BBK port timing vs. Lucky7 port timing w/ 43.8mm piston - Pocket Bike Forum - Mini Bikes
 
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post #1 of 16 (permalink) Old 12-15-2004 Thread Starter
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BBK port timing vs. Lucky7 port timing w/ 43.8mm piston

i have a lucky 7 bike with a 43.8mm piston, i have a stroker crank on the way and i need to know how to change the port timings. people keep saying to raise the roof of the BBK exhaust port 2mm and lower the floor of it 1mm and make it 31mm wide. i have already ported my cylinder/cases. but i am installing the crank with the same cylinder and piston as it came with. i want to know if the bbk cylinder out of the box has the same deminsions as the stock cylinder on my lucky 7 bike.
i keep hearing the new lucky 7's come with the bbk already installed. but i tried to widen my exhaust 70% of the piston which is about 31mm but there doesnt seem to be enough casting around the exhaust port of my cylinder to cut out that much metal. i think to raise the roof and widen it that much i would have to pack JB weld around the whole exhaust port(outside) to have enough material there to be able to cut it out.
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post #2 of 16 (permalink) Old 12-15-2004
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Quote:
Originally Posted by cspyy
i have a lucky 7 bike with a 43.8mm piston, i have a stroker crank on the way and i need to know how to change the port timings. people keep saying to raise the roof of the BBK exhaust port 2mm and lower the floor of it 1mm and make it 31mm wide. i have already ported my cylinder/cases. but i am installing the crank with the same cylinder and piston as it came with. i want to know if the bbk cylinder out of the box has the same deminsions as the stock cylinder on my lucky 7 bike.
i keep hearing the new lucky 7's come with the bbk already installed. but i tried to widen my exhaust 70% of the piston which is about 31mm but there doesnt seem to be enough casting around the exhaust port of my cylinder to cut out that much metal. i think to raise the roof and widen it that much i would have to pack JB weld around the whole exhaust port(outside) to have enough material there to be able to cut it out.

Be carefull lowering the floor of the exhast port if the cylinder you have has the label SY446- something, as the exhast port floor is 2mm lower than the other BBK heads out there. The roof is in about the same position as the older heads. On the SY-446 head the piston is about 2mm above the floor at BDC which means to me that there would be no benifit to lowering it.
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post #3 of 16 (permalink) Old 12-15-2004 Thread Starter
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well should the floor of the port be at the top of the piston when its at BDC?


what about the roof? where should it be, i have already raised the roof of the exhaust and transfers 1mm and run no base gasket.
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post #4 of 16 (permalink) Old 12-15-2004
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first off I hope you mentioned that you have a factory big bore when ordering your crank, the wrist pin is different on many of the factory big bore over the big bore kits. Second the porting specs cannot be that simple since there is so much variance from head to head on these bikes. Third, you can widen the exhaust that much, you only widen at an angle (cone shaped towards the barrel) so you will not bust thru. I hope this helps.
Quote:
Originally Posted by cspyy
i have a lucky 7 bike with a 43.8mm piston, i have a stroker crank on the way and i need to know how to change the port timings. people keep saying to raise the roof of the BBK exhaust port 2mm and lower the floor of it 1mm and make it 31mm wide. i have already ported my cylinder/cases. but i am installing the crank with the same cylinder and piston as it came with. i want to know if the bbk cylinder out of the box has the same deminsions as the stock cylinder on my lucky 7 bike.
i keep hearing the new lucky 7's come with the bbk already installed. but i tried to widen my exhaust 70% of the piston which is about 31mm but there doesnt seem to be enough casting around the exhaust port of my cylinder to cut out that much metal. i think to raise the roof and widen it that much i would have to pack JB weld around the whole exhaust port(outside) to have enough material there to be able to cut it out.
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post #5 of 16 (permalink) Old 12-15-2004 Thread Starter
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ok, well i hope im getting the right one. i have read some where on here about someone having bushings that slip over the wrist pin because its smaller than the one that fits the piston.

it makes it difficult to try and degree in all the ports when the head is made onto the cylinder. so if all of them are different what do you think i should go by or do?
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well the piston hat came wiht my BBk must be an odd one cuz I got the SY44F-6 I think its labled and my piston sat about 3mm below the exhaust port at BDC with the FCSC.

but yeah I busted through on the roof opn one side and just JB welded it shut and it seems ot be holding so far. I f'd the port up though cuz I lost alot of power, I should be trying the stock manifold/reedcage/carb and stock gearing tonight to eliminate all problems but the port, except the stock jet wont handle my needs so I really wont know but hopefully it will help.
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post #7 of 16 (permalink) Old 12-16-2004
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Quote:
Originally Posted by blueR1cag
well the piston hat came wiht my BBk must be an odd one cuz I got the SY44F-6 I think its labled and my piston sat about 3mm below the exhaust port at BDC with the FCSC.

but yeah I busted through on the roof opn one side and just JB welded it shut and it seems ot be holding so far. I f'd the port up though cuz I lost alot of power, I should be trying the stock manifold/reedcage/carb and stock gearing tonight to eliminate all problems but the port, except the stock jet wont handle my needs so I really wont know but hopefully it will help.
It would be nice of someone out there to give specs in distance from BDC or TDC of the ports for porting instead of just saying take this much off here and that much off there as these things vary significantly. I guess the best thing is to find the specs in timing angles and the do the math to see where you are at and then go from there. This is why I decided to leave mine stock and see how it works first and then I will start checking into the proper timing specs and do the math. I am afraid of widening to much as I had a ZH-1 head widened to 31mm and I couldn't run the bike for more than 2 minutes before the rings would break.
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post #8 of 16 (permalink) Old 12-16-2004
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Quote:
Originally Posted by gmenge
I am afraid of widening to much as I had a ZH-1 head widened to 31mm and I couldn't run the bike for more than 2 minutes before the rings would break.
Must have been widened incorrectly, that the rings where catching one of the edges of the port and breaking. Remember to "Ovalize" your ports and leave a good 4mm minimum of cylinder wall between ports for the rings to bear on. "Ovalizing" (or oval shape) greatly reduces the chance of the rings catching an edge and breaking. Also don't forget to chamfer all edges.
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post #9 of 16 (permalink) Old 12-16-2004
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my piston has 2 recessed pins, one in each ring groove and my ring ends were notched so that the rings cant rotate at all and the ring gaps were at the back where no port is on mine so theres nothing for them to catch.
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post #10 of 16 (permalink) Old 12-16-2004 Thread Starter
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Quote:
Originally Posted by gmenge
It would be nice of someone out there to give specs in distance from BDC or TDC of the ports for porting instead of just saying take this much off here and that much off there as these things vary significantly. I guess the best thing is to find the specs in timing angles and the do the math to see where you are at and then go from there. This is why I decided to leave mine stock and see how it works first and then I will start checking into the proper timing specs and do the math. I am afraid of widening to much as I had a ZH-1 head widened to 31mm and I couldn't run the bike for more than 2 minutes before the rings would break.
kinda hard to degree in your motor when the head is made onto the cylinder.
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if you need the wristpin adaptor for the bbk, Tyler has them at Adrenaline Motorsports

********, baby!
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Quote:
Originally Posted by Bikoholic
Must have been widened incorrectly, that the rings where catching one of the edges of the port and breaking. Remember to "Ovalize" your ports and leave a good 4mm minimum of cylinder wall between ports for the rings to bear on. "Ovalizing" (or oval shape) greatly reduces the chance of the rings catching an edge and breaking. Also don't forget to chamfer all edges.
Actually I did not do the porting myself, I purchased the head from Adreneline motorsports. They replaced it with an unported BBK SY446-6 head and piston. There may have been some other problem with it, I don't know.
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Quote:
Originally Posted by blueR1cag
my piston has 2 recessed pins, one in each ring groove and my ring ends were notched so that the rings cant rotate at all and the ring gaps were at the back where no port is on mine so theres nothing for them to catch.
Same as mine. If the port is too wide and not chamfered properly the rings could catch, but that may not have been the problem. Anyway I am not going to do any porting until I get the true scoop.
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Quote:
Originally Posted by cspyy
kinda hard to degree in your motor when the head is made onto the cylinder.
If you know the stroke, then measure from the top of the inside of the cylinder to the top and bottom of the ports you should know exactly what your port timing is by calculating the degrees of the crank from position of the roof and floor of the exhaust port.
My only problem is not knowing what the port timing specs should be for best performance. If I new the correct port timing angles it would be fairly easy to calculate location of the ports.
Basic trig is really all you need.
Again if someone has the timing in degrees for the BBK and with the stock stroke, (which is posted somewhere here) I would be able to calculate the correct location of the port roof and floor. Also would the height of the transfer ports (calculated angle of the crank at which they would close) affect what timing you should have for the exhaust ports? I don't know, that is why I am asking.
Thanks for any help
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Quote:
Originally Posted by gmenge
Actually I did not do the porting myself, I purchased the head from Adreneline motorsports. They replaced it with an unported BBK SY446-6 head and piston. There may have been some other problem with it, I don't know.
This may be an old thread but does anyone no anything about the zh-446 head.This is the head that pbu uses for their sleeper kit.I have this kit.The bottom and espeacialy mid is great.Top end,cant get her to rev out.Jet pro 1st pipe,ada fiber glass reed,rocket key,stack and filter,72 main jet,needle in 3rd position.2nd position engine dies 4th position engine boggs. 6/63 gearing gets 35mph.Have I tach'd this head out or besides the dual boost ports can this head be modded for more power.Any reviews about this sleeper kits porting or duration?
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Quote:
Originally Posted by cbtlr
This may be an old thread but does anyone no anything about the zh-446 head.This is the head that pbu uses for their sleeper kit.I have this kit.The bottom and espeacialy mid is great.Top end,cant get her to rev out.Jet pro 1st pipe,ada fiber glass reed,rocket key,stack and filter,72 main jet,needle in 3rd position.2nd position engine dies 4th position engine boggs. 6/63 gearing gets 35mph.Have I tach'd this head out or besides the dual boost ports can this head be modded for more power.Any reviews about this sleeper kits porting or duration?
Hi,
I have been unsuccessful so far at getting over 10,000rpm with a highly modded engine. See post for info on mods.

https://www.pocketbikeplanet.com/showthread.php?t=14692

I have messed with the transfers and the exhaust and the boost ports and nothing seems to make any diff. Since my cylinder is already messed up I am trying everything because I have nothing to lose as this cylinder is useless to me the way it is. My port timing is 129 transfers and 170 exhaust.
I have also reworked the boost ports so they are squarish and angled the roofs so they are pointing at the plug.
I am wondering if the transfer ports are just too small on the 44mm head.
The stock 40mm head has much larger transfers than the 44mm.
Since my cylinder is useless I might try making the transfers deeper to see if there is any diff.
As for the carb, I made sure that the pump pop off pressure was set correctly. The walbro carbs are always set incorrectly stock(pressure was set way to high). Still no diff.
Another thing is you should get rid of the Rocket key. I tried advancing and retarding and still no diff. Advancing caused the motor to run hot and lose power. Just for the heck of it you may want to try putting the rocket key in backwards/retarding and see if it will rev higher. I have read somewhere that advancing gives more low end and retarding gives higher rpm. I did not see any differences in top end though.

01R1

Last edited by gmenge; 06-13-2005 at 11:29 AM.
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