Something is majorly wrong

I own a 1997 XR 400. I was recently riding and it started to run rough. It sounded like my plug was fouled so I changed it. That did not solve the problem. I decided to cut my day short and spend some time the the bike in the shop. After it had cooled down, I tried to fire it up again. It still ran choppy and I noticed that one of my header pipes was red hot after a min or so. I tore the head off and nothing fell out or appeared broken. I noticed the one of the ex valves was perfectly clean where the others were carbonized. What is all this meaning? Does anyone have an idea about my problem.

Sounds to me like the exhaust valve was tight. When the valve is held open during the power stroke the hot gasses blast the valve clean and heat up the exhaust pipe. Make sure the valve spring is not broken and the valve is not sticking in the head. You may have been able to fix the concern with a simple valve adjust.....not to ruin your night or anything.

I figured it was sticking, but I wanted some other opions on the subject. As an engineer myself, hats off to the designer of the valve train. Props to that man.

If it had a Broken valve spring, it wont start. The exhaust valve would fall open at will, thus, No compression, and it wont start. Its a single cylender engine, if it has no compression in that cylender, it wont run. It has no other pistons to turn it over.

So it cant be a burnt valve either, because thats the same. it wont have any compression.

And I also doubt that it may have seized the exhaust valve for a moment and got hot and burnt the carbon off it, because for that to happen, the power would of cut out instantly, because again of the instant full lack of compression.

Ummmmmmm, I think we need a bit more info on exactly what the noises sound like when running.

It may have overheated and seazed the piston for a moment, and scored the bore and piston. Actually if its making the sounds I think it may be, I bet thats what it is!

Thats not realy, overly a major problem. Well it is a Major Problem, but its pretty straight forward to fix. All you have to do is order a new oversize piston, full gasket set, and get your barrel bored out, then put it all back together.

That happend to me once, It sounded terible when running. Once I pulled it apart, and pulled the piston out, it was obvious that the piston and cylender was the problem.

But if its the big end, on the crank, all you have to do is order a new crank pin, and send the crank and conrod, with the new crank pin, to a good bike shop to get the pin changed. Then put it all back together and it will be fixed.

So I think the problem may be in the bottom half. What you need to do now is, drain the oil out into a tray, then have a close look at it in the sun light, and if the oil looks metalic, If its got very fine sparkly metal all through it, its been ceased. If not, it may be somthing else.

Yea so, if you could give me a more detailed opinion, of exactly what the noises sound like, and how it runs.

Good luck! :cry:

#1- I've never seen a broken valve spring on a motorcycle or car cause a valve to fall open. It only makes the spring weak and causes the valve to float or stick. I'm not saying it can't cause a valve to fall open, I've just never seen it happen.

#2- One exhaust valve partially open on a multi-valve single cylinder engine will only lower compression, not drop it to zero. Most multi-valve single cylinder engines will still run with an exhaust valve partially open.

#3- Only one exhaust head pipe turned red: there is the open valve during the power stroke.

#4- I have seen a tight exhaust valve (adjustment too tight) cause the exact problem that was described in this post multiple times. The valve gets tight from running and lack of maintenance which eventually causes the valve to hang open ever so slightly. As someone of your expertise knows, valves get tight not loose as the seat and face wear.

There are any number of concerns that could cause the stated problem but I would have started by checking the adjustment on my valves.

Firstly, I'd like to say that Im Not having a go at you, Im just sharing my knowledge. And also, I am a Cylender Head Reconditioner, and I work on cylender Heads from cars trucks and motor bikes, Petrol and desiel everday. And have seen all the engine failure's concerned with the cylender head. And that involves alot of broken valve spings! and lots of other major catastrofies.

- #1- I've never seen a broken valve spring on a motorcycle or car cause a valve to fall open. It only makes the spring weak and causes the valve to float or stick. I'm not saying it can't cause a valve to fall open, I've just never seen it happen.

Valve springs do break. If they break, it no longer has the strength of the unbroken spring to hold the valve shut. It will stay open.

Yes the valve wont fall all the way through and hit the piston, because the spirng cap and collets and broken spring are still up there to hold it up, yes it will just float open.

Now, if this was to happen to a four cylender, or just an engine with more and one cylender, the rest of the pistons still firing, would still turn the engine over, then it would only be running on 3 cylenders. But it would have NO compression on that cylender with the open valve!

BUT, for this to happen to a single cylender it will have absolutly NO compression at all instantly! It will cut out straight away and will just just blow past the open valve. And It will not be able to start.

- #2- One exhaust valve partially open on a multi-valve single cylinder engine will only lower compression, not drop it to zero. Most multi-valve single cylinder engines will still run with an exhaust valve partially open.

Ok, so I think what your saying is if the tapetts are adjusted up too tight? is that rite? If yes, you are corect, if a tappet is tighten ever so slightly too tight, it will only JUST have continous pressure valve and lower the compression. BUT if the valve was open only a slight fraction more, it wont seal, thus, No commpression! It will blow past the valve, it wont run and wont start.

So I have to say, no you are wrong when you said;

Most multi-valve single cylinder engines will still run with an exhaust valve partially open.

No sorry thats Impossible! I dont know what exact measurement your are refering to when you say partially open. A single cylender engine WILL NOT RUN with a valve partially open!

Yes it may run with a valve thats not seating entierly properly, it will have a lack of commpression, and hard to start, But not with a valve partially open.

Think about it, if one of the valves are slightly open, whats stopping the air and fuel from getting blowen straight past the valve? Nothing at all! It will have no compression.

- #3- Only one exhaust head pipe turned red: there is the open valve during the power stroke.

Like I said before, If one of the valves were open on the power stroke? It wouldnt of been running in the first place!

How could one of the exhaust valves possibly be open??? :cry: It would of just blowen past the valve! no compression, it wouldnt fire, it just dosnt work like that!

I think you getting confused with an engine thats got more pistons. Like I said at the start, with a 4 cylender, if one exhaust valve is stuck open, that cylender Wont fire, but it will have the rest of the pistons to keep it turning over.

- #4- I have seen a tight exhaust valve (adjustment too tight) cause the exact problem that was described in this post multiple times. The valve gets tight from running and lack of maintenance which eventually causes the valve to hang open ever so slightly. As someone of your expertise knows, valves get tight not loose as the seat and face wear.

Yes so I think i covered this statment eirler. If the valve was held open from the tappet being too tight, it would have lower compression. Though that all depends on how much the tappet is holding it open! if its any more than a fraction it will have No compression, it will blow past the valve. But if its only just, it will fire but with a lack of compression.

So, in the end, when it was said that one of the ex valves were perfectly clean where the others were carbonized, well, that could also be possible that the ex valve that had more carbon on it, was actually Not opening at all! The one that had no carbon on it would of been running normally. But the other one may have stayed shut, thus, only one ex valve opening, which leads to more exhaust getting pushed out the one port, and only getting one header pipe getting extra hot! So that may explain the header pipe ordeal.

BUT! For one valve not to open, that would mean a broken rocker arm! And he said he tore the head off and nothing fell out or appeared broken. :cry: SO, That just stuffed up that idea then.

How can you be a "cylender" head reconditioner when you cannot even spell cylinder or diesel for that matter? ......... and your thesis is incorrect.

I tore the top end down on the bike today. The piston and cylinder wall is fine. One of the exhaust valves was grey in color and carbon free, the other was the usual black as well as the intakes. I took the spring off and found it to be fine. I did notice that when I took the valve in question out, it had a catch and it also had a wear spot on the stem about a half inch long. I inserted it back and fount is was a catch and not my imagination.

Yes ok im a bad speller.

But seriously, I would like to know exactly what you think is incorrect about my thesis??

Yes ok im a bad speller. But seriously, I would like to know exactly what you think is incorrect about my thesis??

A bottom end concern would not be the likely cause of the symptoms described in this post.

Oh that, Yes well that was only just a guess.

I think I may have miss read the origonal question a bit, and just got carried away at questioning your posts.

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