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Old 08-21-2015, 02:01 PM   #16
KirkN   KirkN is offline
 
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Good point - I'll have to inspect up in the valve guides. Nothing obvious on the valve stems, though.

And, since I'm not convinced I've really got a smoking gun even yet, I'll go ahead and pull the cylinder off and inspect the piston / rings. Cylinder walls look good as far as I can see, but I could have a stuck ring(s).

Meanwhile, my new head gasket shipped and says it should be here by Tuesday. So, hopefully by mid-next week, I'll have it back together and see if I have compression.



 
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Old 08-21-2015, 02:28 PM   #17
bogieboy   bogieboy is offline
 
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silly quesfion... the "chuffing" you heard.... are you positive it was from the carb, and not maybe from the crankcase vent? just thought of that... that was the first sign I had issues.... I had a reLly high crankcase pressure.... and come to think of it the walls of my cyl looked fine as well...


 
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Old 08-21-2015, 02:37 PM   #18
KirkN   KirkN is offline
 
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That's a good thought too. No, not 100% sure, but my breather feeds into the airbox, and I did have the rubber carb-to-airbox hose pulled back off the carb and thought it was coming from the carb.

But you're right, and that's another good incentive for me to pull the cylinder and inspect the piston and rings.


 
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Old 08-21-2015, 06:42 PM   #19
bogieboy   bogieboy is offline
 
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if you have it down that far you may as well do em anyways... I got the piston and a set of rings for around $15-20 off ebay.... cheap insurance at this point....


 
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Old 08-22-2015, 04:15 PM   #20
KirkN   KirkN is offline
 
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And, it's bogieboy for the win!!

Lapped the intake valve and got it to hold acetone in the port for a good 5 minutes with no drips.






So, next step was to pull the cylinder off. Yep, ALL 3 RINGS are stuck fast in their grooves. I've never seen such a thing in a motor with so few hours / hasn't been sitting inert for years. Huh.

Can't even get the oil ring (3-pieces - upper, lower and center wavy piece) to move. Got one bit of the 2nd ring to pop free a bit, but hard to even tell where the end gap IS on the first ring.

So, new piston, ring, wrist pin, circlip set plus base gasket on it's way. Only $20 for the set and should be here next weekend or so.

Cylinder still looks good, but I'll give it a quick hone before the new parts go in.













 
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Old 08-22-2015, 09:08 PM   #21
bogieboy   bogieboy is offline
 
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and now we know the cause of the loss of compression....LOL my bike only had 320 mi on it when I got it and thats how it came to me... wonder about the piston expanding too quickly from the stuck throttle Nd the rings getti g stuck from that? who knows....


 
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Old 08-22-2015, 09:51 PM   #22
jct842   jct842 is offline
 
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I would imagine acetone would cut the varnish that is holding those rings in.


 
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Old 08-22-2015, 10:26 PM   #23
humanbeing   humanbeing is offline
 
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We can guess the maker from stamped logo & letter
Examples http://item.taobao.com/item.htm?id=42153157591 | http://item.taobao.com/item.htm?id=40158406458 of the mainstream player. Some cheap one that NEVER heard will f***ed in no time
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Old 08-23-2015, 12:23 PM   #24
Weldangrind   Weldangrind is offline
 
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I see some striations on the piston, but nothing to worry about. If you get a decent piston and rings, you should be good to go. Like you, I'd hone the cylinder first (I use a master cylinder hone for that).
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Old 08-25-2015, 02:03 PM   #25
KirkN   KirkN is offline
 
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I would imagine acetone would cut the varnish that is holding those rings in.


wonder about the piston expanding too quickly from the stuck throttle and the rings getting stuck from that? who knows....



So, now I have some additional food for thought: I was able to remove the 2nd ring and the oil control ring(s) last night, and it appears they were being held in place by grit. When I got them out, it was clear that a very fine grit was all in the ring grooves and was acting as a wedge, holding the rings stuck in place. I cleaned the rings and the grooves a bit, and they seemed to move freely again! The top ring is still resolutely stuck in place, though.

That got me thinking about the original cause of the sticking carb (which I hadn't really gone into at all) - yep, the whole inside of the carb throat, including the throttle slide and it's bore contained the same fine grit. It was clearly the cause of the throttle slide sticking.

Hmmm.... where did that come from? Back to the airbox - yep, the air filter foam was degenerated and had left a large gap at the bottom of it's contact area. And of course, on this bike, there's no airbox cover. The top of the airbox is wide open, and when the seat is installed, it doesn't really prevent the back tire from flinging mud/dirt up over the top of the battery and into the airbox. The inside bottom of the battery box and the airbox was filled with fine sand in all the corners.

So, I think the poor motor was sucking in sand and it jammed both the throttle slide and the piston rings. I also think it might have screwed up the intake valve sealing. And, I think that's what gives the piston sides that 'sandblasted' look, as opposed to the usual wear marks one sees.

So, always be sure to check your air filter! I think when this goes back together, I might remove the airbox-to-carb rubber tube and just install a 2-stage foam pod type filter.

And, I'm going to try to figure out a shield or deflector for under the seat to help keep the tire from just flinging mud right into the area.

Thoughts and comments?



Last edited by KirkN; 08-26-2015 at 06:11 AM.
 
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Old 08-25-2015, 10:02 PM   #26
Weldangrind   Weldangrind is offline
 
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Excellent detective work. Now you know why I don't use the stock airbox on any of my China stuff. Here's what has worked for me: http://www.ebay.com/itm/Red-42mm-Ang...e5ec4c&vxp=mtr
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Old 08-31-2015, 12:25 PM   #27
KirkN   KirkN is offline
 
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Success!

Got the bike put back together Sunday. New piston, rings and gaskets showed up Friday. Honed the cylinder and put it all back together. Got the motor back in the bike and enough stuff back together to hear it run for 5 ~ 10 seconds on a shot of spray start. Woo Hoo!

At one point, I was turning it over with the e-start to get oil pumped up to the head, and I did a quick compression test, even though it's never been fired and was cold. It made about 150psi, so I'm well pleased. Shop manual says 178psi, but that's warm and with seated rings.

As for air filter, I used a Uni-style foam universal. All I did was remove the stock carb-to-airbox rubber tube. Fits well, so I'm hopeful this won't happen again. Especially when I fabricate a few bits to help deflect rear tire mud flinging.

So, there we go. Lesson learned. Thanks to everyone for links, support and discussion.

Kirk



 
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Old 08-31-2015, 11:31 PM   #28
Weldangrind   Weldangrind is offline
 
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That's awesome news! You might need a larger main jet with that new filter.
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