Intake valve won't close

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  #1  
Old 02-23-10, 04:25 PM
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Intake valve won't close

Hi,

I have a B&S md 204412 type 0142e1 code 050119e. Not sure what horse it is but it is on my 5500 watt portable generator. I bought the generator a while back I am not sure how many years but I only used it once or twice in the first year and it ran great and then as generators due it stayed in storage. I went out to start the motor the next season and I found that it would rotate and stop at one point. I could rotate the motor back and it would stop roughly at the same point . I took the valve cover off (OHV) and found that the intake stem was not rising as high as the exhaust. I loosened up the rocker and found that the valve would rise and apparently seat with the rocker tension off. I also found a bent push rod. Both valves will move fairly easily when pressed with a hammer handle. I heard the valve guides can come loose in these heads and bend the push rods but my problem seems to be more with the valve stem not rising enough rather than lowering enough. Is there a decompression mechanism that could interfere with the valve movement?

Thanks Dan.
 
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  #2  
Old 02-23-10, 04:30 PM
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Does the push rod move up and down when rotating the engine? Sounds kinda like the lifter is stuck since the valve moves freely.
 
  #3  
Old 02-23-10, 04:50 PM
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Originally Posted by cheese View Post
Does the push rod move up and down when rotating the engine? Sounds kinda like the lifter is stuck since the valve moves freely.
Yes the pushrod does move on both the intake and the exhaust
 
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Old 02-23-10, 05:04 PM
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Originally Posted by cheese View Post
Does the push rod move up and down when rotating the engine? Sounds kinda like the lifter is stuck since the valve moves freely.
What could cause the lifter to stick? Can the same varnish that seizes the valve stem in the guide cause the lifter to stick?
 
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Old 02-25-10, 01:24 AM
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No, I don't think so. Cooked on oil could cause a lifter to stick. So... the valve doesn't close all the way, and the lifter moves all the way down, and the valve does close all the way with the rocker arm off, right? If so, then that says either the valve clearance is too tight or the camshaft is holding it open somehow.
 
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Old 02-25-10, 05:48 AM
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Originally Posted by cheese View Post
No, I don't think so. Cooked on oil could cause a lifter to stick. So... the valve doesn't close all the way, and the lifter moves all the way down, and the valve does close all the way with the rocker arm off, right? If so, then that says either the valve clearance is too tight or the camshaft is holding it open somehow.
Must be the cam because if I backed the rocker adjuster all the way off the valve would still be held open. As far as the lifter moving all the way down I have to assume it does not because there is plenty of pressure on the push rod holding the valve open. When you watch both valves operate it is clear that there is much less movement on the intake side compared to the exhaust.
 
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Old 02-25-10, 04:52 PM
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The camshaft can't hold the valve open that far if the engine and cam is at TDC position.

Take a flashlight and look at the lifter. I'm thinking it is damaged and not falling back down to the cam lobe.
 
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Old 02-26-10, 05:35 AM
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Originally Posted by cheese View Post
The camshaft can't hold the valve open that far if the engine and cam is at TDC position.

Take a flashlight and look at the lifter. I'm thinking it is damaged and not falling back down to the cam lobe.
Thanks, I am out of town but as soon as I get back I will check it out.
 
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Old 03-05-10, 05:02 PM
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Originally Posted by cheese View Post
The camshaft can't hold the valve open that far if the engine and cam is at TDC position.

Take a flashlight and look at the lifter. I'm thinking it is damaged and not falling back down to the cam lobe.
Well I took a look and it looks like the top surface of the lifter maybe damaged a bit which would keep it from sliding all the way back down the guide. I assume these lifters can be removed and replaced from the topside? Can I replace a lifter without replacing the cam? That may seem silly but in a car you are supposed to replace the cam and the lifters as a set.
 
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Old 03-06-10, 12:51 AM
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The lifters are replaced from the inside of the engine. It must be removed and opened up. The lifter has to slide through, and if the end is damaged badly enough, it may be hard to get it through. If the cam looks like both lobes are in good shape and come to a nice high point at the peak, I'd use it and look for a second-hand lifter. Make sure the lifters you use have a completely smooth flat surface with no marks or impressions of any sort. Completely smooth. Lube them well before installing. Most small engine shops should have a few laying around.
 
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Old 03-06-10, 05:10 AM
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Originally Posted by cheese View Post
The lifters are replaced from the inside of the engine. It must be removed and opened up. The lifter has to slide through, and if the end is damaged badly enough, it may be hard to get it through. If the cam looks like both lobes are in good shape and come to a nice high point at the peak, I'd use it and look for a second-hand lifter. Make sure the lifters you use have a completely smooth flat surface with no marks or impressions of any sort. Completely smooth. Lube them well before installing. Most small engine shops should have a few laying around.
Thanks for your time. I will do some shopping around and see what I can come up with.
 
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Old 03-14-10, 12:27 PM
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Ok, I now have the lifter replaced and the engine would start and stall because the float was stuck. So I took the carb bowl off and cleaned things up and I know longer have fuel flooding the carb and running on the ground but I have no fuel getting into the engine at all. The bowl is full but the plug is dry. There is a round spring that I was unsure of its original location so I put it in the center of the bowl and pushed the bowl straight up and then tightened down. Is this the right placement of the spring or did I just pint the float down so the needle never leave the seat?
 
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Old 03-14-10, 07:01 PM
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Is it a Nikki carb? Plastic float connected to a plastic inner body that drops out of the carb? If so, the spring is in the right place. It could have a plugged main jet.
 
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Old 03-14-10, 09:14 PM
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Originally Posted by cheese View Post
Is it a Nikki carb? Plastic float connected to a plastic inner body that drops out of the carb? If so, the spring is in the right place. It could have a plugged main jet.
That describes the carb perfectly. I will check out the jet thanks
 
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