Rebuild ideas(attack of mice)


10 replies to this topic
  • treukauf

Posted August 11, 2006 - 11:30 AM

#1

Well my 2000wr 400 (converted to yz) wouldn't start yesterday because it wasnt making much for compression. I could push it over by hand. So today I started to tear the bike apart and found the exhaust was completely packed with sunflower screenings( we feed them to el cows) all the way to the valves. I pulled of the cylinder head and much to my dismay the piston looked like a charcoal firepit. :thumbsup: . I ran the bike on sunflower seeds. I guess you could say its a failed bio fuel experiment lol. The cylinder looks great, and I can still see the crosshatching. This bike has never been rebuilt and ran great. I'm going to send the head in and have them go through it because i'm not sure why I was losing compression. The piston rings seem ok. When I pulled the spark plug it almost appeared to have antifreeze on it so I was wondering if it could be the head gasket.

Now for the question section.

1.Would it be a good idea to replace the piston.( it appears that the cylinder would only need honing.) Even if the ring endgap checks out withing specs?

2.While i'm in here I was wondering what i could do fore mods.( I love power) I know the yz runs like 12.8 to 1 and my wr runs like 12.5 to 1, but isnt the connecting rod and the wristpin hole larger on the wr's. What kind of piston should i buy? stock or wiseco or...I want to be able to run 91 octane which i have been. Do they make a 12.8 to 1 to fit my wr. I've already yz timed so i'm not sure if theres much else to do besides hot cam.

3 BIG BORE option. What would it cost to get an oversized cylinder and piston?Thanks for the help and remember next time you see a mouse kill that little b@$%^&%^.

  • JSanfilippo

Posted August 11, 2006 - 12:15 PM

#2

Go big or go home. You're gonna spend the money for a rebuild, might as well get a big bore for it

  • GCannon

Posted August 11, 2006 - 12:53 PM

#3

Get a close look at the small end rod bearing and wrist pin. Now is a good time for that.

  • 450_rider

Posted August 11, 2006 - 05:18 PM

#4

I'm pretty sure that the YZ's are 12.5:1 as well as the WR's.

  • treukauf

Posted August 12, 2006 - 06:45 AM

#5

What are you guys using for pistons. wisecos or are the factory ones just as good? 450 you might be right about the compression. For some reason I remember seeing that the newer yz 400s had 12.8 but my manual for a 99 yz shows 12.5-1 but below it says 12.1-1 to 12.9-1.

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  • Yamaster

Posted August 12, 2006 - 08:27 AM

#6

I dont like wiseco's two-stroke pistons, because in my opinion they develop piston slap too early. Had it had happen BAD on my old yz and my friends newer yz. There four-stroke ones seem to be good, my dad has one and its been doing great. But I prefer pro-x, vertex or stock for pistons. They just seem to fit tighter.

  • 642MX

Posted August 13, 2006 - 04:43 PM

#7

Dont forget to buy a wash plug for the exhaust. And maybe get some mouse traps too.

  • texas_hippie

Posted August 15, 2006 - 05:36 PM

#8

That lack of compression could also be a valve leaking by. You might want to investigate what those seeds did to the area where the valves seat. Might be a cheaper fix than all that piston work. Any signs of milkiness in the oil? That would indicate coolant leaking through the head gaskets. I'm not a professional mechanic by any stretch of the imagination....just some things that came to mind while reading your post.

  • Birdy426

Posted August 15, 2006 - 09:52 PM

#9

Now for the question section.

1.Would it be a good idea to replace the piston.( it appears that the cylinder would only need honing.) Even if the ring endgap checks out withing specs?


Depends on how many hours are on the bike and how hard you ride. My thought is you can never be too conservative on those kinds of things. If I had my bike that far down, I would at least re-ring...but if it was the first time since 2000, I would definitely replace the piston as well.

2.While i'm in here I was wondering what i could do fore mods.( I love power) I know the yz runs like 12.8 to 1 and my wr runs like 12.5 to 1, but isnt the connecting rod and the wristpin hole larger on the wr's. What kind of piston should i buy? stock or wiseco or...I want to be able to run 91 octane which i have been. Do they make a 12.8 to 1 to fit my wr. I've already yz timed so i'm not sure if theres much else to do besides hot cam.

Connecting rod is the same between YZs and WRs. 426 small end is bigger than 99 and older 400s. You will be amazed at the difference across the powerband that the higher compression piston makes. Wiseco, JE and others make 12.5:1 and 13.5:1 pistons. As to the comment about Wiseco pistons being noisey, they are. That's life. On my scooter, I got away with a 13.5:1 Wiseco piston and hot cams and still was able to run 91 octane pump premium. Others have not een so lucky. You will like the hot cams, too. A little more hit in the middle and a lot more on top.

3 BIG BORE option. What would it cost to get an oversized cylinder and piston?Thanks for the help and remember next time you see a mouse kill that little b@$%^&%^.

Now you're talking. The Luke's Racing 440 kit is 415 bucks if you send them your old cylinder. Eric Gorr's pricing is similar. The bigger piston is a bit heavier than stock, so it tends to slow down the rpm build up a little bit. It really complements the "hyperactivity" that the high compression piston and hot cams add into the motor. When I went big, however, I needed to switch to race gas to keep the dingles and pings away.

As far as those little rat-bastards are concerned, I share your frustration. They are forever chewing thru wire harnesses and fuel/vacuum lines around the house...

  • treukauf

Posted August 16, 2006 - 01:13 PM

#10

Thanks for the great help Birdy. I really wish I knew where I saw that the wr's had a different connecting rod. Maybe its because mine is a 2000 wr 400 and the other manual I looked at was a 2000 yz 426. I'm pretty sure all this engineering crap i'm taking is destroying my memory. I just dissassembled the heads and removed the valves and checked the valve seat are using some machinists die and it looks good so I think i'm just gonna ride her till she pops lol. I would go big but snowmobile season is coming up and the old polaris has been begging for a little laughy gass. Yeah i definately will be rebuilding that one. Thanks.

  • steade

Posted August 25, 2006 - 05:45 PM

#11

Go for the Big bore from Lukes. its like a new bike... up in every gear.




 
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