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Post by pistonguy on Sept 22, 2015 8:24:27 GMT -5
pull your plug and turn the engine by hand a few times and watch the valves to see that they are moving properly. if they seem to be, you may have to pull the head and check inside. those big clearances cause a lot of pressure, flow, and no flow at the wrong times. you may have bad valve seats, burnt piston, or what not currently giving you a not so healthy combustion chamber. Pressures? Cylinder pressures? im confused If so how does a extra .001 in valve lash cause cylinder pressure to go up? and then cause all the bad ju ju for the component listed? |
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Post by lain on Sept 22, 2015 9:43:46 GMT -5
Well if you have done everything right so far then you must go back and diagnose the issue as if it is brand new and unrelated. It is possible a dirty carb, bad plug or coil or cdi or a clog in the muffler or something else weird could have been causing the hard starting if the valves have done nothing to help. The gap should be 0.004, that's two zeros before the 4 not one after the point mark.
An extra 0.001 wont hurt it but you need to find the best tune for your machine. I just use 0.004 as a standard starting point and adjust from there as far as 0.003 to 0.005. I have actually adjusted as far as 0.006 without issues just clicking noise, just saying it can operate if it isn't exactly right, but you benefit much more from tuning ti to your specific engine which may or may not even be the gaps recommended by us or the manual.
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Post by tvnacman on Sept 22, 2015 10:04:57 GMT -5
Check mechanical timing. A broken woodruff key .
John
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Sophomore Rider
Currently Offline
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Post by dyoung1167 on Sept 22, 2015 20:09:35 GMT -5
i'm not going back to quote some of the numbers you say you set them at as many before me stated were way too big, but if your valves were set at them then the piston got way far into the combustion process and then nearly zero in the exhaust process. look it up (4 cycle animation) and i think you will see what i am referring to.
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Post by dickyh on Sept 23, 2015 5:40:01 GMT -5
dyoung1167 Thanks for the info! So what damage have I done? I have checked everything others have suggested and all is to par. Getting good spark, fuel, etc. I am about to pull the cylinder head next and check the valves and piston. I'm reluctant to do so as I never have, but my only option at this point. I'm thinking of buying a new cylinder head with valves and a new piston. I'm just wondering if I can simply refurbish what is already there if not damaged. This is unknown territory for me, but I've successfully changed pretty mush everything else on this scooter thanks to watching a lot of youtube vids. BTW, I have a 161QMK engine, if this would help with any diagnosis.
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Post by pistonguy on Sept 23, 2015 5:53:32 GMT -5
dyoung1167 Thanks for the info! So what damage have I done? I have checked everything others have suggested and all is to par. Getting good spark, fuel, etc. I am about to pull the cylinder head next and check the valves and piston. I'm reluctant to do so as I never have, but my only option at this point. I'm thinking of buying a new cylinder head with valves and a new piston. I'm just wondering if I can simply refurbish what is already there if not damaged. This is unknown territory for me, but I've successfully changed pretty mush everything else on this scooter thanks to watching a lot of youtube vids. BTW, I have a 161QMK engine, if this would help with any diagnosis. STOP! Do NOT Remove your Cylinder or Cylinder head at this time. dyoung1167 has provided misinformation on possible damage from being +.001-.00Big Valve lash or the reverse. or even much larger. Even a Lash that is Too Tight will only just Hang Open Slightly under Operating temperatures causing her to bog down, stall and not restart till she's cool. tun as the lash closes up more difficult to No start. You stated .0045 (Big) ? thats Four Thousandths and Five Ten Thousands of a inch, that is ok or Four and a Half Thousands, same thing. Thats Not big it darn near on the money. + or - .001-.002, thats one and two thousandths, is providing that much More or Less Cam. +.001 wil Provide More Gross Cam Lift and Duration, (all the cam numbers), same in the reverse of -.001. Now that I have you confused, sorry. Did you check the Flywheel Key (woodruff key)? How bout the Cam Chain tensioner? How many mile on the 161QMK? |
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Post by dickyh on Sept 23, 2015 6:11:14 GMT -5
pistonguy I set it to .045, not .0045. as for the woodruff key, I have no idea where that is or how to check it. The cam chain tensioner seems fine. I honestly think I screwed something up internally preventing proper combustion. the scoot has less than 5K miles on it.
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Post by steve on Sept 23, 2015 7:39:40 GMT -5
Yep, setting it at .045 is far too big of a gap. You likely damaged the cylinder. Just spend the $80, or so, and replace the cylinder and head. A lot of people in this thread missed that you initially set your gap WAY too big, at .05", instead of .005". I don't know exactly what was damaged, but you just need to replace the top end. New cylinder, and cylinder head, and you will be good to go. No need to try to find exactly what is messed up, and take a month to figure it out. Just replace it.
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Post by cyborg on Sept 23, 2015 8:31:04 GMT -5
very confusing thread,,there should have been no damage from setting the valve lash too big,,it would just be low on power from running late in the timing sequence because of the large gap,,,i think you have multi faceted problem here,,,just for peace of mind i suggest you check the rocker arms ,,i think you cracked one ,,,not from anything you did ,,,it may not be completely broken off just cracked and bent,,,also check the springs , keepers and retainers,,,,,,a nice clear pic of the valve train area would really help us determine whats going on here,,,,also it could be a bent valve holding open,,,you may not have been at TDC when you set them and the piston touched a valve and bent it ,,,
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Post by dickyh on Sept 23, 2015 9:19:05 GMT -5
here are 3 images of this area. Nothing here looks off... One comment however is at TDC the intake rocker arm has a little play but the exhaust has none. don't remember if it ever did, but all the vids I've watched shows a little play on both rocker arms. sorry about the images being upside down... when I uploaded them they got fliped    |
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Post by steve on Sept 23, 2015 10:19:40 GMT -5
No. Nothing looks off.
Your exhaust valve would have been barely opening at .05". I'm not sure what kind of damage that could have done, but those gasses had to go somewhere. You could have unseated the rings. You could have blown the valve seals. It's hard to say. Both rocker arms should have play at TDC, if the lash is set right.
Like I said, I would just replace the top end. It would not hurt anything to just replace the head first, and if that doesn't fix it, replace the cylinder and piston. You can't replace the piston without honing, or replacing the cylinder.
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Post by dickyh on Sept 23, 2015 10:26:41 GMT -5
No. Nothing looks off. Your exhaust valve would have been barely opening at .05". I'm not sure what kind of damage that could have done, but those gasses had to go somewhere. You could have unseated the rings. You could have blown the valve seals. It's hard to say. Both rocker arms should have play at TDC, if the lash is set right. Like I said, I would just replace the top end. It would not hurt anything to just replace the head first, and if that doesn't fix it, replace the cylinder and piston. You can't replace the piston without honing, or replacing the cylinder.
Yeah, I just bought a new top end kit and a cylinder head with valves, everything complete. A very expensive lesson learned.
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Post by pistonguy on Sept 23, 2015 10:28:30 GMT -5
pistonguy I set it to .045, not .0045. as for the woodruff key, I have no idea where that is or how to check it. The cam chain tensioner seems fine. I honestly think I screwed something up internally preventing proper combustion. the scoot has less than 5K miles on it. The Key is on the Flywheel end of the Crank shaft Pull the cooling fan cover, remove Flywheel nut and flywheel and the key is in its slot. By +.004 or +.045, won't cause internal damage. I amazed some are telling you you junked a top end with too big a valve lash |
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Post by dickyh on Sept 23, 2015 10:31:02 GMT -5
checked it is is fine...
I adjusted to .04 NOT .004 (BIG DIFFERENCE)
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Post by pistonguy on Sept 23, 2015 10:36:09 GMT -5
Yep, setting it at .045 is far too big of a gap. You likely damaged the cylinder. Just spend the $80, or so, and replace the cylinder and head. A lot of people in this thread missed that you initially set your gap WAY too big, at .05", instead of .005". I don't know exactly what was damaged, but you just need to replace the top end. New cylinder, and cylinder head, and you will be good to go. No need to try to find exactly what is messed up, and take a month to figure it out. Just replace it. Somebody teel me How from Experience one Damages a Cylinder by too big a Valve lash. Peeps sayin you've hurt something but can't tell ya What. Internt Bunk!! not going to hurt a darn thing in a gy-6 The Only thing that Will Happen with a Intake set at .045 is the Valve Never Lifted Enough to let a Charge in and it Wont Start. Period! a few got him going down the Wrong road now. |
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