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piston creating vacuum on up stroke 03 450r

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So as i was riding along one day my bike shut off n locked up as i came to an idle. Bottom end and Top and replaced about a year ago. Got it home pulled out spark plug and i can kick it over but felt like there was still a compression stroke occuring. so removed the head and jug, everything spins free and moves as it should. Bolt the jug on with out the head and with it clamped tight on the cases it gets hard to kick but only on the up stroke. down stroke goes smooth and as it should. Removed stator covor and can see it blowing out the oil/air on the down stroke through the reed valve. so split the cases and everything looks as it should, reed valve is working as it should. Put it back together and same issue. BALLS.  Now im a diesel tech and rebuild engines all day, and have rebuilt several 4-stroke/2-stroke engines never had this problem before.  Is there something that lets air in from the crank case on the up stroke so the piston doesn't create a vacuum? simular to the reed valve for letting the air/oil out on the down stroke?  I'm at a loss guys. the search has revealed no answers for me or the manual.

 

thanks in advance. free 6-pack to the one that can help me

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A vacuum isnt whats binding the up stroke. The compression you think you feel is the cam forcing the valves open and the flywheel magnet passing the stator poles.

 

How are you allowing the cam chain to circulate the bottom gear with the head off? If you want to see how easy it is to rotate the engine with the cylinder in place, take the stator off. Its amazing how much the magnets pull.

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Shawn this is obviously over your pay grade. So please go crawl back under the troll bridge you came from.

Maybe I wasn't clear enough but just the jug was bolted on not the head and when the engine rotates n its on the up stroke it's very hard for it too move up. And you can hear air hissing by the Rings very slowly. almost the same effort as it would take kickstarting it with the spark plug in under normal conditions. but on it down stroke it goes with no effort and you see if it's spitting air and oil out of the reed valve.now hopefully there is somebody out there smarter than shawn that can help me.

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oh boy

I just realized the problem here

The man has a quad as his avitar.

Edited by nesc103y

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Shawn this is obviously over your pay grade. So please go crawl back under the troll bridge you came from.

Maybe I wasn't clear enough but just the jug was bolted on not the head and when the engine rotates n its on the up stroke it's very hard for it too move up. And you can hear air hissing by the Rings very slowly. almost the same effort as it would take kickstarting it with the spark plug in under normal conditions. but on it down stroke it goes with no effort and you see if it's spitting air and oil out of the reed valve.now hopefully there is somebody out there smarter than shawn that can help me.

Well... That escalated quickly.

It sure makes it hard for people to try and help you when you're an ass to them.

Save the two stroke.

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If you're gatting a "vacuum" on the up stroke, your crank case ventilation systemicon1.png is restricted.

Check that first.

 

Edited by Home Skillet

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Shawn I apologize for the harsh comet. It originally only showed mepart of the post. And it looked like you called me a f**k.so I thought you were just being a smartass. I have no idea why. But now I see you have a real comment it thank you

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I had the cam chain turnin on my finger as I held it for the cam would have been. The resistance I'm feeling is more than from the stator or the valves compressing. But that was already eliminated by having the head off. And if I didn't have the jug clampdown tight in the air could squeeze out by the base gasket it went up and down fun. This is enough resistance where when you have the spark plug in its too much to kick over. I check the ventilation system and on the crank side advanced through the valve cover and that's not the issue right now. And the one way read valve for the oil is working correctly where it will spit the oil from the crankcase into the stator cover on the down stroke of the piston as it should but it's the upstroke that is a problem

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Shawn helps people out more than all the other "helpers" combined... myself included. braaap.

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The sealed crankcase below the piston is unique with the reed valve, sounds like the question is how much vacuum resistance is normal when the piston is moving up. 

I dont know the answer to that one, maybe someone else does.

Wondering if possibly there is a small opening or orifice to limit vacuum resistance?

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Above my pay grade... :lol:

 

There might be a small vacuum created when kicking, but none of these things seal up all that well, so there's almost always a tiny positive pressure in the bottom end. Which is how they were designed to scavenge the bottom end in the first place.

There is also the common occurance that the vacuum created in the bottom end is enough to migrate the oil past the seal from the trans into the engine, but it can also get blown the other way too, from the engine to the trans.

 

Ive had more of these things apart than most of the guys here. And trust me, the flywheel magnets pull pretty friggin hard. The cylinder on this engine has an exagerated angle on the crank, meaning that the piston/rod has an advantage on the crank during the power stroke. On the upstroke, the rod/crank angle is exaggerated to the disadvantage, which is when I think many of the rod failures occure on the upstroke. But thats a different conversation.

 

I know you said you'd just recently done the top end, but check the piston skirt for an excessive collapse. There's so little skirt here that the piston turning sideways in the bore is a real possibilty.

 

My job on TT here, and its a job, trust me, is to keep the forum informative. People dont get to call each other names, unuseful stuff lands in the shit can, I do it myself. Ive deleted more stuff and banned more guys that I care to recall.

 

Drop that cam chain out, take the stator cover off, leave the cylinder bolted to the cases and see if the resistance is still there. If its a vacuum, it'll be there, the seals on the crank and the reed in the bottom arent affected by the stator cover. Its going to blow oil all over the place out the reed though.

 

If there's still a resistance, Id start by rotating the crank by hand to eliminate the kicker gear train from the percieved resistance.

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Above my pay grade... :lol:

 

There might be a small vacuum created when kicking, but none of these things seal up all that well, so there's almost always a tiny positive pressure in the bottom end. Which is how they were designed to scavenge the bottom end in the first place.

There is also the common occurance that the vacuum created in the bottom end is enough to migrate the oil past the seal from the trans into the engine, but it can also get blown the other way too, from the engine to the trans.

 

Ive had more of these things apart than most of the guys here. And trust me, the flywheel magnets pull pretty friggin hard. The cylinder on this engine has an exagerated angle on the crank, meaning that the piston/rod has an advantage on the crank during the power stroke. On the upstroke, the rod/crank angle is exaggerated to the disadvantage, which is when I think many of the rod failures occure on the upstroke. But thats a different conversation.

 

I know you said you'd just recently done the top end, but check the piston skirt for an excessive collapse. There's so little skirt here that the piston turning sideways in the bore is a real possibilty.

 

My job on TT here, and its a job, trust me, is to keep the forum informative. People dont get to call each other names, unuseful stuff lands in the shit can, I do it myself. Ive deleted more stuff and banned more guys that I care to recall.

 

Drop that cam chain out, take the stator cover off, leave the cylinder bolted to the cases and see if the resistance is still there. If its a vacuum, it'll be there, the seals on the crank and the reed in the bottom arent affected by the stator cover. Its going to blow oil all over the place out the reed though.

 

If there's still a resistance, Id start by rotating the crank by hand to eliminate the kicker gear train from the percieved resistance.

 

With the engine fully assembled theres going to be some leakage/blowby past the rings when the piston is going up to counteract creating a vacuum in the lower crankcase at least on the compression stroke. With the head off its a little different situation. 

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