Cedge
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- Jul 12, 2007
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This post is an update on the ongoing trouble shooting and adjustment phase. Getting everything in balance is proving to be a bit of work, but its been fun and frustration hasn't yet entered the picture. The good news is that the engine now runs!! For non-technicals, this is about as far as you'll want to read. For those who find birthing pains of interest, read on.
The past week has been a series of near misses. The engine really wanted to run when John and I tried to get it going. However, something was not as it should be and the attempt failed. After a bit of consultation with John and Bill Johnson, I had a better idea of what could be preventing success and went back into the internals of the engine to have a look.
Problem one.... low compression
When making the piston I was used dimensions that were established for use with cast iron rings. After breaking the second set of rings, even before ever getting them near the cylinder, I opted for nitrile "O" rings instead. Rather than cut the piston grooves again, I decided to sand down the O rings to fit. Bad choice. This resulted in very thin rings that eventually stretched under friction, broke and caused a total loss of compression.
Solution.... cut the piston grooves deeper giving me nice fat O rings which were then given a slight flat to seal against the cylinder wall. Add a bit of oil and a good seal was made, and the compression/vacuum improvement was very noticeable.
Problem two....
The valves had been lapped for the 3rd time and they "seemed" to be making a good seal. On a hit and Miss engine, the intake valve has to open under vacuum, which is indicated by a tiny, barely visible "fultter" of the valve spring keeper. This has to happen after each exhaust stroke, even when the flywheel is turned by hand. I knew it was working when the drill motor was applied to turn the engine, but I couldn't be sure about it at low rpm. Bill suggested bluing the seats and getting a better indication of how well the seats were actually lapped. It's an old trick and one I'd used in the past, but had slipped my mind during this build. Lets just say "seemed" was a bad assumption.
Solution....
Tear down the head and use the lathe to turn the valves with a fresh load of grinding compound... add a dash of patience and more mark up dye. Results... nice clean even valve seats and after reassembly, another noticeable leap in compression. Scratch one more itch and add another mark in Steve's column
Problem 3.... not my fault....LOL
I'll be using an ignition module which functions exactly as the typical automobile from the days of breaker points, coils and condensers. These fire when the points open, causing the coil to unload and fire the spark plug. Dead simple... extremely short duration and easily targeted to the timing point you want. Many of these engines are made to use a buzz coil that functions like the old model T ford ignitions. These operate somewhat backwards to what I'll be using. These fire the plug when the points close... not open. The high intensity spark, which you can probably weld exotic alloys with fires as long as the points are closed... ie.. across the whole flat of the ignition breaker cam.
John is a fan of the buzz coil and since he was a little dubious about my ignition system, opted to use the much stronger buzz coil. This proved to be both a good attempt and a bad solution.
Oddly.... the two systems use opposite sides of the breaker cam's flat to high point transition... one system fires as things close... the other system fires as the points open. Here is where duration of the breaker cam becomes a problem. My engine was designed for the system I'm now using, rather than the buzz coil. The 3/8 face of the flat allowed the fire to overlap into the intake phase of the stroke as well as wanting to fire at an extremely high advance setting, holding well past top dead center.
A change made to the breaker cam to cut its duration by half "helped" but was not a complete success. I finally went back to the original cam and abandoned the buzz coil. This let me dial in and hit the sweet spot in the timing, using the system I' was going to use in the end.... add another mark to my column.
Problem 4....
Fuel mixture.... I'd made the carb to spec but it is a touchy little beggar. I had doubts about it so I took it off and modified my fuel tank for use as a Vapor carb. After having a bit of near success, Zeusrekning and I were not feeling warm and fuzzy with it, so I replaced it, once again with the original aspiration set up. The problem there is that I'd modified the carb a wee bit to possibly become a means to add air to the vapor carb when needed. Bottom line, the needle was shorter and adjustment was a bit limited.
After a number of "almosts" we began to wonder if air flow was being restricted, so I turned the carb core a bit to give us more incoming air flow. More "almosts" later Tim and I called a day. Later in the evening I swapped the ignition systems and ran the needle valve all the way in, figuring to start from scratch when I next had time to play.
Today I knew I'd be tied up with family events from early morning until well into the afternoon. While waiting on my wife to finish getting the grandson ready to go, I put the battery powered drill motor to the engine and pulled the trigger. To my amazement, the engine sprung to life and ran for the better part of 15 seconds.... Cedge is now totally chuffed and knows he won't get to play for hours to come....(sigh)
Fast forward to this evening and I've had the engine running as long as 5 minutes before friction. due to heat, stops it. I've got the cooling system off the machine. so it will be reinstalled tomorrow and we'll see if a bit of heat reduction will add to the running times. Then its time to add the governor back into the mix, which already appears will need a bit of tweaking, now that I have some idea of the speeds the engine at which it will be running.
It's ongoing, but I'm stomping on bugs, probably driving my advisers completely nuts and generally having more fun than the law allows. Sorry there are no photos, but the recent action has been quite fluid and very fast, while the subject matter has not been very photogenic. I'll try to do better when video time rolls around.
Steve
(Cheshire possum grin firmly affixed)
The past week has been a series of near misses. The engine really wanted to run when John and I tried to get it going. However, something was not as it should be and the attempt failed. After a bit of consultation with John and Bill Johnson, I had a better idea of what could be preventing success and went back into the internals of the engine to have a look.
Problem one.... low compression
When making the piston I was used dimensions that were established for use with cast iron rings. After breaking the second set of rings, even before ever getting them near the cylinder, I opted for nitrile "O" rings instead. Rather than cut the piston grooves again, I decided to sand down the O rings to fit. Bad choice. This resulted in very thin rings that eventually stretched under friction, broke and caused a total loss of compression.
Solution.... cut the piston grooves deeper giving me nice fat O rings which were then given a slight flat to seal against the cylinder wall. Add a bit of oil and a good seal was made, and the compression/vacuum improvement was very noticeable.
Problem two....
The valves had been lapped for the 3rd time and they "seemed" to be making a good seal. On a hit and Miss engine, the intake valve has to open under vacuum, which is indicated by a tiny, barely visible "fultter" of the valve spring keeper. This has to happen after each exhaust stroke, even when the flywheel is turned by hand. I knew it was working when the drill motor was applied to turn the engine, but I couldn't be sure about it at low rpm. Bill suggested bluing the seats and getting a better indication of how well the seats were actually lapped. It's an old trick and one I'd used in the past, but had slipped my mind during this build. Lets just say "seemed" was a bad assumption.
Solution....
Tear down the head and use the lathe to turn the valves with a fresh load of grinding compound... add a dash of patience and more mark up dye. Results... nice clean even valve seats and after reassembly, another noticeable leap in compression. Scratch one more itch and add another mark in Steve's column
Problem 3.... not my fault....LOL
I'll be using an ignition module which functions exactly as the typical automobile from the days of breaker points, coils and condensers. These fire when the points open, causing the coil to unload and fire the spark plug. Dead simple... extremely short duration and easily targeted to the timing point you want. Many of these engines are made to use a buzz coil that functions like the old model T ford ignitions. These operate somewhat backwards to what I'll be using. These fire the plug when the points close... not open. The high intensity spark, which you can probably weld exotic alloys with fires as long as the points are closed... ie.. across the whole flat of the ignition breaker cam.
John is a fan of the buzz coil and since he was a little dubious about my ignition system, opted to use the much stronger buzz coil. This proved to be both a good attempt and a bad solution.
Oddly.... the two systems use opposite sides of the breaker cam's flat to high point transition... one system fires as things close... the other system fires as the points open. Here is where duration of the breaker cam becomes a problem. My engine was designed for the system I'm now using, rather than the buzz coil. The 3/8 face of the flat allowed the fire to overlap into the intake phase of the stroke as well as wanting to fire at an extremely high advance setting, holding well past top dead center.
A change made to the breaker cam to cut its duration by half "helped" but was not a complete success. I finally went back to the original cam and abandoned the buzz coil. This let me dial in and hit the sweet spot in the timing, using the system I' was going to use in the end.... add another mark to my column.
Problem 4....
Fuel mixture.... I'd made the carb to spec but it is a touchy little beggar. I had doubts about it so I took it off and modified my fuel tank for use as a Vapor carb. After having a bit of near success, Zeusrekning and I were not feeling warm and fuzzy with it, so I replaced it, once again with the original aspiration set up. The problem there is that I'd modified the carb a wee bit to possibly become a means to add air to the vapor carb when needed. Bottom line, the needle was shorter and adjustment was a bit limited.
After a number of "almosts" we began to wonder if air flow was being restricted, so I turned the carb core a bit to give us more incoming air flow. More "almosts" later Tim and I called a day. Later in the evening I swapped the ignition systems and ran the needle valve all the way in, figuring to start from scratch when I next had time to play.
Today I knew I'd be tied up with family events from early morning until well into the afternoon. While waiting on my wife to finish getting the grandson ready to go, I put the battery powered drill motor to the engine and pulled the trigger. To my amazement, the engine sprung to life and ran for the better part of 15 seconds.... Cedge is now totally chuffed and knows he won't get to play for hours to come....(sigh)
Fast forward to this evening and I've had the engine running as long as 5 minutes before friction. due to heat, stops it. I've got the cooling system off the machine. so it will be reinstalled tomorrow and we'll see if a bit of heat reduction will add to the running times. Then its time to add the governor back into the mix, which already appears will need a bit of tweaking, now that I have some idea of the speeds the engine at which it will be running.
It's ongoing, but I'm stomping on bugs, probably driving my advisers completely nuts and generally having more fun than the law allows. Sorry there are no photos, but the recent action has been quite fluid and very fast, while the subject matter has not been very photogenic. I'll try to do better when video time rolls around.
Steve
(Cheshire possum grin firmly affixed)
