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Post by JerryScript on Jul 2, 2014 23:00:01 GMT -5
So about a week and a half ago, I was giving my nephew a ride home from work. It was about a 10 mile drive, uphill against the wind with temps in the low 100s. About 1/4 along, I lost power, could barely get above 30mph. I'm thinking to myself, you just screwed up your CVT with all that weight on there (my nephew weighs about 240lbs). First chance I had I took the CVT apart and inspected everything. Nothing out of the ordinary, and only one weight showing a bit of wear. I put her back together and continued riding with no power for the next week (crying and cussing along the way). I finally had the time to pull the valve cover off, and I couldn't believe what I found. The top 1/4" of the intake valve is gone, sheared off clean at the top of the spring seat, with the rocker arm having a full 1/4" of play (I really don't understand how it started at all under these conditions). For the time being, I screwed down the tappet as far as I could and gapped it to the top of the spring seat. Put the valve cover back on, and she started right up, and I have my power back, though not all the way to my previous top-end. Anyone else have something like this happen? Could the end of the valve really have broken off clean like that, or do you guys think there is more than meets the eye? I realize I've done a bandaid job by gapping the tappet to the spring seat, I'm just doing that till I can grab a new head from Scrappys. Anyone care to guess what I'll find when I do pull the head? Here's a pick of the part that is sheared off, I didn't grab a pick when I was doing the work, but will when I get the new head.  |
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Freshman Rider
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Posts: 65 
Likes: 11
Joined: Apr 8, 2014 13:17:56 GMT -5
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Post by bashan on Jul 2, 2014 23:36:47 GMT -5
My impression would be there's very little holding the valve spring in place. I'm amazed you've got this far without catastrophic results. If the retainer let's loose that valve is dropping and you'll be replacing more than the head. No, I've never seen what you described happen and, from what you described, you've been incredibly lucky so far.
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Post by skuttadawg on Jul 2, 2014 23:38:23 GMT -5
A buddy of mine broke off his exhaust pipe and muffler and rode it for two months like so . he did not upjet so it was running very lean which made it run hotter . The exhaust valve head broke off of the stem and ate up the head and piston and he had to buy a new top end kit
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Post by JerryScript on Jan 6, 2015 15:48:19 GMT -5
I've been riding with the intake rocker arm tightened all the way down to the ring on top of the springs since this happened about 6 months ago. I've had to re-adjust twice during that time frame, and lost some power and a few mph on the top end, but it was actually running well otherwise, so I pushed it off. So, end of the story finally happened yesterday. I had just turned onto a downhill stretch of road with 45mph speed limit, so of course the rest of the traffic quickly accelerated to 50mph+. I got to 45mph, and heard a crack, then scrapping. I immediately pulled over. I carry my tools with me, and I knew it was most likely the valve, so I pulled the valve cover right there. Sure enough, the rocker arm on the intake had cracked the black ring on top of the valve springs, and was pushed down into the springs. As luck would have it, I was only 1.5 miles from ScrappyDogScooters, so I hiked down there and bought a new 47mm performance head and head gasket. I got back to my scooter, pulled the head right there on the side of the road, inspected the piston and jug (piston has chatter marks, but should be fine, jug is fine, whew), put the new head on, slapped the rocker arms on,  my BN139-QMB has the higher valves!!! The performance head has the shorter valves, which need longer rocker arms than heads with the longer valves! By now it's past 5pm and Scrappy's is closed!  Called a buddy with a truck to come grab my scooter. I could have just bought a new intake valve and spring assembly. Instead, I'm heading over to Scrappy's today to get proper rocker arms for the new head. All of this would have been avoided if I had just rebuilt/replaced my head 6 months ago!  Oh well, my new 150cc I ordered last week should be here by Thur or Fri, so this weekend I'll be  |
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Post by rcq92130 on Jan 6, 2015 18:01:02 GMT -5
I am kind of stunned this would happen without catastrophic results. The collets which keep the springs compressed and in place are held on by an indent in the valve stem that is --- what? --- only about 1/4 inch from the end? So if you break of 1/4 inch you are basically right NEXT TO the collet indent, and i would have thought the force of the springs against the collet would cause it to break free almost at once. And then, of course, with the valve dangling down into the combustion chamber the very first turn of the crank means the piston is gone (maybe more). How is it the collet didn't pop free  |
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Post by hillbillybob on Jan 6, 2015 19:47:15 GMT -5
It's kinda sad that this scooter's life was so short. After spending all that money, on so many performance parts, to only last a year and 4 months, is down right pitiful.
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Post by JerryScript on Jan 6, 2015 20:10:31 GMT -5
I am kind of stunned this would happen without catastrophic results. The collets which keep the springs compressed and in place are held on by an indent in the valve stem that is --- what? --- only about 1/4 inch from the end? So if you break of 1/4 inch you are basically right NEXT TO the collet indent, and i would have thought the force of the springs against the collet would cause it to break free almost at once. And then, of course, with the valve dangling down into the combustion chamber the very first turn of the crank means the piston is gone (maybe more). How is it the collet didn't pop free It's been a mystery to me the entire time. 1/4" may be overstating it, but there was nothing above the collet, and I'm thinking perhaps when it snapped off it actually shattered a bit at the end, wedging itself into the collet. I've found the bit's of the keys in my last few oil changes. When it first happened, I couldn't believe I was able to start it for a week before adjusting the rocker arm tappet all the way down, it was slapping back and forth like one of those one-handed clappers, and required me juicing the throttle several times to get it to crank (accelerator pump)! Over the past 6 months, I re-adjusted the rocker arm tappet a few times to keep it snug, and it actually held like that, GY6 Rules! (That being said, I will never put off a repair like this again, don't know what got into me, it's like I was pushing it to see when it would fail) It's kinda sad that this scooter's life was so short. After spending all that money, on so many performance parts, to only last a year and 4 months, is down right pitiful. She's not dead! I went over to Scrappy's and got the correct rocker arms (you don't see the difference without them side by side, 3mm), put her together this afternoon. Started up as soon as she sucked gas into the carb (fourth try). Took her around the block to warm her up good, did a quick a/f adjustment for the new head, then out for a 3 mile test ride at varying speeds, no problems thank goodness! It's not a great head, just Scrappy's plain 47mm head (not the greatest casting), but it brought my girl back to life!  One bit of damage I forgot to mention, it blew my uni clean off when it first failed and that final combustion came back through the carb, lucky it didn't damage the carb itself! |
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Post by JerryScript on Jan 6, 2015 20:13:57 GMT -5
If anyone needs a set of rocker arms for a tall valve head (not big valve necessarily), I'll send my old one to you for shipping cost. Same goes for the EGR tube (new head is non-egr), and a stock tall valve head that needs the intake valve replaced, cleaning, lapping, and hand porting if your into that. Used, but otherwise nothing wrong with them, so no reason to throw them away or collect dust. I know some members have had trouble finding these particular parts, so let my trouble help someone out and it's all good!  |
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Post by rcq92130 on Jan 6, 2015 20:17:43 GMT -5
So here is what I can't understand. This is a photo of a GY6 valve. Notice it's only about 1/8th of an inch from the top of the collet indent to the top of the valve stem. So, if even 1/8th inch broke off the collets would flay away, the springs would go sprong, the valve would just drop down into the combustion chamber, and excitement would reign.  Was it maybe the ADJUSTER that broke (the part that screws into the rocker arm and contacts the end of the valve stem)? |
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Post by JerryScript on Jan 6, 2015 20:41:10 GMT -5
So here is what I can't understand. This is a photo of a GY6 valve. Notice it's only about 1/8th of an inch from the top of the collet indent to the top of the valve stem. So, if even 1/8th inch broke off the collets would flay away, the springs would go sprong, the valve would just drop down into the combustion chamber, and excitement would reign. Was it maybe the ADJUSTER that broke (the part that screws into the rocker arm and contacts the end of the valve stem)? It looks like it sheared off from the indent up, there is one side where the indent is still visible, the other side is smoothly sheared off. I don't understand how it stayed wedged in the collet, other than part of a key possibly being wedged in with it?!? Here's some pics:   |
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Post by rcq92130 on Jan 6, 2015 20:55:03 GMT -5
Wow.
My suggestion: get your butt out and buy as many lottery tickets as you can, because you are ON A LUCKY STREAK !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
ps: wonder where the broken off piece ended up. Or maybe for some reason it just got milled down by the adjuster .... ? If your valves are not stainless, maybe if you stick a magnet down into the sump you will find a little prize waiting for you.
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Post by JerryScript on Jan 6, 2015 21:08:05 GMT -5
Yeah, now might be a good time to invest in one of those magnetic oil drain plugs.  |
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Post by jerseyboy on Jan 6, 2015 21:20:43 GMT -5
Hey it didn't leave you stranded either,,thats the best part..lol..thats a china girl for ya!
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