Engine Reassembly Notes

[bob mitchell]

    Jack Long, professional diesel mechanic, and my good friend, came over today and we reassembled my engine.  These are notes that I will never be able to keep in my head, so I write them down. First of all let me say something about the process. I have met more fine people with this engine than any other thing in my life, except maybe the boat, of which they are included. But the idea that there is no way to force a time schedule on bonding with and repairing your engine is a valid approach with great rewards. What was a mystery is now feels like home. The familiarity that a long term process creates is an end in itself. The engine is the ford/osco diesel 172, which I have come to believe was the standard engine for the east coast boats. The earlier west coast boats had a Mercedes. Currently there is a boat in sonomish named Swan that is being sold for parts and has a mercedes engine for sail, but I prefer my Ford tractor engine for it's simplicity and parts availability.

        To specifics, after each main and rod bearing is installed ( which means of course a piston with rings is installed in a cylinder) turn the crank to see if it turns freely. There should be no binding, although of course rotation will get slightly harder with each new piston. Everything must be clean - Jack uses compresssed air to go over the whole block before he even starts. After the crank and cam are in he takes motor oil and slathers the cylinders thoroughly, and he greases all moviing parts with white lithium grease. Next the piston is put in a ring compressor, and the piston is slipped in the cylinder. If you mess up and break a ring you can hear the noise. The photo below is the ring compressor compressing the rings so the piston can be inserted into the cylinder.     I guided the piston rods from the back in this process to keep them from scraping the crank journals and cylinder walls.

The pistons are labeled "front" but the rods are labeled with a number, or some people refer to the "tang" which is the grove that the shell fits in that keeps it from spinning in the bearing. The tang or number is specified to either be on the cam side or the opposite side - and it important in the sense that the engine was assembled in balance, one way or the other, and needs to go back that way. (in the ford/ osco the tangs or numbers go on the opposite side of the cam).

     After torqueing the rod bearings they still should not be to tight to turn the crank. In fact it is critical that they have "side clearence" as well, which means if you grab them with your hand and try to wiggle them back and force on the crank shaft, they should!!!! (to some small degree - and if you coated everything with white lithium grease, to lubricate the new rebuilt engine before the engine oil get there - you will be able to see it squish in and out as you try to wiggle the rod on the crank.) If you have no side clearence it probably means you installed the piston wrong - but if the machine shop that assembled the piston got the rod backwards, the piston could be facing forward correctly, but the rod wrong - happened to us - so you take the piston back out and pull the piston wrist pin (its easy) and turn the rod around, and try again.

    In the next photo the engine balencer and oil pump can be seen(hand is on oil pump, balancer is geared device to left). The engine balencer, which smooths out the engine vibration, must be timed.

There are two sets of marks, one set being on the pair of balancer gears and the other being between the crank shaft gear and the balancer.  Also, even though you may aquire a 172 block to rebuild, (in case the walls of your original block have already been rebored to many times) that does not mean it will necessarily be tapped for an engine balencer. Some were, some weren't. And while on that engine variations topic, there were 3 or four different sizes of rods produced, with variations in the wrist pin diameter. There are also variation in the rocker arm styles and dimensions.

     The oil pump is driven by the cam via a shaft sticking out of the bottom of the fuel injector drive. In other words, the fuel injector pump runs off a gear on the cam. The fuel injector drive has a gear that meshes with the cam gear, and must be set into the cam gear correctly for the slotted drive to be in the correct timing position for the pump. It is incidental and not relevant to the timing that the oil pump is driven by a hexagonal shaft that extends out of the fuel pump drive. So indirectly, by virtue of the fact that the cam drives the fuel pump, the cam gear also drives the oil pump.

   Probably the most fundamental skill in getting your ford osco, or any engine, to run well is the ability to determine top dead center of the number one piston (nearest the front). That is the poisition the crank must be in for the cam, which runs off the crank and drives the injector pump, to be in the correct position so that the injector pump injects the fuel into the cylinders at the correct moment.  That of course assumes that you lined up the timing marks of the cam gear and the crank gear during initial assembly.  The problem in determining top dead center of the number one piston is that the engine is a four cycle, which means the crank turns two revolutions per cycle creating the compression stroke and the exhaust stroke. So you could be looking at the piston at the top of the cylinder, or other timing marks, and it could be the exhaust stroke - 180 degrees out of time.  One key in determining the top dead center of the compression stroke is that both valves will be closed, which also means the cam lobes will be facing downwards.

So once you find TDC (top dead center) you can insert the fuel injector drive into the block with the larger semi-circle

facing the block (see manuel). The fly wheel marked with degrees, which is viewed looking from the front of the engine back towards the flywheel, on the starboard side (get a mirror), and the timing window marks on the Roosa Master fuel injector pump are also involved. The photo below shows the fuel injector drive slot on the side of the engine. The injector bolts right on top of this with a drive tang that sits in the slot.

    The one questionable event of the day was the difficulty seating the main rear bearing vertical oil seal. It is just not obvious that it seated correctly, so I will be keeping an eye on that. Perkins rear seals are repudited to be tricky, and now I know what they meant (perkins made this diesel for Ford).