Rebuild won't run?



20 replies to this topic
  • allryder

Posted June 06, 2016 - 02:22 PM

#1

So a month back I was riding my bike and the bike had been smoking for a few weeks now. All of a sudden while riding I lost power and it felt like I was in too high of a gear, so I down-shifted. I did this and slowed down and let off the throttle to attempt to see what was wrong. The bike died when I was slowing down, and I could not start it back up. I took it home and ordered a rebuild kit because I knew it needed one and that it finally broke. My brother took the bike apart and found low coolant and low oil, both which I checked before going riding for about an hour. The cylinder was taken off and the cylinder coating had come off in several places, so I ordered a new cylinder. Everything was put back together, timing was checked several times and valves were just slightly out of spec but we figured we would check again after break in. We put everything back together and the bike wouldn't start after many kicks. Then we took the subframe off and verified that the bike was getting fuel(it was). Next we took apart the carb anyway and cleaned it. The second time taking it apart it looked like the valves were hitting the piston top because there were black circles on it. There was a lot of carbon on the valves so we cleaned that and are waiting to put it back together soon. The bike is a 2006 yz450f. Any suggestions on what to do or why it could not be starting?

  • cjjeepercreeper

Posted June 06, 2016 - 02:23 PM

#2

Do you have the piston in backwards, or valve timing way off?



  • allryder

Posted June 06, 2016 - 02:26 PM

#3

Do you have the piston in backwards, or valve timing way off?

Piston definitely isn't in backwards and I'm fairly certain the timing is right.

  • Hakkalugi

Posted June 06, 2016 - 02:44 PM

#4

Are you getting spark? You said youre getting fuel. 



  • Kickstart97

Posted June 06, 2016 - 06:22 PM

#5

Check spark

  • allryder

Posted June 06, 2016 - 06:33 PM

#6

Are you getting spark? You said youre getting fuel.

Ahhh yes I forgot to mention this I am getting spark. Is there a way that it could be sparking at wrong time? That's timing though right

  • Hakkalugi

Posted June 06, 2016 - 07:45 PM

#7

hit it with starting fluid and see if itll give you a little fire 



  • billygildark5007

Posted June 06, 2016 - 08:18 PM

#8

So it was smoking before the rebuild and afterwards it's still smoking? What color is the smoke?
Also if the valves were slightly out of spec and there was possible contact with piston why would you leave them to wait and see? If it skipped timing once (or improperly assembled) and still runs please don't test your luck...
What was included in the "rebuild kit"?

  • allryder

Posted June 07, 2016 - 02:38 AM

#9

So it was smoking before the rebuild and afterwards it's still smoking? What color is the smoke?
Also if the valves were slightly out of spec and there was possible contact with piston why would you leave them to wait and see? If it skipped timing once (or improperly assembled) and still runs please don't test your luck...
What was included in the "rebuild kit"?

The rebuild kit included the head gasket and base gasket, piston & rings, and circlips. Then I also got a new cylinder because the old one's coating came off.
I thought the reason it was hitting the piston was because there was a thick layer of carbon deposits.
It isn't smoking after rebuild, it isn't starting after the rebuild. It was smoking white/blue before the rebuild.

hit it with starting fluid and see if itll give you a little fire

Yes tried this nothing happened

  • Hakkalugi

Posted June 07, 2016 - 04:05 AM

#10

something is way off then, probably timing.



Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 0bigsilver6

Posted June 07, 2016 - 04:22 AM

#11

something is way off then, probably timing.


Agreed with this. Use a long screwdriver to find the piston at its highest point and see if it lines up with the TDC mark on the flywheel. If not, the flywheel key may have sheared off or something of the like.

  • Still Bill

Posted June 07, 2016 - 05:34 AM

#12

"Fairly certain"?  So, what you actually mean is "I don't know"?



  • allryder

Posted June 07, 2016 - 06:33 AM

#13

"Fairly certain"? So, what you actually mean is "I don't know"?

No what I mean is I was sure it was right until it didn't run and there are several suggestion now I am not so sure

  • billygildark5007

Posted June 08, 2016 - 06:25 PM

#14

Is it possible to post pics of the all the timing marks?

  • allryder

Posted June 14, 2016 - 11:18 AM

#15

ImageUploadedByThumper Talk1465931892.035713.jpg
So this is what the flywheel timing looks like. There are three lines on the flywheel... Which one do I use?

  • grayracer513

Posted June 14, 2016 - 01:40 PM

#16

The first two lines from the left to right are often joined by a horizontal to form a sort of "H".  These are for a strobe timing check.  The third line, the farthest to the right, is TDC.  Use that for cam timing.



  • allryder

Posted June 25, 2016 - 06:17 AM

#17

Thanks so i did that and it finally fired up but ran for at most a few seconds but this happened several times. Then the motor seized up and I found that the timing chain was complete junk. Just put in a new one and also a new tensioner just in case. I put it back together and tried to start it without the tank or subframe on and it didn't fire at all. There was a small squirt of fuel when I opened the throttle so there was still fuel in the carb so it should have at least fired right?

  • grayracer513

Posted June 26, 2016 - 06:17 AM

#18

If the chain was at fault for the engine seizing, it was because a valve(s) hit the piston.  They could have become bent.  Do you have compression?



  • allryder

Posted July 04, 2016 - 03:04 PM

#19

If the chain was at fault for the engine seizing, it was because a valve(s) hit the piston. They could have become bent. Do you have compression?

No I don't I just sent the head away to be serviced and before they do anything they are going to inspect it. One valve looked messed up when I took the head off, think it's broken?

  • grayracer513

Posted July 05, 2016 - 06:37 AM

#20

The worst case when a valve bends is that it breaks the bottom of the valve guide.  If they hit really hard, there can be damage to the piston, and the lifter may be broken.  It gets worse from there, but usually only if the valve head breaks off the stem.  You should be OK. 







Related Content

Forums
Photo

Megabomb Fitment by 288yz450


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
Forums
Photo

First Hare scramble tips by dhend8


Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
Forums
Photo

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F


Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies
Forums
Photo

Is it worth it? (Cam and High compression piston) by macgi77


Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.