Hello,
I thought that some of the stunt boys may be interested in what I have learnt in regard to the fits of the ringed 60 Super Tigre stunt engine.
I have now rebuilt about 6 of these engines for use in Cl stunt. Some of the engines were brand new and some had little service, 1 had about 10 years of consistant use( It must have been a good one from the start). The common denominator amongst all these engines was the poor piston / cylinder fit. Some engines were almost impossible to hand start and some would not tune to a satisfactory level when they did start.
The answer to this sealing problem is the out of round cylinders, even from new in some cases. I have cylindrically ground 2 of the cylinders and made new pistons from high silicon material, replaced the ring and both worked fine. A time consuming process that many people without good machine shop facilities will not be able to undertake.
The easier solution appears to be the following. Remove old cylinder and piston, throw the piston ring over your left shoulder and buy yourself and Acro-lap tool http://www.acrolaps.com/( these are available in the USA, difficult to source in Australia). Lap the cylinder with this tool until the cylinder appears round from the top of the exhaust to the top of the cylinder, use light oil and fine valve grinding paste or diamond if you have some. This will give a parallel bore which may not be to some peoples liking but in these engines it works!
SCRUB THE CYLINDER BORE WITH DETERGENT AND HOT WATER. USE A TOOTH BRUSH!!!
You need a new ring for the engine, some Tigre rings are about if you look hard or have one made. Minimum ring gap is essential, no more than 3 thou no less than 1 thou ( Not sure if you will get a tigre ring with this gap)
Assemble the engine with care and plenty of light oil and carefully run the engine in, particularly if you have only got 1 thou ring gap. It will get bigger with running. Castor oil is the best for this purpose and let the engine 4 stroke for 10 minutes or so.
The engine should have good compression at this stage. A ringed engine may have better compression in one direction than the other. This is caused by the location of the ring gap, if it is towards the exhaust side it will seal better in the direction of rotation and the opposite for the transfer side. Do not ask me why this is as I do not know the answer, but that is what happens.
I am sure there will be people who disagree with this simple practical process but it works> If you have a better one please feel free to write the article with your ideas.
Good luck!
Andrew Heath (Aussie F2A)
I thought that some of the stunt boys may be interested in what I have learnt in regard to the fits of the ringed 60 Super Tigre stunt engine.
I have now rebuilt about 6 of these engines for use in Cl stunt. Some of the engines were brand new and some had little service, 1 had about 10 years of consistant use( It must have been a good one from the start). The common denominator amongst all these engines was the poor piston / cylinder fit. Some engines were almost impossible to hand start and some would not tune to a satisfactory level when they did start.
The answer to this sealing problem is the out of round cylinders, even from new in some cases. I have cylindrically ground 2 of the cylinders and made new pistons from high silicon material, replaced the ring and both worked fine. A time consuming process that many people without good machine shop facilities will not be able to undertake.
The easier solution appears to be the following. Remove old cylinder and piston, throw the piston ring over your left shoulder and buy yourself and Acro-lap tool http://www.acrolaps.com/( these are available in the USA, difficult to source in Australia). Lap the cylinder with this tool until the cylinder appears round from the top of the exhaust to the top of the cylinder, use light oil and fine valve grinding paste or diamond if you have some. This will give a parallel bore which may not be to some peoples liking but in these engines it works!
SCRUB THE CYLINDER BORE WITH DETERGENT AND HOT WATER. USE A TOOTH BRUSH!!!
You need a new ring for the engine, some Tigre rings are about if you look hard or have one made. Minimum ring gap is essential, no more than 3 thou no less than 1 thou ( Not sure if you will get a tigre ring with this gap)
Assemble the engine with care and plenty of light oil and carefully run the engine in, particularly if you have only got 1 thou ring gap. It will get bigger with running. Castor oil is the best for this purpose and let the engine 4 stroke for 10 minutes or so.
The engine should have good compression at this stage. A ringed engine may have better compression in one direction than the other. This is caused by the location of the ring gap, if it is towards the exhaust side it will seal better in the direction of rotation and the opposite for the transfer side. Do not ask me why this is as I do not know the answer, but that is what happens.
I am sure there will be people who disagree with this simple practical process but it works> If you have a better one please feel free to write the article with your ideas.
Good luck!
Andrew Heath (Aussie F2A)