modifying the guts of your engine?

G

Genisisonyx29

New Member
okay so one of my dads bestfriend rebuilds indians from scratch and i must say he does an amazing job at it! anything i need help with on my bike he does it for free if he has the extra parts. the other day he had told me that he could balance out my cranks, lighten up my flywheel and bore out my cylinder wall and piston. my question is how much of an increase will i see on my china girl and will it be safe for the engine.
 
Balancing the crank will help the engine last longer, since you are talking flywheels that helps on four strokes a lot. You may be able to bore some cylinders but in the two strokes the chrome on the cylinder is too thin.
 
Concur. You can't bore a Chinese 2 stroke. The aluminum cylinder has a thin chrome liner that if bored out will put steel piston rings against soft aluminum. Don't do it. Even if you did you won't find oversized pistons or rings to fit.

As for balancing, there is a lot of information here on that subject. Pages and pages of pros and cons and ways to do it correctly. Use the search feature, keyword 'crank balancing' and you'll have plenty to read. I'm sure your Dad's friend is an accomplished motorcycle mechanic but you have to remember, these aren't motorcycles. They are not Harleys or Indians, or Hondas or BMWs. They're very inexpensive little 2 stroke engines meant as a hobby/novelty and they aren't built like the quality engines I mentioned.

There are ways to get a little more performance from them but increasing the cylinder diameter isn't one of them.

Tom
 
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2door is right, those of us old enough to remember the blunder GM made with the Vega engine knows the results. A aluminum cylinder will wear like crazy, all the early Vegas smoked. GM fixed the problem starting with the 75 model with steel sleeves but the image of the Vega was tarnished dooming the model. Too bad to because the steel sleeve engine was a good one.
 
I wondered about sleeving a chinagirl and boring it out. Custom oversize pistons and rings are available...but the lack of quality stopped me. I don't think they would hold up under a bored and ported cylinder without some major rebuilding. I'm too lazy.
 
If you first find a compatible piston and then bore out the cylinder, taking into account the thickness of the Nikasil plating after the re-plating is done, you can overbore a chinagirl cylinder. There are many cylinder plating shops around.
L.A. Sleeve Co. is the first place that comes to mind.
Do bear in mind that this is rather expensive and simply adapting a moped piston and cylinder would be cheaper, faster and quite possible easier in the long run; and has been done many times before by other members.
Check out foureasy's thread:
http://motorbicycling.com/showthread.php?t=14204&highlight=4easy
 
Yes, there are alternatives. What I didn't want to see was this young man allowing someone who might not be familiar with the Chinese 2 stroke to ruin his engine. My answer was a simplification and addressed his question. "Will it be safe for my engine?" This tells me that he is concerned with cost and the life of his investment.

When looking at the alternatives, better exhaust, proper tuning and gearing there are much less costly/exotic ways of gaining a little power that would not require expensive machine work or re-plating. Just putting the OP's question in persepctive, guys.

Tom
 
I meant to my bestfriends dad. anyways ya ur right about the cyclinder wall. BUT I found foreasy's thread on his 2 stroke puch hybrid. that thing is so bad @$$! I think I might invest in something like that later down the road. I have another question though, I have the port matched billet intake from piratecycles, but my exhaust isn't port matched. what cab I use to port match the exhaust port? my dad wont help me with it because he doesn't believe it will make a difference but I know it will.
 
Have your dad's friend balance the crank, have him inspect/replace the bearings with better quality, and have him inspect the casting to make sure there aren't any flaws that need to be cleaned up while the motor is apart. (Make sure he knows the QC on these motors is dicey at best and he should inspect for poorly finished parts!) Have him replace all the studs in the motor with higher quality studs when he rebuilds, that should give you a nice improvement in smoothness and reliability compared to running the motor right out of the box. None of these parts will cost you very much, if you have a qualified mechanic willing to do the work for you I say go for it....
As you have learned already, you can't really bore the cylinders out on the china girls without getting into expensive plating. Best to either run them stock or perhaps tryout a moped cylinder....
 
I use a die grinder with a tear drop shaped carbide rasp to shape up parts, a word of caution, be careful! Carbide will eat up aluminum fast.
 
First make a template of the exhaust port by cutting a suitable piece of sturdy cardstock or a piece of cereal box to match the cylinder exhaust port. You must keep the bolt holes fitting tightly to the bolts or studs so the template cannot wiggle around. Do not bolt it down, it must fit tightly all by itself. Use an exacto knife to cut the port hole in the cardstock, using the port itself to guide the blade.

Now use a permamant marker to color in the exhaust pipe flange.

Put some bolts through the exhaust pipe flange and then put the template onto the bolts and flange. Here is where it gets tricky. The bolts fit loosely into the flange holes so the template can wiggle around. You gotta figure out exactly how the flange will be resting up against the cylinder and place the template in this exact spot.
Use a couple of nuts to hold the template in place.
Use a scribe or the exacto knife blade tip to trace the template into ink you already put onto the flange. It will scratch through the ink leaving an easily visible line on the flange.
Remove the template and use a Dremel tool or similar with a good, sharp carbide burr and carefully carve the exhaust pipe to the line you scribed.
Be careful as most of the time you will end up cutting into the weld bead that attaches the flange to the pipe. You can cut into it a little bit, but go too far and it will be seriously weakened and could fail when you are riding down the road.

The other alternative is to fabricate an aluminum spacer, about 3/4" to 1" thick with the cylinder port matched on one side and the exhaust pipe flange matched on the other side. This method is very time consuming though.
 
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