Seized engine damage from "transfer of shock"?


6 replies to this topic
  • xlr8r

Posted January 17, 2007 - 07:29 PM

#1

Hey,
I posted a thread earlier about my seized piston due to a F-up I won't repeat anytime soon. It envolved not priming my oil pump after a rebuild. My new question is: Is there such think as damage caused by the transfering of the shock of a piston seizing thus locking the wheel at 45mph? A piston seizing is a pretty violent stop with a lot of enursia(sp?) behind it. Would that sudden stop likely cause things like crank-bearing, timing chain, gear, etc.-type-damage. Rockers still look great (I've been told that's next in line after the piston seizing from no oil in the top end). I also oiled and molied the hell out of every thing during the rebuild. Engine only ran about fifteen minutes (most of that was idling). Primarily I'm worried about "shock damage" rather than lack of lubrication. Thanks!

  • rcnutt

Posted January 17, 2007 - 07:39 PM

#2

sounds like a machining problem ie. clearance/tolerance issues

  • steed2

Posted January 18, 2007 - 05:54 AM

#3

sounds to me like a tolerance issue also
did u have it bored? did u have the bottom crank brg. replaced? what did u exactly do?

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  • steed2

Posted January 18, 2007 - 05:56 AM

#4

also to answer ur question no i bet everything is fine i seized my 94 yz250 at 60mph wide open and everything was fine {and that was a yamaha...lol}
she'll be ok

  • cleonard

Posted January 18, 2007 - 11:06 AM

#5

Hey,
I posted a thread earlier about my seized piston due to a F-up I won't repeat anytime soon. It envolved not priming my oil pump after a rebuild. My new question is: Is there such think as damage caused by the transfering of the shock of a piston seizing thus locking the wheel at 45mph? A piston seizing is a pretty violent stop with a lot of enursia(sp?) behind it. Would that sudden stop likely cause things like crank-bearing, timing chain, gear, etc.-type-damage. Rockers still look great (I've been told that's next in line after the piston seizing from no oil in the top end). I also oiled and molied the hell out of every thing during the rebuild. Engine only ran about fifteen minutes (most of that was idling). Primarily I'm worried about "shock damage" rather than lack of lubrication. Thanks!


I've seized many engines and never had this type of damage. They were mostly two strokles though.

Usually seizuers don't actually happen in an instant. What happens is the friction goes up and up. It usually stops the engine over a few turns. There shouldn't be shock type damage. Take a close look at the rod as it is one of the parts that can get bent. The crank is another. I think that the XR6 crank is just pressed together. A shock stop would twist the bid end rod pin between the two sides. Look for the sides being even. The forces are also applied to the transmission and the primary gear. Same for the balancer.

The classic case of sudden stop damage is in an airplane. If a mishap occurs that causes the prop to strike the ground, the engine gets stopped in an instant. I have seen such an engine. The crank was twisted and some of the rods were tweaked.

  • xlr8r

Posted January 18, 2007 - 06:29 PM

#6

Sorry, the question was a bit cumbersom so I'll try to clarify. I [I]do[I] know what seized the piston (no oil in the top end from the oil pump not being primed after a complete teardown). What I was wondering now is whether I should start replacing the fairly new timing chain, tear into the case for another look at the crank (again), etc. As I'm sure you can imagine I'd rather not take the whole thing apart again just out of paranoia. Thanks for the words of encouragement. "I'm sure it's fine" is what I hoped to hear.

The work I did prior to the seize was replace the counter-shaft and seal, piston bored, new valves and re-seating.

After the seize I re-checked the rod and it looks good. Small end clearance is good. Gap between lower rod and balancers is a little bigger than the manual would like it to be, but it was the same prior to the seize.

  • Mikeysduck

Posted January 18, 2007 - 08:18 PM

#7

It sounds like the top end is off. Can you put a dial indicator, through the opening? Check the crank halfs for round. Mark the high spot on both halfs..You should have a better idea. If you put it back together and it runs ok but vibrates more than before... the crank did twist.





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