Radiator cap not fit, anyone have similar problem?

[diyforever]

I ordered and received new radiator cap model A-8100-B. Seems that it bottoms out at the radiator shell and therefore cannot get it to grab the radiator neck. Has anyone had similar problem and if so what is generally done. I guess cut 1/4 inch from cap or grind shell neck to allow cap to fit or are there other caps or ......Appreciate your thoughts

[Mitch//pa]

what cap did you have on previously? the cap you purchased is well made and should fit. did you change the radiator or shell? you shouldn't have to grind anything

[diyforever]

The original cap was not the right one. It basically stayed on the neck by luck. Completely rusted and no tabs to grab the radiator neck. Reminds me of a flat gas cap. Came with the car. I had the radiator rodded out and hoping to put a good cap on it. I checked space between shell and radiator and there is no space. Shell completely rests on radiator.

[Barber31]

I had a similar problem but my remedy may not be what you're interested in doing. It seemed the cap would go down the radiator neck but bottom out on the radiator shell before the tabs could even reach the notches on the inner radiator neck. So instead of cutting the cap shorter I just "unfolded" the inner neck of the radiator. I basically brought the tabs higher up out of the radiator. It did the trick and no problems that I can see but that might be frowned upon by some. My radiator will eventually be replaced so it wasn't to big of a deal for me.

[Mike V. Florida]

Seems like the original owner had the same problem hence the cap used. Sound like a reproduction radiator with a neck that is too short or the pads in the bottom of the radiator are missing so the shell is resting on the cross member and the radiator is sitting too low.

[diyforever]

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Wondering if there is another type of cap that I can use while I figure out the real problem. Not sure I should run car w/o cap...

[Ron Lachniet]

I had the same problem with mine. I think some after market radiators were not the same. I just cut some off the bottom of the cap until it fit. Once the cap is on you can't tell the difference.

[Big hammer]

Post #4 and or fiddle with cap tabs I think that's what I had to do

[Mitch//pa]

alot has to do with the quality of the replacement radiator or if it has a repo shell which wont fit correctly. sawing or bending things is usually the option at that point but dont run it without a cap or a losse fitting one. my replacement 1930 Bergs radiator with original shell fits like a glove all the way around. no problems with the same cap you purchased or with a motometer

[bambooboy]

my trk came with a chrome rad shell(on front seat)when I got around to installing it,i had your same problem.i used a small 3 corner file all around top of shell.prob took off 1/4".mine was thin material,so was easy job. tom

[diyforever]

Thank you all for sharing your experiences. This forum is awesome. I'm probably over thinking it but leaning towards cutting the $19.95 cap little at a time till fits. Shell and radiator are a little more expensive. Will cut with cutting wheel and hope cap doesn't burn and discolor...

[P.S.]

I ordered a repro (Vintique) radiator cap for an all original 29 fordor. The cap came today, and like yours, does not fit. Same problem. However, the repro cap hits the "ledge" before the threads grab. I think the repro threads just don't start soon enough.

Looking at the original cap, the threads go almost clear down to the bottom whereas the repro has no threads for the bottom 1/4" of the cap.

And, before you guys climb all over me about putting a repro cap on an original car... A previous owner drilled the original cap for a motometer. It's all rusted and gross, so I wanted to go back to a stock cap without a motometer.

[LopezCarguy]

same thing I had with the repot radiator shell..I think only solution is to take it off and grind back edge down so shell sits level and then radiator cap will bottom out evenly..Dick

[Purdy Swoft]

The A-8100-B radiator cap is the tabbed 30-31 stainless steel style cap . If the cap is Vintique brand, that may be the problem . The repro Eaton caps are pretty good . If its an Eaton the cap probably is not the problem. There is a concave spacer that solders between the upper tank and the radiator neck. If the neck was removed and replaced and the spacer was left off, the cap will never fit . If the cap is the threaded 28-29 style A-8100-A chromed style , The threads never reach for me . I always have to grind a good bit off the bottom of the cap for the cap to reach the threads and tighten up .

[Drive Shaft Dave]

Originally Posted by Purdy Swoft

The A-8100-B radiator cap is the tabbed 30-31 stainless steel style cap . If the cap is Vintique brand, that may be the problem . The repro Eaton caps are pretty good . If its an Eaton the cap probably is not the problem. There is a concave spacer that solders between the upper tank and the radiator neck. If the neck was removed and replaced and the spacer was left off, the cap will never fit . If the cap is the threaded 28-29 style A-8100-A chromed style , The threads never reach for me . I always have to grind a good bit off the bottom of the cap for the cap to reach the threads and tighten up .

Purdy, I am having trouble picturing in my mind about the concave spacer that solders between the upper tank and radiator neck. Do you have a photo or diagram of this. Thanks , Dave

[Tom Wesenberg]

The 1928-9 threaded cap is made from two pieces of brass soldered together, and can't rust. I also have an example of the same cap, except it's made from chrome plated steel, so I'm sure it's an older reproduction cap.

Bert's probably has a good original nickel plate brass cap, or mint restored ones show up at the national meets.

[Mitch//pa]

the part # listed in the OP is a-8100-b is the eaton cap. i never had a problem with those fitting either

[George Miller]

Along with what ever one else said. My 30 truck has a original radiator, and a original shell from a car. The cap would not fit. What I found was the shell was raised up at the top from the braces pulling back to much. They were pulling against the hood so hard that it raised the shell just a little. Adjusted them and the cap fit.

[P.S.]

Originally Posted by Tom Wesenberg

The 1928-9 threaded cap is made from two pieces of brass soldered together, and can't rust. I also have an example of the same cap, except it's made from chrome plated steel, so I'm sure it's an older reproduction cap.

Bert's probably has a good original nickel plate brass cap, or mint restored ones show up at the national meets.

I should elaborate.

The hardware used to attach the motometer was some cheap stuff and it is what has rusted and caused the brass cap to react with it and corrode to the point of material loss. Its not salvageable.

[Tom Wesenberg]

I think Dan Bixby has very nice restored caps, but I don't have his contact information.

[Purdy Swoft]

Originally Posted by Drive Shaft Dave

Purdy, I am having trouble picturing in my mind about the concave spacer that solders between the upper tank and radiator neck. Do you have a photo or diagram of this. Thanks , Dave

Dave, I don't have a picture. I'm sure that I have one somewhere in my stuff but it would take a massive search to find it. I don't see it listed in any of my parts books . Its been a while since I replaced a radiator cap neck on a 30-31 radiator and my description may be off , It is like a big washer that acts like a shim that would slightly raise the neck. I remember this on the last one that I did . They may not all use this part. Maybe someone else that has recently replaced a neck on a 30-31 radiator will remember this.

[Pfuerst1]

This is what I have found out trying to get the damn radiator cap to fit on my 28-29 AA:

1 The treaded portion or height of a Model A radiator neck can vary up to 1/2"
2 Reproduction/after market radiators seem to have a shorter neck than an original and are "curled over" on top rather than being a straight threaded pipe. The curled over top can be difficult to thread a correct radiator cap on.
3 The neck height on some reproduction radiator shells maybe "taller" or higher on the radiator neck than with an original shell.
4 If you look at an original gas cap there are about 1/2" of threads and a 1/4" lip below them. An original radiator cap has about 5/16" of threads and a 3/16 lip. There is also a height difference, 1 1/16" for the gas cap vs. 15/16" for the radiator cap.
If you look at a gas cap there are usually three vent slots along the beginning of the threads and a vent hole in the center of the cap.
5 There are reproduction radiator caps out there which are basically an unvented gas cap. If you look closely, the three vent slots are still there but no center hole in the top of the cap. The cap is too tall and if you try to screw in onto the radiator neck it will grab a few threads and then the lip of the cap will bottom out on the top of the radiator shell and will not seal.
6 The radiator cap may use a thin neoprene gasket that is also used in the gas cap rather than the thick gasket material that should be used in the radiator cap.

So, bottom line is that one or more of these conditions can be the problem.

[Drive Shaft Dave]

Originally Posted by Purdy Swoft

Dave, I don't have a picture. I'm sure that I have one somewhere in my stuff but it would take a massive search to find it. I don't see it listed in any of my parts books . Its been a while since I replaced a radiator cap neck on a 30-31 radiator and my description may be off , It is like a big washer that acts like a shim that would slightly raise the neck. I remember this on the last one that I did . They may not all use this part. Maybe someone else that has recently replaced a neck on a 30-31 radiator will remember this.

Thanks Purdy for the info, this is something that I would never have thought of.

[P.S.]

OK, so here is a comparison of the original radiator cap (that was drilled out for a motometer) and the Vintique repro I bought from Brattons.

Look how much taller the repro on the left is than the original on the right. Even the 'knurled' part is taller on the repro. The lip at the bottom of the original is rolled over and ends up at about the middle of the flat part of the repro.

The repro won't even begin to thread onto the radiator. The original fits perfect and bottoms out on the shell at exactly the same time it gets snug on the washer.

Any ideas?

[Pfuerst1]

The radiator cap for a 28-29 from Vinitque is basically an unvented gas cap with a wimpy neoprene gasket in it. It will not seat down and seal the radiator because it is about a 1/4" taller than a real radiator cap so it bottoms out on the radiator shell. Another good example of where reproduction parts aren't. Anyone know of a supplier that makes a real radiator cap??

[Tom Wesenberg]

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Try Bert's for the real cap. Even if it's a bit rough, at least it will fit and work. I install my rough cap for normal use. No reason to let a thief have my good cap.

[Steves46]

I know this is an old thread but I just received my A8100C Cap(not the B series) from Mikes A Fordable Parts and it will not fit and seal properly.

[BORN2L8]

When I got my new cap it wouldn't fit either. First strike for me was an older aftermarket honeycomb radiator. The neck on the radiator was too low and the rim at the shell hole wouldn't allow the cap to go in far enough to seat. I measured the distance from the radiator neck seat area to the bottom of the shell hole then transfered that measurement to the new cap. This was from the seat area on the cap down. I then measured that distance to figure how much shorter to cut the cap marking that on the outside. I used masking tape to mark the cut on both sides of the line to protect the surface. I slowly cut the new cap bottom short with a hacksaw. I cleaned up the edges with a file and sanding. Worked fine and you can't notice the cap was shortened when its on.

[Kit Foster]

I had this same problem with a restored 30 Standard Roadster I bought about 18 months ago. It came with a Ford script MotoMeter, which I disliked (ruins the looks, I think and the car never overheated), so I removed it and bought a repro cap (Macs 28-24548-1, if it matters). Would not "snick" into place and remained loose. All of the possibilities mentioned in this thread seemed plausible. I did not have complete knowledge about the parts and processes used in the restoration. The radiator mounting looked right - don't know if the radiator is original. However, I have a nearly identical unrestored car (bought the "new" roadster because I realized I would probably not live long enough nor have enough money to finish the old one), so I tried its old cap on the new car. Fits a treat, and snicks properly into place.

In comparing the two, I find the "ears" on the original cap are a thin-ish spring steel, with give to them. The repro cap has thick, immovable ears, with no give. Does anyone make repro caps with spring steel ears?