The 50mm+ BBK Thread - Only if you've installed one please

[chico357]

I installed my 52mm ncy bbk in April this year and ride WOT most of the time. Before I did the upgrade, I noticed a ticking noise after leaving it running on idle for about 5hrs straight parked in my front yard. I'm surprised no one stole it. I could never isolate the noise and figured it may be the crankshaft bearings. I forgot about it when I did the upgrade but still noticed the noise. The crank lasted about a month after the upgrade. It had maybe about 12k miles total. I don't think the cause of it was the bbk upgrade though and related to leaving it running on idle for so long. I replaced it with a used crank from another motor I have on Memorial day weekend and it's still running fine. The used crank had maybe about 5k miles with another 3k added in since replacing it and isn't making any ticking noises nor giving any signs of failure.

[humanshield]

60% lasted over 3000.

Not bad


I wish I could change my vote because by end of September I should be over 5,000 miles

I still feel that for scooters used for daily commuting and not treated like a racing scooter, the 50mm BBK can be an excellent choice.


I think it just depends on hard hard you run it and how often you run it hard.
Most people who've had them fail do seem to confess they beat the crap out of it.

[90GTVert]

You should be able to change your vote when the time comes. BTW, the 70cc poll is 100% over 5,000 miles so far.

[humanshield]

Aug 22, 2016 14:55:29 GMT -5 90GTVert said:

You should be able to change your vote when the time comes. BTW, the 70cc poll is 100% over 5,000 miles so far.

In my mind, this was never about the 47mm kit.   We all knew it was a "safer" bet simply because the piston was lighter.

What I was attempting to do was get evidence on whether the larger 50mm kit was a viable option since all I ever saw was negative comments about it yet mine has been perfect (for me and my needs) for nearly 4,000 miles now.

If I built another motor today, with the use I've already had from my 50mm kit, a 47mm kit would not be a consideration for me.
I would go with at least another 50mm BBK.

The extra torque around town for my needs is a huge plus.   I'm not out racing.   Just commuting with an occasional full throttle run.  I am happy cruising at 35 to 37mph in most situations with the extra power to reach 46 or so if necessary.

If I get 5,000 miles or more from my 50mm BBK, I will probably try a 52mm Kit at least once.  I'm comfortable with an engine change every 3,000 - 5,000 miles.   it's worth it (to me).   Maybe not to others.

For my needs (and the needs of many commuters) a slower revving but very torquey motor might be the best ticket.

For higher revving, racing type hard use, the 47mm kit is probably a better choice.

[90GTVert]

OK. Before this thread was started, you seemed to be looking for actual proof that the 50mm stuff is known to fail early. Sure, they work.

I've rode some of my scoots 2,000 miles a month, WOT a lot of the time, so maybe I'm a little biased on what makes a durable engine. Then again, my TaoTao is 3 years old with 5,000 miles on it. If it's too slow, I don't really enjoy it. From what I've seen, 47mm is fast enough that I'll actually want to ride it for no reason but to ride it, and reliable enough that I won't kill it right away. As I've said before though, I can't put the 50mm in and tune it to rev low and even my 2Ts that run up to about 70MPH or the 150 get ran hard, so there's little chance of an easy life with me on one.

Everyone likes something a little different, and that's not a bad thing. From what I'm seeing so far, I won't stop recommending 47mm bores though. I still think it's the choice if you want to keep the engine going longer and ride/tune it however you want (and don't want to stick with 49cc). Maybe I'm wrong, but I think an awful lot of people beat on small scooters. At least that's the impression I get with how many people expect them to climb hills and take on headwinds at 40MPH+ and cruise on 50MPH roads and so on. That's more like what my 155cc GY6 did, WOT.

[Deleted]

Aug 21, 2016 9:58:17 GMT -5 ThomasTPFL said:

I havr one on my son's bike. Same starrider kit I think. It's probably around 500 or so miles now, no gauges on that bike.

It gets whooped. Downtown riding, nothing but on/off throttle.

Its still going strong but the engine is getting noisier and noisier.

My next 139qmb build, probably this bike when it breaks, will get a crank just because I have a friend who did the true 100cc+ build on his and the performance is rather amazing.

Is there such a thing as a true 100cc build for the gy6?  Everything I have read tells me that it is really 80cc but, I have not read everything there is out there, of course.

Bill

[90GTVert]

Aug 22, 2016 19:28:48 GMT -5 PirateLabs said:

Is there such a thing as a true 100cc build for the gy6?  Everything I have read tells me that it is really 80cc but, I have not read everything there is out there, of course.

Bill

52.4mm bore and 44mm stroker crank puts you at ~95cc. That bore with a stock stroke is ~90cc.

[farmer54]

I'm wondering if anyone has used the airsal piston thar STG offers in a build yet? It weighs slightly more(3.5grams) than stock so I'm interested in doing a build over winter. Yea just got a used ice bear trike to replace my reverse trike and need to upgrade the stock engine. Frank (farmer54)

[humanshield]

I'm about to build another motor and it will use the Airsal 50mm piston along with a 23mm big valve head.

Will post about it as I get to it.

[Deleted]

Aug 22, 2016 21:05:43 GMT -5 90GTVert said:

Aug 22, 2016 19:28:48 GMT -5 PirateLabs said:

Is there such a thing as a true 100cc build for the gy6?  Everything I have read tells me that it is really 80cc but, I have not read everything there is out there, of course.

Bill

52.4mm bore and 44mm stroker crank puts you at ~95cc. That bore with a stock stroke is ~90cc.

But he said his friend did the True 100cc+ BBK...so in reality, 95 would be the max and that is using a stroker crank.  OK, Thanks.

Bill

[Deleted]

OK I have been thinking about this deal with our piston weights. Could we not machine our BBK pistons to look something like this one?




I am not talking about the work done to the top nor the cut outs for the valve clearance, I am talking about making a short side skirt. I think we can modify these to be pretty light by doing so. Once again, I have been watching the Surfer series on top fuel drag racing in the 60's and they ran very tight pistons in their cylinders...about .005 clearance. All of the other guys were running like .030 clearance and were getting piston slap. I have no idea what the standard BBK piston clearance is but, if we shortened the skirt, I don't think we would weaken the part at all and, reduce drag and piston slap. (Like you see the wear on the lower sides of the skirt on the piston) This, of course, would be highly experimental but, what if a BBK piston could be made to weigh the same as a stock one? What would the longevity of that build be?

I had first mentioned possibly drilling holes around the skirt to make it lighter but now, looking at many high performance auto pistons, why can't we do this?

There indeed may be a very good reason why we can not, I just don't really know.

Bill

[joshua864]

Aug 25, 2016 9:15:22 GMT -5 humanshield said:

I'm about to build another motor and it will use the Airsal 50mm piston along with a 23mm big valve head.

Will post about it as I get to it.

Might as well use the 52mm

[90GTVert]

Aug 27, 2016 14:30:29 GMT -5 PirateLabs said:

OK I have been thinking about this deal with our piston weights. Could we not machine our BBK pistons to look something like this one?




I am not talking about the work done to the top nor the cut outs for the valve clearance, I am talking about making a short side skirt. I think we can modify these to be pretty light by doing so. Once again, I have been watching the Surfer series on top fuel drag racing in the 60's and they ran very tight pistons in their cylinders...about .005 clearance. All of the other guys were running like .030 clearance and were getting piston slap. I have no idea what the standard BBK piston clearance is but, if we shortened the skirt, I don't think we would weaken the part at all and, reduce drag and piston slap. (Like you see the wear on the lower sides of the skirt on the piston) This, of course, would be highly experimental but, what if a BBK piston could be made to weigh the same as a stock one? What would the longevity of that build be?

I had first mentioned possibly drilling holes around the skirt to make it lighter but now, looking at many high performance auto pistons, why can't we do this?

There indeed may be a very good reason why we can not, I just don't really know.

Bill

I'm sure you can lighten them to some degree. I think getting a BBK piston, especially the largest of them, to weigh what a stock piston does and not fall apart may be a bit of a fantasy. It's going to be a compromise of strength and stability vs weight. You probably won't know how much is too much till things start coming apart.

[Deleted]

Aug 27, 2016 16:32:34 GMT -5 90GTVert said:

Aug 27, 2016 14:30:29 GMT -5 PirateLabs said:

OK I have been thinking about this deal with our piston weights. Could we not machine our BBK pistons to look something like this one?




I am not talking about the work done to the top nor the cut outs for the valve clearance, I am talking about making a short side skirt. I think we can modify these to be pretty light by doing so. Once again, I have been watching the Surfer series on top fuel drag racing in the 60's and they ran very tight pistons in their cylinders...about .005 clearance. All of the other guys were running like .030 clearance and were getting piston slap. I have no idea what the standard BBK piston clearance is but, if we shortened the skirt, I don't think we would weaken the part at all and, reduce drag and piston slap. (Like you see the wear on the lower sides of the skirt on the piston) This, of course, would be highly experimental but, what if a BBK piston could be made to weigh the same as a stock one? What would the longevity of that build be?

I had first mentioned possibly drilling holes around the skirt to make it lighter but now, looking at many high performance auto pistons, why can't we do this?

There indeed may be a very good reason why we can not, I just don't really know.

Bill

I'm sure you can lighten them to some degree. I think getting a BBK piston, especially the largest of them, to weigh what a stock piston does and not fall apart may be a bit of a fantasy. It's going to be a compromise of strength and stability vs weight. You probably won't know how much is too much till things start coming apart.

Well, I was thinking about the 47mm to begin with.  I think this is totally possible to do BUT, your are right, you will not know if you removed too much metal until it is too late.  I think, however, with a little common sense, maybe, just maybe, we could get the 47mm piston close to the stock piston weight.  I would enjoy close as opposed to having a very weak piston.  Come on Brent, you know just how robust the Chinese make this type of metal right?  (Actually hard to type that with a straight face, ha ha)

I was just putting this out there for possible consideration.

Bill

[farmer54]

Hi I've been watching this thread with a lot of interest as it evolves into the weight of a piston and how to reduce it. Somewhere on youtube there is a video showing the weight of the three pistons for a GY6 50cc, a 39mm is 63 gram, a 47mm is 84 grams and a 50mm is 95 grams. STG weighed the 50cc  Airsal piston and it was 66.5 grams, not sure if it was weighed the same way or not but if close I gotta believe it isn't much more than a 47mm piston weight. farmer54