Intake valves hitting piston

i dont know if my story matters here but it mite
back in 09 i did a crank in a kx250f i used a 08 cank i thought it was the same it wasnt and i had the same poblem you have so i moved the intake cam a couple teeth and the bike ran fine come to find out the 09 crank had the keyway fo the flywheel in a differnt place, so i ended up putting the rite crank in
did you buy it used? whats it got for a crank
maybe check and make sure the flywheel key is still there

Theres a possibility the Piston could be in backwards.....please dont ask why i say that

Yea its used. Its a low hour bike, all original. I took the flywheel off to replace the cam chain, the key is still good.

My intake clearance is .15 on one and .13 on the other. Within the service manuals spec. Hotcams card says .15 for clearance. Is the .02mm going to matter? Thats all i can think of

walent215 wrote:

Theres a possibility the Piston could be in backwards.....please dont ask why i say that

Haha thanks but i definitely checked that one

Dunno bout you guys but the intake cam looks like it needs rotated a tooth to match the exhaust.. my 450s cams are at the same opposite angle at tdc

.02 will not cause that issue

In the 2nd picture, was that taken at what you believe is TDC? If so, your cam gear alignment is off by a significant amount.

With the dots aligned properly, like shown in your 1st pic, the exhaust cam lobes should be pointed at about 10 o’clock and the intake cam lobes should be pointed at about 2 O’clock. Like it is shown in KB’s post on the 450.

Another way to check the gear alignment, is by confirming the circular hole in the cam gear is inline with the camshaft’s lobes.

The cam gear can spin on the shaft on these models, it’s happened to mine before. They should index the cam gear onto the shaft but they don’t. You can tack weld the gear in place like I have done.

pCp 252 wrote:

In the 2nd picture, was that taken at what you believe is TDC? If so, your cam gear alignment is off by a significant amount.

With the dots aligned properly, like shown in your 1st pic, the exhaust cam lobes should be pointed at about 10 o’clock and the intake cam lobes should be pointed at about 2 O’clock. Like it is shown in KB’s post on the 450.

Another way to check the gear alignment, is by confirming the circular hole in the cam gear is inline with the camshaft’s lobes.

The cam gear can spin on the shaft on these models, it’s happened to mine before. They should index the cam gear onto the shaft but they don’t. You can tack weld the gear in place like I have done.

My 2nd pic is where the motor stops turning. The very last picture i replied with is where TDC is.

Also, i rotated the intake cam to make it more flat(opposite but same angle as exhaust cam lobe) and that did not help the situation.

pCp 252 wrote:

In the 2nd picture, was that taken at what you believe is TDC? If so, your cam gear alignment is off by a significant amount.

With the dots aligned properly, like shown in your 1st pic, the exhaust cam lobes should be pointed at about 10 o’clock and the intake cam lobes should be pointed at about 2 O’clock. Like it is shown in KB’s post on the 450.

Another way to check the gear alignment, is by confirming the circular hole in the cam gear is inline with the camshaft’s lobes.

The cam gear can spin on the shaft on these models, it’s happened to mine before. They should index the cam gear onto the shaft but they don’t. You can tack weld the gear in place like I have done.

kb228 wrote:

My 2nd pic is where the motor stops turning. The very last picture i replied with is where TDC is.

Also, i rotated the intake cam to make it more flat(opposite but same angle as exhaust cam lobe) and that did not help the situation.

This is the 250 at tdc not a 450. Sorry for the confusion.

Your cam timing is way off as described in previous post as the lobes are out of position.

Paw Paw

Paw Paw 271 wrote:

Your cam timing is way off as described in previous post as the lobes are out of position.

Paw Paw

Can you elaborate? Comparing the service manuals diagram and this picture, the lobes look fairly close.

Fairly close is just not good enough. Compare you photo to the manual photos.
When you put in the valve kit...Did you do it or a good shop? Was the piston to valve clearances checked?

Paw Paw

Paw Paw 271 wrote:

Fairly close is just not good enough. Compare you photo to the manual photos.
When you put in the valve kit...Did you do it or a good shop? Was the piston to valve clearances checked?

Paw Paw

I put them in. Figured a brand new head & valves wouldnt have an issue. After looking through the service manual, theres not even mention of checking that when replacing the valves/top end. I dont even know what the value should be.

Im at the point where im going to use a long screwdriver to find tdc and compare it to the mark on the flywheel - dont like doing this but its worth a shot.

Also if hotcams messed up on the cam gear timing, ill have to have them replace it.

Or i need to double up on base/head gaskets.

As mentioned above check alignment of camshaft gear to the cam lobe, the round hole should line up with the top of the lobe.

RCF wrote:

As mentioned above check alignment of camshaft gear to the cam lobe, the round hole should line up with the top of the lobe.

Thanks, that makes sense.

After work ill throw a stock cam in and just make sure i dont have a piston/valve clearance issue. Once that checks out ill get hotcams to replace my cam with a good one.

I fixed this.

The flywheel has 3 marks in 3 different locations for some reason. Obviously i mixed them up. I used a long screwdriver in the spark plug hole to find tdc, lined up the closest mark to the ignition cover, timed the cams and the motor turns over.