The Stovebolt Site Forums The Shop Area Engine Shop GMC 302 Freeze Plugs

I’m working on my Big Bolt again (1953 350-24 with a GMC 302), and finally got the cooling system plumbed up and filled with water, only to realize that there are 3 of the freeze plugs that are rusted through and leaking!

The freeze plugs seem to measure 1.210” by measuring the block (with the plugs still installed as I don’t want to pull them without having replacements)… I can’t seem to find a freeze plug online anywhere that is 1.210”…. 1 see 1-1/8 and 1-1/4 everywhere, but none that are 1.210!

Help!

I have found that Dorman makes 1-7/32 plugs but they list them as being for 1.222-1.235” application.

I have also found Dormans 1-3/16 plug which is for 1.187-1.199”

It seems the 302 may use an odd ball size that is not available anymore?

GMC Master Parts Book lists five "Engine Cylinder Block plugs" part number 663032 at 1 1/4" for all 228-302 GMC sixes from 1939 to 1960.

Thanks for the reply.
I’ll have to knock a plug or two out and get better measurements with the holes cleaned up.
The GM part number you listed will definitely point me in the right direction!

The 663032 cross references to a Dorman 555-022 which is listed as the 1-7/32 one I found earlier. I ordered a set of them and we will see how that goes tomorrow! I’ll check back then!

Let’s see some photos of your progress. We are always appreciative of showing our pride and joy!

For sure! I will update my build thread in the project journals section soon! Made decent progress over the past couple of weeks. Now I’m fighting freeze plugs. Once they are fixed and I figure out why it won’t pump it’s own fuel then I will take some pics and update the build thread!
I appreciate everyone’s help as the parts and knowledge on these old “big bolts” is very limited!

Workinpro…..
Sure like the truck on your project journal, Is this the same one? ……’53 .
On the fuel pumping situation, on my 54 302, I had it quit pumping, opened it expecting
a rotten old diaphragm ruptured, but found quite new looking parts, diaphragm and all.
Put it back together and it seemed to have been plugged up from old fuel or something.
Worked fine!
Hope yours is as simple.
Love the truck.