In November 2003, I had the pleasure to visit JPX Italia, the manufacturer of the Cors-Air M21Y engine. At my request, Mr. Oscar Meschiari chief engineer and designer, built an engine and let me photograph the whole process step by step.
This material was written after many pilots encouraged me to do so.
I receive constant calls and letters from people asking me why the Cors-Air engines are so dependable and why they start up so easily.
As you will see below, the Cors-Air powerplant is manufactured with high quality standards like no other engine in its class.
In the same time, having the end user in mind, all the operations have been greatly simplified by the constructor and basically, one does not need any special tools to overhaul this engine.
Since all two strokes are very similar, I hope, the following will be a good reference material for those who overhaul their engines.
All the pictures are published in a larger format to be able to show details.
Those who do not have DSL connection will have to wait a while until the pictures open but I think it will be worthwhile.
Any positive or negative feedback on this article will be highly appreciated.
Before we start, I invite you to have a look at a sectioned Cors Air engine. They will let you understand better how a two stroke engine works.
JPX Italia only assembles the engines. All the parts are manufactured using cutting edge technology by several contractors. Among them is, the now famous Malossi which makes the cylinders, heads and crankshafts.
The picture below presents the crankshafts ready to receive the bearings.
JPX Italia, does not use a press to install the bearings on the shaft.
The bearings are heated to a certain temperature and then installed on the shaft by hand. This method is better because the bearing is easily inserted and no mechanical damage is done to the shaft or bearing. This is possible only on very precisely made crankshafts.
Once the bearings are installed on the shaft, we can now proceed to assemble the engine.
The Cors-Air M21Y like no other engine in its class has a horizontally split crankcase which means that NO bearings need to be pressed in the housing. As you will see, the crankshaft with the bearings is installed by hand!
The picture below illustrates the installation of the four crankcase pins which will hold the crankcase together.
Next, the crankshaft is put on the half of the crankcase.
Important note: after placing the shaft on the crankcase, please make sure that it is well centered , that is, the distance between the crankshaft and the crankcase is equal on both sides of the bearings.
Once the above operation is finished, a special gasket maker is applied on the other half of the crankcase. Please note that we only put equally distanced "spots" on the joints and later, we spread the sealer (gasket maker) evenly.
With the gasket maker evenly spread, the second half of the crankcase is added.
The next step is installing the bolts that will hold the complete crankcase together.
After pressure is applied (by torquing the nuts), the excess of the sealer (gasket maker) will flow out and for esthetical reasons, it can be removed with a screwdriver after it becomes tacky.
With the crankcase finished, we will proceed to install the four cylinder pins. In order to make sure they will not come out when removing the cylinder head bolts, I personally use a little Locktite (medium) compound on the threads. The pins do not have to be overtorqued. Once, on one of my Solo 210 engines, one of the pins ( I changed the original design) broke and it was much easier to remove it. The pins will hold even if not overtorqued because the cylinder head nuts will put pressure on them anyway.
Next, we put a generous amount of oil (two stroke oil) on the connecting rod needle bearing.
Now, the cylinder base gasket can be installed. The gasket should be oiled on both sides or a gasket dressing can be used. This will allow an air-tight fitting and will prevent stray air to be sucked into the crankcase.
Stray air sucked into the engine can cause a seizure and it can enter the engine by the following ways: leaky carburetor/reed valve gaskets, leaky oil seals on the crankshaft, leaky cylinder and or cylinder head gaskets or cracks in the crankcase.
Once in a while, an engine should be checked for such leaks but this subject is beyond the topics of this article.
With the cylinder base gasket in place, we prepare the piston for installation. Please note that we also oil the side holes of the piston where the pin will be installed.
Next, one of the wrist pin safety rings is installed. Please use a small flat screwdriver with rounded edges. It is imperative that the piston is not scored or damaged!
The piston is installed on the connecting rod without the rings and now it is the time to oil the grooves.
Before installing the piston, we must make sure that the small arrow on top of the piston points towards the exhaust port. If it is not, BIG damage will occur once the engine is started because the two edges of the rings will pas over the ports (intake and exhaust) and not in between them as they should. They will most likely score the cylinder or will even break!
The piston orientation is valid for ANY other two stroke engine!
As you will see below, before the piston is held next to the connecting rod, the wrist pin is already on one side of the piston and the needle bearing is also in place. All we do is align the piston with the pin and push the pin in place.
Next, we need to center the wrist pin pushing it from the left or right until the distance between it and the two safety rings is the same.
Before installing the cylinder head, we need to install the piston rings. In case of the Cors-Air M21Y the rings are a little different. They are slightly bent upwards and can be installed only in this position. The bent rings will seal better than the regular ones found on other engines.
Needless to say that the ring gap should be placed over the little studs implanted in the grooves of the piston. Failing to do this, one will not be able to install the cylinder and by forcing it, damage to the rings and or cylinder will occur.
Before inserting the cylinder, its walls need to be oiled as well.
Next, the cylinder is installed. We pull the cylinder over the top of the piston, align the ring gaps with the studs, squeeze the rings with fingers or use a special ring setting tool. Because not many pilots have a ring setting tool, I asked Mr. Meschiari to perform this procedure by hand.
The trick to it is to remember where the little studs are. We turn the first ring, align the gap with the stud and pull the cylinder over to the next ring. We set the second ring as described above and the cylinder can be pulled down until it sits on its gasket.
Very important note: The piston rings of the Cors-Air engines are bent upwards. Looking carefully at the rings we can see this. The outside rim of the piston is bent with respect to the internal rim.
The bend must be upwards, towards the top of the [piston.
If after installation the rings do NOT turn freely in the piston grooves, the rings are upside down. They must be removed and flipped 180 degrees. Installing the rings with the wrong side up will cause BIG damage to the cylinder walls!!!
Before installing the cylinder head, I strongly recommend to hold the cylinder down and turn the crankshaft a few times. If no grinding sound is heard, it means that the piston is pointing in the right direction. As stated above, if the arrow on the piston does not point towards the exhaust port, damage to the cylinder and rings will occur.
I stressed this again because on some old engines, while removing the carbon deposits, it may happen that the operator will scrape off the little arrow on the piston.
Therefore, when we remove an old piston we must make sure we remember its position. If no arrow is present, I recommend scoring one with a sharp tool, pointing towards the exhaust port.
Next, we install the cylinder head and torque the bolts.
Modern engines do not have a cylinder head gasket. They have instead a special "O" ring embedded in the cylinder head.
Once the cylinder head is removed, the "O" ring should be replaces as well. I experimented with the "O" ring on the Cors-Air engine and I reused the old one 3 times. This was achieved by using a small amount of antiseize compound on the ring.
However, I do NOT recommend reusing the "O" ring.
Older engines have cylinder head gaskets. These should be coated with oil before installation to ensure an air-tight fit.
Failure to use oil may cause leaks which will rob the engine of power, can damage the gasket or allow stray air to enter causing a too lean mixture. As mentioned above, stray air may cause a seizure on ANY engine.
Finally, the cylinder head nuts or bolts (depending on the engine) should be torqued to the manufacturer's values.
Overtorquing a bolt or a nut will not seal better. It will only damage the head warping it and it will cause leaks even when a new gasket or "O" ring is used!
If this happens, the head can be saved if the contact surface is sanded. The procedure is very simple: using a wet/dry type sandpaper of at least 220 grit held on a piece of glass, we sand the contact surface of the cylinder head making circular motions and checking the effects from time to time. If the head is badly warped, it is better to replace it with a new one.
The next step is to install the two flanges on the engine. They are: the reduction flange and the ignition flange. In case of the Cors-Air engine both of them contain the oil seals. This procedure requires that a gasket maker (sealant) is used. The gasket maker (sealant) should be gasoline resistant!
After the flange is in place, we install the bolts and torque them to the manufacturer's specifications.
The reduction flange is installed just like the ignition flange (above)
Next, we install the ignition module in the flange.
The Cors-Air like most modern engines, has electronic ignition with no "points" in it.
After torquing the ignition bolts, we install the flywheel (magnetic wheel) and make sure the woodruff key is in place.
I use a small amount of Medium Locktite compound which I apply directly to the shaft.
Next, the reed valve is installed. On older Cors-Air engines there was a paper gasket under the reed valve housing.
Newer models do not have a paper gasket. They only have the rubber on the reed valve housing. I use gasket dressing on them to make sure the connection is air-tight.
Once the reed valve is in place, we can install the carburetor plate.
Next, we install the electric starter. Please use Medium Locktite compound on the two fastening bolts. Newer engines also have an additional bracket that secures the electric starter.
The picture below shows the additional starter bracket found on newer engines.
Before installing the carburetor, the carb gasket needs to be oiled or gasket dressing can be used as well.
Now, the engine is ready to receive the reduction pulleys and the reduction belt.
I found that the belt can be installed easier if it is wetted before. It will slip easier onto the pulleys and will be less likely to be damaged (its grooves) if wet, when it is forced on the pulleys.
Now the engine is ready and to make sure everything is in order, the ignition and the spark are checked as shown in the picture below (the spark plug is connected to a tester and power is applied directly to the electric starter)
After this procedure, the engine is ready for shipping.
Note: we did not present how the exhaust system is mounted on the engine because it is shipped separately to the end user.
I would like to thank Mr. Oscar Meschiari of Cors-Air Motors (JPX Italia) for letting me photograph the whole process. Without him, this article would not have been possible.
None of the above pictures or text can be copied, published and distributed without prior agreement with the author or Aerocorsair USA.
However, links to this article posted on other web sites, are acceptable.
Like no other manufacturer or engine distributor in the industry we published this article so end users can have an illustration how the engine is assembled. This article can be used when overhauling the engine.
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