couple overhaul questions for the experts

[superdave474]

I am attaching several photos in reference to my questions. First, when assembling the oil pan, block, and flywheel housing, I noticed the oil pan and block were not 100% flush with each other. I told myself it was a slight imperfection in the way they fit, and that the housing gasket along with a layer of sealant would take care of it. Now I'm growing a little nervous that i should have investigated it a little further, and don't want to get this in the boat and realize I've got oil spraying all over the compartment. How often do you see this situation? (Misaligned housings, not oily engine compartments because someone didn't do their homework)

Also, I am attaching a picture of two distributor bodies. Can you tell me the difference between these, and if you have a preference? Or if I am being a little too particular?

And lastly, the two distributor caps. both in very good condition, but the contact points are not identical. On one cap, they are further recessed into the cap than on the other. I don't know if these are two different model caps, or if the points are in the right location with different plastic forms around them.

Much appreciated.

David
Smiley face just because

[Don Moyer]

David,

The misalignment in your photo is rather troubling, and it raises a question in terms of the alignment on the other end of the engine. The noticeable misalignment between block and oil pan on the flywheel end of the block should carry through and create a misalignment between the back of the oil pan and the back of the aft housing of the reversing gear. In my judgment, any such misalignment between the aft housing and oil pan would be more
problematic in terms of oil seepage.

Assuming you have both alignment pins installed between the block and oil pan, the front of the block and oil pan should line up perfectly. The only time I recall seeing such a misalignment is when we have to replace a block or oil pan, and the alignment pin holes don't line up perfectly. In a few of these cases we've had to assemble the block, pan, and flywheel housing without the alignment pins to create a perfect fit in front of the block and oil pan, and then "adjust" the alignment pin holes a bit with a file before reinstalling them.

With respect to differences in distributor caps, we have had a few reports in the past year or so from folks who discovered that a particular cap and rotor combination will simply not work on their Atomic 4. The largest consideration appears to be in the clearance between the tip of the rotor and the contacts inside the cap. Here are two particularly interesting excerpts from Brian Geraghty. Brian did a really credible job of defining the affects of excessive clearance between caps and rotors on his engine:

In a distributor/spark plug system, the spark has to jump 2 gaps each firing event, the spark plug (.035 inch) and the gap from the rotor to the cap. Generally, the larger gap is the controlling factor as to whether the system produces a spark (cylinder pressure is also a factor) and I would be looking for the rotor tip gap to be at least similar to the spark plug gap to assure spark production.

Following is a second report from Brian involving troubleshooting hard starting and rough running on his engine:

I noticed the arcing wear pattern on the inside of my distributor cap indicated the arcing of the spark going to the top of the cap post at each terminal, instead of horizontally to the downward projection of the post. With the radius of the rotor difficult to measure with just the part, I made a fixture to measure the radius and found the difference in the radius to be 0.050 inch between the two designs (of rotor) that I had! That means the (spark from) the shorter rotor had to jump about 0.100 inch to reach the post on the side, so it took the likely shorter vertical path. With a greater gap than the spark plug, this situation with the short rotor is prone to hard starting and misfire.

To summarize the cap/rotor issue raised in your question, given the difficulty most of us would have of actually measuring the internal dimension between the tip of the rotor and the contacts on the inside of a distributor cap, it would seem wise to simply replace a cap and rotor of the same manufacturer to insure compatibility. When first learning of the potential for problems caused by excessive rotor tip to distributor cap contact clearance, we cut an opening in one of the distributor caps from our online catalog and confirmed proper clearance (.035" or less) between the tip of a new rotor and the contacts in the inside of the cap.

Your distributor question is considerably easier than the first two. Both distributors are late model Delco distributors. The one with the vent hole in the bottom of the housing is considerably newer (circa late 1970's), but otherwise completely interchangeable.

Don

[superdave474]

misalignment

Thanks Don. I'll take a closer look this afternoon, but all of the housings went together very smoothly. I was actually a little disconcerted at how easily the reversing gear and aft housing slid into place. I was expecting that I would have to wrestle with it for an entire afternoon, and it went into place in a matter of minutes. All the pins are in place on oil pan and aft housing. nothing seemed misaligned except on the very forward part of the block/oil pan. It was almost as if someone had milled the front of the pan (where the flywheel housing meets) by about 1/32 of an inch.

I'll double check the aft housing alignment where it meets the pan at the coupling.

[superdave474]

alignment pictures

don,
I just took a few pictures of the misalignment. it looks as though alignment at the far aft end of the engine may have may be off just a touch, but is much less pronounced than at the flywheel. I ran a .004 gauge between the coupling and the pan/aft housing joint, and it won't go in. It did, however, sink all the way in between the flywheel and the oil pan, just below the block, on the port side of the engine. Won't slide into the gap on the same place on the starboard side, which is the side pictured in yesterday's post.

So, what I am thinking is, would it be possible, or advisable, to loosen the bolts holding the housings together slightly, and retorque them in a sequence that may favor bringing the existing gaps closed? for instance, tighten up the coupling, then the flywheel, then everything in between?

I can't imagine how this could be off in the first place. Everything was in good condition and immaculate when I put them together, and nothing seemed too tight or loose as I was working..

[Don Moyer]

Your assessment is probably correct. If the rear flanges seat flat against the oil pan and aft housing, you should be OK. I'll be very surprised if the area around the flywheel housing leaks, especially if you put a good amount of sealer on both sides of the gasket.

Don

[Don Moyer]

David,

It probably would be a good idea to loosen all 12 block bolts (6 on each side of the block) and the 8 aft housing bolts (4 on each side). However, you'll have to tap out both alignment pins between the block and pan or the block and pan won't be able to move in relation to each other.

After the bolts are all loose and the pins removed, the pan and block should move just enough to relieve the stress imposed by the misalignment. If this happens, you'll have to tweak the alignment holes to reinstall the pins. If there is no shift between the block and pan with everything loose, there probably isn't enough misalignment between the aft housing and pan to worry about.

Don