Not as bad as I thought. It is worse....



9 replies to this topic
  • BrandonW

Posted July 26, 2002 - 10:34 AM

#1

At lunch today I grab my multi-meter, and I am planning on making something happen.

1. Pull the tank/seat and take a look at the spark plug.
FIRST PROBLEM: Spark plug grounding rod has been struck, and it was touching the electrode. Changed to a different plug, and it is sparking! No electrical problems as first thought.

2. Drained oil to see if there was any foreign debris, and nothing came out of the frame drain hole. Opened up the engine drain, and a little more than a quart came out of that.

3. Put a new plug in, added oil, and kicked it over (with decomp pulled in). Nothing was hitting or sounding strange, so we put the gas tank back on and tried to fire it up. Would not fire, and I realized that I am able to defeat the engine, by hand, without the decomp lever being pulled in. Not easily, mind you, but if could put all of my weight on the kickstater, and I could get the engine to turn over.


So, what caused the grounding rod to get bent? Why was it so low on oil? Is this that phantom loss of compression, and it will come back, or, do I have a hole in the piston?

Well, on a good note, I don't need to figure out how to run a multi-meter.

Sounds to me like I have to take the valve cover off and take a look-see.

Anybody have some clues?

Thanks,
Brandon

  • BrandonW

Posted July 26, 2002 - 12:45 PM

#2

Just got back from the local shop, and they think that it was in dire need of a valve adjustment. They believe that that the piston hit a valve, and a piece of either the piston or valve has broken off.

Anybody else had this happen? Sounds like I need to pull off the head and assess the damage.

Can you bore a 400 and stuff a 426 piston in, or are they the same bore with a different stroke?

Not happy and the wallet is going to feel this.

Brandon

  • YZ400Court

Posted July 26, 2002 - 05:07 PM

#3

The 400 and 426 pistons are not interchangeable. You have to change the rod also as the piston pin is a different size. I just finished the 426 conversion on my 400 after a broken valve. In retrospect I should have parted it out and saved for a new 450....oh well.

  • Team_Oatmeal_Pie

Posted July 26, 2002 - 06:47 PM

#4

I have seen some twisted folk think the decomp lever should be used as a Jake Brake.

  • JOSHUAZ2

Posted July 27, 2002 - 02:14 AM

#5

how could valve adjustment cause a piston hit? unless you did a valve adj and put in too much shim which would have caused the motor to be down on power and get worse with heat. i would discount any thing this dealer said and get a second opinion. these engines do stick valves and this could cause a strike, breaking off a piece which then would have bent the ground. without pulling off the head you'll never know.

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  • chabon99

Posted July 27, 2002 - 10:12 AM

#6

I'm going through the same ordeal except I'm one step ahead of you. I lost compression (some)and couldn't figure out what was wrong. Finally decided to tear it down and sure enough I had a light seize-the piston was smeared and had damaged the cylinder wall but was still sliding up and down. Your options are: buy a stock cylinder (too expensive) buy a 420 kit from Stroker (which is what mine was and from what I've found out-this happens all too often)$400 with trade in of your cylinder, or re-sleeve your cylinder and use a wiseco piston. LA Sleeve quoted me $330 for the re-sleeve, piston and gasket set yesterday. It's not hard to tear it all down but I had a heck of a time getting the piston and rings to slide into the cylinder last time. My own fault for not using correct tools. The manual is a great help-Honda could learn a lesson from them with the stupid owners manuals they provide with their bikes.

  • freestyle111

Posted July 28, 2002 - 01:28 AM

#7

you should run leakdown test before you go any further.it will take all guess work out of dagnosing your motor problem.i have leakdown tester if you want to borrow it.its vary simple to use all you will need is compressor.let me know if you want to use it.i'll pm you

  • YZ400Court

Posted July 28, 2002 - 02:54 PM

#8

Originally posted by chabon99:
Your options are: buy a stock cylinder (too expensive) buy a 420 kit from Stroker (which is what mine was and from what I've found out-this happens all too often)$400 with trade in of your cylinder, or re-sleeve your cylinder and use a wiseco piston. LA Sleeve quoted me $330 for the re-sleeve, piston and gasket set yesterday.


List price for the cylinder from Yamaha is under $300 bucks, I paid $245. I bought a new 426 cylinder and weisco 12.5 to 1 piston for the 426 cylinder cheaper than any other alternative I could come up with. I had to replace the con rod anyway, and decided on the 426 stuff after a conversation (e-mail) with BK. The expensive part is the head, just pray that is okay.
Posted Image

  • freestyle111

Posted July 29, 2002 - 06:17 PM

#9

you can get info on how to perform leakdown test if you do search on netPosted Image

  • oz426

Posted July 30, 2002 - 12:17 AM

#10

Could someone please tell me how hard should it be to turn the engine over by hand without the de-compression lever held in. as Brandon says how his bike has lost compression and he can now push it over by hand with difficulty. i have a brand new 2002 wr 426 which i have only just broken in and i found that i was able to push on the kickstart and turn the engine over by hand with some difficulty. although the bike seems to run fine. is this normal?




 
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