C2: How to decipher bell housing date code?

[Gary B.]

My bell housing has the casting number 3858403 and I'm trying to figure out how to decipher the date code. Paragon sells used 403 bell housings and their catalog indicates that the date code designates the month and week of casting. On the pad on the RH side of my bell housing are the letters GM in a serif font, with the casting number below. Still further below the casting number are two circles, each with a single diametral line. In the left hand circle, the line is oriented at the 10 minutes before 4 clock position. In the right hand circle, the line is oriented at the 5 minutes before 5 clock position. Beneath these two circles is the digit 1, in a font about 3/8" tall or the same height as the casting number. I'm guessing the numeral 1 is a mold number, but how does one decipher the two circles with the lines?

Thanks,

Gary Beaupre

[Harry Sadlock]

Re: C2: How to decipher bell housing date code?

Best I can recall:

Left circle - within the circle is a number. Below the number there are a number of dots. The number represents the month and the dots represent the week. A 3 over 2 dots should be March, 2nd week.

Right circle - the info in the circle represents change numbers and deviation notice (essentially status)

Harry

[Joe L.]

Re: C2: How to decipher bell housing date code?

Gary-----

The circle with the dots in the bottom half is the date information source. The number in the top semi-circle represents the month (e.g. "3"= March). The dots in the bottom of the circle indicates the week of the month (e.g. two dots= 2nd week of the month). That's all the date information that there is on these castings. Without year information, the dates are somewhat useless; 1/2 of the castings out there of a specific casting number would be "correct" for any given car that used that casting number.

The other circle provides information relative to blueprint change # and any deviation, if applicable. If one could obtain all of the blueprint history data for these pieces, then, perhaps, one could infer the year or year range of manufacture. But, I don't think that info is available.

[Gary B.]

Man, those numbers and dots must be small!

Joe, Harry,

At the moment I'm working from a digital photo of my bell housing since it's presently away being hot tanked, but for the life of me I can't see numbers and small dots inside either circle in my photo. I'll look more closely when I get the bell housing back from the hot tankers.

Thanks for the deciphering code,

Gary

[Wayne M.]

One date span -- Late '65

Gary -- Joe's right about uncertainty as to the year, even if you can read the date on the multi-year production run of 3858403, but I found circle with 6 on top of the line, and two dots below [2nd week of June] on unrestored bellhousing on L78 # 235xx [July 3--Aug 2 production], and this seems to be in the timespan I'd sorta expect.

[Gary B.]

Re: One date span -- Late '65

Wayne,

I'm going to get my magnifying glass out when I get my bell housing back from the hot tanker. I thought for sure the lines themselves meant something, but now I very curious to see the numbers and dots.

Gary

[Joe L.]

Re: One date span -- Late '65

Gary-----

I certainly hope that the "hot tanker" is going to use something besides a traditional hot tank solution. The solution used in "hot tanks" (the old-fashioned kind that are used to clean cylinder heads, blocks, etc.) is a highly caustic solution. This works fine on cast iron or steel which is impervious to caustic. However, aluminum is an amphoteric metal (i.e. it is soluble in both strong acid as well as strong basic solution). If you immerse an aluminum bellhousing in a traditional "hot tank" you not only won't be able to see the dots afterwards, you might not even be able to see the bellhousing.

[Gary B.]

Hot tanking

Joe,

Well, now you've got me scared. I've been waiting for a month to have the bell housing hot tanked, but the place doing the job has a broken circuit breaker, so that tank won't fire up. Maybe it's time to retrieve the bell housing before he repairs the circuit breaker...

Gary

[Joe L.]

Re: Hot tanking

Gary------

Most "hot tank guys" fully understand that they can't be used for aluminum, but there might be a few "novices" out there that don't. The fact that he accepted the part for "hot tanking" makes me wonder if he might be using a solution which is compatible with aluminum. I'm not aware of any "hot tank", aluminum-compatible solutions, but there may be some. For the most part, hot tanks have been pretty much eliminated by environmental requirements in many areas.

[Craig S.]

Re: Hot tanking

Gary - he may be using a jet spray cleaner with heat and solution like a large dishwasher, that's what most shops use these days,and the solution is safe to aluminum parts. Most machine shops regularly deal with aluminum heads etc regularly, and no longer use the old hot tank process. Not only does it eat the part, but ruins their solution, so I really doubt that they would insert your bellhousing into that type of cleaner if they still use it...Craig