Engine Strip - Help required

7 replies to this topic
  • Gordon

Posted October 18, 2001 - 11:48 AM


YZ400 - 1999

Clutch plate broken, fragment of plate missing (5 - 8mm in size) I suspect it is lying in the bottom of the crankcase but have been unable to 'flush' or pick it out.

Guess I will have to strip motor.

Anything to look out for - I was planning a basic strip down and rebuild - checking bearings, valve clearances etc and possibly replacing piston rings. Is there anything else the bike is prone to that I need to check or replace as a matter of course?

At least the clutch has not damaged anything else!


  • Hick

Posted October 19, 2001 - 11:58 AM


If you replace the main bearings removing and reinstalling the crank may give you some trouble. You will obviously need a press to replace the bearings.

I suppose you can use a press to remove the crank but you may mushroom the end threads. Installing the crank with a press is not a good idea because I don’t think you can get a crank jig for it. But there are two 6 mm holes drilled and tapped into the left case half behind the stator meant for a Yamaha crank removal/installation tool. Based on the picture in the manual this tool looks a lot like a steering wheel puller.

I just made my own out of a piece of angle iron with three holes in it and a piece of 6 mm threaded rod. Make the center hole 10 mm for the crank and put a 6 mm hole on either side the same distance apart as the two holes in the case. Then you can push the crank out or pull it in using the piece of angle, two lengths of 6 mm rod and three appropriately sized nuts.

I was quoted over $200 for the tool that was recommended in the manual. Whatever.

The cases on my ’00 came right apart, no puller or prying was required. Be careful with the many dowels and pins in the cases, case covers, cylinder, head, cam caps, water pump, they are everywhere. Don’t forget all the seals, you should probably replace them all while you are at it (countershaft, shifter, impeller, blah, blah, blah).

You may want to flush all the oil passages, both internal and external. There is a copper tube that feeds the gear sets running transversely from right to left. You may want to remove that before you split the cases to avoid bending or damaging it. You should also check inside your magneto/flywheel, anything metallic may end up stuck to the magnet. Any debris in your cases may have ended up stuck to the pick up screen for the secondary oil pump which is inside the cases and is driven by the main oil pump.

The straight key on the right side of the crank has given me, and many other ’00 YZ/WR owners, lots of trouble. Don’t know why the ’99 doesn’t have this problem but I would make sure this key is nice and square. As for the clutch of course you want to make sure the boss and basket aren’t overly grooved, worn parts may have been what caused the breakage to begin with.

I’ve had my ’00 apart twice, so if you hit any snags I may be able to help you out.

  • Shawbridge Husky

Posted October 19, 2001 - 02:54 PM


I just had the bottom end done on my '99 and as usual I have an unfourtunate story for you. ( story of my life )

I decided to glass bead the timing gear and the keyway groove / spline on the crank before sending it out for rebuild. It came back from crank shop looking great and had my local independant bike shop rebuild the trans / cases and replace all tranny bearings including crank bearings. ( he put my counterbalancer in wrong BTW )

Once all together and back in my again newly painted frame I look a last look in the crank cavity before slipping the top end back on. Guess what I saw dribbling out from the center holes in the center of the crank halves? Some lovely glass bead particles! ( about enough to cover the end of a paper-mate pen cap ) There ya go you loser!

Well loser here flushed it out with WD40, rinsed out the tranny with paint thinner and then filled up with oil overnight and dumped following morning. Then loser calls up crank builder and was told that it could of been an oversight but vouched that main oil passage of crank was cleaned as part of rebuild process ( I hope! ) I put everything back together and broke in bike for about 1 1/2 hours slow revs , dumnped oil / filter and refilled with new oil / filter. Back out 2-3 more hours and again dumped oil and just cleaned filter this time. First oil change was grey with filter full of lint and a few metallic particles. Maybe a few glass beads here and there but not sure. Second oil change looked much better and filter was almost still new looking so just cleaned it. Refilled with fresh oil again and hope that all will be right for a while now.

There still seems to be minor clatter as before but hope that it is normal operating noise. Only time will tell in my case. Lesson : it's hard to soar like an eagle when you are surrounded by turkeys!

[This message has been edited by Hugh LePage (edited October 19, 2001).]

[This message has been edited by Hugh LePage (edited October 19, 2001).]

[This message has been edited by Hugh LePage (edited October 19, 2001).]

  • Shawbridge Husky

Posted October 19, 2001 - 03:04 PM


[QUOTE]Originally posted by Hick:
[B]If you replace the main bearings removing and reinstalling the crank may give you some trouble. You will obviously need a press to replace the bearings.

Hick, Brian at Moto-X said that he heated the cases and froze the bearings and everything went right in for my rebuild. ( He made a clicking sound as he described it )Is this OK?

[This message has been edited by Hugh LePage (edited October 19, 2001).]

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  • Hick

Posted October 19, 2001 - 08:21 PM


Originally posted by Hugh LePage:
Hick, Brian at Moto-X said that he heated the cases and froze the bearings and everything went right in for my rebuild. ( He made a clicking sound as he described it )Is this OK?

I should back pedal a bit and say you may not need a press.

When I put new bearings in my ’00 I froze the bearings and heated the case with a torch and I still most definitely needed a press (trust me), but this was into a brand new set of case halves.

Having said that I did (briefly) consider reusing a bearing I had forgot to order (the one that the shift drum rides on I think) and I couldn’t get it out of the old case without a press either. By the time I popped it out I was certain I didn’t want to reuse it. I have a 20 ton press.

  • YZ400Court

Posted October 20, 2001 - 05:01 AM


My 2 cents:
If your in that deep, replace all the bearings. Inspect closely the transmission gears and dogs for wear. Check tolerance on the shift forks and replace if even close to being out of spec. Replace the intake and exhaust valves, they are inly $10.00 each. Replace the connecting rod, it is only $50.00 ($120 after the pin and bearing), and it is the weak link in the engine. I have broken 1 rod and dropped 1 valve. The valve was due to missed shifts (transmission shift fork wear). The rod was apparently just at it's usable life. If your on a budget, at least replace the rod, and just inspect the rest.

BTW, Here is a link to Ronnies, they have great prices on all YZ parts.
Pretend it's flat and give it the gas.

[This message has been edited by YZ400Court (edited October 20, 2001).]

[This message has been edited by YZ400Court (edited October 20, 2001).]

  • wpattison

Posted October 20, 2001 - 06:22 AM


from my experience, splitting the cases and replacing the crank bearings on this motor is much easier than on a two-smoke. since the cases don't seal, the clearances are not as tight on the 4-stroke. i was able to split my cases, replace both crank bearings, and slip in a new crank assembly with no press, no special tools, and no effort. i used the frozen bearing/heated case method, and the bearings practically dropped in.

depending on your individual price point, you may find it cheaper to buy a complete crank/rod assembly from yamaha than to buy a rod and have the crank rebuilt. you also get peace of mind. i had a fiasco last year that was the direct result of a very poorly rebuilt crank...

will pattison
racer, engineer

  • want_a_450r

Posted October 20, 2001 - 06:55 PM


i just got done rebuilding a 400 and you just have to remember where the dowls came from and not take to long so you don't forget what your doing...as for that crank bearings ..my local dealer pressed my crank and berings in for 30 dollars which ain't bad

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