"I've read the other respo
"I've read the other responses and agree. I just last weekend purchased a Glasspar Marathon with a 50HP Force. It had been sitting idle for several years and after once I determined that the top cylinder was not getting spark even after switching coils it was time to pull the flywheel (FW). I have a professional (NAPA AUTO) gear-puller assembly with all the different 3 bolt sets commonly needed. The FW had three 1/4"X20 threads per inch (TPI) holes for the puller. But...No amount of heat, penetrating oil or tapping could budge it (the bolts need to be at least class 5 hardened type...NAPA or other same class provider..not ACE or Home Depot). {Never apply pressure to the point that you don't think you couldn't push it a little more.
The puller's next larger bolts were the 5/16"X18 then the 5/16"X24 TPI and finally the 3/8" bolts.
In steel, brass and even iron tapping a fine thread is no problem...But...In aluminum it’s much more difficult. So, I went 5/16"X18. Pre-drilling isn't necessary because you already have the 1/4"X20 hole which make the drilling a piece of cake (almost). Take a small piece of rigid wire 4-6" long and put a small 90 degree bend at one end so that the wire has about a 1/16" bent 90 degrees to the wire. Slide the wire down hole with the long piece of the wire touching the threads and the short leg pointing away from the crankshaft. You are looking for the bottom side of the FW. Once you have found it secure a pair of vise grips or needle nose pliers etc. on the wire at the top of the FW. Measure the distance from the pliers to the bend and that is the minimum distance you'll be looking to drill and tap. Remember that both the drill and the tap are shorter than their active cutting surface so you'll need to go a little further but not much.
If you only have a bottom tap I suggest you purchase a thru-tap. Starting a bottom-tap can be a nightmare because it has no starting taper to ease you into the work.
Place the FW so the Top Dead Center (TDC) mark is facing the sparkplugs. This will keep you from drilling thru a capacitor.
Using a number "G" drill, I drilled the three existing holes until I was just thru the FW.
Using mineral oil (MO can be purchased at almost any local drugstore) with 10% vegetable oil added as a cutting fluid I applied a small amount to the tap and a small amount down each hole just prior to that hole being tapped. Turning the tap handle clockwise two times, I then turn it counterclockwise one turn. After three or four sessions like that I remove the tap completely and blow off the chip buildup with either a spray of WD40 or a blast of air and then rewet the tap with the MO. Vacuum off don't blow off any tapping chips because they may all into engine and cause problems later. Continue tapping until thru FW.
Carefully inspect the FW for hairline cracks that originate from the three threaded holes. If there is any crack the FW still must be pulled but it cannot be safely used. It cannot be repaired, it must be replaced.
Install the FW nut so that all the nuts threads are engaging the top of the crankshaft.
Install bolts with at least three washers per bolt if the slots in the puller's head are wider than the bolt being used. Screw the bolts into the FW until you reach the FW's thickness measured by the bent wire. Check to see that the distance from the FW to the top of the Puller's arm is the same. Install the Puller's screw so that its point is in the crankshaft countersink. Snug the screw and attempt to determine if all three bolts are being evenly engaged by the Puller's head. If there is a bolt looser than the other two tighten it if possible or loosen the other two...reapplying pressure with the Puller's screw.
Now you are ready to pull the FW. Place vise grips or small clamps on the starting gear of the FW on each side of the starter so that the FW can’t move in either direction.
Apply torque tot he screw with a minimum 3/8" drive 6 point socket (prefer 1/2" drive) and a 12" breaker bar or ratchet with a 12" steel pipe slide over the handle to increase you torque and increase your control. Apply torque until you fell you could turn the handle 1/4 to 1/2 a turn more.
Remove the socket and tap the Puller' screw with a 1-2 pound brass mallet or a claw hammer hitting a 2X4 placed atop the screw. You may also want to tap the underside of the FW with the mallet or hammer. Be careful not to strike engine components, wiring, or the FW starter gear. Tap one side several times and then the opposite side.
Back the screw off 1-1 1/2 turns and then reapply torque. Repeat the steps until she breaks free. Do not place your hand or other object on top of the FW will the bolts are under torque.
Once the FW is off inspect both its top and bottom for cracks.
Never run the motor with the FW nut not fully tightened down. A big hesitation or backfire will sheer the woodruff locking key in half. I am sorry to say, "I speak from experience.
If you haven't already gotten the FW off let me know the outcome.
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