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Post by calmissile on Oct 23, 2011 2:13:20 GMT -5
After considerable troubleshooting I found the problem and want to share. It may save some a lot of time and money. I bought a Tank Urban Touring scooter that was not running. After replacement of several parts (coil, CDI, carb, etc) I finally got it running but it would not idle and was almost impossible to start. Once it did start it would run fine at fast idle and higher but nothing would cure the problem. Exchanged carbs again and tried another coil and CDI. It was clear that fuel was getting to the engine and I was dumfounded as to what the cause was.
Reading on another forum, I found that the valve adjustment on these engines are somewhat critical and change over time (particularily they get tighter over time).
As a last ditch effort I decided to pull the valve cover and check the valve clearance. Sure as hell, the exhaust valve (the lower rocker arm) had less than zero clearance (the valve was not closing completely, even when cold).
As I remember in my youth, it is better to hear them than smell them, so I adjusted them a little loose (while the engine was cold). About .004" on both.
When I put it back together, the engine purrs like a kittten and will idle almost down to zero RPM. It sure was a wakeup call to me! Anytime the engine starts running ratty, the first thing I am going to do is check the valve clearance.
Hope this help anyone else with these symptoms.
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Post by 89newbie on Oct 23, 2011 8:43:29 GMT -5
Valveitus is the name of the syndrom. It comes from not hardened valve heads and lack of seat inserts. As the engine runs in the heat and pounding from the rocker hardens the stem head, and seats the valve in the aluminum head. As this occours the clearance diminishes to "0".
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Post by Pony66 on Oct 23, 2011 8:48:49 GMT -5
I have valve seats in my head.
Its the valve stems that heat and stretch. This reduces your valve lash when the motor gets hot. Not enough valve lash and they can seize or not open enough to run. When the scooter starts to die at stop lights and hard to start, check the valve lash.
This is regular maintenance on any vehicle that does not have hydraulic lifters and has solid lifters. My mustang came brand new with instructions to set the valve lash.
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Post by sprocket on Oct 23, 2011 15:21:59 GMT -5
There are no lifters ... the rocker arm on the GY6 engine contacts the valve stems...the gap is between the rocker arm and the valve stem
It is called valve regression...in the GY6.. the aluminum heads are soft and the valve and seats push into the head..eventually it slows down after about 3000 miles...
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Post by qwertydude on Oct 25, 2011 10:27:11 GMT -5
Keep an eye on the valves from now on. I find if you ever let it get to the point where starting becomes difficult, the valves will tend to recede faster than if you just kept them adjusted the whole time. So check it again in a couple thousand miles and see if it's receding and adjust accordingly. After doing this for a few adjustments the valve recession usually settles out and you'll be back to a normal adjustment routine. But then again how many people here keep their scooters past 10,000 miles anyways? At those kinds of miles valves are your least concern as parts start really wearing out.
Often times on my scooters I only ever need to adjust them every 6,000 miles or more even, and that's well before they'll become too tight to idle and start correctly.
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Post by sprocket on Oct 25, 2011 11:37:39 GMT -5
People think that continuous valve adjusts only occurs on Chinese GY6 engines... Nothing is further from the truth.... the Honda C70s and C90s were always needing gap adjustments, only difference they provided a nice plug port you could remove to do it...if you had really, really tiny hands  |
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Post by qwertydude on Oct 25, 2011 22:29:17 GMT -5
Yeah with those tiny plug ports I actually cheated and simply adjusted them by feel. You can actually get pretty darn close with enough practice feeling how much wobble there is between the adjuster and valve.
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mcinoh
New Puppy Dawg
Posts: 1
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Post by mcinoh on Sept 26, 2012 22:10:34 GMT -5
Thank God for the intenet. I came across this post and follow the suggestions. Cracked open the valve cover and sure enough, zero valve clearance on my exhaust valve. Scooter is running great! Thanks for taking the time to post this.
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Post by jlee on Sept 26, 2012 23:38:33 GMT -5
People think that continuous valve adjusts only occurs on Chinese GY6 engines... Nothing is further from the truth.... the Honda C70s and C90s were always needing gap adjustments, only difference they provided a nice plug port you could remove to do it...if you had really, really tiny hands Yeah, it's definitely not a scoot-only maintenance chore. I used to do a valve lash adjustment on my VW Bug at every oil change. That one was easy. Doing it on my Kawi 454 is a real bugger - gotta drain & drop the radiator, pull the gas tank, coils, vaccum & cooling hoses just to get the valve cover off. Makes me grumpy when the valves turn out to be spot on, which they usually are.  |
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