Rebuild? 49cc to 100cc. By therellik (Read 918 times)

[therellik]

I have been looking for a rebuild kit for my 49cc Jonway. What I have found are BBK upgrade kits that are cheaper than that 49cc rebuild kits. So is it worth rebuilding to a 100cc BBK? My 49cc is burning oil like crazy and I don't want it to seize up on me being I ride it out of town quite a bit.



I have a few BBKs on watch on ebay ranging from 40 to 150 dollars.

I also have questions about changing the oil pump on this as well being I cant find a video of changing the oil pump at all. 

[cyborg]

Check the library here,, there's gotta be a video or section on oil pump change,, as far as the bbk goes call scrappy dog or parts for scooters,, they'll set you up,, tell them your a member of scooter doc

[2stroked]

If there is not a video for what u need here look for videos by 90GTVert.
Be careful going with the "100" cc kits. That's a lot of pressure on a stock crank. It can and has been done, it just reduces the reliability a little. The "80" cc kits will boost performance and not beat the crank as much.
Remember, you et what you pay for with the Chinese made parts. Autotech55 on eBay sells or sold kits from Taiwan that are a little higher quality.

[jct842]

Have bought from auto tech too, good stuff.

[czmdiver]

Apr 28, 2017 20:37:27 GMT -6 2stroked said:

If there is not a video for what u need here look for videos by 90GTVert.
Be careful going with the "100" cc kits. That's a lot of pressure on a stock crank. It can and has been done, it just reduces the reliability a little. The "80" cc kits will boost performance and not beat the crank as much.
Remember, you et what you pay for with the Chinese made parts. Autotech55 on eBay sells or sold kits from Taiwan that are a little higher quality.

Pressure as in Cylinder Pressure?
If my PSI is the same how is that so?
Or do you mean Pressure as in the Extra Weight of the larger piston,pin and rings of the 100cc bore?

[2stroked]

Apr 30, 2017 5:07:00 GMT -6 czmdiver said:

Apr 28, 2017 20:37:27 GMT -6 2stroked said:

If there is not a video for what u need here look for videos by 90GTVert.
Be careful going with the "100" cc kits. That's a lot of pressure on a stock crank. It can and has been done, it just reduces the reliability a little. The "80" cc kits will boost performance and not beat the crank as much.
Remember, you et what you pay for with the Chinese made parts. Autotech55 on eBay sells or sold kits from Taiwan that are a little higher quality.

Pressure as in Cylinder Pressure?
If my PSI is the same how is that so?
Or do you mean Pressure as in the Extra Weight of the larger piston,pin and rings of the 100cc bore?

I mean pressure as in that much larger piston beating on the big end of the crank.
The pressures exerted by the repeated start stop of that bigger piston will be higher than the pressures caused by the stock or 80cc piston.

[czmdiver]

www.ebay.com/itm/Scooter-Big-Bore-Kit-100cc-50mm-Bore-QMB139-GY6-Scooter-Performance-Parts-Kit5ch-/322472446010?hash=item4b14db083a:g:5QgAAOSwdsFUPq5H&vxp=mtr
Being a professional in the industry the Fake parts by these thieves really irks me. can this Retard do Math?
And it even gets better.
www.ebay.com/itm/Scooter-Big-Bore-Kit-105cc-52mm-Bore-QMB139-Large-Valve-Performance-Kit5Black-/322397017180?hash=item4b105c145c:g:YpAAAOSw4DJYgjO~&vxp=mtr
I think we have been down this road before, there is No Such Thing as a 100cc Displacement BBK for a QMB-139
I know I have some Dane Bammage but the last time I did the math a 50mm bore came out to a tad over 81cc.
On the 52mm BBK (that you have to bore the cases to fit) it works out to 87.9cc
Only with the 52mm bore and a 44mm Stroker Crank can you get to roughly 87.9cc.
Thieves and Crooks they are.

[czmdiver]

May 1, 2017 9:45:24 GMT -6 2stroked said:

Apr 30, 2017 5:07:00 GMT -6 czmdiver said:

Pressure as in Cylinder Pressure?
If my PSI is the same how is that so?
Or do you mean Pressure as in the Extra Weight of the larger piston,pin and rings of the 100cc bore?

I mean pressure as in that much larger piston beating on the big end of the crank.
The pressures exerted by the repeated start stop of that bigger piston will be higher than the pressures caused by the stock or 80cc piston.

 
We would really need to weigh the overbore pistons to make this claim.
I see many QMB-139 BBK's with a Reverse Dish as to keep the OE Compression Ratio the same as Stock in +11mm overbore and +12mm overbore, this will also keep the Piston weight down.
Working with some +2mm 73mm product I have is actually 16 grams Lighter than the OE piston I was working with.
There is no such thing as a 100cc kit for the QMB-139 Fiddy. only a 50mm at a tad over 81cc and a Bore the cases 52mm Bore coming out at 87.9cc
I also have some 61mm bore for my 150, I have a 61mm Forging with a +110 Dome Rise and a Slipper Type Skirt that is 13.84 Grams Lighter than the 61mm Cast Flat Top Piston Boat Anchor I also have.
13.84 Grams is ALLOT on the same 61mm Bore.
and my pictures are not uploading, grr, I can provide a link to my thread if ya want.

[2stroked]

All these 139qmb stock pistons are boat anchors. From what I have seen. I honestly can not say 100% that a "100" cc kit is bad for the stock bottom end, I am just going by what I have read, and heard on most of these forums. 90GTVert says the so called hunded cc kits are hard on cranks... I trust his word on these scoot engines as if they were gospel

[czmdiver]

May 1, 2017 20:03:47 GMT -6 2stroked said:

All these 139qmb stock pistons are boat anchors. From what I have seen. I honestly can not say 100% that a "100" cc kit is bad for the stock bottom end, I am just going by what I have read, and heard on most of these forums. 90GTVert says the so called hunded cc kits are hard on cranks... I trust his word on these scoot engines as if they were gospel

I'm the type that backs up my posts with actually hands on experience and documentation, in my almost four years of hanging around three of these boards I've never seen anyone post up the gram weight differences pictures of any of the Pistons other than Me.
There is No Such Thing as a 100cc kit for the 139qmb, only in Name are these Scamming Lying Thieves calling a 50mm or 52mm bbk a 100cc and a 105cc. do the math.
Genuine 100% Guaranteed Fake Parts.

[2stroked]

First, look on Brent's board, I am relatively positive that he, or somonr there has posted weight of each.
For the arse hats that lie to sell their shauddy product, it's not ethical, but from their point of view, it's probably easier to sell a "" 100 "" cc kit than to tell the truth and sell the same kit as the honest 87.5.

The only.four poke I will own and ride are m 250's. If I wantw another fiddy, it's going to be another two stroke. Those, those I know dam God and wel what will and will not work and or cause damage.

As for scientific facts and truth, the rare too many horror stories( actual first hand accounts ) about the decreased life of a stock 139qmb crank when a 50+mm cylinder is shoved down their throats. As for the difference ein power from the 80cc kits as compared to the (no where near)100cc kits, there can't be enough gained performance to risk it.

I will go to Brent's board, locate what I am talking about,df the admin here is okay with it I will post a link. Again, only if the Admin is alright with it.

[2stroked]

Apr 28, 2017 20:37:27 GMT -6 2stroked said:

If there is not a video for what u need here look for videos by 90GTVert.
Be careful going with the "100" cc kits. That's a lot of pressure on a stock crank. It can and has been done, it just reduces the reliability a little. The "80" cc kits will boost performance and not beat the crank as much.
Remember, you et what you pay for with the Chinese made parts. Autotech55 on eBay sells or sold kits from Taiwan that are a little higher quality.

The entre reason I put the number one hour ndred in quotes was to emphasise the act that they are only CALED by that name. No, I didn't say that, and your credit, you did.
Regardless, my opinion stands, as just that, MY opinion. I would never in good conscience recommend the 50+mm kits for a stock 13qmb bottom end. I can not see there beig enough of a gain in performance to justify the added stress. Will go look for m sources later, but am on way to a rather pertinent Dr. Appointment.

[2stroked]

49ccscoot.proboards.com/thread/18322/80cc-100cc

Some good reading on this very subject:
49ccscoot.proboards.com/thread/16593/50mm-bbk-thread-installed

[czmdiver]

May 2, 2017 9:08:47 GMT -6 2stroked said:

49ccscoot.proboards.com/thread/18322/80cc-100cc

Some good reading on this very subject:
49ccscoot.proboards.com/thread/16593/50mm-bbk-thread-installed

Ok that was a painfully long read, my eyes are bleeding and I'm going from uncontrolled laughter to fits of crying with the beginner level spores.

Neil and Bob aka 90GTVert and humanshield, what a joke these two are, half truths, little data, constant incorrect verbiage and internet parroting. 
OMG were do I even begin, a whole bunch of speculation, Neil states he runs his wot, ok at over 8,000 rpm and grenade it at over 9,000rpm, Ok fine if he's going to do so build the darn engine to do so.
Bob state a BB piston that could weigh the same as std. bore is a Fantasy, Really? Bob obviously Knows nothing of Piston design or technology.
It took six pages for Bob to have the epiphany that you May need to match the Combustion Diameter to the Bore Diameter. Huh? what is this Room #101 group A? Uh ya on the 50mm and 52mm with a Stock Head most Likely the Airsal Domed pistons are "Ghosting" the Head, uh ya you'll junk a rod,wrist pin, lower bearing all day doing that.
Not one in eight pages mentioned measuring the Squish clearance.
I see many are installing the larger BBk's on Clapped out high milage Motors the blame it on piston weight/pressure.

Bob also claims to have built car hot rods, Nitrous this Blown that, but he's going to have his cylinder head Fly Cut, Huh? ya Fly cut Valve reliefs on Pistons and Mill Cylinder heads.
h and Im crying over Bob's break-in procedure, A No load run, creates to much heat etc, what a joke this guy is.
And both Neil and Bob claim higher hp brings higher mph. really? ya only get to the same mph with more hp faster, one Must either or both Increase the Rpm or Gearing to achieve a Higher MPH. unreal these two are.
Omg then Lapping Valves, Im still crying. I spend countless hours facing a Valve to a precise angle then Cut the Seat to a perfect 1/2 Degree Difference Angle and upon startup they hammer home to a near perfect vacuum and these two think and put in writing that there going to make  my work better by Lapping the valves?  Ever wonder why No Engine mfg in the World Lapps valves? the only reason lapping and grinding compound is still sold is because these two idiots purchase it.
Not once did Neil or Bob mention doing anything to the Crank, Not even putting on a truing stand to check it. Bob states he checked the rod for freeplay. oh boy thats allot.
There going up or down in piston weight and not even mentioning Balancing the Rotation Assembly. unreal
I would bet the Cranks were barely in spec to begin with, ya wanna run a 50mm or 52mm WOT at 8 0r 9 grand.
I could do it all day, Its $65. bucks to have your crank Trued and the Pin Welded. wanna really go fast? a Pocket lighten is $265 or a Pork chop lighten is $285. easy stuff.

[2stroked]

Ohhhhhkaaaayyy.....
Look, I simply stated y firm beliefs tonthe OP, then performes a real quick search. I didn't read the threads any further than the search results.
Any half assed mechanic knows lapping valves is an antiquated practice and it's easier I machine eboth valve and head then let the motion and combustion process do the rest. However , most folks also do not have access to a lathe, CNC etc. and just attempt to do what they can wih what they have.
Nothing g personal, but I have spoken to 90 and read more of his thread and watched more videos done by him than any other scooter guy. I don own a puny 4t fiddy. However, the dude is spot on and 110% about two strokes. That said, I believe most every bit of his tech writings on these bikes. Again, I don't and won't own a 139qmb based scoot. I did however ow. A 1e40 based screamer.
If I want to go fast, I will either jump on a two stroke, OR, spend the same am not that mor folks spend upgrading a 139 to just buy a good used 150cc.
90GTvert and his forum have been and continue to be a wealth of valuable information. It's like EVERY forum, you read through, then separate the bullsh!t from ignorant a$$ pokes from the correct information. No forum is gonna hold all truths and no bull$h!t.