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Post by Deleted on Dec 25, 2011 20:23:07 GMT -5
It is my understanding that the qmb motors were originally designed for 47mm bore 72cc. 39mm bores were only installed on them for the American market. The bikes i sell locally are 47mm 72cc right out of the crate. No problem with putting a 47mm bore on a 50cc qmb motor because that's where they were originally designed for. Yes this is 'hearsay' but the fact that my new bikes right out of the crate have 47mm bore back this hearsay up. When I first installed my 50mm bore my first impression was that it would not last due to the vibration. compared to a 50 or 72 even it really thumps. that was 3000 miles ago and its still running strong so i would agree that the statement above is not accurate. The hoca 44mm stroker crank that Parts For Scooters sells was designed specifically for bbk's according to hoca. It has +2.6mm throw, a shorter rod for piston to valve clearance issues and apparently is balanced. According to our new member larry001964 who is using a 52.4mm bore and this 44mm stroker crank making his engine a 94.89cc it is much smoother than a stock crank with 50mm bore. I am planning the same build as well using a 13" wheel and rear disc brake and dual rear suspension in 2012. I was reading your build 1fastqmb, and in all honestly a little jealous, heheh but seriously I like your dual suspension much better than my "Sports Suspension".. My scooter was upgraded up to a 72 cc back in Nov, 2010 I got 4000 miles on it before the rod began banging... I originally wanted to rebuild it using the Narkru heavy duty crank but it was not available at the time, So I elected to do the Hoca 44 and upgrade using the 85cc kit... There was a lot of speculation about this crank and I honestly was hoping to use my misfortune to answer some of these questions.. I'm an Industrial mechanic by trade so I felt i could do it.. When my 72 failed I was really pushing it very very very hard, doing driving it was never designed to handle, but i needed to get a job, and i was in all honestly desperate, I was unemployed almost 2 years, my back was against a wall and I had to do something to get out of that mess.. I em not kidding when i say i packed up all that would fit on my scooter, drove 75 miles to move to a place where i was within 34 miles of the job. All of this was Hwy driving, and wot driving ( Traffic forced you to WOT ) ... It was an act of desperation really it was.. I got the job and started driving back and forth every day, And my scooter died in the process.. So I really don't blame the failure on the scooter so much as what i did to it to get a job... I knew at the time I was pushing it, and prayed it would make it another day, when my scooter did die, ( Died 30 miles from home ) I could not even get mad, I knew it had given me it's all... The performance I'm getting now is almost on par with a 150, I think a 150 would take off quicker than me, but from a speed stand point I'm on par with them.. Still tweeking it... what kind of wot speeds are you seeing now? i hope for a true sustained 90% throttle 55mph. |
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Post by jmkjr72 on Dec 25, 2011 20:28:22 GMT -5
but in reality with a cvt set up it should be built to ride at wot or the very top of the power band all the time
cvts work there best when at the upper rpm range of there power band
and every 2 stroke i have built has been tuned to run in the upper part of the power band
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Post by larry001964 on Dec 25, 2011 20:45:55 GMT -5
I was reading your build 1fastqmb, and in all honestly a little jealous, heheh but seriously I like your dual suspension much better than my "Sports Suspension".. My scooter was upgraded up to a 72 cc back in Nov, 2010 I got 4000 miles on it before the rod began banging... I originally wanted to rebuild it using the Narkru heavy duty crank but it was not available at the time, So I elected to do the Hoca 44 and upgrade using the 85cc kit... There was a lot of speculation about this crank and I honestly was hoping to use my misfortune to answer some of these questions.. I'm an Industrial mechanic by trade so I felt i could do it.. When my 72 failed I was really pushing it very very very hard, doing driving it was never designed to handle, but i needed to get a job, and i was in all honestly desperate, I was unemployed almost 2 years, my back was against a wall and I had to do something to get out of that mess.. I em not kidding when i say i packed up all that would fit on my scooter, drove 75 miles to move to a place where i was within 34 miles of the job. All of this was Hwy driving, and wot driving ( Traffic forced you to WOT ) ... It was an act of desperation really it was.. I got the job and started driving back and forth every day, And my scooter died in the process.. So I really don't blame the failure on the scooter so much as what i did to it to get a job... I knew at the time I was pushing it, and prayed it would make it another day, when my scooter did die, ( Died 30 miles from home ) I could not even get mad, I knew it had given me it's all... The performance I'm getting now is almost on par with a 150, I think a 150 would take off quicker than me, but from a speed stand point I'm on par with them.. Still tweeking it... what kind of wot speeds are you seeing now? i hope for a true sustained 90% throttle 55mph. Well I don't have a gps, what I did was to mark out 4 miles of road confirmed it was 4 miles with google maps, and timed it. I ran it several times, I should note that my tack was at 8000, I still had throttle but didn't push it any harder. It's still a brand new engine, 1200 dollars worth of overhaul, so I'm still a little apprehensive on pushing it or holding sustained WOT very long. until I'm thru the break in period.. Here are my results. I decided to do it this way as it would give me an overall average speed, factoring into the equation wind and hills... 4 miles. took me 4 minuets 5 seconds to drive it. 58.7755 mph 94.5900 kmh I'm still tweaking the cvt to make use of the additional torque, need to buy 7 gram Dr.Pully 6 grams are too light. |
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Post by Deleted on Dec 25, 2011 21:02:44 GMT -5
stock size valves in the head you used?
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Post by larry001964 on Dec 25, 2011 21:10:43 GMT -5
stock size valves in the head you used? I think the NCY Head, came with a 21mm intake valve and an 19mm exhaust, I think, what ever is standard on the NCY 50mm head. I didn't change anything on that just slapped it on as it was... |
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Post by Deleted on Dec 25, 2011 21:36:08 GMT -5
you might need even taller gears. im planning a 13" wheel and gears too. you ave a 10" right?
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Post by larry001964 on Dec 25, 2011 21:45:00 GMT -5
you might need even taller gears. im planning a 13" wheel and gears too. you ave a 10" right? Yea my tires are 10's and my engine is a short case. What I really want to do is to get my rpm's down to 7000 for cruising, I can feel the variator opening up, but my rpm's just keep climbing as it does. so yea maybe taller gears yet... The starting problem is of much more concern to me as i work second shift, coming out at night I need it to start a lot more easily than it currently does... I em planning on moving there in a month or so that will make it a lot easier on my scooter too... My apologies if we have hijacked this thread, I em really feeling guilty about that, can we post more in the stroker thread ? |
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Post by Deleted on Dec 25, 2011 22:42:52 GMT -5
yeah i feel the same way sorry for hijacking your thread doc.
yeah the stroker thread will work.
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Post by usmcdoc on Dec 27, 2011 6:08:16 GMT -5
1FASTQMB....ya didn't hi jack my thread....this is all good info...as my original post was about the rumors of detonating of these whimpy QMB139...which is 'hear say'.....cause as you can read above MANY posted their great success with BBK's and other Hi Po parts. Too many here 'jump on the bandwagon' and go along with rumors and fairy tales...without even trying a BBK.....or any other performance enhancing parts. We chastise our children for believing in rumors....and opinions of others....yet do that very thing on here. Sure I know a guy that ruined an engine with a 100cc BBK......cause after running it out of oil in the stock 50cc configuration with 4,200 miles on it....the top end seized..so he replaced it with a BBK which only gave him about 300 miles before the engine was junk.... But hell....when you run a stock engine dry of oil till it locks up....you can rest assured the piston and rings were not the only engine component that was compromised and prematurely worn.Even though scoot crank bearings are ball bearings vice babbitt bearings such as in a car engine....running the with zero oil will damage them.Even kids with skateboards have ball bearing wheels....and they keep them oiled to avoid an early demise.As you know the 50cc scoots are built as 72cc...for use in other countries...but bored only to 39mm here to comply with the 50cc rule.soooo...if they run perfectly at 72cc...how is the 100cc(83 actual) going to turn your engine into a grenade.....it's only 11cc's more. Keep us posted on your build......as we need 'real life' feedback here....not just opinions or 3rd hand horror stories.(kinda like that experiment we did in school....you whisper a sentence to somebody...and by the time it gets to the last kid in line....the sentence has been embellished and changed dramatically)......  |
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Post by ososlow on Dec 27, 2011 12:56:56 GMT -5
i have scrappies 100cc bbk on the stock bottom end, with 5.5g sliders and a 1k c spring, i regularly see 9000+ rpm without a problem.... so far. i have more miles on this set up then i did with the stock set up when it blew. but i am only 5'8" and 140lbs
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fng
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Post by fng on Dec 27, 2011 14:49:29 GMT -5
Ah, good info. So, 139QMB stock should be able to have a 47mm piston anyway...I'm not looking to be a speed demon...I just want to be able to get out of the way a little quicker...here in SE north carolina, mostly the drunks ride these for loosing their license from too many DUI's...the public is becoming aware of the scooter epidemic, but i would feel better if I had just a little more power under my ass. (Ps I'm not riding a drunk cycle...I find this fun!)
So what I'm gathering is a 47mm is ideal and you can get away with a 50mm...but with my luck, I'd have a high speed, unscheduled, engine dissasembly.
...or I could just grow some and get the 50mm....decisions decisions...
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Post by Deleted on Dec 27, 2011 15:18:39 GMT -5
.the public is becoming aware of the scooter epidemic ? |
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Post by Deleted on Dec 27, 2011 15:29:03 GMT -5
As you know the 50cc scoots are built as 72cc...for use in other countries...but bored only to 39mm here to comply with the 50cc rule.soooo...if they run perfectly at 72cc...how is the 100cc(83 actual) going to turn your engine into a grenade.....it's only 11cc's more. exactly. in other countries most 4ts are '80cc' (72cc 47mm). the ones i sell the company just puts 49.5cc on the mco to get them into USA but they dont change the motor they just jet it down real small to kill the power and put one of those restrictors in the airbox. a 50mm vibrates more but im at 3000+ miles and counting and it runs oh so good. a 47mm top end should cause no issues whatsoever. many folks who report the problems put a bore kit on a well used bottom end then complain because the bearings went out. if a motor has a good bit of miles i would do a crank bearing job and if i was going that far i would put in the stroker....if funds allowed it. going from 39mm to 47mm is a big increase and the power gain is really impressive. I didnt see a really big gain since my motor was 47mm already. even a 44mm (61cc) the power is much improved. a true stock 4t 39mm is scary in traffic i could never deal with that. |
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Post by Deleted on Dec 27, 2011 15:58:53 GMT -5
if anyone wants one of my stock 72s i can have it delivered to your door $850 with 1 yr warranty on engine. they are well made, fully unsealed Japan carb and new for 2011 dual rear shocks. Better front brake than previous years too. i189.photobucket.com/albums/z31/jjones112570/000_0273.jpga uni filter with an #88 main and a timing advance cdi with some 5g rollers they really wake up  I was running along with 45mph traffic easy after the above additions before i went 50mm. |
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fng
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Post by fng on Dec 27, 2011 23:17:32 GMT -5
.the public is becoming aware of the scooter epidemic ? its kinda starting to look like china around here with all the scooters rolling around... |
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