I bought a motor off ebay that has a locked up bottom end. It came with every thing except the piston, cylinder, head and carb. Im thinking about buying an athena 82cc big bore kit. It comes with a new head, piston and cylinder. The top speed of the bike right now is 50-55 mph. I dont want to lose power on the bottom and im happy with the stock performance but I want more top end. With this kit and higher gearing can I achieve more top end mph without losing low end torque? Its been a long time since I have rebuilt a motor like this, the last time was back in the early 90's as a kid when I had a couple of cr 80's but if I remember correctly the two crank halfs have to be pressed apart and pressed back together right? Also the big bore kit is gonna cost me around $500 on ebay, Does anyone know where I could find a kit like this cheaper? Also if anyone has experience with one of these kits what jets should I use in the carb with the big bore kit? Athena claims with this kit the motor will make 19hp which is 7 more hp than stock, I find this kinda hard to believe as Im only going 17cc's larger than stock although the compression ratio will be bumped up to 12.6. Are there any cooling issues with this set up? Im new to building minis but I have a strong mechanical background and im confident that with the aid of the local machine shops press I can complete this build fairly easily. Any help would be greatly apprieciated. Thanks, James
01 kx65 build
knuckleduster271
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I bought a motor off ebay that has a locked up bottom end. It came with every thing except the piston, cylinder, head and carb. Im thinking about buying an athena 82cc big bore kit. It comes with a new head, piston and cylinder. The top speed of the bike right now is 50-55 mph. I dont want to lose power on the bottom and im happy with the stock performance but I want more top end. With this kit and higher gearing can I achieve more top end mph without losing low end torque? Its been a long time since I have rebuilt a motor like this, the last time was back in the early 90's as a kid when I had a couple of cr 80's but if I remember correctly the two crank halfs have to be pressed apart and pressed back together right? Also the big bore kit is gonna cost me around $500 on ebay, Does anyone know where I could find a kit like this cheaper? Also if anyone has experience with one of these kits what jets should I use in the carb with the big bore kit? Athena claims with this kit the motor will make 19hp which is 7 more hp than stock, I find this kinda hard to believe as Im only going 17cc's larger than stock although the compression ratio will be bumped up to 12.6. Are there any cooling issues with this set up? Im new to building minis but I have a strong mechanical background and im confident that with the aid of the local machine shops press I can complete this build fairly easily. Any help would be greatly apprieciated. Thanks, James
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3,900 Posts
The Athena BB kit is probably awesome, but check out the Lukes Racing setup. I like this one better as it has a Wiseco Piston, and some thick cylinder plating. I'd run a KX85 carb, then get a pipe. I'm planning on that same build after I'm done with this KLX140 project. --L*64
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Hot Rods crank you don't have to wory about pressing/truing. If you have to buy a top end anyway, I would deff look at one of the 80+cc kits. Athena or any (I think the lukes comes with porting) ported for low mid range will give low mid-range. Good thing about ordering one built is you can tell the builder what you want. Eric Gorr (Forward Motion) does really good work and may offer suspension tips based on what you can afford to spend. That leaves e-bay carb from an 85. Or there is a Mikuni flatslide 28 that you can find reasonable sometimes new.
Since you want low-end and with the big bore, I would look at FMF torque pipe.
We are running a KX65 flattrack. Could not afford to have suspension re-done. Went to 10w fork oil in rear shock and 15w fork oil in fork, stiffer springs, worked good to stiffen it up for 95lb rider. Not the ideal, but better than nothing.
Since you want low-end and with the big bore, I would look at FMF torque pipe.
We are running a KX65 flattrack. Could not afford to have suspension re-done. Went to 10w fork oil in rear shock and 15w fork oil in fork, stiffer springs, worked good to stiffen it up for 95lb rider. Not the ideal, but better than nothing.
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467 Posts
knuckleduster271 said:
You can get over 19h.p. but its more than just porting, we spend alot of time on R&D to get the torque curve and spread we achieve, Here's our kit on ebay check it out. Item number: 4543497706. If you have any questions please ask.
Gene
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The lukes kit is a little out of my price range at $900, I can get the athena kit for $475 shipped and there is a guy local that ports & polishes fairly reasonable and hes not just a ******* with a dremel tool. Its actually cnc work and he has a reputable shop in this area. A good friend had him do a 450 yamaha and 400ex head and it was by far the biggest power gain over all the bolt ons. He only charges $150 for a single cylinder 4 stroke head so maybe a 2 stroker will be cheaper. I thought about using the hot rods crank/rod combo but wouldnt it be cheaper to just get bearings and use the stock crank? When the lower end seizes does it normally trash the crank? I remember I did have to replace one crank in a cr80 because the keyway by the flywheel got all chewed up. Like I said I was like fourteen last time I done one of these and my memory is kinda cloudy from the debaucherous behavior of my later teenage years. So what kind of gearing combo would I need to achieve a 65-70 mph top speed? Thanks for all the help, JamesLuckystar64 said:
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Bumppppppppppppppppppppp
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knuckleduster271 said:
Make sure whoever you send it to knows 2-strokes. Changing port sizes or port timing on a two stroke is a lot like designing a cam for a 4-stroke. The ports in a 2-stroke do the same job as the cam in a 4-stroke, but in a very different way. Someone that knows what they are doing can do a very good job. Think of it like this, when you pay the two stroke guy for porting, it is like paying for the bore, headwork, cam and cam design, on a 4-stroke.
It may look like a lot of money for porting, but price the cylinder porting and over-bore + plating with a reputable builder for your 2-stroke and then compare that price to Cylinder bore + head porting + valve job + valves/springs/keepers/retainers + cam for a 4-stroke (not to mention the cost of a name brand head).
I like my 4-strokes but a 2-stroke (properly maintaned) will cost less in the long run.
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5,341 Posts
If you want a little more power out of it once you figure out the jetting, you can remove the airbox and use a pod filter, some v force reeds, and a power wing. It should bump you up to about 19-20hp. It will be quite a weight reduction and better air flow too. Overheating shouldnt be an issue as long as you have the suggested coolant level (preferably Engine Ice
). Good luck with the build.
Universal Air Filters
Afterburnermx -Dirtbike & ATV store with great selection,prices and service!
Afterburnermx -Dirtbike & ATV store with great selection,prices and service!
Pro Circuit 304 Factory Sound Silencers
Pro Circuit Works Pipes
). Good luck with the build.Universal Air Filters
Afterburnermx -Dirtbike & ATV store with great selection,prices and service!
Afterburnermx -Dirtbike & ATV store with great selection,prices and service!
Pro Circuit 304 Factory Sound Silencers
Pro Circuit Works Pipes
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