Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Maverick Spark
#7
Properly timed maverick spark is essential to the long term survival of the Mac engines if they are going to be run at rpm above 12,000 for the 100 cc motors and 11,500rpm for the 101s. The most common failure of the Mac engines when used for racing and revved up high is rod failure due to tension loads. The failure will occur in the form of a broken rod bolt or structural failure of the rod at the narrowest point of the beam right below the wrist pin boss. The failures are the result of inadequate combustion chamber pressure when the piston reaches TDC. In order to achieve enough combustion chamber pressure to help offset the inertia of the piston the ignition timing needs to be 30 degrees BTDC plus or minus 1 degree at high rpm. The problem is that it is very difficult to control detonation down at the bottom end of the rpm range with 30 degrees of advance so the magic of maverick is that the engines can be set up with static timing controlled by the points and condenser at 24/25 degrees BTDC and then the engine will transition to 30 degrees when the engine speed reaches the point where the points can no longer follow the cam.... or as it is often referred to as "float". When the points float the timing is determined by the relative position of the coil legs to the magnets in the flywheel. The 91 series combination of crank key location, five degree flywheel and coil location happens to work out just right and the only thing needed is careful attention to the point tension so make sure the float does not happen too low in the rpm scale. The 101 engines came with the standard flywheel so the timing is approximately 25 degrees when the points float and that is simply not enough advance to keep the engine from self destructing. The first thing anyone running a 101 engine should do if you plan to race it hard is to replace the original flywheel with a 5 degree version. It is also important to note that the static timing setting plays an equally important role as point tension in determining if and when the maverick transition occurs. Many racers struggle with carburation problems with the 101 series engines and they "solve" their heating issues by setting the timing way down at 21/22 degrees BTDC. When the points are set for that level of static timing they open less in terms of gap and for a lesser portion of the rotation of the crank. Accordingly, if set up with plenty of point tension the low lift/short duration setting results in the points being able to follow the crank up to a much higher rpm so they never float and maverick spark is not achieved. To "save" your 101 engine from near certain rod failure the engine needs to me timed at 24/25 degrees static and have a five degree flywheel.
Steve O'Hara
Reply


Messages In This Thread
Maverick Spark - by Scott Elkes - 07-18-2019, 09:12 AM
RE: Maverick Spark - by Gary Wlodarsky - 07-19-2019, 06:46 AM
RE: Maverick Spark - by ted johnson - 07-19-2019, 07:55 AM
RE: Maverick Spark - by steve welte - 07-22-2019, 09:53 PM
RE: Maverick Spark - by ted johnson - 07-23-2019, 07:49 AM
RE: Maverick Spark - by David Luciani - 07-23-2019, 09:24 PM
RE: Maverick Spark - by steveohara - 07-23-2019, 10:24 PM
RE: Maverick Spark - by Scott Elkes - 09-12-2019, 10:05 AM
RE: Maverick Spark - by steveohara - 09-13-2019, 01:58 AM
RE: Maverick Spark - by doug tenney - 10-10-2019, 10:35 AM
RE: Maverick Spark - by ted johnson - 10-10-2019, 11:37 AM
RE: Maverick Spark - by steveohara - 10-16-2019, 12:27 AM

Forum Jump:


Users browsing this thread: 1 Guest(s)