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Old 06-10-2014, 05:19 AM
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Davezilla Davezilla is offline
Motorized Bicycle Elite Member
Join Date: Mar 2014
Location: San Antonio Texas
Posts: 2,710
Default Re: Looking to buy first bike engine kit and i need help deciding which is the best?

I fully agree as well... There are so many sellers of these kits it's mind blowing on ebay alone... and everyone is claiming theirs is better in some way or faster than the other kits when they all come from the same place... they just buy them in bulk from the lowest price suppliers and then ship them out without ever opening the box to see what's inside. Then since most people leave positive feedback before they actually install and run these, they look golden to new potential buyers with very few negative feedbacks for bad engines.

With that being said, there are a few that do check their products to make sure they're up to standards, and some even swap out the hardware and bearings so your new engine will last more than a few rides up the street.

if you prefer the PK80/F80 type engines, Dax or Neil are teh guys to buy from, there are others but I can't think of who they are off the top of my head right now, but you really can't go wrong with either of them. If you want the GT5 or GT5a type, there are sites that sell these including Grubee's site, these engines are slightly different and some parts don't interchange with the rest of the China Girls, but as mentioned above, those who run them really really like them.

I don't run any of these without taking it apart and checking that everything is up to the task, but I gotta say it's nice to be able to buy a Dax bottom end and not have to do that, I can pretty much just add my performance parts and go...

The reason I was asking about teh GT5 cylinders and their port size was because if they are actually bigger, they would save a little porting time, but I can cut out 1mm or so pretty fast with the tools I got here so it's not really that big of a time saver. I do however, take any new jug and check all the ports for plating overhanging because if not cleaned up and chamfered it will start to flake off in those areas and the engine will fail in short order if a ring snags on teh excess plating or if it starts flaking off because once it starts it's pretty much game over for that cylinder, and it's a lot cheaper to just replace one than it would be to have one replated.

I can also agree about buying just the bottom end from Dax and building it up from there so you can learn these things better, or if you're already a good mechanic, it's an easy way to save a few buks, it's ALWAYS a good idea to at least pull the cylinder off and check the ports for excess plating overhanging into the ports because this is a failure point because in short time the plating will begin to peel back in these areas and the fix is as easy as filing or carefully dremeling the plating to match the port openings, then finish the job by chamfering the openings for a smooth surface for the rings to pass over... Opening up the ports is a sure way to get better performance as long as you don't go too wide or too high on the exhaust side or too low on the intake side. Cutting ramps into the piston crown at the transfers and exhaust also help, and so does cutting off about 5mm from the bottom of the skirt on the intake side, don't worry too much about the port being partially closed at BDC because if you open it all the way by cutting off more from the bottom of the piston skirt, the intake duration will be too high and you'll lose a lot of low end power, but there's a lot more on porting to read up on before grabbing the dremel and letting er rip, and I wouldn't recommend doing it if you've never done it before without asking a lot of questions and reading up on it first, there's a lot to gain by doing it right, and a lot to lose by cutting out too much...
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