Damaged my YZ400f motor :(

2 replies to this topic

Posted August 30, 2006 - 10:57 PM


hey folks,
First off, ill start by saying i believe i damaged my yz400 motor(99 model) on my last riding trip, and now i need some help and input on what would be the best way to go around it.

Story is...
Was going through a creek, waist deep, very rocky surface, and me beeing a noob with trail bikes means i dont have too much experiance, but im very motivated and like trying and giving everything a go, so why not!
Anyway, i fell off and the bike was covered in water for about 10sec, stalled.
I then pushed it to dry land and used the decomp. lever to get teh water out of the system, and after a while(it took a long time to get it started again) it eventually started but would only idle, and as soon as i accelerated, it woudl stall. But my main concern is, after starting it for a few times, it then suddenly started making a big end/piston slap kinda noise, so i left it at that

1). I would be after a rebuild kit, where could i find these(dealers?) and what would i get with a kit? If anyone can give approx. price, that would be helpfull as well.
NOTE: i live in australia, and would need someone that will ship internationaly! , does TT sell these parts and overseas shipping?

2). Should i stick with teh stock oem, or someone like wiseco? I heard wiseco make a bit more noise, so i would be leaning towards teh oem kit.

I have removed/dissasembled the top head/piston/cylinder/clutch assembly and side covers to check the gears ect thats inside teh case.
I havent split teh casing apart yet as i dont see no problems with teh rod, has slight side to side movement but no UP and DOWN movement!
The cylinder head seems to be in good nick.

Problems i found so far:
1) piston to cylinder bore clearance - got 0.20mm ( max is stated at 0.10mm?) Would this be the reason i get the noise?

2) 2nd piston ring gap is excessive- 1.16mm (max is 0.80mm?)
Cylinder bore condition seems good, yet to measure it tho, no tools at the moment.

3) another confusing part i dont get is...
when i checked my timing, i lined up to TDC, exhaust cam was lined up with head(normal) BUT... Inlet cam was one tooth off( was one tooth higher then where it was meant to line up with head).
Now, the question is, is this normal? as ive been reading something about YZ timing so not sure if this is what they mean by that!!! OR , did it jump a tooth???
When they talk about yz timing, what do they exactly mean? i dont wanna put it all back how i think it should go in and then later on find out it was meant to be one tooth out/different, if you know what i mean?
By one tooth out, i mean teh inlet cam will/is timed differently then what teh book says it shoudl be( book says lined up with cylinder head line.

Sorry for soo many questions.
I will also be doing all this myself.
Thanks guys and hope to hear from you soon

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  • grayracer513

Posted August 31, 2006 - 08:09 AM


It likely wouldn't run under a load because of water in the float bowl. Water is heavier than gas, and separates from it, so it sits at the bottom. The pilot jet is at a higher level in the bowl, so it could have been clear of the water while the main jet was blocked by it.

Your piston is loose, but the noise should have been there before the fall. It could have been the result of water blocking off the oil filter, and/or mixing with the oil and reducing its ability to maintain a good film.

For a trail ridden 400, I'd stay with OEM. It's cheaper and more reliable, and the bike comes pre-engineered for it.

YZ vs. WR timing is a difference in the lobe centers of the exhaust cam only. The intakes are the same. If you line up at TDC and your intake cam is one tooth farther counter clockwise than it should be, as your post seems to indicate, it is advanced, and it's unlikely that that could have happened by itself, and was probably assembled wrong at some point. If it is one tooth farther clockwise (retarded), that could have happened on its own. Either way, be sure to inspect the teeth on the crank for excess wear, and check the chain tensioner. Replace the chain.

More on the YZ Timing Mod

  • yami racer

Posted August 31, 2006 - 08:58 AM


grayacer513 :applause: :applause: :thumbsup:

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