'll be surprised if this is the issue.

I will speak with shop people and run the tests you suggested.

Will keep you posted

Thank you

Vic

Nessism's advice is to be listened to.
Don't be pulling anything apart yet.
Assuming you aren't trying to start it in gear, just remove the spark plugs and crank the engine around by the kick starter using your foot then do it by hand.
You should be able to do it with very little effort by foot and only a little harder by hand.
Put one spark plug in at a time and see how the actual compression effects the effort.

baldy110 wrote: I didn't mean take it apart while it is hot I was simply telling you how I do things. If everything went together smoothly and you have this problem now when it gets warm your left with one choice at this point. Taking the top end apart one piece at a time until you find the problem. Now I am assuming this problem was not present before putting in the piston kit. If not then it is something that was introduced when adding it. Most aftermarket piston kits need a larger piston to cylinder wall clearance since the pistons are forged, not cast, they have different expansion rates. If the machine shop set the clearance to the stock piston specs then problems will come up, I have had shops do that.

+1
Air cooled engines need air flow over them while running.
Use a fan in front of the bike if you are 'tuning while stationary.


.

I never tune while the bike is stationary

I take a ride
Then i stop
Make some changes with air screws
Then turn the engine on and ride again
Always reading oil temperature on a display i installed

Temperature when i stop is always around 80° celsius. When i start the engine to ride again temperature is never more than 90° celsius

Ape did .002 clearance on mine and my ring gaps were set right at .0085 for the top rings (3 were right on and 0ne I opened up from .0055) and .011, .0115 to 13.5 for the second not having to do anything to them.

Sorry to chime in late here- but I'm running a very similar set up to you and Baldy. 720 Wiseco kit, ZR7 4-1 exhaust, VM24's with dyna jet stage 3 kit, dyna ignition... I've also never had issues cold or hot. Compression is where it should be for the high compression kit, and it spins over easily when cold or hot. Pretty well as easily as the stock set up.

Hopefully it's nothing too severe for you.