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Old 11-14-2016, 12:01 AM   #1
XR400FAN1996
 
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Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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
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Old 11-14-2016, 08:45 AM   #2
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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.
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Old 11-14-2016, 02:47 PM   #3
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

stuck or bent valve.
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Old 11-14-2016, 05:12 PM   #4
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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.
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Old 11-14-2016, 09:20 PM   #5
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

Can we move this to the XR400 thread?

http://www.twtex.com/forums/showthre...t=xr400+thread

1,480 posts so far!
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Old 11-15-2016, 04:04 PM   #6
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

Thanks to everyone for the quick responses. I will try the compression checker first to see what it tells me.
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Old 11-15-2016, 10:59 PM   #7
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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.

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Old 11-19-2016, 12:19 PM   #8
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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/...psssjcfev5.jpg
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Old 11-19-2016, 04:20 PM   #9
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

Moved to the TWTex XR400 Thread

http://www.twtex.com/forums/showthre...thread&page=74

Reason being that some really good XR400 experienced guys are automatically notified when this thread gets a new post but may not notice the new one.
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Old 11-20-2016, 09:46 AM   #10
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

Quote:
Originally Posted by XR400FAN1996 View Post
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/...psssjcfev5.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.
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Old 11-20-2016, 10:45 AM   #11
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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.
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Old 11-20-2016, 04:54 PM   #12
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

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.

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Old 11-21-2016, 02:13 PM   #13
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Re: Xr400 Huge Gap Rocker/Sub-Rocker to Top of Valve Stem

OUCH! But it looks like you may have dodged a bullet..
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