motor problems..help a. s. a. p

[red400ryder]

we just rebuild a motor on a 400ex and we have run into some problems that i never have encountered on my rebuild.....his bike was running good..we went riding for awhile and in about an hours time his bike was smoking and plus seemed to lost power to him...and it would not idle at all..got it home and now it won;t start....he had the problem of not idleing before and adjusted the valves and fixed it..i have two questions..1. the dowel pin in the cyclinder combustion chamber..there are two..the one in the front is in..the one in the back is not... would that cause any problems at all...2. is it possible the valves are tightening as the motor runs...need help a.s.a.p. thanks mike

[red400ryder]

just to let everyone know.....i guess since the motor cooled down alittle it now starts but still won;t idle plus smokes still..so please help and answer my questions whoever is able..thanks mike

[bigvforcer]

the valves can tighten while the motor is running. ususally if the vlaves tighten it won't start. The starter will crank and it will sound fast, there is no real load on the starter. Almost like all the compression is gone because the valves are stuck in the head because the are to tight. Hard to explain over the net. As far as your other problem I am not really sure if that would affect the performance or not

[wilkin250r]

What exactly do you mean "is it possible the valves are tightening as the motor runs"? Are you talking about adjusting your valve clearance? If so, do you understand the theory of WHY you adjust the valve clearance?

The second dowel pin out is NOT good. The dowel pins are designed to line up your cylinder properly. If one of them is out, your cylinder may not be centered properly, which will cause stress and wear on one side of the piston. Now, don't get me wrong, it's not GUARENTEED to be a big problem, but it's POSSIBLE to be a big problem.

Did you try the simple fix, like replace the spark plug? Also, what exactly did you change inside the motor, why did it need a rebuild?

[BLEEDRED]

...do you understand the theory of WHY you adjust the valve clearance?

I thought I did, but you make is sound so intriguing, please elaborate.

It seems that the smoke could be caused from a piston ring being installed upside down. Just a thought.

[44oEX]

wilkin I think he means the pin in the cylinder and head. not the one on the cylinder to the base.

So the worst thing that can happen is that the head will not be right where it's sepposed to be.

[Trevor]

MAYBE A PROBLEM WITH THE RINGS OR A OIL SUPPLY PROBLEM? DID YOU PUT THE OIL FILTER IN BACKWARDS? JUST AN IDEA!

[wilkin250r]

It's really not that hard. Valve clearance is probably 0.004 inches? I know it is on the 250X.

When you adjust the valve clearance, you are adding a small space between the rocker arms and the valves. This space is very important, because when things heat up, they get bigger. As your engine and valves heat up, the valves will get longer. In theory, your valves will get 0.004 inches longer as they heat up, and close this gap.

If you had zero valve clearance, when your valves got 0.004 inches longer, they wouldn't close all the way, they would still be 0.004 inches open. That would obviously be bad.

If your valve clearance is a little too big(0.010), your engine should run okay, but it will create impact on your valves and rockers (kinda like a hammer hitting a nail) and cause them to wear out faster. In theory, you would want the smallest gap possible when the engine is at maximum tempurature, because this is when the valves are the longest.

If your vavle clearance is WAY too big, your valves won't open fully, and it will throw off your cam timing. But honestly, it's rather hard to get that far off (0.050).

So, to answer your original question, YES, the valve clearance will get tighter as the engine heats up. That's the whole point of the valve clearance to begin with, to allow room for the valves to expand and close that gap. That's why you ALWAYS adjust the valve clearance when the engine is cold.

[wilkin250r]

Originally posted by 44oEX
wilkin I think he means the pin in the cylinder and head. not the one on the cylinder to the base.

So the worst thing that can happen is that the head will not be right where it's sepposed to be.

Well, that won't cause wear on the cylinder and piston, but it could have other potential problem. It increases the changes of a valve hitting the piston, but that's really unlikely. More likely it will cause the timing chain to wear out quicker. Regardless, it's not going to cause problems within an hour.