I have a 41 Sedan and I have an stock sending unit.

The unit bolts into the original 216 engine and also in the 235 without any adaptor.

Now I have the 848 head and it looks like I need an reduction bushing.

I found one in a spare head but it was to big (outer diameter).

Are ther different sizes made?

HELP!

Thanks, Frank

Dear Frank;

Sure are.

If you sent us the exact size you need, someone probably has one for ya.

Good luck.

I had a simular problem. I went to the auto store and bought a bag of misc sized Adaptors. I also went to the hardware store and bought a pipe reducer and found out that that doesnt work.

First, you need to reuse the original fitting as the inside is specific to the application. I believe the pre-electrical sender heads were 3/8" NPT. The later heads I believe are 1/2" NPT.
Therefore, you would need a 1/2"NPT X 3/8"NPT bushing along with the original fitting. I can try to verify the sizes when I get home from work tonight.

F;

Those sound like the right sizes.

"Years ago" there was a specific adapter for that, which held the 'bulb' & allowed It's fiting to tighten against it, sealing both the threads & the bulb. Otherwise it would leak around the line.

The smaller fitting may not be a tapered thread which NPT is.

The threads in the 'larger'(elec sender) are a tapered (NPT) thread, probably 1/2".

Someone here will have one "laying around"......

The later heads are 1/2" NPT. I'm not able at this time to verify the earlier head size, but it has to be an NPT thread. You cannot get a good seal with straight thread. All of the water related connections are tapered thread, as well as most oil ones also.

F;

Brian is correct, most (99%) are.

On this; the bulb seals against a flange in the head/adapter to make the seal. Otherwise; all you would need would be a bushing, to reduce the size.

I'll look for an adapter this weekend.

I had a similar problem with the original 216 I had in my '40. I wanted to use a modern temp gauge and no matter how had I tried, I could not get a unit to fit. One major problem I found is when I found the proper 3/8"-to-1/2" NPT adapter, the new temp probe would not fit down into the 3/8" part of the adapter. The bulb was too big! One was too short and it bottomed out against the head! One I just couldn't get to stop leaking! I never had so much frustration and over a gauge installation!

I solved my problem by going with an electric gauge instead of an mechanical one. I love mechanical gauges as you know when they don't work. The electric ones, you just never know.
With a 6 volt system and 12 volt gauge, you use a resister to step up the voltage. You can buy those at Chevys of the 40's.

Eventually I went to 12 volt system and a more modern block.

RapRap
1940 ChoppedChevyCoupe

Okay; this is a different situation.

In this case you need to drill the head to 1/2" NPT. Then the 'modern' sending units will fit, but sometimes need a bushing.

Frank already has that (modern hole) in his head.

This has driven Pro. mechanics crazy many times over the years.

Thank`s for the input Gentlemen,
but meanwhile a friend of mine did some magic on his lathe and...

... e voila. It fits it don`t leak.

Frank