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Post by stepthrutuner on Feb 14, 2011 22:30:22 GMT -5
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Post by stepthrutuner on Feb 15, 2011 14:16:43 GMT -5
$275 for an 80cc new 139QMB delivered to your door ain't bad.
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Post by 90GTVert on Feb 15, 2011 14:35:12 GMT -5
Not at all. Never heard of issues with those either. I wanted one for a while to see what was diff about it. Never saw one go that cheap when I was looking some time ago.  |
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Post by rocketdog on Feb 15, 2011 20:26:28 GMT -5
Some how I've missed out on this thread. If it's an 80cc kit your looking for, I would suggest an Airsal. You can run it with a stock head no valve worries. I checked it. I didn't check the big valve NCY head, but by the looks of it, it should be ok. The problem with most cylinder kit is that they don't make a decent piston to go with it. Airsal does. At least for an 50mm kit. I have yet to find one for a 47mm. I think I'm going to have one custom made. Here's a couple of pix. Here's Enviros 47mm cylinder next to his Airsal 50mm kit  Here's the wieght of the 47mm cylinder as opposed to the Airsal 50mm   Airsal 50mm piston.    As opposed to other QMB139 Pistons, this ones dome comes just a bit into the head. Above the cylinder deck. But leaves a lot of relief for the valves. I'm going to put it in my Kymco Filly. RD |
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Post by stepthrutuner on Feb 15, 2011 20:59:11 GMT -5
Anxious to see how it runs out. Looks good.
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Post by rocketdog on Feb 15, 2011 21:13:57 GMT -5
It'll be a few months before I plug it in Step. I have to get two other scooters ready for the Twist n Gone. I'll get back to you. My plan is to run that kit with a shot of squeeze and see if I can't blow it up. I'll do a write up.
RD
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Post by tomcas on Feb 15, 2011 21:59:09 GMT -5
No it did not, but I saw nothing that would lead me to believe that a lack of oiling caused my engine failure. Did you change the oil after an hour or so? Maybe you had some fine particles loosen up in the break in. |
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Post by stepthrutuner on Feb 15, 2011 23:14:07 GMT -5
It'll be a few months before I plug it in Step. I have to get two other scooters ready for the Twist n Gone. I'll get back to you. My plan is to run that kit with a shot of squeeze and see if I can't blow it up. I'll do a write up. RD Sounds like a bang up plan. ;D |
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Post by 90GTVert on Feb 15, 2011 23:35:16 GMT -5
No it did not, but I saw nothing that would lead me to believe that a lack of oiling caused my engine failure. Did you change the oil after an hour or so? Maybe you had some fine particles loosen up in the break in. lol I changed the oil after the first start and run. I do that with every 4T when I do engine work. Then I changed the oil after 50 miles maybe. I'd guesstimate another 5 oil changes in 2,000 miles. Pretty sure it's safe to say negligence regarding oil changes was not the cause of failure. I also clean out the screen on every oil change. |
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Post by lshigham on Feb 16, 2011 2:56:38 GMT -5
Those Arisal kits are the dogs bollocks, they have a good reputation for their 2T stuff in Europe. Polini make a 47mm for the 139QMB too.
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Post by tomcas on Feb 16, 2011 7:16:47 GMT -5
Did you change the oil after an hour or so? Maybe you had some fine particles loosen up in the break in. lol I changed the oil after the first start and run. I do that with every 4T when I do engine work. Then I changed the oil after 50 miles maybe. I'd guesstimate another 5 oil changes in 2,000 miles. Pretty sure it's safe to say negligence regarding oil changes was not the cause of failure. I also clean out the screen on every oil change. It certainly sounds like you got it covered. I'm at a loss why it failed. Maybe when you take it apart and look at the bearing you will have a better idea as to the cause. |
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Post by 90GTVert on Feb 16, 2011 8:41:15 GMT -5
It's been apart for a long time now. The crank is in the trash. I never split the crank to really see what the rod bearing looked like. You can't really see much otherwise. Best I can tell you is there was glitter in the oil after the failure and it was seized up in one spot as the video below shows. The crank bearings were fine. The top end was fine. Only issue appeared to be the big end bearing.
Just to provide more info, it was tuned to run out at around 9,000RPM. I'm pretty sure it went above that the night it failed, as I hit my max speed of 51.46MPH that night. It failed an hour or so later. I really don't think a big heavy piston spinning at high revs is good for these little things. RD had some weights somewhere and I gave him a weight for a piston, now I can't remember what the numbers were or find them. I wanna say the 50mm was around 2x the weight of a stock piston. Then you crank it up to 9,000-10,000RPM compared to the revs they are setup for stock and a little more compression and all that is just a lot of stress on cheap Chinese stuff. That's my opinion anyway. I'd bet you could tune it more conservatively regarding revs and compression and drive it easier than I did (remember I hovered around 300lbs and rode WOT a good bit of the time) and see a lot more mileage.
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Post by rocketdog on Feb 17, 2011 7:14:59 GMT -5
<----Searches his pockets for the scraps of paper he writes crap down on> Well I can't seem to find my weight info either. I can measure them again easy enough. That sounds about right to me as well GT. And your theory seems plausible as well. By keeping the variator weights up a bit and the revs down a bit things might be a bit better. You could up gear the the transmission as well. If seen a few different ways to go about that.
RD
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Post by 90GTVert on Feb 17, 2011 8:15:44 GMT -5
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Post by burnttoast on Mar 26, 2011 14:43:57 GMT -5
wow, well this thread is making me reconsider doing a 100cc QMB build hmm. Longevity and reliability are both important goals.
what are the rev limits of the stock 50cc? and what is the stock qmb crank size?
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