Hawk 250 Won't Start, Stuck Valve?

[FatHead]

My new Hawk 250 was running fine for about the first hour at the ORV park. Just gently riding some trails to break it in. Then it died, and couldn't be restarted electric or kick. I brought it home and checked everything from the spark plug to air filter and fuel. All good. The carb seemed fine too (though I'm no expert). I read on here about valve clearance sometimes being an issue, so I pulled the valve cover. As I was trying to find TDC I noticed that only the exhaust valve was moving. I've gone through several cycles and the intake valve never moves. The curved rod that pushes the rocker up and closes the exhaust valve moves freely, but the matching rod for the intake valve is barely visible (so I'm assuming it is stuck down) and therefore never pushes the valve closed.

Any ideas on how to fix this would be greatly appreciated. This is my first dirt bike since childhood, and I'm no spring chicken...I'm also no mechanic so please use small words lol.

[Ol,fart]

Originally Posted by FatHead

My new Hawk 250 was running fine for about the first hour at the ORV park. Just gently riding some trails to break it in. Then it died, and couldn't be restarted electric or kick. I brought it home and checked everything from the spark plug to air filter and fuel. All good. The carb seemed fine too (though I'm no expert). I read on here about valve clearance sometimes being an issue, so I pulled the valve cover. As I was trying to find TDC I noticed that only the exhaust valve was moving. I've gone through several cycles and the intake valve never moves. The curved rod that pushes the rocker up and closes the exhaust valve moves freely, but the matching rod for the intake valve is barely visible (so I'm assuming it is stuck down) and therefore never pushes the valve closed.

Any ideas on how to fix this would be greatly appreciated. This is my first dirt bike since childhood, and I'm no spring chicken...I'm also no mechanic so please use small words lol.

My knowledge of this little engine is pretty limited so bear with me. The push rods(from the rocker down into the cylinder) pushes up to open the valve(the big spring closes it) my understanding is both pushrods are operating off of a single lobe on the camshaft . That would eliminate a bad cam.
That would leave a bent or broken pushrod. Or maybe the pivot device between the cam and pushrod(I don't know it's name 2 lobe cams don't use it)

[Ol,fart]

Cscmotorcycles.com calls it lower rocker arm. I looked it up for a tt250 it's the closest thing they have to a hawk. But they by far have the best website for engine/transmission parts. Understand there are differences, the tt250 has a counterbalanced version of the same engine so some things will be different.
Call them if you need help, there helpful I wish I had bought my bike from them.

[FatHead]

Originally Posted by Ol,fart

My knowledge of this little engine is pretty limited so bear with me. The push rods(from the rocker down into the cylinder) pushes up to open the valve(the big spring closes it) my understanding is both pushrods are operating off of a single lobe on the camshaft . That would eliminate a bad cam.
That would leave a bent or broken pushrod. Or maybe the pivot device between the cam and pushrod(I don't know it's name 2 lobe cams don't use it)

I suppose I should pull the rocker assembly off and pull the push rods to check them out. You are correct that the spring closes it. So I guess it is stuck in the closed position...which would explain why it won't start LOL.

[TominMO]

It isn't stuck in the closed position because the gap from the pushrod to the rocker arm is too large? But that should not be the case if it was running fine before. Although it might have happened if the locknut for the adjuster wasn't tight.

Is it possible that the rocker arm moved sideways somehow, and is no longer in contact with the pushrod?

You might call up your dealer and ask if they have seen this before.

[Thumper]

You can remove the valve cover (three 10mm bolts, if it is like mine) and turn the crank to see if the valves are opening and closing. There is a window to see the T mark (top dead center) on the left side of the top of the engine. Take out the spark plug to make it easy to turn over with either the kick starter or the cranshaft end (port on left case cover).

You can check the valve clearance while you do this.

[Megadan]

From your description it sounds like the valve is not coming back up but the rocker arm is freely moving.

If I had to guess, I would wager the intake valve is stuck as you are assuming. Why it is stuck is a different question.

If it got stuck due to a lack of lubrication or the stem bent? Maybe somebody in the engine factory in china lost a bolt down the intake and it wedged into the valve. Might be possible that the valve seat came loose and is wedged between the head and valve.

No matter what, I would start by setting to TDC and then removing the rocker arm assembly to get it out of the way. It's 3 bolts and super easy to remove.

Next, I would tap on the valve with a rubber or nylon hammer to see if a couple of strikes might release it. If not, it's only a few more nuts and bolts to get the head off, and a head gasket is cheap. Worst case scenario you need a new head. If you keep in contact with the people that sold the bike to you, and they had some sort of warranty, you might be able to get a new head and gaskets from them. If not, a new head isn't that expensive, and you can make a slight upgrade with a TT250 or Brozz head which have better casting quality.

[Megadan]

If you need a little primer for removing the head, I made this video a couple years back that can at least provide a little information for you. The quality isn't very good, so take it for what it is lol.

[FatHead]

Originally Posted by Megadan

From your description it sounds like the valve is not coming back up but the rocker arm is freely moving.

If I had to guess, I would wager the intake valve is stuck as you are assuming. Why it is stuck is a different question.

If it got stuck due to a lack of lubrication or the stem bent? Maybe somebody in the engine factory in china lost a bolt down the intake and it wedged into the valve. Might be possible that the valve seat came loose and is wedged between the head and valve.

No matter what, I would start by setting to TDC and then removing the rocker arm assembly to get it out of the way. It's 3 bolts and super easy to remove.

Next, I would tap on the valve with a rubber or nylon hammer to see if a couple of strikes might release it. If not, it's only a few more nuts and bolts to get the head off, and a head gasket is cheap. Worst case scenario you need a new head. If you keep in contact with the people that sold the bike to you, and they had some sort of warranty, you might be able to get a new head and gaskets from them. If not, a new head isn't that expensive, and you can make a slight upgrade with a TT250 or Brozz head which have better casting quality.

So I took the head off and sure enough the intake valve is stuck in the down (open) position. I pulled the rods and they are undamaged, but the intake rod was no longer captive between the lifter and the rocker. I believe it likely dropped out of place and was no longer aligned properly to contact the rocker cup that generally catches the top of the rod. I will contact 360powersports tomorrow and see about a new head. They say they have a 1 year warranty. I bought this bike right before winter and it only made it 6 miles into its first ride.

[FatHead]

Is there a way to pull the intake valve to see what the stem looks like?

[Megadan]

Originally Posted by FatHead

Is there a way to pull the intake valve to see what the stem looks like?

With the valve stuck down, it will be somewhat difficult to compress the spring enough to remove the retainer from the spring assembly in order to pull the valve through. If you can manage to find a way to get the retainer off you would attempt to drive the stem through with a small punch.

I agree that the pushrod likely fell down when the valve stuck and the rocker was no longer there to keep it captive.

[Thumper]

So if the valve is really stuck down, and you can see this happening when you rotate the crank (rocker loose, but valve not coming up), then it sounds like the only way to address this would be to pull the head to remove the valve, right?

So, push the valve up from the inside of cylinder dome, then use a valve spring compression tool to remove the retainer and drop the valve out...

If the valve stem is bent, is it unwise to straighten it and attempt to use the same valve?

[severely]

Originally Posted by Thumper

So if the valve is really stuck down, and you can see this happening when you rotate the crank (rocker loose, but valve not coming up), then it sounds like the only way to address this would be to pull the head to remove the valve, right?

So, push the valve up from the inside of cylinder dome, then use a valve spring compression tool to remove the retainer and drop the valve out...

If the valve stem is bent, is it unwise to straighten it and attempt to use the same valve?

Yes, you must remove the head to replace the valve. And yes you CAN straighten valves. Problem is sometimes when straightened they develop stress fracture along the head/stem junction and break off in high rpm situations. How much is a new valve? Versus a new head/cylinder/piston if you drop the valve. Make sure the valve guide isn't broken/cracked when you remove the valve from the head. Good luck.

[TxTaoRider]

I wouldn't even consider trying to straighten a valve, especially when they are so inexpensive to just buy a new one.

[Megadan]

My own personal guess is the valve guide to stem clearance was a bit too tight, and being a Chinese made engine on the cheap, they didn't lube the stem during assembly. Dry stem + tight clearance + hot motor = stuck valve.

I would try to get some kind of light oil around the stem and guide.inside the port and them some love taps on the valves from both ends with a soft hammer to see if you can maybe unstick it enough to seat. If so, you could then release the retainer and pull the springs and valve.

Otherwise, hopefully they just warranty the whole top end and send you a new head.