Valve Sticking. Diagnosis Help.

10 replies to this topic
  • sliderbkt

Posted October 21, 2001 - 02:03 PM


I was riding over the weekend. After stopping to talk for a minute on the trail I went to start my bike and noticed the compression was low. I was about a mile from the truck so I tried to start it, amazingly it started and seemed to run ok. I very easily rode back to the truck and began tearing it down.

Now that it's home I have taken the valve cover off. The exhaust valve (decomp side) is not fully closing. Looking in the exhaust port I don't see a great deal of carbon. The valve moves freely, but doesn't close all the way. It stays open roughly a 1/4in.

My question is: Is there anything to do before I take the head off? Or, any other advise?

FYI 1998 400 all stock w/ 8oz flywheel weight.

[ November 02, 2001: Message edited by: sliderbkt ]

  • sirthumpalot

Posted October 21, 2001 - 03:03 PM


I'm just guessing here, but is there clearance between the cam and the lifter when the valve is hung open? I have not seen the top of the valves on one of these things yet, but I'm wondering if something on top of the valve is out of place and is holding it open. For example, maybe the shim poped out of place, etc.. Probably not it but just a thought.

  • sliderbkt

Posted October 21, 2001 - 03:11 PM


No, I have the gap between the cam lobe and the top of the lifter. Without having the head off, I have a few ideas:

1. Bent Valve
2. Foreign object on valve seat
3. Problem with valve spring

  • sliderbkt

Posted October 22, 2001 - 09:04 PM


Well, I know a little more than I did before. Tonight I took the exhaust cam off. I noticed that the lifter was not free to move like the others. I have managed to move it up enough to close the valve fully. I can't get it the rest of the way out though. At a minimum I am going to need a new lifter after I have scuffed it. I am unsure why it would be so tight. At this point I am afraid that I am going to be looking for a new head. Any advise?

  • Boit

Posted October 23, 2001 - 02:24 PM


There are some quality cylinder head shops out there that might be able to help you. Try shops such as Powroll, Thumper, Stroker, Replika Maschinen, Best MC Repair, and Eric Gorr.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • sliderbkt

Posted October 23, 2001 - 06:32 PM


I may need to have it worked on eventually. For now I am moving slowly, this is my first time into the engine. Today I got the stuck lifter out, it took a pair of vise-grips and some muscle. The lifter doesn't show any noticable damage, with the exception of the damage that I did. At this point I beleive that the valve is bent, and because of the bend it is causing the lifter to stick. I am going to pull the head tomorrow and measure the run-out on the valve. I'll keep you updated.

  • Boit

Posted October 24, 2001 - 11:13 AM


One last thought about the valves. When washing the bike, make sure you put the piston at compression and plug the exhaust tip with a rag of rubber plug. After washing, start the engine and let it run for about 3 minutes or so. Shut it off and put it back on compression. If water runs down the exhaust pipe and gets on the exhaust valves, the water can displace the oil and the valve(s) can seize.

  • sliderbkt

Posted October 25, 2001 - 05:34 PM


Here's the latest:

I have the valve out, I don't think it is bent. I haven't measured the run-out, but it looks straight. The problem is the lifter bore. The lifter cap still sticks in the head. I am going to call a local machine shop tommorrow to see if there is anything that they can do. I'll let you all know.

[ November 02, 2001: Message edited by: sliderbkt ]

  • sliderbkt

Posted November 02, 2001 - 10:42 PM


Just keeping you guys informed:
With the valve out, it was obvious that the lifter bore was out of round. It was not visible, but the lifter would get stuck. So, with advise from the local Yami dealer and a local machine shop, I used emery cloth to work the bore until the lifter fit. Everything is back together now, all it took was a new lifter and a new head gasket. I started it today and she idles very smoothly. But, the true test will be when I get into higher rpm's. Wish me luck! :)

  • Boit

Posted November 02, 2001 - 12:56 PM


Thanks for the update. Sharing the end result here can help a lot of guys.

  • lump-dog

Posted November 03, 2001 - 04:33 AM


Had the same EXACT problem ('98 400). Once I opened 'er up, I couldn't find anything wrong with the valve, exept a "bur" had developed in the head and would keep the bucket from coming up past it (causing the valve to hang). Only happened when the bike was cold (first start up of the day). Once I got past that, it would start fine. I emery clothed the bur out, replaced the valve, spring and bucket for good measure, and haven't had a problem since.


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