The Good, the Bad and the Ugly.

I have been a mechanic for about 25 years, In fact I started in my Fathers shop when I was probably 12 years old.
I have played with all sorts of motors, But none quite as poorly assembled as a China Girl.
But I have a soft spot for them, mostly because of the price.
This is my 5th Motor, and with in about 20 minutes of my wife returning from town with it today I had it stripped.
The point of this thread is to show others that if you intend buying one of these motors, I advise you do the same.

The Good.
This motor came with a center fire head, which although has lower compression gives a better burn, has more cooling capacity and will generally give better torque than the angle fire.
It has a 40mm stroke, again giving better torque and a slight increase in capacity.
The kit came with a better plug cap, not the one that falls apart!
And this motor did not come with the expected metal shavings and Chinese soil that 2 of my other motors had inside.
Everything came greased and oiled, which again was lucky.
It also came with the clutch removal tool, which not all kits do.
The exhaust is of reasonable quality compared to one of the others I received.
It has needle rollers in the big end, and all of the bearings look to be reasonable.
The Exhaust port flange is of the larger shape allowing a better match to a larger pipe.
And the motor has 8mm head studs opposed to 6mm which one of my motors came with.
The Tank is not dented!
The rag joint bolts are 8.8.

The Bad.
This motor came with a GT5 style piston and rod, this is mostly a hassle as the piston is hard to get in OZ.
Although not as bad as some the crank seals where not straight.
The crank has not been polished where the seals run and will surely wear those seals in a short period.
Although the barrel was cast to take a 40mm inlet it does not have a 40mm stud spacing?
The piston was installed backwards, I'm sure the arrow is meant to point to the exhaust port.
The head nuts were not much more than hand tight, either were some of the studs.
Spring washers under the head nuts, never seen that on any other motor.
The clutch had been over greased, contaminating the parts that are meant to be dry.
It has the usual damaged Phillips head screws, only one of which was tight enough to warrant damage?
The crank is of the narrow (non counterweight) variety, leaving way to much void in the cases, and lousy primary compression.
One of the main bearings came out with the crank instead of staying in the cases, giving the impression it must be a loose fit.
The rings are of the cheaper variety, the better ones are lightly grooved to wear in faster.
Most of the woodruff keys seem a little loose, much better if they are a snug fit to the crank at least.
But the worst is going in the Ugly column.

The Ugly.
The head's mating surface is damaged, this does not worry me as I planed to modify the head, still it probably would have caused a leak.
But the barrel, will be sent back!
It has pitting in the bore, and porosity bubbles on the mating surface, so if the head didn't cause a leak this would have surely.
The crank has several 'marks' as though its been 'adjusted' with a cold chisel?
And the sharp edge on the step down to the clutch taper would surely damage the seal on assembly.
And the mag was not centered.

Previous motors were worse than this one and all had 'issues'.
I'm sure there are better ones, but if you buy an Ebay motor kit, think seriously about pulling it apart before you run it.
I can only fit 5 photos to this page, but there are more ugly things I could have put photos up of.

Thank's MBR I did notice the piston was the right way a bit later on, that could be confusing for some (ME).
It's the only piston out of seven with the arrow going the wrong way?
I don't know that these are good Quality spring washers, so I might leave them out.
I have contacted the seller over the barrel, last motor I got from them had a flat spot on the clutch flywheel teeth, and they gave me a $30 refund, so hopping for the same.
I'm going to check my port timing and squish, and see if I can deck the barrel, it may still be usable, if not with a 40mm crank then with a 38mm crank.
Last night I matched the transfers in the cases to the barrel, and opened and lapped the mouth out to 35mm to suit my frame.
Given the narrow crank, I'm planning to stuff the cases with a bit of old alloy street sign, which I have already done to two motors, and I'll be making an extra set this time for another older motor that I have in bits.
But first I have to get this bearing of the crank, and there is no room for a puller and two screw drivers didn't seem to want to budge it.
I have made a template for the case matching, and wanting to get my primary compression up I only take what I need to out of the cases, to get a nice smooth match.
I still plan to take a little more out of the rear of the port, to match better the opening in the barrel skirt.

With the right two screwdrivers, I get the bearing off the crank, and give the sealing surfaces a polish with 600.
I also give the sharp edge to the clutch tapper a carful filing with a needle file.

I got a little more done this arvo.
Happy with the porting of the cases, I cleaned them stuck them in the oven for 10 mins and fitted the new main bearings.
I then set up the motor in my 'engine stand' and hooked up my $2 'calibrator'
(kids protractor).
The port timing of this motor aint to bad standard, it could do with a little bit off the piston skirt to get 60 deg on the inlet (currently 55 deg), but other wise for it's intended use I don't plan to change things.
The exhaust opens at 105 and the ramped transfers at 120.
I gave the head a polish and a narrow (2mm) squish band.
Now I'll bolt it all together without head gasket, and do a squish test, to see how much I can deck the jug to give a .7mm squish.

Without a head gasket I get spot on 1mm squish.
So with a standard head gasket measuring .6mm, I figure I'll take .8mm off the barrel and tension the head down and recheck.
I'm hopping that .8mm is enough to remove the bubbles in the mating surface!

With my trusty belt sander, I carefully remove the .8mm evenly from the barrel, It hasn't removed all of the bubbles, but does look as though it may seal.
I then give it a polish with some wet and dry paper and reinstall.
This time, again without headgasket, I get .3mm, lovely.
I realize that such a narrow squish band is not likely to do much, but getting the squish right now will allow me to install an aftermarket head later if I wish, and it seems the right thing to do.
Next I will give the barrels fins a tidy, for this I start with a flap disc on the angle grinder and then with a 'smooth' file.
Although I'm happy with my port timing I will still widen and polish the exhaust port, widen and 'texture' the inlet, and tidy up the transfer ports.
My Boss is away, and it's been raining here for days and doesn't look like stopping, so project time!
Of which I have many!
This motor was suppose to be going on the 'Twin Carb Soft tail' but does not have the needed wide inlet stud spacing for the manifold that I made, and I'm still trying to figure out if it's going to swap some parts with another motor to make it all work, or if I should just modify my inlet manifold? I'm curious to see how well balanced this crank is before I make any decisions.
I was thinking to swap cases with the Soft tail's motor and ?????

With a Dremel.
I'll have to do my new head soon, and will post up some picks as I Go.
Here is a finished head, Nearly finished and a raw head.
And the tools I use.
First I scribe a line to where I want my squish band to go.
And very gently, guess my squish angle and cut to about .5mm off the line.
Next using the mini flap disc, which are better for the job once there worn in a little.
I also remove any extra thread from the sparkplug hole, the middle head has had extra taken out of the threads to run a 3 prong plug.
Then I lap the squish in using wet and dry on the crown of an old piston.
If you don't need the piston again then the sand paper can be glued to the piston crown.
Next, the impregnated rubber polishing wheel, a bit of wet and dry and then the stitched buff.

Which head are you using?
Angle fire or straight fire?
The straight fire comes with no squish band, the center head has been shaved considerably and has a wider squish, the narrow squish band probably does little other than help me set up the motors ideal piston head clearance, and removes sharp edges.
In my opinion the angle fire will give too much compression for average motor if set up 'properly'.
And I take a fair bit out of the dome on an angle fire to lower the compression, as they have inadequate cooling for high comp' in the tropics.

Just through up a pic of my angle fire with decomp valve in my last post.
This was still getting around 160 Psi, after reshaping, and decomp valve was added as it was bending my cranks trying to start it through my shift kit.
My other angle fire is much the same minus decomp valve, and with correct squish it still pings above 8000.

Yes I have been meaning to try an 8.
I think it's probably to do with the initial advance I have from the crank I'm using.
Plus the Mid summer temp's.
I really want an aftermarket CDI for it with a bit of top end retard, as the extra advance down low has this motor pulling well, but would like to build it my self as postage to OZ starts to make things a little pricey.
However If I could get one for a good price here in OZ I'd be happy to pay a pro.
I've been meaning to make up a shopping list for all the things I want that I can only get from the states, It would be good if I could work out a combined postage somehow.

There are at least two different 'standard' barrels for these motors.
The 'larger' one is from a 40mm stroke motor, the other from the 38.
The larger one is superior in every way.
It has more metal around the ports, it often comes with a ramped transfer port, has much more fin area, but is generally about the same height. Around 70mm somewhere.
If your running a 38mm stroke, you probably want the barrel to be closer to 68.5mm in my experience.
I havn't quite finished with this transfer port, but I see this as one of the most essential mods to getting these motors to flow properly, You want to do identical port work to both transfers, and make sure you get the flow pointing towards the intake. A transfer port should also tapper in, so I take a little out of the transfer inlets whilst matching as smoothly as possible to the opened up cases.

That's what I need.
Still for the price + postage to OZ.
I'm thinking of building my own as I have a little experience with electronic circuits,
And I probably want 3 of them.
I have read through the Build your own pages, and would love to hear from someone in OZ that has built one, To give some idea of the best place to source the right bits.