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About srdav

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  1. srdav

    Locked up XR440

    Tom, Thanks for your input. Within 1 minute of the lock-up event (skidded to a stop) I started the bike on the first kick and it runs just fine with no indication of vibration or noise problems. I then rode 2-3 miles home thru all gears with no repeat. Once home I lets it sit for an hour or so and restarted on the first kick and with no noise. Engine rotation is slooth and normal thru the kick starter with plenty of compression. This is really a mystery as to what could bind so tightly to lock up the back tire and then show no symptoms immediately afterwards. Steve
  2. srdav

    Locked up XR440

    No. It is the original stock crank and rod
  3. srdav

    Locked up XR440

    Thanks, I will pull off the head and check the cylinder wall. I did verify the piston to bore fit accurately as well as the ring end gaps before reassembly a few days ago. Back to the original failure a few months ago, the removed piston measured under size at the skirt to the tune of about a .020 clearance with the bore. This was not due to wear as the cross hatch area was still visible on the bore as well as the original lathe machine marks on the piston. No sign of oil starvation or excessive heat. Have you ever experience a piston lock-up that resulted in deformation like this to the piston? I know that the piston to bore fit was correct when I originally modified it to a 440. Steve
  4. srdav

    Locked up XR440

    I have a problem that I can not resolve. I punched my 2000 XR400 into a 440 with a Hotcam about 2 years ago with nothing but good results. A few months back during an easy ride, my transmission countershaft sheared just inboard of the right side bearing. When the shaft broke I was decelerating and the engine was at mid to low rpm. Well, $800 in parts and 2 months later, I just finished reassembly. When I had the engine apart I checked every part I could item for signs of damage or wear and replaced anything which was outside usable limits. No significant finding except for the countershaft and a galled piston and scratched sleeve. The major items replaced this time were: New 11:1 89 MM piston New overbore Sleeve New Countershaft and bearings All new seals New sprockets and chain I am confident that the engine is properly assembled. During my first easy break-in ride I was going along at about half throttle in 4th or 5th and the engine came to an immediate stop (locked up). The back tire skidded until I pulled in the clutch. I pulled over and found no signs of any external damage and then started it on the first kick and was back riding again. No repeat for the next few miles home. No abnormal engine noise, no erratic shifting, no other signs of anything wrong. Has anyone out there ever heard of an intermittent engine lock-up on the XR400? Any thoughts on what could have been the root cause of the original countershaft failure? Would love to hear any advise you might have.