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Post by 90GTVert on Aug 14, 2017 7:17:46 GMT -5
We've got poll threads for 47mm and 50mm+ bore 139QMBs already, so I wanted to see if we could gather some info on the stroker crank equipped setups from people that have used them. Please only vote if you have personal experience with a stroked 139QMB/GY6 50. It would be very helpful to include : -Stroker crank used -Bore size -Any other details of the setup known -Any idea how/why it failed -Do/did you run the scooter hard or just cruise -Was it "de-tuned" (commonly using heavier rollers to keep RPM down) You are able to vote twice on this poll, but please only vote once for each stroker engine that you've built. The option is there in case someone has experience with more than 1 build. Thanks to all who participate. These threads can help us gather information to make better educated decisions in the future. Check out the other poll threads here : 47mm BBK Poll50mm+ BBK Poll
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Post by Kick start on Dec 15, 2017 10:45:46 GMT -5
I'm using ScrappyDog 44mm stoker HD crankshaft with Airsal 50mm Racing High Compression Piston. The starter im using is a GY6 High Torque Performance starter from scrappydog as well. My main problem is finding a battery that can turn the engine over on it's own. But in 20° weather it can be hard. Right now I'm using a 9s-YTZ10S it's for a Yamaha r1 it has 190cca but when I turn the key on the battery is only at 12.6v and scents it not tuned yet it's hard to start and not broke in yet as well.
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Post by 90GTVert on Dec 16, 2017 9:36:28 GMT -5
A Battery Tender when parked overnight wouldn't be a bad idea.
The lithium batteries offer a lot of cranking amps. Prices are higher though and if they go dead they may be no good anymore.
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Post by Kick start on Dec 16, 2017 13:10:30 GMT -5
A Battery Tender when parked overnight wouldn't be a bad idea. The lithium batteries offer a lot of cranking amps. Prices are higher though and if they go dead they may be no good anymore. Yeah I message you about the batteries already. I have two wps lithium batteries that went bad. But when I just had it started two days ago the battery was dieing when running at idle. Give it a bit of gas it gets a slow charge? I' thinking of trying a evo2 8 cell ballistic 103-011.
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Post by 90GTVert on Dec 16, 2017 16:15:29 GMT -5
Maybe a lot of load on the electrical system is keeping it from charging at idle. Lots of lights/high watt lights or something like that?
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Post by jackrides on Dec 16, 2017 22:10:46 GMT -5
Mr. Start, what's your compression ratio, or, cranking pressure with a compression tester (throttle open)?
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Post by Kick start on Dec 18, 2017 8:24:18 GMT -5
Mr. Start, what's your compression ratio, or, cranking pressure with a compression tester (throttle open)? I don't know. I can give it a try when I get home today.
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Post by Kick start on Dec 18, 2017 19:37:36 GMT -5
Mr. Start, what's your compression ratio, or, cranking pressure with a compression tester (throttle open)? I don't know. I can give it a try when I get home today. On a 13.0v battery it hit 220psi.
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Post by jackrides on Dec 18, 2017 22:18:10 GMT -5
That seems really high, but some more opinions would help.
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Post by 90GTVert on Dec 19, 2017 4:52:41 GMT -5
220psi is definitely enough that it will tax the starting system. Upgrading battery cables to something larger may help. I've used 8AWG car stereo cables on my scoots before and noticed some improvement. Otherwise, you'll have to have a good battery and keep it charged, whether that means finding/fixing charging or draw issues or keeping it plugged in regularly or both. If you haven't rode it hard yet, there's a possibility that you end up with spark knock and/or it runs hot. Hopefully all clearances are good. If squish and piston to valve clearances are good, you could open the combustion chamber a bit to lower compression if you find that necessary. Many use additional gaskets, but tighter squish is more ideal if all else works out.
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Post by Kick start on Dec 19, 2017 16:31:00 GMT -5
220psi is definitely enough that it will tax the starting system. Upgrading battery cables to something larger may help. I've used 8AWG car stereo cables on my scoots before and noticed some improvement. Otherwise, you'll have to have a good battery and keep it charged, whether that means finding/fixing charging or draw issues or keeping it plugged in regularly or both. If you haven't rode it hard yet, there's a possibility that you end up with spark knock and/or it runs hot. Hopefully all clearances are good. If squish and piston to valve clearances are good, you could open the combustion chamber a bit to lower compression if you find that necessary. Many use additional gaskets, but tighter squish is more ideal if all else works out. I have already did bigger battery cables. I did change the headlights to 50/50w and running lights and there are two headlights and two running lights. Running lights are led. So I guess I'm just going to change them back to what they where. I do get spark knock at low rpm. I think my idle needs to be high then 1500rpm for it to go away. Maybe around 1800 or 1900 rpms
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Post by jackrides on Dec 19, 2017 16:52:55 GMT -5
You should be using 93 octane gas or higher. In really cold weather, use a lighter engine oil of very high quality; if you have a way to add a little heat to the crankcase area when parked overnight it would help.
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Post by Kick start on Dec 20, 2017 8:02:16 GMT -5
You should be using 93 octane gas or higher. In really cold weather, use a lighter engine oil of very high quality; if you have a way to add a little heat to the crankcase area when parked overnight it would help. I always use 93. I'm using 15w50 synthetic Yamaha oil. The engine only has less then 10hr on it so it still needs to break it in still. The evo2 8 cell ballistic 103-011 give a 13.6 turn key voltage with 240cca. My wps Featherweight Lithium Battery gave the same turn key voltage and only had 135cca or 150 cca and that turned over and started no problem. It the charging at idle that' doing it that needs fixing.
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Post by jackrides on Dec 20, 2017 13:34:04 GMT -5
it's normal for idle to not generate charging voltage. The headlights usually run from ac from the stator, so they may not effect the charging power. 90GTVert is right about adding a base and/or head gasket. That will add a lot of life to your build. I'm really looking forward to your post breakin performance results!
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Post by james82nd on Feb 15, 2018 15:36:08 GMT -5
I have a TaoTao 2014, stoke Crankshaft 41.4mm with a 52 mm big bore kit from Hoca with pop up Piston, my head is a Taida big valve 19mm exhaust with 21.5 or 22mm Intake, I run a keihn 24mm carb with 39 pilot jet with 107 main. Cr7hix iridium plug, with performance air fileter 42mm and Exhaust. My clutch is a NCY 107mm with blue and yellow torque spring. It will get up to 62MPH top speed with crusie of 50-55MPH running the Hoca 2.55 secondary gears
stock HP was 3.5 with 49cc...I guess it is 7.5 to 8HP with all the mods I also went from 50mm BBK to the 52mm. It made a huge difference with just the extra 2mm. My head also has a three angle valve seat job from scrappy dogs.com
mine is not broken in yet either with only 150km on the 52mm BBK
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