• Welcome to the Two Wheeled Texans community! Feel free to hang out and lurk as long as you like. However, we would like to encourage you to register so that you can join the community and use the numerous features on the site. After registering, don't forget to post up an introduction!

Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

Joined
Dec 16, 2014
Messages
3
Reaction score
0
Location
Rosenberg
Just got a 1996 XR400 that will not start. The bike has been sitting a long time so did normal clean, check, carb rebuild, new plug etc. Bike still would not start but would backfire once or twice. Looking further I found a huge gap between rocker/sub-rocker and top of valve stem on left intake. Other valves had normal gaps. Anyone seen this before and if so what was the cause? Stuck valve? Bent rocker? Any advice/comments appreciated before I take the top end apart. Thanks
 
Sounds like a stuck valve. It is hard to say with out looking. Try to measure the valve height compared to the other one. You could also do a leak down test.

I would most likely do a leak down or pull the head to inspect as the valve maybe bent if it was stuck open when the piston came through its cycle while trying to start it.
 
You can check for a bent valve without having to obtain a leak down tester if you already have a compression checker, one of the ones with several hoses that fit different size spark plugs and has a single gauge. Remove the valve from the end of the hose that screws into the spark plug hole. Put the cylinder on top dead center (TDC) on the compression stroke. Hook an air hose to the compression tester hose. 20PSI would be OK. More will make it more difficult to keep a big single on TDC. Lots of leakage through the carb=bent intake valve. Leakage through the exhaust=bent exhaust valve. If you have both, you either have it on Exhaust TDC or you have more problems than you think.
 
Sounds like you need to take the head off and look at the valve, if you are lucky it's just stuck in the valve guide due to corrosion, but it could be bent. Either way the best solution is to take the valve out, clean it up (or replace it) and put it back together. It's not hard to do if you have the right tools, but you would need to order a head gasket, rocker cover gasket and exhaust gasket before you start to keep down time to a minimum.

Gary
 
I used the compression checker and found lots of air through the carb. Removed head and found previous owner is almost as good a mechanic as I am. He apparently dropped a screw into intake manifold somehow and didn't know or didn't care to take the head apart and remove the screw. Screw is holding left intake valve open. See photos. I am not sure how much or if any damage has been done but will let a shop figure that out.

Thanks to all for your responses.

http://i1259.photobucket.com/albums/ii544/sw183938/XR400_Valve_Problem_2JPG_zpsssjcfev5.jpg
 
I used the compression checker and found lots of air through the carb. Removed head and found previous owner is almost as good a mechanic as I am. He apparently dropped a screw into intake manifold somehow and didn't know or didn't care to take the head apart and remove the screw. Screw is holding left intake valve open. See photos. I am not sure how much or if any damage has been done but will let a shop figure that out.

Thanks to all for your responses.

http://i1259.photobucket.com/albums/ii544/sw183938/XR400_Valve_Problem_2JPG_zpsssjcfev5.jpg

It might not have done much damage. The screw might be softer than the valve and seat. You could remove the screw and lap the valve and see how it looks.
 
oh so lucky! if it had made it into the cylinder it would have done considerable complete destruction.

screws are soft, seats and valves are hard, remove screw and do a leak down test.
 
I would be checking the piston very carefully, these bikes run very small squish clearances, so the piston has probably hit the valve/bolt. It might not have done any damage, but it would be a shame to put it all back together and then have the piston fail shortly afterwards. As you have the head off, it's not much more work to remove the barrel and check the piston and ring glands.

Gary
 
Back
Top