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Motorized Bicycle General Discussion All topics regarding bicycles with engines.

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Old 01-21-2014, 05:54 PM
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rogergendron1 rogergendron1 is offline
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Default Re: How many engines

Originally Posted by mkatt4x4 View Post
From reading tons of threads on this forum, it seems a lot of motorized bicycle enthusiasts go through many engines. Which makes me wonder if the kits are $170'ish and the engine is $100'ish, whats the range for the GRUBEE SkyHawk GT5A 66cc Angle Fire Slant Head Bike Motor before it dies, with normal use....of course. And is there anything else recommended to upgrade on this kit, to make it more reliable and last longer?

i had a grubee gt5 before my dax race motor.... i spent over3 weeks trying to blow it up !!!! it never siezed !!!! i ran that like motor you never saw motor run before !!! i even heald the throttle wide open in nuetral no load for a good min every day trying to see if i could sieze it !! i would pourposly rid as hard as possable reving it up wide open all the time and holding it there, pulling the clutch in wile rideing at wide open throttle and letting the motor wind out then dumping the clutch and repeteing this over and over, long burn outs on the concrete, super high rpm down hill riding, reving it as high as possable to see if it would blow, i even ran it on a 50/50 mix of rubbing alcahaul and gasoline mixed 70 to1 and reved the crap out of it wile riding as hard as i could for 2 days on that mix and the only thing that happend was she ran a little hot ! finaly i ran it on strait gas with about 25% acetone added in and rode it 5 mile to work !!!! i cant believe it made it like that !!!!! on the way home though it over heated and slowly siezed going up hill 1 mile from my house so i pedaled before i removed the motor i was riding the bike around adjusting the rear hub for free play and i dumped the clutch on acsident ..... to my suprize she turned over and wanted to start !!! W.T.F......!!! some how it unfroze itself !!!!

apon tear down of the engine, i saw the cylinder was severly scored and scratched and the piston dome was blue from over heating and scraped up bad on the skirt, the rings were worn so bad they were rounded out LOL and shiney !! the chrome was flaked off the jug to the tune of 30% of it missing and the play in the needle bearing was real flopy and loose....

but even with all that castostrofic damage to the top end and running on cheap gas mixed with acetone and no oil ..... it still wanted to start back up !!!!!!!

this changed my mind on the china girl and this incident is what made me go for another 2 stroke rather than use the 4 stroke i had planned, it would appear that as long as you have a well tunned carb your motor will take a serious beating !!
here to stay and compleatly insane ! deal with it lol
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Old 01-21-2014, 07:11 PM
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Greg58 Greg58 is offline
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Default Re: How many engines

I have a grubee 48cc that has around 1300 miles on it, the only thing that has been replaced is the crankshaft seal behind the magneto. I ride at 25 to 26 mph so the little 48 CC is humming pretty good, some have not had good luck with grubees but all six that I built or helped build are still ruining.
Your results may not be the same,Greg
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Old 02-05-2014, 01:17 PM
Scootmeister Scootmeister is offline
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Default Re: How many engines

Two more ideas. Excess heat kills these engines so get it tuned properly. Second, the stock airfilters are crap. Grit and debris will destroy any engine so get a good filter with either an oiled foam or filter element to keep the combustion chamber clean. Your rings, your cylinder wall, and your bearings will last longer.
"If bulls didn't have horns, everyone would be a Matador".
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Old 02-05-2014, 03:03 PM
Theon Theon is offline
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Default Re: How many engines

I am on my motor number 5, but only cause I love em' (3 running and 2 being built).
My motors don't do that many miles, but I use them hard.
Only thing that has stopped any of them is the Mag coil (get a spare). and a seal went on an old motor that I didn't build, but there was nothing else wrong with the old girl.
However, I do recommend going over the motor properly before running it if your going the EBay way.
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Old 02-05-2014, 07:05 PM
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maniac57 maniac57 is offline
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Default Re: How many engines

I have long maintained an Air-cooled piston port two stroke is one of the most reliable engines in the world. Only three moving parts if you don't count the reduction gears.
Crank, rod, piston.
The rest is details...treat these engines like they were designed and they last forever. Most quality related failures will occur within the first few days so once it's sorted out, they just do miles. I recently sold a running ht with well over 10k miles of 250lb adult use.
Still running the new owner back and forth from work every day.
If more is better, then too much is just enough.
If you can't afford it, build it yourself.
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Old 02-05-2014, 08:29 PM
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Allen_Wrench Allen_Wrench is offline
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Default Re: How many engines

Two motorbikes - but only one Dax-purchased China Girl. Don't know how many thousand miles (I keep it as well-tuned as I can). Four years old, going on five I think. What Maniac says is largely true. Maintenance with these two-smokers is minimal, but extremely important: proper oil mix, proper jetting, clutch in good shape, well adjusted magneto, good spark plug that is gapped just right, etc. I even took the time to do port matching, got a performance air cleaner, high-end plug and wire, and other bits. She hums really nicely. Hardly any vibrations at all.
Now, I've worked on plenty of other small engines for other things. But I've only ever needed the one bike motor. I'll replace it when I have to.

"There is nothing wrong with wanting a motorbike that is an extension of your personal taste and fashion sense; if you must ride somewhere, I say do it with style!"
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Old 02-07-2014, 11:49 AM
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maurtis maurtis is offline
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Location: Kyle, TX
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Default Re: How many engines

Between 400 and 500 miles on my BGF 66cc before the wrist pin bearing blew. I knew it had to be replaced but I could not get the wrist pin out, so let it ride. I had upgraded pretty much everything except that, which should have been the first thing since they are known to go.

But I rode it at full throttle whenever possible. Break in was taking it easy for about a mile... LOL.

I then moved on to electrics which have been nothing but pure joy. And while I do have a real motorcycle, I am sure that one day I will build another gas bicycle since it is a feeling that cannot be reproduced otherwise. If I went with another China Girl, it would be a balanced Dax. But more likely a 4 stroke, either the 79/99cc Preddy or one of the multispeed Lifans on a stretch.
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