Autopsy of an American Bantam Engine: Part III

Welcome to the final installment of the disassembly.  Could the engine come apart a little more?  Yes.  In fact, the oiling system will probably need to be taken out of this engine, but everything is at a stand still until I know what condition the crankshaft and rods are in.

Remember that rear main bearing carrier I showed you a photo of the other day?  That is the last obstacle between us and the crankshaft.  Although the piece is cast iron, it has been wedged into an aluminum crankcase for decades, and beside being shrink fit into the crankcase, it also may have some corrosion between the two parts.  This is why you need a heat source to expand the aluminum to make it easier to pull out the main carrier.

First, take the two bolts you bought and thread them into the to holes in your bearing carrier.  DO NOT thread them all the way down or attempt to pull the carrier out without heat.  If you do, you will probably be experiencing extreme anger and frustration, as the carrier ear snaps off and the carrier remains steadfast in its hole.  Threading the bolts in now will prepare you for when the engine is up to temperature so you wont waste valuable time and expansion while searching for parts.

The last time I did this, I consulted the ABS’s engine manual which encouraged using an oven to expand the aluminum.  Not wanting to put anything Bantam in my oven, I spoke to a club member who suggested the idea of a space heater.  He recommended one of those radiant heaters,  however, they have gotten very hard to find.  I instead bought a stanley unit from Lowes.  Then I made a little heat corral of cardboard boxes surrounding the engine in the middle of my garage to ensure that as much heat as possible soaked into the engine before being stolen by my frigid garage.  This time, I had something better, a metal crate with wooden sides to corral the heat.  Either way, don’t get reckless, and please make sure that your heat corral is not on the verge of becoming a heat source itself.

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Aiming the heater at the back of the engine and closing it in, I set my timer for 20 minutes.  Set to high heat and high fan, I began my wait.  As I said, keep your eyes on your set up.  Here is my observation station and view:

Once the first twenty minutes has passed, check to see how warm your crankcase feels.  More than likely, you’ll need to run the heater for at least another 20 minutes at full blast.  After 40 minutes, I turned off the heater as the aluminum was feeling quite warm and began to tighten the upper bolt.  Immediately, I was able to see the carrier pulling away from the top.

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You should only crank each bolt a little bit before moving to the next, hoping to remove this as evenly as possible.  The lower bolt however did not turn without a lot of resistance and the lower part of the carrier showed that it wasn’t ready to budge yet.  So I turned the heater on and set the timer for another 15 minutes.

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At the end of the 15 minutes, I tested the lower bolt and as it threaded deeper into the carrier I saw it separate from the block at the seam where they are joined.  Moving between the two bolts at even increments, the carrier came out very easily and exposed the crank entirely at the rear.

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Reaching in through the bottom of the block with one hand, I carefully slid it out to my other hand.

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Here is the bounty of our efforts:

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The next step is to take this crank and the connecting rods to the machine shop to see what I’m dealing with.  Although you can have the crank hot tanked, I’ve heard that you don’t want the rods hot tanked as it can adversely affect your babbit.  You should hand clean the rods with good detergents like brake parts cleaner, etc.

I will be taking this crank in and asking them to check it for cracks, straightness, and size of the journals.  I’ll also be asking them to check the rods for cracks and the size of the bearing material.  It’ll take a few days until I know for certain what the results are, but it’s always important to know that the most important parts in your engine are in good shape.  As the old adage goes, without a crank, there can be no Bantam engine.

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