Noob head question

[wdglide]

Whats the difference between the heads (if any) with early pans. I have a 48 head on the rear and a 50 on the front.

[Bigincher]

You're probably looking at the number cast into the head, on the underside of the pushrod 'shelf'.
That number is not the date of manufacture, but is the year that the part was introduced. For instance, you will see the 48 on the heads on 1948 and '49 models. The '50' heads ran until ... 1956 I think was the next change. The actual date of manufacture is denoted by a number and a letter cast into the heads on separate little 'pads'.
The difference between the 48 and 50 style heads are subtle, but both are 'plumber' style intakes, while the '56 has o-ring style intakes.
There are other cosmetic differences, but I'll let someone else get into the details. I know of two members here who have expensive knowledge on the subject.

[wdglide]

Ahh. Great info.

Mine is a '51. So, The rear head is likely not "original" to the bike. I also have an o-ring intake, so there must have been a conversion.

Thanks!!

[Bigincher]

Have you looked at the date codes to determine the heads are '51 ?

[wdglide]

No, I haven't

[RUBONE]

Conversions are common on older heads, and regretfully often caused more harm than good. The '48 head has a passage in the fins (with fins lacking) where a welch plug covers a drilled hole. '50 and later don't have it. The last plumber heads are '54, the '55 head castings are O-Ring but unto themselves and one year only. The '56 casting changes multiple times and the casting codes are not always visible from the exterior.

[cdndewey]

I'm going to go have to take a look in my stash. I think I have a 56 casting with a plumbers intake on it. Not sure of the actual casting date.