Time to take off the head and have a look.


11 replies to this topic
  • henrysdad

Posted April 15, 2005 - 07:58 PM

#1

My 2000 426 is my street/trackday bike. At the end of last fall it got really hard to start. Come spring,I checked the valve clearances. All good and it starts on the second kick. Still fast. Change the oil. Day 2 return to hard starting, still fast. Day 3 strands me at the gas station. I do not have enough compression to need the compression release. check valves ,clearances good,everything is moving properly. So I pour oil in the cylinder,put the plug back in, still low resistance.

Off with the head I suppose. I have no idea of the hours on this machine so I will do a top end, and I want a 450 exhaust cam anyway.

Do I have to remove the cams to remove the head?

I guess we'll all know this weekend how it looks.

  • Guest_BrandonV_*

Posted April 16, 2005 - 07:23 AM

#2

Yes, you need to remove the cams to remove the chain. I dont think there will be enough slack in the chain to get it off the cam gears. Its easy, I did it a few weekends ago for the first time and I had the head and cylinder off within an hour including draining all fluids and removing all necessary components.

You gonna do a top end job while its apart?


Edit: Dont drop the clips from cams into the motor when you remove the cam caps.

  • 02YZ426

Posted April 16, 2005 - 08:01 AM

#3

Be sure to stuff a rag or something in the case so that clip doesn't drop in the bottom end. Its funny, it doesn't seem to matter how many times this is mentioned here, but guys still think they can catch that clip and it alway ends up in the bottem stuck to the magnet on the flywheel.

  • henrysdad

Posted April 16, 2005 - 08:46 AM

#4

Thanks for the tips. I'll watch those cam retainers.I plan on ,piston/rings ,cam chain(maybe chain guides?),450 exhaust cam, and whatever the head needs.I'll have a look at the counter balencer gear keyway while I have everything appart. may as well go thru the waterpump too. check out the oil pump maybe?

how hard is changing out the counterballencer gear from keyway to splines??

  • Guest_BrandonV_*

Posted April 16, 2005 - 09:13 AM

#5

Gotta replace that half the crank with half the 01' 426 crank. If you've got the money and feel the need then go for it. You can replace the rod bearing before having it pressedback together,

  • 02YZ426

Posted April 16, 2005 - 01:51 PM

#6

Also have a good look at the valves when your in there too. Dont overlook them, just because they are in spec doesnt mean that they cant be the problem. Maybe one or more of the valves are sticking a bit causing you compression loss. Have a good look at the valve guides for abnormal wear, and do a leak down test.

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  • Frostbite

Posted April 16, 2005 - 05:06 PM

#7

This mysterious compression loss problem is reaching epidemic proportions! :naughty:

  • henrysdad

Posted April 23, 2005 - 05:20 PM

#8

Well I took it apart. To my suprise everything looks acceptable. I used thinner in the ports an very little weepage if at all past the valve seats. Cam followers are all in great shape and free to move. The bore has the slightest wearmarks on the exhaust side. I will probably have to have it re-plated or relpace it. I do not have a valve spring compressor that is small enough ,so the valves could still be the problem.
The symptoms were, compression for one kick,then not enough compression to need the decomp lever. And no starting ,at all. So.. A valve could be hanging open. I may get a big bore. we'll see how much money I can come up with.

  • biznet1

Posted April 23, 2005 - 07:26 PM

#9

Well I took it apart. To my suprise everything looks acceptable. I used thinner in the ports an very little weepage if at all past the valve seats. Cam followers are all in great shape and free to move. The bore has the slightest wearmarks on the exhaust side. I will probably have to have it re-plated or relpace it. I do not have a valve spring compressor that is small enough ,so the valves could still be the problem.
The symptoms were, compression for one kick,then not enough compression to need the decomp lever. And no starting ,at all. So.. A valve could be hanging open. I may get a big bore. we'll see how much money I can come up with.

You don't have to have a spring compressor. My friend made one for his which is simply a handle with the end that fits evenly on the spring. They aren't hard to push down long enough to drop your keepers in.

  • grayracer513

Posted April 23, 2005 - 07:43 PM

#10

Your '00 has stainless valves which can be lapped or reseated by a competent machinist. Find out who your local dealer sends their heads to and pay him a visit. The labor to have him replace your valve seals and clean up and inspect the valves and seats won't cost much, and could be very worthwhile. Your compression problem is probably due to tired rings or carbon on the valve stems. Before re-plating/reboring, compare the cost of a new cylinder.

  • MNellis

Posted April 25, 2005 - 07:35 PM

#11

I had a local performance machine shop lap the intake valves on my RC51 (2) and install the springs (I didn't have the tool) and it was less than $25. Pretty cheap.

  • henrysdad

Posted April 27, 2005 - 04:16 PM

#12

The worst looking part of all is the head gasket. The head has no warpage. Valves are near perfect. Valve guides are excellent. Springs are good,but I think I should replace them. Valve seals too.
The bore and piston skirt have up and down wear marks .Dimentionally intact though.rings are great.
No coolant in the oil,vice versa.

Head gasket?? looks like a crapy 3 piece thing,coming appart. I did not do a leakdown test.

I suppose a 5 year old mx bike needs motor work.I'll spend a bunch of money , install the 450 cam,and be back on the road soon.





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