Here is a cheap and safe method for separating 3pg engine crankcase halves

[kyerik]

2 weeks ago, I picked up a non-running 1991 Marathon 2 cycle off craigslist for $250. After getting it home, it would only sputter a little with the choke set at 90% (compression was 140psi). so, I BBQed the muffler, verified fuel pump output, new spark plug (good spark), cleaned all parts/passages of the carb twice and put in fresh gas- still only ran ran rough with choke almost all the way on. So- I figured that the crank seals were bad and that it was sucking air by them and leaning it out- I also noticed a little play in the crankshaft bearings. So- knowing I'd need to replace the bearings, I cleaned up the motor and tried splitting the crankcase halves with a rubber mallet- that didn't work for me. Here is my solution (which worked very well).

Materials needed:

A cheap 3 hole steering wheel/harmonic balancer puller
Three one quarter inch thick steel brackets (to extend the reach of the puller- I got these at Lowe's a few years ago)- they are gold in my pics
3 2.5 inch 3/8 bolts, nuts and washers (to hold the extension "wings" on the puller)
a 3/8" coarse thread tap (for the clutch side of the crankcase)
a 1/4" coarse thread tap (for the flywheel side of the crankcase)
3 long 3/8 bolts
3 long 1/4 bolts
A 1/4" drill bit and a drill

The pic below is the clutch side. Three of the holes for the bolts that hold the case halves together are about 120 degrees apart and are the perfect size for a shallow tapping with a 3/8 tap (be sure to run the tap in straight and slow- just go in about 1.25 inches- you are only tapping the outer half of the case)



The pic below is the flywheel side. There are three blank holes in the flywheel side crank half. They are not threaded- lightly drill/clean these out with the 1/4 bit but do not drill out any more material than 1/8 inch or else you could get into the crank case. Run the 1/4 inch tap in the holes until you feel it get hard then STOP because the tap has bottomed out. The 1/4 inch bolts will only thread in about 3/8 to a half inch- just snug them up with a wrench- then start pulling. This one finally started moving with a POP- I can't imagine getting it off with a rubber/plastic mallet.



This method may work for the 2pg as well if the bolt holes in the cases are identical.


FYI- the flywheel side crank seal was in really bad shape (the rubber lip had worn completely through on one side)- although it looked OK from the outside- and the flywheel bearing was the one with the most play so maybe the extra wobbling on that side simply wore it out. The rings look OK and the bore looks OK, but the piston skirt has a few scratches (the air filter hose wasn't hooked up to the carb when I bought it...)

[simple man]

Used to use a similar setup to remove lower units from outboard motors.
Thanks for the post, it will help some folks!

[loflyer2880]

Great first post kyerik...

[kyerik]

Important correction- On the flywheel side, I used a smaller drill bit than 1/4" (obviously you can't drill a 1/4" hole and tap it to make threads for a 1/4" bolt to grab on to)- I don't recall what size it was- maybe somewhere around 3/16"- I have a tap/drill set and used the bit that was supposed to be used with the 1/4" tap.

[racin161]

If I recall a #7 is tap drill for 1/4" but 3/16 bit will work but only 40-50% threads.

LOU

[DonoBBD]

Small tip to test if the crankcase seals are the problem is to wave an unlit propane torch around the crank ends. If the seal is leaking it will suck the propane in and the RPM's of the motor will run up verifying the crank seal is leaking. When trying to start or run the motor.

[racin161]

Sounds like a good tip to me

LOU

[pachanga90]

You can also spray starting-fluid or silicone near the crankseals,if the motor speeds up,you have a leak.Its' a little safer than the torch,since usually the side of the motor is oil-soaked anyway.

[frodrummer]

Quick question, I am getting set up to separate my 2pg case. On the flywheel side, mine does not have the 3 unthreaded holes as depicted in the photos above. It does however, have 3 smaller screws that are in nearly the same place, but not exactly the same positioning as the 3pg. The screws are holding on a large 5-6" ring behind the flywheel. I actually tried my M6 bolts from my flywheel removal setup and they fit perfectly. Here's my question: Will the M6 bolts hold up under the tension created by the balancer puller? Not sure how much it's gonna take to separate the halves, and dont want to strip the exhisting holes.

[kyerik]

How deep do the threads go? If you can get them threaded in 1/2" you will probably be OK with a moderate amount of pressure. Could you easily drill and tap for the next larger size if the worst happened (the threads stripped out)?

Pull the clutch side off first and save this side until last- that will also reduce the strain on those threaded holes (it takes a little extra force to break the adhesive seal between the halves).