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Post by humanshield on Oct 21, 2016 16:10:42 GMT -5
I installed my 50big bore cyclinder last night, i was very surprised how well it does speed is great way more than i thought it would have. Hopefully i can make mine last 5k plus miles. Good job! I'm right at (or maybe slightly past) 4,000 miles now and she's going strong. But let me admit...I don't really run it like I'm racing. Often I just smooth off from the light at about half throttle. Most of the time I keep it at or below 7,000 rpms. "Sometimes" I do gun it....and "Sometimes" I push it to WOT....it's just not often....maybe 10% of my riding time? The other 90% I ride it like I'm just casually gettin around. Good thing about the 50mm piston with an A9 cam...I can go easy on it and still pass stock scooters because of the xtra torque. And with 3/4 throttle usually can pass the 47mm BBK scoots. Make sure you err on the side of rich.....ride it don't thrash it and it should last a long time. I'm definitely shooting for 5,000 miles plus and should reach it easily. Would be great to have TWO votes for 5,000 miles plus  Keep us posted. Oh..Use PREMIUM gasoline for the first 500 miles. it'll help it run cooler during break in.  |
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fergulious
Scoot Member
Posts: 59 
Location: Thomasville NC
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Post by fergulious on Oct 21, 2016 17:07:21 GMT -5
yes that all i use. Well ill definitly be pushing for the vote. I drove to work everyday 30 miles Each way so we will know soon
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Post by humanshield on Oct 21, 2016 17:15:23 GMT -5
yes that all i use. Well ill definitly be pushing for the vote. I drove to work everyday 30 miles Each way so we will know soon Did you get a head with your kit or did you use your stock (same) cylinder head? |
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Post by humanshield on Oct 28, 2016 15:32:43 GMT -5
After some research, I do believe I've found what might be the most common cause of failure of 50mm BBK's
That would be using a stock head, having a 5cc volume with the 50mm piston.
Here's the problem....the head squish area is too small. Yes, it will "work" and yes, the power will be pretty impressive, but the heat generated will be excessive and the load on the bearings will be excessive...both causing early failure.
The 47mm piston kit doesn't suffer this problem simply because the displacement is smaller and doesn't reach critical pressures or temperatures due to excessive compression like it does with the 50mm piston.
Of course there are many other potential pitfalls but I have right at 4,000 miles on my 50mm BBK and she's running as strong as ever.
Apparently, the 21mm heads stopped being produced OR...sellers stopped including them with their BBK's and to save money went with stock heads.
So there you have it folks. I honestly believe this is the most likely cause of most 50mm BBK failures. Not ALL. As I said, there are other pitfalls and the 50mm piston requires a bit more care when installing everything to get it right vs the 47mm kit due to the increased stresses. But they work. And they can last.
The 47mm kit will still probably last "longer" but I can see over 5,000 miles easily when done right and not abused constantly.
I'm, right at 4,000 now and going strong on the 50mm kit. (With the 21mm 8cc volume head)
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fergulious
Scoot Member
Posts: 59
Location: Thomasville NC
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Post by fergulious on Nov 2, 2016 22:53:05 GMT -5
Update on 50mm jug with the Airsal piston. humanshield was right like i figured he would be smooching did occur but only on he intake valve both set at .004 exhaust cleared failed just after 15 miles i heard it and rode it home 20 mins away lol. got home pulled the top end and broke off the whole intake valve relief on piston, so i put the 50mm piston that came with the jug in the cheap chinesse kit (which was a mistake all together NOMORE CHINESSE) I got about 900 miles with it before blow-by occur.
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fergulious
Scoot Member
Posts: 59
Location: Thomasville NC
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Post by fergulious on Nov 2, 2016 22:54:30 GMT -5
So since the blow ive installed a quality NARAKU 47mm BBK. Ill post the new build over to the 47mm thread...
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Nov 3, 2016 0:04:26 GMT -5
Finished installing mine with that 23mm head late last night, compared to the 47mm with a stock head I was running, launch is about the same, acceleration is a bit better, top end may have suffered a bit, after 50 miles and oil change, I pushed it to 7500rpm briefly which gave me 36mph but you could tell the power was falling fast, I've kept it under 5000rpm during the first 50 with a lot of residential street slow and go every block or so to seat the rings etc. New carburetor comes tomorrow but I don;t have the jets yet, current one has #90 main/#30 idle, with the bigger displacement and valves, I figured I'd start fresh with a #100 main/ #35 idle and see what flies.
Reading your comments, I think I should go back and get the A9 cam too, and then blame everything on the tranny.
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Nov 3, 2016 23:25:34 GMT -5
What's your variator/clutch setup humanshield?
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Post by msnothing on Nov 4, 2016 9:07:24 GMT -5
Having read both the 47mm thread and this one, I do see one variable that may also factor into the failure rate of either BBK upgrade - manufacturer. Are there some manufacturers that fail more often? (And of course the inverse, some that rarely fail!)
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Post by humanshield on Nov 4, 2016 9:40:47 GMT -5
What's your variator/clutch setup humanshield? Bone stock Chinese parts. I tried a Koso variator early on (against Brent's advice) and regretted it. |
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Post by humanshield on Nov 4, 2016 10:16:38 GMT -5
I think it has more to do with installation and use.
The 50mm BBK creates more heat and more compression. So right off the bat, if you do something wrong it is more likely to show up right away and do more harm.
I'm having a hard time myself finding 21mm heads that are supposed to go with the 50mm kit so if they are supplying stock heads with the 50mm kit OR...people are trying to use the stock head...that WILL cause failures.
A stock head's volume is 5cc's (Too much compression on a 50mm BBK)
A 21mm (intake valve) head's volume is 8cc's (perfect for the 50mm BBK)
A 23mm (intake valve) head's volume is 13cc (too low compression for a 50mm BBK without a stroker crank or domed piston)
I have 4,000 miles on my 50mm BBK at this point and it's doing as well as a stock motor. Granted, I'm no scooter racer but I do run it hard occasionally. It is the "cheap" chinese kit I paid $56.00 for the entire kit WITH head.
My opinion is that a 50mm BBK is nearly as reliable as a 47mm BBK regardless of how many people have failures because those failures appear to be related to installation errors, misunderstanding the dynamics of the higher compression and heat, improper break in failures and failure to properly tune the motor for the larger displacement.
It takes patience and work to get a motor with a 50mm BBK tuned in just right. I even had trouble in the beginning with mine. You CANNOT just slap one in and go. That is not possible. You have to understand how rings work, how to properly install and set rings, how to avoid damage when sliding the cylinder over the new rings, how the wrist pin clips should be installed, understanding compression, understand that the higher compression and friction will generate more heat during break in and on and on and on. It is NOT as easy as bolting it all on.
These are the exact same failures that result from ANY motor when increasing displacement 60% and failing to do it right.
That said, I might change my opinion to the following......
The 50mm BBK is recommended ONLY for the EXPERIENCED engine builder who knows how to build and tune for high compression and the differences in dynamics when going that much more in displacement. Without some knowledge of these things, your chances for success with a 50mm BBK are much less.
I would recommend a 47mm BBK for the non experienced engine builder / tuner. It is far more forgiving.
If you have good success with your 50mm BBK it is probably because you did everything right and had a reasonably good grasp of what you were doing. Not saying others are idiots at all. But the 50mm BBK is more demanding and requires you get everything right. Plenty of people here are capable of doing that.
I've been building engines in cars since the 80's and have built racing, turbo charged motors and nitrous assisted racing motors. I've also done some advanced things like changing nearly inaccessible tunnel bore cam bearings (not easy)....so I have a little bit of an advantage in experience.
No doubt, there are some here who can teach me plenty regardless. Brent has FAR more scooter experience for example.
YMMV
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Post by humanshield on Nov 4, 2016 10:20:04 GMT -5
Update on 50mm jug with the Airsal piston. humanshield was right like i figured he would be smooching did occur but only on he intake valve both set at .004 exhaust cleared failed just after 15 miles i heard it and rode it home 20 mins away lol. got home pulled the top end and broke off the whole intake valve relief on piston, so i put the 50mm piston that came with the jug in the cheap chinesse kit (which was a mistake all together NOMORE CHINESSE) I got about 900 miles with it before blow-by occur. Sorry to hear that bubba. Was hoping you'd join the successful 50mm BBK club. Where did you get your kit? Yep, the AirSal will not clear the intake valve. You have to do some piston clearancing. You can't just slap these things together and hope for the best. You gotta KNOW what's what before hand or know how to figure it out. If you did not carefully break in the motor during the first 500 miles, and or if the mixture was not on the rich side, both those things could have caused cylinder and or piston/ring damage. I can tell you a 50mm BBK will run REALLY hot in the beginning. I rode mine about 1 mile then let it cool for the first 20 miles. Then slowly increased the distance. |
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Post by humanshield on Nov 4, 2016 10:28:28 GMT -5
Finished installing mine with that 23mm head late last night, compared to the 47mm with a stock head I was running, launch is about the same, acceleration is a bit better, top end may have suffered a bit, after 50 miles and oil change, I pushed it to 7500rpm briefly which gave me 36mph but you could tell the power was falling fast, I've kept it under 5000rpm during the first 50 with a lot of residential street slow and go every block or so to seat the rings etc. New carburetor comes tomorrow but I don;t have the jets yet, current one has #90 main/#30 idle, with the bigger displacement and valves, I figured I'd start fresh with a #100 main/ #35 idle and see what flies. Reading your comments, I think I should go back and get the A9 cam too, and then blame everything on the tranny. The reason your launches are slow is due to low compression. My scoot will walk away from a 47mm BBK all other things equal. If you can get the compression up to about 160 to 180 with that head, and get the cam you will be blown away at the difference. Your scooter will nearly be as fast as a 150cc scooter up to about 55. It would be unlikely that you would come across a 2T scoot that could beat you. Only the really highly modified, big money 2T's would have a chance against you. Look at the video I posted of my race on my fast 150cc scoot vs the guy on the modified 4T with 50mm BBK and cam (plus a few other mods such as straight through custom pipe and 24mm carb). It was close and he did not have the 23mm big valve head. |
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Post by spaz12 on Nov 4, 2016 12:23:25 GMT -5
Finished installing mine with that 23mm head late last night, compared to the 47mm with a stock head I was running, launch is about the same, acceleration is a bit better, top end may have suffered a bit, after 50 miles and oil change, I pushed it to 7500rpm briefly which gave me 36mph but you could tell the power was falling fast, I've kept it under 5000rpm during the first 50 with a lot of residential street slow and go every block or so to seat the rings etc. New carburetor comes tomorrow but I don;t have the jets yet, current one has #90 main/#30 idle, with the bigger displacement and valves, I figured I'd start fresh with a #100 main/ #35 idle and see what flies. Reading your comments, I think I should go back and get the A9 cam too, and then blame everything on the tranny. The reason your launches are slow is due to low compression. My scoot will walk away from a 47mm BBK all other things equal. If you can get the compression up to about 160 to 180 with that head, and get the cam you will be blown away at the difference. Your scooter will nearly be as fast as a 150cc scooter up to about 55. It would be unlikely that you would come across a 2T scoot that could beat you. Only the really highly modified, big money 2T's would have a chance against you. Look at the video I posted of my race on my fast 150cc scoot vs the guy on the modified 4T with 50mm BBK and cam (plus a few other mods such as straight through custom pipe and 24mm carb). It was close and he did not have the 23mm big valve head. Hate to burst your bubble there, but a mild 2T (Athena basic and Leo Vince pipe) is faster than a 150. With the right gearing it will even have more top speed. |
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Nov 4, 2016 13:10:34 GMT -5
Part of the problem was the carburetor, I went ahead and slipped the new carb on with the stock 90/30, and I got noticeably more acceleration without bogging, I can actually give it full throttle from the start and it just keeps pulling until about 35 where it starts to wimp out to 39 tops.
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