420 Auto Crankshaft Removal

I am bringing a neglected 420 Auto back to life and am having a heck of time getting the crankshaft pushed through the left case.

I am using the Tusk Case Splitter to push the crank through the left case. The first splitter I used broke under significant pressure - thankfully Rockymountain ATV replaced it at no charge. I'm also applying encouraging "taps" with a hammer on the case splitter bolt when under load. Today I tried applying heat with a heat gun on the inner race while using the case splitter. No luck.

Any tricks of the trade you guys can pass along would be greatly appreciated!

Thanks,
Scott

Try pulling the right case off the left. The heat you were applying was not helping because the crank stub end and inner bearing race are similar materials that expand at close to the same rate. Now that you applied that heat, you need replacement crank bearings.

Thanks for the note jimspac. I've actually already split the cases. The right case is off of the crank and am trying to remove the crank from the left case so that I can replace the bearings and seal.

What do you guys think of this idea; drilling a dimple in the case splitter bolt and using an air impact driver in the dimple while the case splitter is under load against the crank end. Do you think that would have any negative effect on the crank?

Thanks for your thoughts on this.

Scott

You may end up pushing out the crank bearing with the crank

I thought about that. If that happens then I can use a gear puller against the bearings (there are two back to back on the left side), assuming I can get the jaws behind the bearing closest to the crank counterweight.

Be careful with the air impact driver as the drastic vibration can throw a crank out of alignment. This is especially true when removing a flywheel or primary gear however I don't know for certain what the effect will be when used on a crank removal tool.

At this point I would soak the inner bearing race-to-crank mating surface with penetrating oil for a couple days then try again. If this doesn't work then I would get out the oxy acetylene torch. I don't think an electric heat gun has the required BTUs to do the job even though it may produce 1000 degrees at the tip the mass of the crank and cases would soak up the heat before the overall temp could reach a point that would do any good.

In this particular case our objective in using heat is to break the bond between the bearing race and crank stub-shaft and not to expand the race to a point that its larger than the crank stub-shaft. With this said apply heat using the torch (use a welding tip not a rose bud to achieve pinpoint accuracy) to the race for 15 to 30 seconds then let it cool and try the splitter tool. We certainly don't want to heat up the entire crank to anything exceeding its normal operating temp. It may take a few attempts of heating and cooling but the bond will break.

Just remember I have seen many cases that have bearings pulled out of the cases with the cranks. This is done at room temp.

What happens is the mag cases bearing ID bores can be damaged beyond use. But in your case I wonder if you heat everything
in oven you may expand the mag faster than steel and the bearings could slide out of case with crank with no damage

It take 400 degrees. At this time the bearings should just drop out. This is not the best way. The crank really needs
to be split , bearing replaced, etc. We are getting cranks down to .0003 for best results now. Min .0005
Pounding does help this

The auto cases are aluminum.

Put a tray on the wood stove put the engine on the tray. As things warm the fits get looser. Of course not as much as if you cooled the inner and heated the outer. I think I answered elsewhere so will leave this thread alone.