rings fried

[greg_gorrell]

today me and a few friends went riding and we were ripping up this lease road racing each other and one of my buddys 400ex started losing power. he said he kept giving it gas to keep it running but when he left off it stalled. at first when he tried to start it, i thought i seized up. his rings were starting to go bad so i kinda figured one broke or something liek that but he let it cool off and it fired up after 20 minutes. it did sound right tho, kinda like there is some knocking going on in there and he did say when he started it before the ride he heard that same knocking. but anyways he took it easy on the way home and we added some oil to it after letting it cool down a bit. he had 10w-30 in it and out temp is around 90 and very humid. so im thinking that the oil got to thin and didnt lude it up enough and something happened. but before all this happened it only smoked a little bit, barely noticable but now as soon as he fires it up it just smokes like hell and doesnt quit. im thinking he is going to need some new rings and even maybe a new piston...maybe a .020 over bore. anyone else have any ideas? we didnt get a chance to tear the motor apart yet.

[RiderTRX400ex]

the knocking sounds like piston slap, happened to me but only HOT and under a lot of stress a few months after i got it all stock... easiest way to tell is do a compression test..

[RiderTRX400ex]

and yea the oil sounds pretty thin to be runnin at that temp...

[greg_gorrell]

yeah i was thinking that the oil is too thin also...it is 10w-30 and it is very hot and humid out...so he changed that and im telling him to get a new piston and rings...im thinking its going to need to be honed to .020 over. but im doing the same with mine and throwing in a high comp piston and some hot cams.

[greg_gorrell]

it sucks trying to keep them cool. i wish they would come out with liquid cooling. but yeah i also smelled his old oil and it smelled pretty burnt up.

I bet the valve seals are gone bad. I had a xr80 that continuily got slower and smoaked bad. the valve seals where junk.

[ReconRider25]

do a compression test. it wont idle if the compression is too low. its probably at the point where its got enopugh compression to run when its colder but when the engine heats up itll start bogging and loose power and wont want to run on its own. you might be able to just hone the cylinder and do rings but youll never know until you tear it apart.

[greg_gorrell]

yeah hes been working quite a bit so this weekend we are going to tear it apart. it stoped by today and it fired right up and idled for 5 minutes until he shut it off. im still telling him to order the piston and rings but im pretty sure the vavle seals arent too bad but like you said we really wont know too much until we tear it apart. what sucks is neither of us have the tools to check the compression.

you cant rent tools like that at vip. the car store that sells windshiled wipers and ****, will they rent out tools also.

[greg_gorrell]

the local shop might have them but the mechanics know about as much as the customers around here.