China Girl Motorized Bicyle Build

[Tohri]

Re: China Girl Motor Build

My experience is: Go out to autozone, buy some decent gasket material, and make a proper gasket. They shouldn't 'Squish out the sides' They should make a nice, solid seal.

They sell the gasket paper in different thicknesses too, so you're aware.

 

[biknut]

Re: China Girl Motor Build

My experience is: Go out to autozone, buy some decent gasket material, and make a proper gasket. They shouldn't 'Squish out the sides' They should make a nice, solid seal.

They sell the gasket paper in different thicknesses too, so you're aware.

Yeah that's just what I'm going to do. One good thing about these thick bs gaskets I bought is they will make a nice pattern for making my own.

 

[Tohri]

Re: China Girl Motor Build

I know I've jumped ship to the greener pastures of the moped world (Seriously, when is Airsal going to make a nikasil lined, reed inducted, boost ported china girl cylinder kit?)

But. having learned much from the wizened moped gurus, Don't ignore even a 1MM difference in transfer port height, it can make or break a motor. Intake and exhaust ports can go up or down a bit without making a huge shange in how the bike runs, but transfers are crucial.
After that, boost porting with windows REALLY need to be cut in these motors. That and properly balanced cranks.

 

[biknut]

Re: China Girl Motor Build

I know I've jumped ship to the greener pastures of the moped world (Seriously, when is Airsal going to make a nikasil lined, reed inducted, boost ported china girl cylinder kit?)

But. having learned much from the wizened moped gurus, Don't ignore even a 1MM difference in transfer port height, it can make or break a motor. Intake and exhaust ports can go up or down a bit without making a huge shange in how the bike runs, but transfers are crucial.
After that, boost porting with windows REALLY need to be cut in these motors. That and properly balanced cranks.

Funny you should mention this. Today I rode about 35 miles. I was expecting my base gasket to start leaking any minute, but it never did. The whole gasket has just about squeezed out. I figure the cylinder has to be a little lower now. My motor was running like a raped chicken all day lol.

 

[biknut]

Re: China Girl Motor Build

The Cadillac is really running good now, but I may not be done fixing it yet. Yesterday on our 35 mille ride it started leaking oil from the head gasket. The sealing surfaces look good, and I used a new gasket.

What I think may have happened is, it's possible that when the broken rod bearing piece stuck in the head, it may have warpped the head. The piston ringland was crushed too.

In addition to that, I mentioned in an earlier post that the base gasket is squeezing out too. It's not leaking though, but might start. This was caused by a crappy gasket one of the webb stores sold me. I can't even remember which store, but it doesn't really matter, because if you buy some tomorrow they'll probably be different ones.

What I did today was carefully remove the head without disturbing the cylinder, and I applied some high temp RTV gasket maker to both sides of the aluminum gasket, and bolted it back down to 145 in lb. I'm letting it cure overnight.

Lets assume it fixed. If that's the case, It's running better than ever. Throttle response is the best I've felt yet, on any of the 5 motors I've sampled so far.

The short header on the SBP pipe doesn't give it much bottom end, but about 20 mph it starts coming to life. Giving it full throttle in the mid range causes a low pitched growl to escape from the intake. It sounds like a motorcycle, and pulls like a little moped. Instead of just idle, and full throttle, there seems to be a lot of throttle.

Advancing the magnito rotor was a nice improvment. Don't over do it though. I wouldn't go more than the width of the key max.

When I changed the cylinder I checked all the ones I had and used the one with the best ports. Each one was a little different.

The crude crank balance I did was well worth the effort. This motor is smoother at higher speeds than low speeds. i think that's backwards from stock.

It's hard to say exactly what effect cutting the piston had, but one thing I know, it didn't hurt anything based on how great it's running. It's something I always do, from now on.

I'll be suprised if this motor won't do 40 mph, and be smooth doing it.

 

[headtrama]

Re: China Girl Motor Build

Auto parts stores sell some stuff called copper coat. It is for spraying on head gaskets It looks like copper paint .I have been using it on my head gaskets with good results with high compression heads .I haven't blown a head gasket yet it is also a good idea to re torq the head every now and then .

 

[maintenancenazi]

Re: China Girl Motor Build

Room Temperature Vulcanization silicon, was never intended to be used as an augmentation for a head gasket.

 

[biknut]

Re: China Girl Motor Build

Auto parts stores sell some stuff called copper coat. It is for spraying on head gaskets It looks like copper paint .I have been using it on my head gaskets with good results with high compression heads .I haven't blown a head gasket yet it is also a good idea to re torq the head every now and then .

Thanks I'll keep that in in mind.

 

[biknut]

Re: China Girl Motor Build

Room Temperature Vulcanization silicon, was never intended to be used as an augmentation for a head gasket.

I agree, but my friend Coaster had the same problem, and this stuff worked for him so I thought I'd give it a try. This is the copper colored stuff, and good for 400 degrees.

 

[mapbike]

Re: China Girl Motor Build

No one should be concerned about using Copper Coat on the China Girl head gaskets.

Been using the Permatex Brand Copper Coat on head gaskets for 25+ years from lawn mower engines to big block jet boat engines, it is an excellent gasket dope for steel or alum. non-coated head gaskets and just about any other type of gasket as well.

Very good stuff.

Something else that works real well as a gasket coating is a couple of good coats of plain ole silver Krylon spray paint, let it dry completely and it works good because the main component in silver paint is Aluminium dust, thats what makes it silver.

Peace, map

 

[biknut]

Re: China Girl Motor Build

Looks like it's not going to leak. I put 20 miles on it tonight. It's not leaking. I wasn't riding it like I stole, but if it only woulld go about 33 mph, then I was riding it like I stole it. It's got about 80 miles on the cylinder and piston now.

 

[biknut]

Re: China Girl Motor Build

This MM Gen II head really makes a lot of compression. With a 36T sprocket getting the motor started takes real effort. I had to employ every trick I could think of just to get the clutch not to slip. I have to really pump the peddles hard as I let the clutch out, or it slows down so much it goes below starting speed. Starting with a hot motor takes concentration. If it doesn't start right away, you can forget about peddling very far with the motor turning over. You won't last 1 yard. Luckily it usually starts right away unless it drags drags down to a stop first. I think most of the time I have too double clutch it, and peddle up to a higher speed on the second try to get it started cold.

 

[biknut]

Re: China Girl Motor Build

More trouble. Yesterday morning I decided to lube my pinion gear. I was putting grease on the gear and turning the motor with a screwdriver, and at TDC it locked. The piston was hitting the head. I guess after the base gasket squeezed out enough, my tight squish was too tight.

I pulled the cylinder and replaced the base gasket with a better one. I guess it's good I did because my new small end bearing accidentally fell out. A close look revealed a nick in one of the rollers. I don't know how it got there. Maybe there was a piece of metal left in there from the first failure? Anyway I installed a new one, and put it all back together.

Now it's running good again. I started trying to tune it. I started with a 68 jet. It's got bad 4 stroking, starting about 26 mph. I changed to a 66. Still bad 4 stroking, and really poor mileage. About 70 mpg. I changed to a 65. Still 2 stroking, but slightly less. I changed to a 64. Much better high speed. When it gets totally warmed up it only slightly 4 strokes. I changed the spark plug to a B7HS from B6HS, because the tuning is getting closer, and it's starting to run hotter. It gets up to about 35 mph now with only a couple 4 strokes along the way.

I think a 63, or 62. will unleash the beast.

 

[biknut]

Re: China Girl Motor Build

 

[biknut]

Re: China Girl Motor Build

 

[mapbike]

Re: China Girl Motor Build

You have a real nice looking bike there biknut, glad to hear you're getting her tuned up real nice, under a load it shouldn't 4 stroke at all and if it does you may want to lean her up just a tad bit more and she'll run even better for ya, mine only 4 strokes when their under a very lite to no load, but under any acceleration there isn't any 4 stroking just a good solid pull up to max rpm's I'm running a 36T on one, a 34T on another and my favorite bike has a 32T on it, it cruises real nice and still pulls my 205lb butt that trying to get back to 185lbs up the hills real good.

once agian, very nice bike, wish I could keep mine all nice clean and shiny like that....

Peace, map

 

[biknut]

Re: China Girl Motor Build

Thanks mapbike,

I think it's a little rich for 60 degree riding, but when it gets to 100 it's probably about right now. I'll try a 63 jet next for the sake of science. I can't understand why it needs such a small jet. i guess it has something to do with the MM head.

After it warms up all the way it has good power all the way through the powerband. That's one thing I like about these china girl motors. They have very broad powerbands, which is what you need with only one gear.


for my next trick, I'm going to install my DAX carb, but I'll wait a week or two.

 

[mapbike]

Re: China Girl Motor Build

Thanks mapbike,

I think it's a little rich for 60 degree riding, but when it gets to 100 it's probably about right now. I'll try a 63 jet next for the sake of science. I can't understand why it needs such a small jet. i guess it has something to do with the MM head.

After it warms up all the way it has good power all the way through the powerband. That's one thing I like about these china girl motors. They have very broad powerbands, which is what you need with only one gear.


for my next trick, I'm going to install my DAX carb, but I'll wait a week or two.

I have one of the RT carbs on a bike and I love it, that engine starts much quicker than it did with the NT's it also seem to be a bit less cold natured, I can't see any gain in top end speed but it does respond well and the engine pulls really good, if you have the same result I've had with the RT you'll like it. I know Tom has said he really likes his, some people aren't that fond of the way the choke works on it but I haven't had a single issue, as soon as my engine fires off I just romp the throttle back, choke goes off and she purrs like she should, very nice little carbs.


Map

 

[biknut]

Re: China Girl Motor Build

So I'm riding around today trying to get used to the 64 jet. It still 4 strokes on top end till it gets good and hot, but at a higher speed. It still starts pretty fast with no choke, and idles cold. and it's still getting poor gas mileage. Top speed so far is 39.8 mph

So then I decided it wouldn't mind a 62 jet.

It's a little harder to start. No choke @ 70 degrees. It still 4 strokes cold, but clears out after about 1 mile of running. Throttle response is good. It hit a new record, for it, 42.2 mph. That was after about 2 miles of warm up. After that I cruised at 35 and had to keep throttling back to keep from going faster. Uphill against the wind slowed it down to about 33.

The NGK B7HS is barely hot enough for this temperature, but it runs pretty good going fast. The idle tends to load up.

It's possible it might like a 61 or even a 60 jet. I don't understand why it likes such a small jet. And why is it using so much gas. When I just got back from this trip it looks like it used less gas. It still has a lot in there. Usually everytime I've looked, it was almost empty. I expect about 60 miles per tank.

I used to get that with a 68 jet, but overall now, with just a MM head, SBP pipe, and cut piston, it feels better and faster, than any of my other china girls. Still with just a NT carb with stock air filter.

 

[mapbike]

Re: China Girl Motor Build

Keep on tinkering and working with that carb. sounds like you're on the right track, just watch the plug color, don't want to get her to lean, but if she is still 4 stroking a bit I'd say you aren't lean.

Glad she running good for ya.....always makes us feel good when they're jinning like that.

Map