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Post by usmcdoc on Dec 25, 2011 11:42:08 GMT -5
BBK fallacy? Many here say if you put an 80 or 100 BBK on your 50....it will destroy the crank bearings within a few hundred miles.(always the ones who never tried it....they just 'heard' about it) Every scoot I own...and the ones I used to sell...when I was running an at home mini dealership....had 80-100(72-83cc in reality) BBK's in them...out of 14 sold no probs so far in those 2 years. One day while at the huge cycle mall in town.....I got into a convo with a certified Honda mechanic about bearings. He told me....and showed me in the parts catalog...that the 50 and 150 engines use the same size bearing 40x17x12 as did a few web sites that carry the crank bearings....so I called them to verify and the stock numbers were the same. One site did show that a few 150 use a 2mm larger bearing....apparently there is a 150 type A engine...and a type B engine...and one uses the larger bearing....not such which one...nor have I ever heard of a type A or B GY6. Therefore even if the A or B was 2mm wider...how come they hold out and the 2mm makes them 'bullet proof' to the added torque and horsepower of the 150?......and the ones on a 50 are said not to....when some 150's use them as well...with no problems. So either the mechanic and web sites are wrong....or we are all just going by the 'hear say' from skeptics that believe all rumors and never tried a BBK?..... My thought is that the 50 with a BBK is typically pushed above 8,000 rpm to get its speed and power...causing the stress.....where as my buddies 150 cruises nicely at 50-55...and around 6,000....which is less stressful on the engine. Anyway..my 1 cents(used to be 2 cents until the Gov increased our taxes)....  |
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Post by 90GTVert on Dec 25, 2011 11:59:39 GMT -5
My SunL 50mm died in 2000 miles, almost exactly. I installed a new crank just to test this along with the kit. I also pushed it over 9,000RPM. Hard to say what the real culprit was. A combo of a big heavy piston and the revs and heat most likely. One thing I think to keep in mind if you try to compare a 150 and a 50-80 is that the big 50mm and above pistons are not good for the engine's balance. That shouldn't be an issue on a 150. Now maybe a 150 with some huge kit? I think the percentage of weight increase would be pretty large with the 39mm going up above 50mm though, perhaps more than any 150 bbk? There's a big thread on this topic here too... 49ccscoot.proboards.com/index.cgi?board=4perfrom&action=display&thread=55&page=1 |
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Post by usmcdoc on Dec 25, 2011 12:17:51 GMT -5
90....first off.....9,000 rpm?...wow now that is smoking fast....how did you get it that fast?.....no matter what I do...I get lucky to reach 7,800. As for the extra piston weight.....causing a higher and off balance crank...I can see how that would affect it.The crank counterweights were not engineered for that extra weight....which would cause vibration or an off balance rotation.....such as a car tire that has not been balanced. Thanks...this may be making sense to me now... :thumb:
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Post by 90GTVert on Dec 25, 2011 12:52:18 GMT -5
I had a cam, different heads, some with larger valves and porting, some stock ported, stock or 150 carb, light weights, pretty much everything. It didn't stay at 9,000+ all of the time, but that's what it took to get it to 50MPH.
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Post by usmcdoc on Dec 25, 2011 13:14:52 GMT -5
90.....most like the BBK cause they want more speed....which as you know is not easy with stock 50cc gearing. We use them on ours for faster acceleration....as we drive in lots of city traffic and a fast 'pull out' into traffic is a necessity for obvious safety reasons. My gf did GPS hers at 51 mph.....but on a 3.50x10 tire it is one scary ride. We think the BBK's are great...when used sensibly and not WOT all day long. Hell I get tired of explaining to those whose scoots I work on....that even a guy with a Chevelle SS with a 396 cowl induction engine....does not drive WOT all day long everywhere he goes. Know its limitations and they do fine....but I also know know a guy that went Elk hunting in Colorado with a .22 rimfire which is beyond its limitations....and it really pissed off the Elk...cause apparently...they don't appreciate a welt on their chest cavity....but that is another Darwin Theory candidate story.... :rofl:
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Post by Deleted on Dec 25, 2011 13:52:49 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 thats 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. |
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Post by usmcdoc on Dec 25, 2011 14:03:30 GMT -5
1Fastqmb.....now THAT sounds like an awesome build you are gonna do....PLEASE keep us posted. So your bikes come as 72's and no issues so far? Now that is what I like to read....facts....not "Well....I heard" stories... :thumb:
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Post by Deleted on Dec 25, 2011 14:20:57 GMT -5
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Post by jmkjr72 on Dec 25, 2011 14:25:31 GMT -5
im not so sure about the issues with the 4 strokes
but i do know with the 2 strokes
its not about bearing size
but the itlian cased hm engines can take more revs befor the dreaded crank issue and its same with the older vespa engines the itlian engiens hold up better then the indian
i think it boils down for those engines to the quailty of the bearings used in the cranks
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Post by 90GTVert on Dec 25, 2011 14:58:44 GMT -5
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Post by lshigham on Dec 25, 2011 18:01:16 GMT -5
My 139QMB made it to 3300 miles with a 52mm kit on before the con rod let go and the engine destroyed itself. As far as I could see, it hadn't seized.
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Post by larry001964 on Dec 25, 2011 19:37:53 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... |
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Post by usmcdoc on Dec 25, 2011 19:46:56 GMT -5
My son in law borrowed one of mine....being too cheap to buy gas...he used the kerosene from the can I heat my work shop with....it ran a few minutes..till the kero got in it...smelled like a Kenworth then died.....had to clean and flush the whole fuel system....  |
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Post by usmcdoc on Dec 25, 2011 19:54:45 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 thats 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.. 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.. 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... larry001964...thanks for the input...and as you said...you were WOT the whole way before it went.Now that is some honest input...but I am sure even the stock 50cc would have done the same running WOT that far....and 4,000 miles at WOT with a BBK is still not bad.....considering you beat on it.... However you had a long drive...had to get there. The way I see it....it held out...did its job.....and I have seen new 150's with blown engines in under 300 miles. |
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Post by larry001964 on Dec 25, 2011 20:15:48 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.. 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.. 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... larry001964...thanks for the input...and as you said...you were WOT the whole way before it went.Now that is some honest input...but I am sure even the stock 50cc would have done the same running WOT that far....and 4,000 miles at WOT with a BBK is still not bad.....considering you beat on it.... However you had a long drive...had to get there. The way I see it....it held out...did its job.....and I have seen new 150's with blown engines in under 300 miles. Thanks usmcdoc, My thinking behind using the Stroker was not speed, it was to build a stronger bike that could withstand the type of driving I'm doing.. Speed is merely the byproduct of the increase in torque, but it was not my main objective.. I was thinking the stroker would lessen some of the stresses on the rod because of it having better mechanical leverage. Also using a crankshaft that was designed from the beginning to accommodate the stresses of a BBK. It is faster but more importantly I'm not pushing it to get the needed performance in getting to work.. That's also why I have the Phoenix as my avatar, before I called my 72 ladybug, but ladybug died, now it's named Fawkes after the Phoenix in Harry Potter that rises from the ashes... Just seemed appropriate to me... |
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