The owner says his maintenance co. says the part number was written inside and so there would be no way to identify it by outside marks. They say the cases are all the same until they are finished out. That I couldn't tell if the case was finished as a PN 641799 or the latest number PN 641800 for a 0-300 D or whether it was finished as a PN 642634 for a IO-360 ES. That any parts that need be such as the filler neck for example could be swapped in the field to create the version needed. This didn't come across as direct as I just wrote it but is the message they've sent several different times written differently and interpreted differently each time.
So I had a thought. I went to the Continental site and viewed several accessory cases part numbers and compared illustrations. I looked at the 0-300D, the IO-360 ES, and the IO-360 K1B.
![641800 0300D 33_005.gif (153.67 KiB) Viewed 2008 times 0-300-D PN 641800](./download/file.php?id=18994&t=1)
- 0-300-D PN 641800
![642634 iIO360ES 33_011.gif (180.86 KiB) Viewed 2008 times IO-360 ES PN 642636](./download/file.php?id=18996&t=1)
- IO-360 ES PN 642636
![641801 IO360KiB 33_17.gif (165.01 KiB) Viewed 2008 times IO-360 K1B PN 641801](./download/file.php?id=18995&t=1)
- IO-360 K1B PN 641801
You will notice each one uses the same illustration. Was Continental lazy or are they really the same? But wait notice there are no holes or studs shown on 641801 for a filter adapter so they aren't all the same illustration. I've already compared the individual part numbers for all the oil pump and relief valve parts listed for each of these 3 engines and they are all the same. What do you think the chance are the casting for each is the same and the basic finish of each is the same? I'm actually thinking its pretty pretty good. And that is exactly what this owners maintenance co. has been saying all along but interpretation has gotten in the way. The installed case has a mark of 641495, I've seem a picture of another IO-360 ES case with the same number molded in. Could the installed case have been finished out as a 0-300 case PN 641800 and the pictured one I have finished out as a IO-360 ES case PN 642634. But there is no difference in the actual case part unless you knew the intended end part.
I plan to call Continental and ask my questions a little differently. And I might call Divco which the Continental rep actually suggested last phone call and see if they can shed some light on this.
When is a bird that quacks like a duck, swims and flies like a duck, a duck? I'm thinking more and more the owner has a PN 641800 0-300-D accessory case that also by weird circumstance could also fit on and look like a IO-360 accessory case.