Well fellas,
If a fella fits a 5 degree flywheel to his Mac engine and the standard timing is 26 degrees BTDC and we allow for the odd bit of mavrick spark then just how much advance can these old geesers handle ??
Mc Bob.
Total zap how much is tooooo much ?
Moderator: Rob Voska
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steveohara
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- Vintage Karting items owned: 1969 Bug Sprint Mc 91B1
1965 Dart Gran Prix twin Mc100s
1963 Bug Scorpion ESll Mc45
Re: Total zap how much is tooooo much ?
Mc Bob,
With a standard flywheel the timing would not change much from the 25/26 static setting, with the 5 degree flywheel the timing will jump up to around 30 degrees when the points start bouncing. Actual results can vary a degree or two based on the position of the coil, amount of compression, strength of the magnets etc.
Regards,
Steve O'Hara
With a standard flywheel the timing would not change much from the 25/26 static setting, with the 5 degree flywheel the timing will jump up to around 30 degrees when the points start bouncing. Actual results can vary a degree or two based on the position of the coil, amount of compression, strength of the magnets etc.
Regards,
Steve O'Hara
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mcbob
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- Vintage Karting items owned: Everything Mac but a Kart but who know's ?
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Re: Total zap how much is tooooo much ?
Thats interesting as some Mc paperwork i got says that Maverick spark can be as much as another 5 degrees ..................
Mc Bob.
Mc Bob.
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Ernie Fisher
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Konig Power
Re: Total zap how much is tooooo much ?
Hey there Mc Bob!
Steve is right on the money concerning point bounce. "maverick" ignition was actually found by accident, with the use of the "kill switch". We used to put a push button kill switch on the karts, using a normally closed button that was placed between the ignition points and the coil. It was found that at low rpms, when the button was pressed, the point circuit was open, and the engine stopped. Here's the interesting part! One of us old guys found that when the button was pressed at higher rpms, the timing advanced, and the engine would seem to "maverick", reaching much more rpms. Depending on the fuels used, and overall engine set up, this system provided a great advantage. On the other hand, engine failure became commonplace, as many tuners were not prepared to compensate for the major timing change. It did not take too long for the "maverick" type kill switch to be prohibited in karting. We all thought all was lost with our "maverick button" being outlawed. But wait a minute!! Being karters, we stopped to think what was happening when the button was pressed with the old "maverick ignition". In essence, we were disonnecting the ingition points. As Steve stated, "point bounce" did the same thing, but the points would "bounce" at various rpms. The button would alow the competitor to semi-control the points, as they were "floating" at the driver's control. The good ole kart racer found that we could control the "maverick spark" without using the button. Since the button compensated for point "bounce or float", the same thing could be controlled with the amount of spring tension on the points themselves. The lighter the spring tension on the points, the quicker "maverick" could occur. The heavier the spring tension, points would float later causing "maverick" to occur later. Spring tension gauges became a very prominent tool to use during engine assembly. We had lost the use of the 'maverick button" but had found another way to accomplish the maverick ignition. I can remember spending hours setting up the 91's with that zig-zag spring on the points. Much time spent on the 101's too, but the point spring design on the 101 made it easier to work with. HMMM--those old Vintage Karters were a "clever bunch'! Primative, but clever!
Ernie
Steve is right on the money concerning point bounce. "maverick" ignition was actually found by accident, with the use of the "kill switch". We used to put a push button kill switch on the karts, using a normally closed button that was placed between the ignition points and the coil. It was found that at low rpms, when the button was pressed, the point circuit was open, and the engine stopped. Here's the interesting part! One of us old guys found that when the button was pressed at higher rpms, the timing advanced, and the engine would seem to "maverick", reaching much more rpms. Depending on the fuels used, and overall engine set up, this system provided a great advantage. On the other hand, engine failure became commonplace, as many tuners were not prepared to compensate for the major timing change. It did not take too long for the "maverick" type kill switch to be prohibited in karting. We all thought all was lost with our "maverick button" being outlawed. But wait a minute!! Being karters, we stopped to think what was happening when the button was pressed with the old "maverick ignition". In essence, we were disonnecting the ingition points. As Steve stated, "point bounce" did the same thing, but the points would "bounce" at various rpms. The button would alow the competitor to semi-control the points, as they were "floating" at the driver's control. The good ole kart racer found that we could control the "maverick spark" without using the button. Since the button compensated for point "bounce or float", the same thing could be controlled with the amount of spring tension on the points themselves. The lighter the spring tension on the points, the quicker "maverick" could occur. The heavier the spring tension, points would float later causing "maverick" to occur later. Spring tension gauges became a very prominent tool to use during engine assembly. We had lost the use of the 'maverick button" but had found another way to accomplish the maverick ignition. I can remember spending hours setting up the 91's with that zig-zag spring on the points. Much time spent on the 101's too, but the point spring design on the 101 made it easier to work with. HMMM--those old Vintage Karters were a "clever bunch'! Primative, but clever!
Ernie
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steveohara
- Posts: 411
- Joined: Thu Jul 19, 2007 2:29 am
- Vintage Karting items owned: 1969 Bug Sprint Mc 91B1
1965 Dart Gran Prix twin Mc100s
1963 Bug Scorpion ESll Mc45
Re: Total zap how much is tooooo much ?
Guys,
When the points are open, either from float or using the driver controlled switch the timing is determined by the position of the magnets in the flywheel and the coil. The magnets are moved 5 degrees in the counter clockwise direction on a "5 degree" flywheel when compared with a standard flywheel so the spark will occur 5 degrees of crank rotation sooner with the 5 degree flywheel. The absolute timing will be dependent on the coil position so it is possible to make a "5 degree" coil if you don't have a 5 degree flywheel by simply machining the slots so it can be moved 5 degrees of crank rotaion in the clockwise direction.
Assuming you bolt the coil on in the stock location the standard flywheel produces around 25 degrees of advance when the points are taken out of the system and the 5 degree flywheel produces around 30 degrees of advance. So, if you time your points to open at 25 DBTDC and you run a standard flywheel you will get no change in timing when the points float but you will get 5 degrees more advance if running a 5 degree flywheel. Now let's say we set the points for a static timing of 22 degrees.... in that case you'll get 3 degrees of advance when the points are open with the standard flywheel and 8 degrees more with the 5 degree flywheel.
Now, here is where the subject gets interesting and this is an aspect that is rarely discussed.... when you change the static timing you change the dwell and the lift in the points and that has a major effect on whether and when the points float. The more advance you use in the static timing the greater the lift on the points and the longer they stay open, thus they are going to float at a lower rpm for a given point tension and vice versa. If you time a motor way down at around 20 degrees static timing you may not get any point float at all since the points barely open and close quickly. In that case it would not matter what flywheel you use.
Let me conclude by saying that the above is a "simple" discussion of the subject and there are some other factors that an electrical engineer would be compelled to point out but those other factors have minute effects so I'm inclined to leave them out of the discussion at this place and time.
In the end, I have found that you simply can't go wrong timing your Mac engine at 25 degrees static timing, setting your stock coil as far to the right(clockwise) as the play in the slots will allow, setting the coil to flywheel gap at .012" on the leading and center post ( in many cases you can't get all three posts to have the same clearance and the trailing post is least important so it can have more gap if needed). If you have a standard flywheel, the point tension won't matter much as the timing will change little if any when they float. If you have a 5 degree flywheel, you want to get the point tension up to around 20oz or more. As Earnie pointed out, the Mac engines had two different types of points... ths super series motors (20, 40, 101 etc) have points that are very easy to get lots of tension..... just straighten the spring and it will have a ton and be careful not to have too much or it will wear out the rub block. The 91 series points are a little tougher to get the tension due to the zig zag shape and you can tighten the bends but it should be done in a way so you don't create a sharp bend that will lead to the spring breaking. I use a .100" drill blank on the inside of each bend when I tighten them up so thay end up looking more like an "S" than a "Z".
Last thing.... some engine builders used to mess with the holes in the side cover so they could rotate the whole assembly a little. What were they doing? Here is the answer.... when you rotate the side cover you rotate the position of the points around the crank and it will change the dwell and lift for a given static timing. Is it worth doing?.... nope... doesn't change things enough to matter.
Regards,
Steve O'Hara
Merry Christmas to All!
When the points are open, either from float or using the driver controlled switch the timing is determined by the position of the magnets in the flywheel and the coil. The magnets are moved 5 degrees in the counter clockwise direction on a "5 degree" flywheel when compared with a standard flywheel so the spark will occur 5 degrees of crank rotation sooner with the 5 degree flywheel. The absolute timing will be dependent on the coil position so it is possible to make a "5 degree" coil if you don't have a 5 degree flywheel by simply machining the slots so it can be moved 5 degrees of crank rotaion in the clockwise direction.
Assuming you bolt the coil on in the stock location the standard flywheel produces around 25 degrees of advance when the points are taken out of the system and the 5 degree flywheel produces around 30 degrees of advance. So, if you time your points to open at 25 DBTDC and you run a standard flywheel you will get no change in timing when the points float but you will get 5 degrees more advance if running a 5 degree flywheel. Now let's say we set the points for a static timing of 22 degrees.... in that case you'll get 3 degrees of advance when the points are open with the standard flywheel and 8 degrees more with the 5 degree flywheel.
Now, here is where the subject gets interesting and this is an aspect that is rarely discussed.... when you change the static timing you change the dwell and the lift in the points and that has a major effect on whether and when the points float. The more advance you use in the static timing the greater the lift on the points and the longer they stay open, thus they are going to float at a lower rpm for a given point tension and vice versa. If you time a motor way down at around 20 degrees static timing you may not get any point float at all since the points barely open and close quickly. In that case it would not matter what flywheel you use.
Let me conclude by saying that the above is a "simple" discussion of the subject and there are some other factors that an electrical engineer would be compelled to point out but those other factors have minute effects so I'm inclined to leave them out of the discussion at this place and time.
In the end, I have found that you simply can't go wrong timing your Mac engine at 25 degrees static timing, setting your stock coil as far to the right(clockwise) as the play in the slots will allow, setting the coil to flywheel gap at .012" on the leading and center post ( in many cases you can't get all three posts to have the same clearance and the trailing post is least important so it can have more gap if needed). If you have a standard flywheel, the point tension won't matter much as the timing will change little if any when they float. If you have a 5 degree flywheel, you want to get the point tension up to around 20oz or more. As Earnie pointed out, the Mac engines had two different types of points... ths super series motors (20, 40, 101 etc) have points that are very easy to get lots of tension..... just straighten the spring and it will have a ton and be careful not to have too much or it will wear out the rub block. The 91 series points are a little tougher to get the tension due to the zig zag shape and you can tighten the bends but it should be done in a way so you don't create a sharp bend that will lead to the spring breaking. I use a .100" drill blank on the inside of each bend when I tighten them up so thay end up looking more like an "S" than a "Z".
Last thing.... some engine builders used to mess with the holes in the side cover so they could rotate the whole assembly a little. What were they doing? Here is the answer.... when you rotate the side cover you rotate the position of the points around the crank and it will change the dwell and lift for a given static timing. Is it worth doing?.... nope... doesn't change things enough to matter.
Regards,
Steve O'Hara
Merry Christmas to All!