18.5 hp intek ohv valve adjustment???

[willie 76]

Poulan Pro 42" 18.5 hp intek ohv

Where to start? Or should I say HOW to start. I put in a new battery, air filter, fuel filter, oil filter, spark plug, cleaned the carb, bowl and float. Still wouldn't start. So I did some asking and looking, was told to adjust the valves. Did that. .004, both intake and exhaust. It finally started. Drove it for about 20 ft. and it started to sputter a little. So I tried playing with the choke, which didn't help. I shut it off and now the son of a motherless goat won't start back up. It's acting the same way it did before, it doesn't want to turn over. I know that it's either something I did or didn't do, but that don't quite narrow it down enough. Can the valves get back out of adjustment that quick? Any ideas would be appreciated.

 

[Rivets]

If the locking nuts are not tightened properly, the valve clearances can change that fast. When I do a valve adjustment, I always turn the engine over through at least two cycles by hand, then double check my clearances, to make sure that everything is tight and correct. I know this does mean it takes longer to complete the project, but it is easier to do than starting over if something is not right.

 

[willie 76]

Rivets, I went back and double checked the valve clearances and they were a little off. (thank you, I will double check from now on) I got them back to .004, and it wouldn't start, same problem, it doesn't want to turn over. I changed it to .003 on the intake (bottom) and .005 on the exhaust (top). This didn't help either it still won't start. What I did notice is that that the bottom rocker goes in just fine, but when the bottom rocker is trying to come out and the top rocker is trying to go in, it is real hard to turn by hand and it makes a suction noise. It's like it doesn't want to let it go.

 

[Rivets]

I suspect what you are seeing is valve overlap. This is where both valves a open at the same time. Four strokes, intake, compression, power, and exhaust. Intalve= intake valve open, piston going down, fuel drawn in. Compression= both valves closed, piston going up, fuel is compressed, and at the end of the stroke, at starting speed exhaust valve will slightly open to release a small amount of compression. Power= both valves closed, piston going down, fuel is being burned. Exhaust= exhaust valve open, piston going up, burnt gases being expelled. At the the end of the exhaust stroke the intake valve will start to open before the exhaust valve closes to help push out the burnt gases.

Are you sure that you are turning the flywheel in the correct direction? Turning it the wrong way will easily confuse you about what is happening.

 

[willie 76]

No sir, I'm not sure I'm turning it in the correct direction, but I was turning it clockwise. As for being confused, well, I've been confused by a whole lot less than this. I've piddled around with it some more this afternoon. I changed the clearances to .004 intake, .006 exhaust. It still didn't want to turn over but for some reason after I let it sit for a while when I tried to start it again it was spinning free but it just wouldn't fire. I changed it back to .004 for both, now we are back to not wanting to turn over. Put it back on .004/.006 still wouldn't turn over. Every time I took the valve cover off, there was a bunch of gas in there, if that means anything. So valve overlap? Does that have anything to do with the timing?

 

[Rivets]

Valve overlap and timing are related, but we are not going there. You have done nothing that would affect the timing. Let's figure out if we have a fuel or spark problem. Please check for spark. If you have good spark, spray some carb cleaner into the carb and see if it fires. If it does not fire check the plug to see if it is wet. Remember, you are my eyes, ears, and fingers in this equation. The better your description, the better we can see what is going on. Report back and we'll go from there. I'm logging off now as I have a 12 hour day tomorrow, but I'll check as soon as I get home tomorrow. I'm sure by that time some over mechanic will have read this and will chime in.

 

[Fish]

On these engines you had a couple of worries. The main problem was that the rocker arm stud would work loose and folks were telling them to adjust the valves...

 

[willie 76]

I got a chance to work on it today. It started right up, (it's been sitting for a few days unmessed around with.) until it ran out of gas. Put more gas in, wouldn't start up. Pulled out the spark plug it is sparking, and today it was dry but last sunday when i pulled it out it was wet. When the spark plug is out the flywheel spins free. I took the cover off of the valves and tried to start it, it wouldn't start but you could hear it hiss and stop where it is trying to turn over but getting stuck. I would turn the flywheel past that sticking point by hand and then try the key again. It would turn for a few strokes, then hiss and get stuck.

 

[Rivets]

When you had the valve cover off, did you notice if the exhaust valve opened slightly as the piston was coming up on the compression stroke? Is this when you. Heard the hissing? The valve should open slightly allow some of the compression to be released for easier starting. This is called compression release.

 

[willie 76]

No sir, I couldn't tell, I was on the backside turning the key, the valves are in the front, couldn't see them. But when it starts that hissing is when it gets stuck and there is nothing easy about it. It takes both hands to turn the fly wheel by hand at that point which is why it seems like it won't turn over.