My bikes engine has lost compression?

Question

I have a 2000 model XR400 and it seized up on me the other day, it started fine but once i had been riding for a bit it died and seized up, it had too much oil in it (dumbass me), i took the spark plug out and put some CRC down there and it kicks over fine but i think it has lost compression, it still has some compression but not like it used to, it will turn over but won't start. I think i have blown a ring or something, I have taken the rocker cover off the cam has a bit of a worn patch. I will take the head off tomorrow. What's the best way to fix it? it it probabally a valve or a piston ring? or have i got it all wrong?

Thanks for any help.

Answer 1

something in your description doesn't add up.  you state it died and seized up ... typically, it seizes up causing it to die... anyway...

borrow or buy a compression tester ($30-40) and check to see what PSI you have.  if it's under about 125 PSI, you need to tear into it and as a minimum replace the rings & have the cylinder honed.  if there is any major scoring on the cylinder walls or piston skirt, you will probably need to oversize bore it with fresh piston, rings to match the new bore.

while you are that deep into the bike, it would probably be a good idea to have the valves & seats resurfaced.  check for any excessive wear on the cam, keepers, tensioner, guide, etc.

Answer 2

Replace both valves and rings. If you do the one always do the other. Why have to do a job twice

Answer 3

might as well rebuild it.

Answer 4

If it has seized up,then odds are you will need a new piston,rebore and replate.

Answer 5

If it seized at the very least it will need new rings and a cylinder hone.More likely is an overbore with a new oversize piston and rings.If you have a compression tester you could check the compression.Test it and then dump about 2 tablespoons of oil in the plug hole and test it again.If the compression goes up with the oil added it's the rings,if not then it's valves.

Answer 6

If your not a motorcycle and ATV mechanic, just take it to a shop, it will be better in the long run.