YZ400F Engine Rebuilt.


10 replies to this topic
  • mxdude1986

Posted March 23, 2009 - 05:14 PM

#1

So im gonna bite the bullet and rebuilt my engine top and botton and new clutch. Can anyone tell me all the parts I would need? for a rebuilt thanks.

  • BRY_426F_

Posted March 23, 2009 - 07:27 PM

#2

what are you looking to spend? are you going to do all of it yourself? I had my bike rebuilt and it cost about a grand in labor to pull the crank/ put in high comp piston, hot cams.. not to mention another grand in parts at dealer cost..I didnt spare expenses.. all in all 2 grand in the hole. you should DEFINATELY look for an Aftermarket crank.. OEM was 500 big ones.. what a punch in the jeans... and if your going to replace the crank and top end i would reccomend replacing the cam chain and various pignon gears.. your looking for a clutch also?!?! holy hell your in for a drought in your wallet.. and for a 400? may be worth parting out your bike and going for anew.

  • mxdude1986

Posted March 23, 2009 - 07:40 PM

#3

Ya thats what I figured I might as well part out the bike and get something newer...sucks I loved my 400

  • BRY_426F_

Posted March 23, 2009 - 07:44 PM

#4

I love my 426fm but its days are short lived.. more power is "in" these days..

  • Birdy426

Posted March 23, 2009 - 08:04 PM

#5

First, why do you think you need a rebuild, both top and bottom? Have you disassembled the motor and measured anything? I would be surprised if you needed valves/seats/guides. The SS parts on the 400s are almost indestructible. Same with camshafts. I would replace springs as they tend to fatigue over time. 7 or 8 bucks a piece x 5. If your cylinder bore is OK, you're looking at a buck and a half for a piston kit. If the barrel is worn, you're looking at about 5 bills for a big bore kit (including gaskets). Moving to the crank, unless the splines/keyways are all dicked up, you don't need to replace the whole crank. A rod kit is another buck and a half, and about a benjamin to rebuild the crank. I would replace ALL of the rolling element bearings in both the engine and transmission. If you note the AFBM numbers on the bearings, someplace like Motion Pro can match them up and get you set for about 1/3 the cost of OEM. Probably another buck and a half for all of them. As far as the clutch, again, what do you need? just plates? Are the fingers on the basket notched? What about the splines on the hub? Only replace what you need to. I would bet that if you do the work your self and only replace what's worn/bad, you could freshen up that bad boy for less than a grand...far less.

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  • 426 NOOB

Posted March 23, 2009 - 09:23 PM

#6

I could not have said it any better^^^^
I can almost guarantee that you wont need a new crank, maybe bearings, but not the crank, you probably wont need cams,valves, seals, guides. If i had to guess, it will probably need just a piston, rings, and bearings. But then again some people have 200 + hours on their 400s and the stock piston is still in spec. So before you part out, just take a peek inside. You might be surprised.

  • husqy360

Posted March 23, 2009 - 11:51 PM

#7

ebay is preety good place to find oem and after market parts for cheap.

  • grayracer513

Posted March 24, 2009 - 06:12 AM

#8

you should DEFINATELY look for an Aftermarket crank.. OEM was 500 big ones.. what a punch in the jeans...

Definitely not. As far as I know, there aren't any. TT OEM sells a new 426 crank for $475, and if the timing sprocket on the left axle is in good condition, you can rebuild the one you have for $150 plus about $100 in labor.

If the cylinder and crank need replacing, consider using the piston, cylinder, and crank (or rod kit) from a 426, basically turning the bike into a 426. The 426 crank parts are slightly cheaper, too.

  • mxdude1986

Posted March 24, 2009 - 06:49 AM

#9

Definitely not. As far as I know, there aren't any. TT OEM sells a new 426 crank for $475, and if the timing sprocket on the left axle is in good condition, you can rebuild the one you have for $150 plus about $100 in labor.

If the cylinder and crank need replacing, consider using the piston, cylinder, and crank (or rod kit) from a 426, basically turning the bike into a 426. The 426 crank parts are slightly cheaper, too.


Hey Gray here is my deal since I see you are always helping ppl out. I got this 400 I had the valves checked they are all within spec. 6hrs since they been checket, But my 2 last rides I been losing coolant through the overflow tube I changed my rad cap still leaking, so changed my water pump seals still leaking so that leaves me the head gasket. So i figured since i have to open the engine I was gonna open the whole thing and replace whatever is worn. Idk if anything has been done to this engine since im the 3rd owner. Another thing that bothers me last 2 oil changes I been getting some pretty good size metal shaving in the oil filter. So that got me wondering what could be they looked like aluminum but im not 100% sure. Im pretty sure im not gonna need a crank bc this bike runs really strong, just wanna replace bearings. Let me know what you think

  • grayracer513

Posted March 24, 2009 - 07:31 AM

#10

  • The valves are in spec, and as long as they are not leaking, I'd leave them. Remember that your engine uses stainless steel valves, and these are lots less expensive to replace.
  • When you replaced the seals in the w/pump, did you also replace the shaft and bearing? If not, and there is any significant grooving there, it may not hold well. That doesn't account for the coolant out the vent, though.
  • Have the rad cap tested to see if it's weak. If not, figure on a head gasket, and throw a set of rings, a piston pin, and new clips in while you are there. Replace the piston and or cylinder as required.
  • Inspect the crank per the manual. Tolerances for play are in the book.
  • On the 400 and the 2000 426, check the condition of the key and keyway that locates the balancer drive gear behind the primary gear on the right end of the crank. If this looks worn, get rid of it. If a new one feels loose, file one to fit out of square key stock.
  • Metal chips: use a magnet to differentiate between aluminum and steel. Alumuinum is likely from the clutch, steel could be anything. If it's an unusually large amount, it may warrant a search. Slivers are one thing, squarish flakes are a bad sign, and usually mean a ball bearing is coming apart somewhere.


  • mxdude1986

Posted March 24, 2009 - 07:33 AM

#11

Thanks grey Ill tear her apart and check everything.





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