My 66cc Stinger Motor

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Ducati250Single

Ducati250Single

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Dec 12, 2015
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I bought a 66cc Stinger motor kit over 2 years ago. I've never had a prob!em with it, other than throwing the drive chain on my maiden ride, (my fault for not having the rear wheel aligned, it was a little cockeyed), maybe I got a good kit, or what I would like to think, was the measures I took before ever mounting it to my bike. I took the motor completely apart, making sure everything looked right. One piston ring had almost zero end gap, so I filed the gap to .014", (when in the cylinder of course, ha-ha!). I made sure there were no vacuum leaks where the carb bolts to the manifold, I set the float height, (which was WAY too high). I also made sure I sealed the wires going into the motor. I lubed the piston, rings and cylinder, as well as the wrist pin bearing. I also squirten a little oil on the crank end of the rod. I also sanded the head lightly, (sandpaper taped down on a peice of glass), to make sure the head was flat. If I hadn't done all this to my motor before running it, I know for sure it would have had a vacuum leak at the carb, causing it to run lean and idle poorly, the ring with next to no end gap would have been a major problem and the high float level would have made it run crappy, SO, what happened instead was a motor that fired right up, ran way better than I ever imagined it would and idled perfectly. I realize not everyone has the desire to take their brand new motor apart, but these motors are so simple, you can take them apart and put them back together in a very, very short time. Another recommendation I would have is to use a good 2 stroke oil for your premix, and by good I don't mean you should be buying the most expensive synthetic oil you can find, oil is no place to try and save a few bucks. I run Pennzoil, and absolutely no issues with carbon buildup on the piston crown or the combustion chamber, or exhaust port. Anther thing I did was to match the transfer ports in the cylinder to the ones in the case. I had to remove a lot of material to make the case ports line up, but its well worth the effort, and yes, you must take your motor completely apart to do this. I took my motor out of my bike, tore it down, ground the ports, put it back together and had it back in my bike and was riding it in about 4 or5 hours, and I took several breaks. My motor runs strong enough now to make spoke breakage an issue...but that's another story.
 
2door

2door

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There are differning opinions as to taking a new engine apart before running it.

One school of thought agrees with you. There have been too many reports of trash found inside a new engine, especially in the crankcase, that would have certainly spelled trouble had it not been found and removed. Metal shavings, spare parts like piston wrist pin clips or piston ring alignment pins have been found..

The opposition to this is the fact that some vendors will not honor a warranty if they find an engine that has been disassembled. The buyer is stuck with whatever they get usually with no recourse. If the buyer is concerned about warranty replacement he/she should give thought to this before tearing their new engine down.

Having worked with a vendor and seeing some of the returned engines I can see why a seller might not want to replace and engine when it was apparent that the buyer didn't know what they were doing either when taking it apart or reassembling it.

Warranty being the issue here it will be the buyers decision to 'chance it' and hope for the best or ignore any warranty claim and assure the inside of their engine is ready for the road.

As for your pre-run procedures, you did everything right and your accrued miles is testament. The only addition I could offer is to check the 'flatness' of the intake and exhaust manifold flanges. They are usually warped from the welding process and require some sanding or grinding to get a good gasket sealing surface.

Thanks for your informative post. By the way; where in Illinois are you? Do you know about the 'Mid-West' cruise coming up in June. We'd like to see you there.

Tom
 
Ducati250Single

Ducati250Single

Member
Dec 12, 2015
43
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Illinois
I did the exhaust and intake sanding procedure on my sanding station shortly after getting my bike going.
I can definitely see why a vender wouldn't want to warrantee a motor after it had been taken apart, and I don't blame them, I wouldn't either, and I didn't intend to lead anyone astray.
No John, I didn't know about the ride you mentioned. I live near Kankakee, is this ride near me? Thanks for the heads up!
 
a_dam

a_dam

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Feb 21, 2009
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I live near Kankakee
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Kankakee? That sounds like a sore on the inside of your mouth.

How you doin', Ducati250Single? Maybe we'll run into each other in 2016 when biking weather returns. I will have to check out that Midwest cruise 2door mentioned.

I seems a shame that someone should do an overhaul on a brand new engine, but from following this forum, if I ever get a Chinagirl its getting closely inspected.
 
crassius

crassius

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Sep 30, 2012
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my kits come with top end apart - I oil bottom and inspect top before I sell to customer, but only once did I find a port that hadn't been properly machined - I do find a lot of heads with a ding near the plug hole that won't run unless I redo the threads there
 
Ducati250Single

Ducati250Single

Member
Dec 12, 2015
43
6
8
Illinois
a_dam said:
Kankakee? That sounds like a sore on the inside of your mouth.

How you doin', Ducati250Single? Maybe we'll run into each other in 2016 when biking weather returns. I will have to check out that Midwest cruise 2door mentioned.

I seems a shame that someone should do an overhaul on a brand new engine, but from following this forum, if I ever get a Chinagirl its getting closely inspected.
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Hey a-dam , i'm actually from Grant Park, that's only 7 miles.
 
Ducati250Single

Ducati250Single

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Dec 12, 2015
43
6
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Illinois
crassius said:
my kits come with top end apart - I oil bottom and inspect top before I sell to customer, but only once did I find a port that hadn't been properly machined - I do find a lot of heads with a ding near the plug hole that won't run unless I redo the threads there
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Hey crassius, sounds like you've sold quite a few kits. I'm kinda thinking of buying another one, I have a few other bikes I'd like to put a motor on. Why do your motors come with the top end off?
 
a_dam

a_dam

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Ducati250Single said:
Hey a-dam , i'm actually from Grant Park, that's only 7 miles.
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Yeah. For us living out in the sticks, you can't get much closer - practically next door neighbors! I'm only 3 miles from Minne Monesse.

I go through town a few times a year - stopping at Trax for pizza and beer.

(sounds like lyrics to a country song)
 
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dbledsoe

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Apr 22, 2015
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I wonder if there is enough chrome in the chrome lined China girl engine cylinder to survive installing torque plates top and bottom of the cylinder, with studs torqued to spec to load the cylinder as it would be loaded when torqued in place on the engine, then hone the cylinder to perfect roundness under torque? The idea being that a cylinder may be round when initially bored but not so much when actually torqued in place on the engine block, especially with an aluminum chrome lined cylinder that does not have the benefit of an iron sleeve to mitigate torque compression distortion.

We did that when building race motors in my Harley drag racing days. It is amazing how much a cylinder bore upsets/deflects/distorts from round, top to bottom, when actually torqued in place on the engine, and what we measured was with the added strength benefit of an iron cylinder liner heat pressed into an aluminum cylinder, something the China girl cylinder does not enjoy. We used torque plates too when boring/honing small and big block Chevy race motors.

Maybe I am overthinking gas bike engine building... scratg
 
2door

2door

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Might be "overthinking" just a bit when you consider manufacturing tolerances and the lack of quality control that goes into the little Chinese 2 stroke. They were never meant to be 'race engines' or intended to be modified to the extent that a lot of guys do to them.

Nevertheless there are power gains to be had if the builder wants to invest the time and money to get the most out of them. However, longevity starts to become a factor. As in any motorsport, race/high performance engines are not expected to last as long as the ones designed for your daily driver. Some might argue that a NASCAR engine is built to run hard for a lot longer than a drag race engine but is 500 miles really all you'd want from an engine that needs to get you to work, every day, for years? Same for the high dollar Indy engines. You can bet none of them would last for 100 thousand, or even 50 thousand miles before they would need extensive rebuild work.

As for honing the plated cylinder; there is a member here, Davezilla, who advocates honing, sans the torque plates, but just enough to burnish, or slightly rough up the plating. I personally have taken the shine off of a new cylinder wall with an abrasive pad just to see if I could see any difference or advantage. It's not easy to tell when you consider the power output differences in these engines even in a stock configuration. My experiment proved inconclusive.

My feeling is that you will see bigger performance gains with proper carburetor tuning, exhaust flow improvements and attention to ignition timing (which seems to be all over the chart from the factories) and port matching and attention to rough casting in the intake and exhaust ports.

Crankshaft balancing is another area where there's room for improvement over stock.

It all depends on what you expect from a motorized bicycle. Racing, where you will not see a long lived engine? Or a dependable, reliable bike that will get you around at or near the speeds that most bicycles are made to be ridden? It's a trade off, to be sure.

Tom
 
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dbledsoe

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Apr 22, 2015
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Tom,

I agree with everything you said. Lots of power to be gained in other areas in more need of attention. I was simply wondering aloud because so many pics I see of CG engines torn down often show a lot of blow by on the piston below the rings.

Don
 
2door

2door

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dbledsoe said:
Tom,

I agree with everything you said. Lots of power to be gained in other areas in more need of attention. I was simply wondering aloud because so many pics I see of CG engines torn down often show a lot of blow by on the piston below the rings.

Don
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Don,
I too have seen the evidence of blow-by on some engines. I have to feel that part of the problem is either improper break in procedures or abuse of the little engine.

When I say, "proper break-in" to me that means not babying an engine and never giving it a chance to run hard during those first few important miles. Heavy oil content, and an engine that isn't allowed to reach operating temperature can, and will, result in piston rings that don't seal well and will lead to the blow-by we've both observed.

Of course I'll get arguments about this because break-in is a subject that will see opinions ranging from one end of the spectrum to the other. Whenever a soft appraoch to break in is advocated I usually fall back on the argument that you won't see a professional woodsman baby a brand new 2 stroke chain saw. They come out of the box and are put to work. No prolonged cool down periods, no running at partial throttle settings and no avoiding WOT.

Yes, I understand that comparing a CG to a quality chain saw engine isn't a precise analogy but I've seen the results of both methods of break-in, hard verses soft and I see more sign of blow-by in engines that were treated too kindly during their early hours.

This will probably ignite a firestorm and I didn't intend to hijack Ducati's thread. Sorry Ducati.

Tom
 
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dbledsoe

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Apr 22, 2015
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Tom,

You'll see no "argument" from me regarding your break in procedure, but I suspect I may get some regarding my experience, and please note, I am speaking from my experience of many years building engines for racing purposes.

Babying an engine is, from my experience, the worst thing one can do followed by over lubricating (a 2 stroke). When we refer to "breaking in" what is really being referred to is seating the rings (wearing them to the shape of the cylinder bore), which is not at all ideally round. One has to understand how rings are designed to work. Their spring tension against the cylinder wall is not what makes them seal, well maybe a little bit. Their sealing characteristics are dependent on compression gases, the fired fuel/air mixture upon ignition. The high pressure gas escapes between the piston and cylinder wall until it meets the first (top) ring. The high pressure gas forces the ring down until it forms a seal at the bottom of its travel between it and the piston. The high pressure gasses then find their way to the back side of the ring, building up pressure between the back side of the ring and the groove in the piston the ring sits in. Those high pressure gasses push/force the ring against the cylinder wall forming the seal. The second ring does the same for the gasses that blow by the first ring.

So what we want is for the ring to see enough friction to basically hone/conform itself to the cylinder wall diameter, a diameter that my not be round. So how best to push that mutual mating... Load the engine to max cylinder pressure to force the rings hard against the cylinder walls and force them to wear in to the shape of the cylinder. Over lubricating and light duty loading will not do that. Riding under light duty conditions simply prolongs the so-called break in period.

I break my engines in by finding the steepest hill I can and go up it at full throttle in order to put max load on the piston and press the ring hard against the cylinder wall. I use the same fuel/oil mix for break in as I do for normal running. If you want to enhance break in use a lousy non-detergent junk motor oil for the break in.

Don
 
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dbledsoe

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As a side note, we used to drill a series of very tiny holes around the circumference of the piston from the piston crown and into the first ring groove to force gas pressure down on to the top of the first ring, which then forced gas pressure to go behind the ring to press it tight against the cylinder wall. TRW negated the need for that by developing their L shaped ring designed to accomplish the same gas pressure ring thing.
 
2door

2door

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Absolutely no argument from me. For the very reasons you addressed above these little Chinese wonders won't respond well to a soft break-in. I have too many miles on my engines to feel that our suggested method is wrong.

To clarify, I do not abuse a new engine but then I don't do that to one that has lots of miles either. I don't hammer the throttle and hold it there for miles. I don't let one sit and idle for long periods either. Excess heat from overheating can do a lot of damage and increase wear. A little common sense applied will go a long way toward giving you an engine you can rely on and that will give you many miles of fun.

The only place we differ is in our choice of lubrication. I'm one of those strange folks who start with that infamous and controversial 100:1 mix. I start a new engine using it and as long as I own it it never sees anything but. And again, this is straying from Ducati's thread and the subject is well covered and discussed in the very old, '100:1 thread'.
http://motorbicycling.com/showthread.php?t=9850

Tom
 
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