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Gentlemen,
The purpose of this thread is to answer some questions that have come up this past week.
A fellow contacted me asking for my help to get his hit and miss engine running. I have had conversations with this gentleman in the past and have given him some ideas that have helped. One being the valve seat cutter to cut the seats by hand and thereby simplifying that process.
His current problem is a lack of compression with a 2.00 bore engine. He told me the valves seal great but when he turns the engine over there is no noticeable compression. The cylinder was bored and then finished to size with a Sunnen hone and then measured with a bore gauge at several different points in the bore. The bore is 2.00 and basically perfect. The piston is iron and has .002 clearance and is machined for 2 piston rings.
As we talked to try and solve what seems like a mystery he mentioned that he had purchased 6 piston rings from the same supplier, all for a 2.00 bore. He said that the end gaps ranged from .012 to .022 and hadn't been filed. I told him that with everything concentric and a light coat of oil the engine should have compression even without the rings. I told him to do another check on the rings. Put them in the bore, square them up and shine a light from the back side to make sure that they were concentrically made. He did and they were.
Now it's
getting more mysterious!
A day later he called and said that when he did the first compression check the bore was dry so this time he oiled the cylinder before turning the engine over. He said that the engine would now bump up against the compression and kick the crank backward.
Now were getting somewhere!
He then asked my opinion on the ring gaps. I told him that even the small gap was way too large and that he should probably see about getting some rings from another supplier. I gave him a name and he contacted them. In the course of the conversation with this suppler he mentioned the problem he was having with the previously purchased piston rings, (the end gaps).
This supplier then asked what he bored his cylinder to. His response was 2.00, exactly what the print called for. The ring man then said, "that's where your problem is!" "You should have bored it .005 undersize and then the ring gaps would be right.
Now hold on to your horses!!!!
I am fast approaching 67 years. I got started with internal combustion engines like many fellows did, playing with old Briggs and Stratton engines and trying to build home-made go carts and mini bikes. From there I moved up to real engines and did many an overhaul with the fitting of new pistons and rings.
Upon my discharge from the Army I got into motorcycles, both the street and dirt variety. I can't tell you how many times I had my dirt bike cylinders bored and fitted new pistons and rings
I'm here to tell you that when a bore dimension is called for whether it be in an American car engine or an English or Japanese motorcycle they don't tell you to bore it .005 undersize so that the ring end gap will fit.
I don't mean to step on any toes here that is why I have left everything anonymous but having heard these remarks I just had to present this story.
Since joining this board and several others I have had many phone calls and requests for help. I will spend hours trying to help out fellow modelers and builders up to the limit of my knowledge. Beyond that if I don't know something or have never had experience with a particular situation I just say so.
Respectfully,
George D. Britnell
http://www.federalmogul.com/korihandbook/en/section_55.htm
The purpose of this thread is to answer some questions that have come up this past week.
A fellow contacted me asking for my help to get his hit and miss engine running. I have had conversations with this gentleman in the past and have given him some ideas that have helped. One being the valve seat cutter to cut the seats by hand and thereby simplifying that process.
His current problem is a lack of compression with a 2.00 bore engine. He told me the valves seal great but when he turns the engine over there is no noticeable compression. The cylinder was bored and then finished to size with a Sunnen hone and then measured with a bore gauge at several different points in the bore. The bore is 2.00 and basically perfect. The piston is iron and has .002 clearance and is machined for 2 piston rings.
As we talked to try and solve what seems like a mystery he mentioned that he had purchased 6 piston rings from the same supplier, all for a 2.00 bore. He said that the end gaps ranged from .012 to .022 and hadn't been filed. I told him that with everything concentric and a light coat of oil the engine should have compression even without the rings. I told him to do another check on the rings. Put them in the bore, square them up and shine a light from the back side to make sure that they were concentrically made. He did and they were.
Now it's
getting more mysterious!
A day later he called and said that when he did the first compression check the bore was dry so this time he oiled the cylinder before turning the engine over. He said that the engine would now bump up against the compression and kick the crank backward.
Now were getting somewhere!
He then asked my opinion on the ring gaps. I told him that even the small gap was way too large and that he should probably see about getting some rings from another supplier. I gave him a name and he contacted them. In the course of the conversation with this suppler he mentioned the problem he was having with the previously purchased piston rings, (the end gaps).
This supplier then asked what he bored his cylinder to. His response was 2.00, exactly what the print called for. The ring man then said, "that's where your problem is!" "You should have bored it .005 undersize and then the ring gaps would be right.
Now hold on to your horses!!!!
I am fast approaching 67 years. I got started with internal combustion engines like many fellows did, playing with old Briggs and Stratton engines and trying to build home-made go carts and mini bikes. From there I moved up to real engines and did many an overhaul with the fitting of new pistons and rings.
Upon my discharge from the Army I got into motorcycles, both the street and dirt variety. I can't tell you how many times I had my dirt bike cylinders bored and fitted new pistons and rings
I'm here to tell you that when a bore dimension is called for whether it be in an American car engine or an English or Japanese motorcycle they don't tell you to bore it .005 undersize so that the ring end gap will fit.
I don't mean to step on any toes here that is why I have left everything anonymous but having heard these remarks I just had to present this story.
Since joining this board and several others I have had many phone calls and requests for help. I will spend hours trying to help out fellow modelers and builders up to the limit of my knowledge. Beyond that if I don't know something or have never had experience with a particular situation I just say so.
Respectfully,
George D. Britnell
http://www.federalmogul.com/korihandbook/en/section_55.htm
