RC-26 Radiator Supply Tank Cap

[David L.]

According to the 1966-1970 Corvette AIM's the radiator supply tank cap lists 6410203 as the part number which I believe is a RC-26 cap. Back in 1989 at a swap meet I found a NOS RC-26 15# cap in a GM box with part # 6410206 (part numbers in the AIM are not always the same as those in the parts catalogs). The NOS cap was exactly like the one in the photo on the left with the "15#" and "RC-26" on the ear to the right stamped vertically. I don't remember where I got this photo. I sold my NOS RC-26 cap back in December 1989.

Last Saturday at a swap meet in Connecticut I bought an original RC-26 cap with the "15#" and "RC-26" stamped horizontally (photo on right) attached to an original supply tank stamped "3016340" dated "68H" (August 1968). I believe both parts to be original and from an early 1969 Corvette.

Does anyone have any idea when the direction & location of the "15#" & "RC-26" stamping on the cap changed on the production line?

[Gary B.]

Re: RC-26 Radiator Supply Tank Cap

David,

I bet Pete Lindahl might hazard a guess.

Gary

[Terry M.]

Re: RC-26 Radiator Supply Tank Cap

David,

Implicit in your question is the assUmption that there was only one assembly line in only one plant. I doubt, since they made many millions of RC26, that either was the case. My belief, for no good reason other than those many millions and the length of time they were used, is that these variations indicate different plants and/or assembly lines and may also possibly be indicators of die replacement or rebuilding from time to time. Others, of course, are entitled to their opinions as well.

[Peter L.]

Re: RC-26 Radiator Supply Tank Cap

Dave - Check the archives. As far as I know there is no "magic mushroom" when it comes to determining the orientation of the stampings on the 1966 GM Production year and new versions RC-26 Radiator Pressure Caps and/or of the stampings on other AC Radiator Pressure Caps. And while the RC-26 was a Corvette only part as far as I know, gathering meaningful data might be interesting because knowing that the cap is the cap that originally came on the car could be difficult to determine and then adding SERVICE caps into the mix presents another parameter. Anyway, I have seen RC-26s with double circles around the AC logo (the ones with the double circle around the AC logo have the AC and RC-26 stampings opposite of those with the single circle around the AC) , RC-26 stamping oriented along the axis of the ears and perpendicular to the axis, and ones with the AC and RC-26 on the same side of the center depression. BTW, less we forget, it should be pointed out that the 63-65 GM Production year RC-26 Radiator Pressure Caps had different stampings similar to the 62-65 GM Production year 307 and pre-1966 GM Production year RC-15 Radiator Pressure Caps. So, it sounds like a good government research project, but if one has something better to do, you will probably want to do that. Pete

[David L.]

Re: RC-26 Radiator Supply Tank Cap

Terry,

It's very possible that there was more then one plant that made AC radiator caps. However, my theory is that the "early" RC-26 caps had the "15#" & "RC-26" stamped vertically on the right "ear" and the "late" RC-26 caps had the "15#" & "RC-26" stamped horizontally just to the left of the right "ear". The "Vette Vues Fact Book of the 1963-1967 Sting Ray" by M.F. Dobbins shows an original 1966-1967 RC-26 cap on page 216. I believe that the photo of the cap is of a 1967 cap & supply tank as many of the other engine compartment photos are of a 1967. The "15#" & "RC-26" stamping is vertical on the right "ear".

Researching radiator caps using my vintage Chev. parts catalogs and Chev. parts history catalogs is very confusing and makes no sense.
6410206 replaced in July 1966 with 3887586
861981 (RC-22) replaced in April 1974 with 6410206

I'm sure that there are very few owners of 1966-1970 Corvettes that still have their original radiator supply tank RC-26 caps.

Dave

[David L.]

Re: RC-26 Radiator Supply Tank Cap

Dave - Check the archives. As far as I know there is no "magic mushroom" when it comes to determining the orientation of the stampings on the 1966 GM Production year and new versions RC-26 Radiator Pressure Caps and/or of the stampings on other AC Radiator Pressure Caps. And while the RC-26 was a Corvette only part as far as I know, gathering meaningful data might be interesting because knowing that the cap is the cap that originally came on the car could be difficult to determine and then adding SERVICE caps into the mix presents another parameter. Anyway, I have seen RC-26s with double circles around the AC logo (the ones with the double circle around the AC logo have the AC and RC-26 stampings opposite of those with the single circle around the AC) , RC-26 stamping oriented along the axis of the ears and perpendicular to the axis, and ones with the AC and RC-26 on the same side of the center depression. BTW, less we forget, it should be pointed out that the 63-65 GM Production year RC-26 Radiator Pressure Caps had different stampings similar to the 62-65 GM Production year 307 and pre-1966 GM Production year RC-15 Radiator Pressure Caps. So, it sounds like a good government research project, but if one has something better to do, you will probably want to do that. Pete

Pete,

I guess it really is a waste of time trying to determine which stampings were used in which years.

BTW, I just found a blue print that I made of a copy of some radiator caps that I once owned. The RC-26 cap and the 307 cap have the same format. The quality of my photo is not good since the photo is of a blue print copy of a regular copy.

Dave

[Paul O.]

Re: RC-26 Radiator Supply Tank Cap

David

I may blow a hole in your theory I have and others have seen known original 1968-1972 RC-26 caps with the RC-26 stamped vertical on the right ear. What we have is a small intermix of over the counter service replacement and standard factory caps with this variation of the perpendicular stamping. Just my thoughts.

[David L.]

Re: RC-26 Radiator Supply Tank Cap

David

I may blow a hole in your theory I have and others have seen known original 1968-1972 RC-26 caps with the RC-26 stamped vertical on the right ear. What we have is a small intermix of over the counter service replacement and standard factory caps with this variation of the perpendicular stamping. Just my thoughts.

Paul,

I appreciate your comment. You may have blown a hole in my theory but that's what this technical discussion is all about. It now seems like the caps with both the horizontal and vertical "15#" & RC-26" stampings were probably issued from 1966 to 1972.

The 3rd type of RC-26 cap with the "RC-26" stamped on the left side near the "AC" and the "MADE IN U.S.A." & PAT'D" stamping on the right side might be the earliest version as the format is the same as the "362" and "307" caps as shown in my poor quality photos in my post @ 11:14 PM on 11/05/2012.

Dave

[Wayne M.]

Re: RC-26 Radiator Supply Tank Cap

The quality of my photo is not good since the photo is of a blue print copy of a regular copy. .. Dave

Dave -- these two pics might be the ones of the type that you're refering to in your blueprint, from the pre-'66 era. [307 above, RC26 below]



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[Terry M.]

Re: RC-26 Radiator Supply Tank Cap

Neat double stamp on the second one. Kind of makes one wonder if the #15 and RC-26 wasn't a second stamping operation after the bulk of the cap was formed and stamped. Kind of makes one go HHMMM!!!

[Gerard F.]

Re: RC-26 Radiator Supply Tank Cap

Dave,

I still have my original cap for a June 67 SB:



The supply tank was changed about 20 years ago but not the cap. The cap is a little cruddy but on the car and I think it still works. Haven't had any problems with it.

However, I always carry a spare repro cap with me on trips.

[Peter L.]

Re: RC-26 Radiator Supply Tank Cap

Dave - I didn't study your photos initially, but after looking at the cap I the right I'm curious about the 15#/RC-26 stamping being just to the right of the center depression and not on the ear. Does this cap have the typical AC radiator pressure cap lower seal and valve? Pete

[Wayne M.]

Re: RC-26 Radiator Supply Tank Cap

Neat double stamp on the second one. Kind of makes one wonder if the #15 and RC-26 wasn't a second stamping operation after the bulk of the cap was formed and stamped. Kind of makes one go HHMMM!!!

Terry: Never heard that theory before, but it makes perfect sense. ie: During this '63-5 timeframe, all AC caps were initially stamped with standard markings, then stamped (separately) according to intended application, probably prior to assembly..

Your post even prompted me to take some paint remover (enamel) to remove those black marks, and have a closer look.

[David L.]

Re: RC-26 Radiator Supply Tank Cap

Jerry,

The cap is in great shape for being 45 years old. It must be that nice California weather. It's a different story in the Northeast.
Thanks for your contribution.

Dave

[Gerard F.]

Re: RC-26 Radiator Supply Tank Cap

Dave,

I did zinc paint it at one time in the past, I forget the product I used. It actually came out nice but it is beginning to flake off as in the picture.

I have the capability to zinc plate things, but knowing the plating process I didn't want to screw up the aluminum rivet or the pressure sensitivity. Plating would screw up the rivet.