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Rebuilding a 
Solo 210 c.c. Engine

By Greg Anderson, 
USPPA, AOPA, USHGA, USUA, EAA, and ASC.


Rebuilding a Solo 210 is an easy process. A process that any powered paragliding pilot with simple hand tools can accomplish within an hour or two. 

Editor note: parts may be purchased from Southern Skies and Mojos Gear. Southern Skies also offers rebuild service for those who feel this is more then they want to tackle.

Our example is an SD48 by Paratour which uses a Fresh Breeze prepared Solo 210 c.c. engine that produces 19 horsepower. Fresh Breeze designs the Solo 210 c.c. engine to maximize power output by using a tuned pipe, oversize cylinder head, and a Bing carburetor. The SD and Fresh Breeze paramotors are extremely powerful, very quiet, and when properly maintained, reliable. 

Unfortunately, any two-stroke engine can seize. And, all powered paragliding pilots should keep this in mind while flying paramotors and always have an LZ (landing zone) in glide distance. Paramotors are not certified aircraft; they are ultralight vehicles and do not carry an airworthy certificate. Remember this safety tip. 

To begin the process, you may want to consider performing an air leak test to determine the cause of the seizure. As you can see, the Bing carburetor has been removed and there is a small plug sealing off the intake side of the engine.
Let's move to the exhaust side of the engine. This air leak testing device can be purchased at most two-stroke engine shops (motorcycles, watercraft, or jet-ski). With this device, pump approximately six pounds of air pressure into the engine. The engine should hold the air for a minimum of two minutes. If the engine does not hold air; there was an air leak. Use soapy water to determine the location. Nice gloves…

A quick, in-the-field method to determine an engine seizure is to remove the exhaust pipe and look inside the cylinder. Carefully, take a screwdriver and gently push against the piston rings. If the two rings move freely, there is a good chance the engine has not seized. If they do not move freely…well, you may want to read on. 
It's apparent: the engine is seized, so let's get on with the rebuild. Paying your spouse wonderful compliments, perhaps some flowers, an expensive dinner out, and you too, can wear her dishwashing latex gloves. Seriously, latex gloves can protect your hands and provides a better grip on little nuts and bolts. A small application of WD-40 or penetrating oil on bolts will make their removal much easier.

Okay, so I could only get one pair of gloves. My neighbor and fellow PPG pilot is removing the back two bolts (you should see his knuckles). There are four bolts attaching the cylinder or barrel to the crankcase.
After all four bolts have been removed; you are ready to remove the cylinder. To make the process easier, apply two-stroke or penetrating oil into the cylinder via the intake and exhaust ports before removing. Carefully remove the cylinder from the crankcase. Turning the cylinder to the left and right and gently pulling down should do the trick. Someone had to take the pictures and you need gloves for that…ha.

As you can see in this photo, the "rings have become one with the piston." The engine severely overheated and seized. There are several reasons for an engine to overheat and seize: improperly mixed fuel and oil; incorrectly gapped rings; improperly jetted carburetor; an air leak. It is very clear that this engine will need a new piston and two rings: cost - $85. Not bored I hope…
To remove the piston from the piston rod, you will need to remove a small black piston pin retainer clip (in this photo, my left thumb is pointing to the location of one clip). A pair of needle nose pliers will do the trick. Remove the clip and the wrist pin should slide out. You may have to tap gently on the wrist pin, apply oil, or heat the piston with a hairdryer. Heating the piston will sometimes allow the wrist pin to slide out. Apply more oil if necessary. You will also find two washers; they are between the piston and piston rod. Don't lose them…unless you want to buy more.

The screwdriver is pointing to the exhaust side of the cylinder which is heavily scorned and should be replaced. The cost is approximately $275 (prices may vary). However, the cylinder can be honed, re-sealed and used again. That's another report.
Here is a photo of the new and old cylinder. Yes, you will have to remove the intake and exhaust manifolds. These two systems will be used on the new cylinder. Be sure to replace the gaskets for the intake and exhaust - cost: approximately $10.

The SD and Fresh Breeze Solo's require a modified tool to remove the exhaust adapter. Uh oh, now we're getting technical. Don't worry! Simply cut a few centimeters off a "perfectly good" hex wrench, and that should it. Again, replace the gaskets. Like those gloves?
Yes! You will have to remove the cylinder head. The cylinder head is still attached to the old cylinder or barrel. However, the intake and exhaust manifolds have already been installed on the new cylinder. You should become familiar with periodically removing the cylinder head. Why? Please keep scrolling…

This photo shows the cylinder head removed from the cylinder (there are six bolts connecting the head to the cylinder). Notice the build up of black carbon on the cylinder head? The spark plug is in the center and barely visible. Replace the spark plug (should be done every 10 hours).
So, what's next? With a Dremel and wire brush attachment, remove the carbon. Use low RPMs and apply even pressure to prevent deep scratches and gouges. A small application of carburetor cleaner speeds the process. Please be careful with flammable liquids.

All of the carbon has been removed. Some powered paragliding pilots will use 1500 grit sandpaper and smooth the aluminum head to a highly polished surface. Some experts believe this process increases the engine's performance.
Now you are ready to re-assembly the cylinder head to the cylinder or barrel. Most professional two-stroke mechanics prefer a compound called 1211 to seal metal and gasket surfaces. 1211 silicone liquid gasket can be purchased at most Kawasaki motorcycle dealerships. Paratour and Fresh Breeze do not use a head gasket on their Solo 210's, but sealant is still necessary. Apply a very thin coat and let it set for 24 hours before starting the engine. However, you can reassemble the head immediately after applying the 1211. If your Solo 210 engine uses a head gasket - REPLACE it. 

The next several photos and steps are crucial for engine longevity. I am holding one of the two rings in my fingers. Yes, you will have to remove the rings from the piston. Be careful, they break easily. Once removed, place one ring into the cylinder.
With the piston, carefully press or tap the ring (do only one) into the cylinder. Push the ring down approximately 0.5 inch. Using the piston will ensure the ring is level in the cylinder. Why are we doing this? Keep reading. At this point, have your buddy go and fetch some pizza and beer.

The ring has been placed in the cylinder. Got pizza yet? This process is called "gapping the rings." It is absolutely imperative that you properly gap the rings. Most experts recommend gapping the rings between 0.012 and 0.020 inches. Most rings come from the factory with a clearance of 0.005 to 0.009 inches (this is too narrow; and your engine will likely seize at high RPMs). For you metric types; gap the rings from 0.305mm to 0.508mm
To increase the ring gap; gently and slowly file the edges down. GO SLOWLY! File 4 - 5 times and re-measure the gap. File 4 -5 times and re-measure the gap. You may have to do this several times. That's okay…you have the time. Hey, what happened to those gloves?

Once properly gapped and at least three pieces of pizza consumed; you are ready to put things back together. The rings can only be placed on the piston one way. Look very carefully at the piston in the photo and you will see a little pin. Look at the edge of the ring and you will see an indention. Make sure the rings do not overlap this pin when placing the piston back into the cylinder. Piece of cake…right?
To connect the piston to the piston rod; you will need six items: wrist pin, needle bearings, two washers, and two clips.Apply two-stroke or penetrating oil to all parts. This will ensure easy assembly.

An easy way to reassemble the engine is to place the piston into the cylinder first (use oil). Be careful to ensure the rings do not overlap the little pin when placing the piston into the cylinder or barrel.
My friend finished the pizza and left. I was left to complete the project by myself. It can be done, but help is always welcomed. To make the job easier, place a few towels, paragliding magazines, etc. to build up the area below the crankcase/engine. The old trusty Craftsman screwdriver is pointing to the built up area. 

When you place the cylinder with the piston already installed on the towels or magazines, it should be within an inch or two of the piston rod as shown in this photo. You can also see the 1211 compound applied to the cylinder. You can also see the bearings placed in the piston rod.

Don't forget this part! Place the gasket on the crankcase or cylinder before reattaching the piston. Yes, there is 1211 compound on the crankcase. Remember, it's the white stuff (1211) which holds the gasket in place. It IS necessary to use both the 1211 and a gasket for an air tight seal.
Remember those two washers? My trusty Craftsman screwdriver is pointing to where they are to be placed. You can see that the wrist pin is partially inserted into the piston. Slip the washer between the piston and piston rod; and continue inserting the wrist pin. Two-stroke oil makes the operation a little easier. The second washer is placed on the other side.

Once the wrist pin is fully inserted, place the clips in the groove. Ensure that the clips are correctly inserted in their grooves.
After sliding the cylinder barrel up to the crankcase, install and tighten the four nuts. Ensure correct torque pressure on all four bolts. Once tightened, conduct another air leak test. Nearly 15% of all rebuilt engines will leak air. Therefore, it is important to conduct this post-rebuild air leak test. If the engine leaks air; it will suck air when running; run lean and seize. No air leak; time to reattach the exhaust and intake. Install a new spark plug and you are ready to fly - almost.

The Solo 210 c.c. engine has been successfully rebuilt. Fresh Breeze and Paratour recommend new engines run on a 4% gas/oil mixture for the first hour; 3% for the next 9 hours; and 2% every hour thereafter. Break in a newly rebuilt engine very carefully…be gentle with throttle applications. The SD48 pictured to the left has 1.5 hours since it was rebuilt. It will run reliable for many hours, but preventive maintenance and pre-flight inspections are imperative to its long life.

Why did it seize? The SD48 had been running for nearly an hour at a fairly high RPM when it seized. Improperly mixed gas and oil and carburetor jetting was a possible cause.

For more information please contact Greg Anderson at: res0bq5u@verizon.net or call 805.495.1876. Greg Anderson has flown powered paragliders since 1998 and logged over 320 hours. In addition, Greg's last SD had nearly 250 hours of perfect operation albeit with meticulous maintenance. Greg's average flight duration is 1.25 hours and he flies routinely in the Southern California area.

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