Picked up an '03 YZ450F


51 replies to this topic
  • G-BRO

Posted July 09, 2014 - 06:44 AM

#41

I love threads like this. Good job. Thanks for posting all of the progress pictures. Good to see somebody putting work into an "older" bike. Please let us know how the bike runs. Did you end up re-using the stock chain tensioner?

  • mvrk10256

Posted July 09, 2014 - 06:46 AM

#42

I did reuse the stock tensioner. However the bike wont run due to the warped head. 



  • grayracer513

Posted July 09, 2014 - 08:53 AM

#43

I did reuse the stock tensioner. However the bike wont run due to the warped head. 

 

Are you sure?  The cams in this picture do not appear to be timed correctly:

 

d4Wv17fl.jpg



  • mvrk10256

Posted July 09, 2014 - 08:59 AM

#44

Lobes facing out. One dot at 12 oclock. 1 dot at valve cover gasket. Its presurizing the crank case anyway.

  • grayracer513

Posted July 09, 2014 - 03:07 PM

#45

Lobes facing out. One dot at 12 oclock. 1 dot at valve cover gasket. Its presurizing the crank case anyway.

 

However, in the picture, your exhaust cam is one tooth retarded (doesn't align with the gasket surface) and there are only 12 pins between the 12:00 o'clock marks; should be 13.  Not right.

 

If you turn the engine starting at TDC, the piston will run down the bore.  When it does that, it displaces 450cc of air UNDER the piston, same as it will on top of the piston when it goes up.  That will be felt as crankcase pressure exiting the breather or whatever else is open.  That's normal.  If it's more than that, that's another matter, just don't get ahead of yourself. 



  • mvrk10256

Posted July 09, 2014 - 04:22 PM

#46

So I took off the valvecover and move the exhaust cam one tooth over. Now there are 13 teeth in between 12 oclock marks. Same thing. I can barely register 20psi on a compression tester. While the piston does displace volume comiing down you can tell what stroke its on when your kicking it. Furthermore if I crank it over by hand with the VC off I can hear a hissing sound down the chain well. 



Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted July 10, 2014 - 06:24 AM

#47

Just about everything you describe is normal.  When the exhaust cam is timed correctly, the auto decompression system holds the left exhaust valve open until about 20 degrees before TDC, so very little compression is going to be created.  Conventional compression testers are therefore fairly useless.

 

Rings have end gaps, so they quite naturally all leak, especially at very low speeds, and that's heard as a hissing in the crankcase.



  • mvrk10256

Posted July 10, 2014 - 06:33 AM

#48

From my understanding a good engine should produce about 190psi of compression w/o autodecomp - if you block it from activating- and about 100 psi if its engaged. Furthermore I have spark, gas, and air and yet the bike doesnt so much as cough leading me to believe there is a lack of compression

  • mvrk10256

Posted July 10, 2014 - 06:37 AM

#49

Might pick up some starter fluid and see if I can get something out of it that way. Pulled the plug and go great spark against the head, timing is correct. carb's AP throws gas the length of the garage.



  • mvrk10256

Posted July 10, 2014 - 09:52 AM

#50

picked up some starter fluid today at lunch. will see if I can get it to caugh or start tonight. If anyone has any clever ideas I am all ears. 



  • mvrk10256

Posted July 10, 2014 - 03:03 PM

#51

Put starter fluid throught thecarb and then without the carb - straight onto intake valves. Nothing. Went to FSAE garage to try the old WR450 and even with auto decomp got 95psi on the comp tester. 

 

So we are back to no compression due to a head issue. 



  • mvrk10256

Posted July 14, 2014 - 09:46 AM

#52

Ended up being the head. Visible leak between oil pasage and head gasket. Bike is being partd.







Related Content

Forums
Photo

Michigan Motocross Tires by 288yz450


Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply
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
Forums
Photo

YZ450F 03 Sparks driving me crazy by SirAttard


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies
Forums
Photo

Snake pit oct 30th by The Anvil


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

Thinking about Yamaha 250... by Arctic Pride


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 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.