A few days ago I was riding the 07 TRX450ER. Ran great, just like any other day. Put it away for a few days, came back today and it wouldn't turn over. By what I mean it wouldn't turn over is that the motor itself wouldn't turn over, like it was seized. When I hit the starter it let out a high-pitched whining noise. Battery was completely charged, so I know it wasn't due to the starter not having enough juice going to it. Pulled the plug to see if no compression would allow it to turn over (did this to see if the starter was bad.) Still nothing. Tried to roll it in gear, wouldn't budge.

Any ideas on what it could be? I have no idea if the PO rebuilt at all, or how many hours total he had into it. I was thinking the cam chain may have slipped, and caused a valve to be stuck open just before TDC, thus keeping the piston from moving.

Thanks in advance.

try turning the engine over by hand, usually on one of the side covers there will be 2 small covers for the timing marks, i think on the left side on a 450 but not sure. remove the center cover( i think the cover has a slot for a large screwdriver in it ), behind the cover there should be a bolt. put a socket and bar on it and turn gently, make sure the trans is in neutral. if it still wont turn over it sounds like you may have bigger problems

Did the same thing I did before, pulled the plug again and hit the starter to see if it would turn over. It did today, bit it would "stick" occasionally. (I think it may have done the same thing the other day, didn't put my finger in the plug hole then to see if it was actually turning over, I only listened to the starter.) Wouldn't turn over at all with the plug in. I think the starter may be bad.

The 06+ 450R is notorious for the starter clutch. 9 times out of 10 when ppl think they need a starter they really just need the starter clutch (one way bearing). The access plug to roll the motor over by hand is located on the right side. It takes a 10MM allen head to remove the plug and an 8MM allen head to rotate the motor.

MX450R, on 27 July 2012 - 08:39 AM, said:

I went up to a local shop yesterday and asked them about it, they said basically what you said. Apparently there is also a way to convert it to a kickstart. I might go that route.