Hyosung GT250R custom engine | GTAMotorcycle.com

Hyosung GT250R custom engine

T

TwinThumpers

Member
Dear GTA memebers,

Just some shower thoughts I had about my next motorcycle. I want to see if anyone knows anything about custom building motorcycle engines. I want to take two blown GT250R engines and custom make the block with a new crankshaft; combining both engines making a 500cc v4. I'm trying to find more information on CNC shops to make a custom crankshaft. I Both have SolidWorks and MasterCAM on my laptop so I could make drawing and send it to a company willing to make it. If anyone knows about combing 2 Vtwin engines that would be great!
 
Pick a better donor motor. The time and cost to do this will be very significant and be only slightly affected by the donor motor.

If you use known crap, not only is it likely to blow (again), but no matter how cool it is, the resale value is almost zero.

Start with two HD engines and you could probably get decent coin for them when you are done. Or if you really want a v4 500, start with ninja 250 or cbr125 motors. Anything other than a housing 250. That was a bad motor.

On a more practical note, how much do you know about engine design and how much are you hoping the machine shop fills in? I would assume you need to work out journal sizes, counterweight size and shape, filler sizes at transitions and almost every other damn thing and the machine shop just bangs out your expensive part (no matter how good or bad it is). A crank is about as complicated as you can get. As a first step, I would strongly consider trying to work with a donor crank instead of starting from scratch. Obviously v4 cranks arent that common, but can you use part of a v8 crank? Crank design is an epically huge job.
 
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it would be a shorter link to hook the two existing cranks together.

but as has been said, the hyosung 250 was a pretty bad design to start with. You'll spend a small fortune on a very low value project, with a predetermined history of grenading , before you "engineer" it.
 
Its not a new idea - there is a few companies that combine motorcycle inline motors to make V configurations. Check out the Hartley H1 - they combine two Hayabusa engines into a V-8.

The cost of one of their dyno'd engines starts at $45,000 US just to give you an idea of the amount of engineering / costs required to pull it off.

if you want a project throw a turbo onto it until it blows up. Or just buy a used V4 off ebay for a thousand bucks.
 
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r3r3r3 said:
if you want a project throw a turbo onto it until it blows up.
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They already are blown up. I don't know if anymore of those are running. There are probably a few forgotten in garages that haven't blown up yet. Probably the closest I have ever heard to a 100% vehicle failure rate.
 
GreyGhost said:
They already are blown up. I don't know if anymore of those are running. There are probably a few forgotten in garages that haven't blown up yet. Probably the closest I have ever heard to a 100% vehicle failure rate.
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One motor isn't blown it's just leaking oil from the head gasket which is an easy fix, the second one I found on ebay was from a totaled Gt250r with only 4,000kms. The issue is that I'm sure that the damage was inside the engine as well since it's oil system is like the old ninja 250s "dry slump".
 
r3r3r3 said:
Its not a new idea - there is a few companies that combine motorcycle inline motors to make V configurations. Check out the Hartley H1 - they combine two Hayabusa engines into a V-8.

The cost of one of their dyno'd engines starts at $45,000 US just to give you an idea of the amount of engineering / costs required to pull it off.

if you want a project throw a turbo onto it until it blows up. Or just buy a used V4 off ebay for a thousand bucks.
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Making a crankshaft requires a milling/CNC machine. My college would never let me use their $30,000 machine for my own personal use. So like other said I should find a crankshaft already made in production. Tie rods and pistons are the easy part. However I can't just weld two hyosung cranks together since they need to be properly balanced or we would get torsion forces that would rip the engine apart.
 
If you are thinking of going this deep into them, you probably know better than most. What actually made them blow? IIRC, it was something to do with oiling, but I am not sure of the exact cause nor what actually got destroyed in the failure. If you really want to use them, phase one of the project should be fixing (or at the very least attempting to fix) that issue.
 
GreyGhost said:
Pick a better donor motor. The time and cost to do this will be very significant and be only slightly affected by the donor motor.

If you use known crap, not only is it likely to blow (again), but no matter how cool it is, the resale value is almost zero.

Start with two HD engines and you could probably get decent coin for them when you are done. Or if you really want a v4 500, start with ninja 250 or cbr125 motors. Anything other than a housing 250. That was a bad motor.

On a more practical note, how much do you know about engine design and how much are you hoping the machine shop fills in? I would assume you need to work out journal sizes, counterweight size and shape, filler sizes at transitions and almost every other damn thing and the machine shop just bangs out your expensive part (no matter how good or bad it is). A crank is about as complicated as you can get. As a first step, I would strongly consider trying to work with a donor crank instead of starting from scratch. Obviously v4 cranks arent that common, but can you use part of a v8 crank? Crank design is an epically huge job.
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I see, so it would be more efficient to use a inline vs a vtwin. The only big issue is the crankshaft and crankcase housing.
 
TwinThumpers said:
Making a crankshaft requires a milling/CNC machine. My college would never let me use their $30,000 machine for my own personal use. So like other said I should find a crankshaft already made in production. Tie rods and pistons are the easy part. However I can't just weld two hyosung cranks together since they need to be properly balanced or we would get torsion forces that would rip the engine apart.
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You could weld safely weld the ends of the cranks together (wrt balance anyway). You don't start to run into serious balance issues until you start relocating the support points (eg if you wanted to get the engines closer together and wanted to eliminate one of the previously outboard bearings to make a smaller package).
 
TwinThumpers said:
I see, so it would be more efficient to use a inline vs a vtwin. The only big issue is the crankshaft and crankcase housing.
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And maybe camshafts. It depends what firing timing you want. And connecting timing between the engines. And a transmission that handles double the power. And. . . .
 
^ both of the above did it the easy way and tied the output together instead of sharing a common crank. Mustie1 built a moped that way. It's pretty cool. I am sure at some point people will post the bike with armfuls of chainsaw motors. Tied output again.

OP, this kind of project is a fun design experiment to solidify 3d cad in your mind and/or show to potential employers. The cost for that is just a lot of time. When you try to bring it into the real world is when the costs are going to go full retard.
 
If you want nice project why not take an ST1100 or ST1300 V4 motor and start from there. There are lots of motors around dirt cheap and they are overbuilt for long term durability and virtually bulletproof.
 
To the original poster: How much experience do you have taking apart and putting together normal production engines? Have you taken one completely apart, put it back together again, and got it running to a driveable condition?
 
TwinThumpers said:
Making a crankshaft requires a milling/CNC machine. My college would never let me use their $30,000 machine for my own personal use. So like other said I should find a crankshaft already made in production. Tie rods and pistons are the easy part. However I can't just weld two hyosung cranks together since they need to be properly balanced or we would get torsion forces that would rip the engine apart.
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LOL, a 30,000 dollar machine today is considered garbage, and shops that have one likely cannot make a crankshaft (unless you're a hobbyist and have OOODLES of creative time on your hands in your hobby shop). You need a half million dollar CNC multiaxis mill/turn, that likely has 50-100k in tooling in it, with a highly skilled and costly cnc programmer to program/run it, and a shop that likely charges $100 an hour or more to do such a custom project, at Id say no less than 60 hours. And of course, a solid model, that is accurate, and engineered so you're not wasting the shops time with drawings on a napkin.

You're also going to need to grind it after heat treating, so another shop is going to have to charge you similar for their time.

This project isn't for the light hearted. It's done by people in the industry that know what they are doing.

Point being, I don't think you can find a compatible crank already made (god bless if you find something), you're gonna have to make one! Thats a lot of money for one component of your fancy idea! Good luck!
 
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