CMP GM Dash Oil Pressure thread size?
 

Does anybody know the thread size for an early GM commercial style dash oil pressure gauge? It doesn't appear to be pipe thread as used on Chev fuel pumps (just a bit smaller) and almost looks like it would take a compression fitting but won't. If it is a compression fitting it might just be my threads are a little damaged and I could retap...but only if that's what it is.

Any ideas?

Looking at gauges I have and by parallel to other parts of the engine oiling system, not from any sure knowledge, my guess is that it would be a Weatherhead fitting. See attached photos of gauge and fitting. Bob Carriere was speaking with someone (from the Kingston area?) who claimed they were available from Motion Industries Canada (in Ottawa) but that you had to buy a bag of 10 to get them. Motion also has a branch in London.
Notes: This is a 2 part compression fitting (tapered nut that fits on the line and matching socket in the gauge. (There were also fittings made with the weatherhead socket and a 1/8 pipe thread that were used on the engine block (for pressure gauge and in different size for the oil filter lines)) Weatherhead has developed into a sub-brand of Eaton for many types of fittings - no longer just the type seen here.

Grant, you are amazing. It appears to be a Weatherhead (Eaton) 6100X2 for 1/8" tube and 5/16-24 threads. Motion Industries lists them at $0.87 each so even if I have to splurge and get a bag of 10 I'm good. The London location might be a 5 minute drive from my office!!

Not sure if this will help at all.

I Bow to......
 

....to the Guru!!!!!

Any chance it’s an SEA fitting or JIC one?

Last night going with the Weatherhead tip I found a Chev restorer's website that confirms the 6100X2. It also talks about the original line being 1/8" steel but that can safely be replaced with 1/8" copper that is much easier to find today. My remaining question is whether 1/8" (primed) will carry the pressure from the engine to the gauge over ~10' or if I should step it up to 3/16" or even 1/4" tube.

The rule in hydraulics is that pressure is equal and undiminished in all directions. If it were a matter of flow, sure go bigger. But pressure...as long as it is not pinched closed 1/8 should work.

I climbed into the Otter today and took of a picture of the rear of the oil gauge. It has the larger tube size and long SAE fitting. The rest of the line is also larger then 1/8”. I’m wondering if there was a change that wasn’t reflected in the parts manual.

Some close up of the fittings from my Cab13. I realize the gauge is the later style but using to show the other type of fitting on the back side.

The round gauge is JIC isn't it? An American standard gauge.

40 psi +
 

Hi All

I'm using 1/8 inch copper and plastic on 235 and 261 engines which run 42+PSI on the pressure to the gauge with no problems. With the non 216 engines 5-20 PSI 1/8 copper works fine on the 235 & 261 engines with higher oil pressure I've installed a T and a second gauge with higher range to monitor oil pressure.

The original gauges, early design, just hit the pin at 30PSI while the second gauge reads around 42 PSI, the original oil gauge has been being over pressured with no ill effects for years.

Cheers Phil

Interesting. If you look carefully at my pic of the Chev gauge below you'll see "0" on the left and "30" on the right, perfect range for a splash 216. Yet painted on the glass dash panel for a GMC 270 (the panel was Fox) the range is "0" to "80" and the 0/30 would be completely covered. But pressure is pressure so how would the gauge figure out which scale to use?

Is the part number for the Fox gauge the same as for the trucks with the 216? If so, the only way I can think of that you could make the gauge read properly for 80 vice 30 would be to re calibrate the spring tension on the gauge itself.

This is why I’m thinking there might be an error in the parts books for the Fox and Otter. I’ll have a go through the GM service bulletins for the Fox and Otter and see if anything mentions that oil gauge.

I got ten Weatherhead Eaton 6100X2 fittings today and they fit the back of the oil pressure gauge perfectly. Looking at the bevels on the male and female ends screwing in the fitting could operate as a compression fitting on the 1/8" tubing (or if not perhaps a flare may be required).

As to Rob's thought that the gauges for 216 and 270 engines may have different numbers and different pressures he may be right. The gauge I have marked for 30 pounds has the numbers 1506373 and 1506375 on it and the one in the Fox parts book is 1506377, presumably matching the 80 pound upper range painted on the instrument cluster glass. Looking at the 30 pound gauge guts I don't think there would be any damage if it was subjected to higher pressure. You just wouldn't know what the pressure was if it read over 30.

Bruce,

I don’t have access to any Fox or Otter manuals but I do have access to C60X manuals.

When Rob posed the question of different pressures/gauges between the 216 and 270 engines, I had a look to see what I could find.

According to MB-C2 the early instrument cluster was graduated 0-15-30 for the 216 engine, and the oil pump was capable of producing 14 psi at 2000 rpm. Various Chev parts lists (Other than C60X) list the correct oil pressure gauge as 1506092.

According to M660-C1 the early instrument cluster was graduated 0-40-80 for the 270 engine, and the oil pump was capable of producing 35-40 psi at 1000 rpm. C60X-04 parts list shows oil pressure gauges 1506379 ( early with red pointer) and 1506377 (later with white pointer) which is also the same number you quoted from the Fox parts list.

If we disregard the 0 and 30 in the upper corners of your gauge, the part number seems to be much closer to the 0-80 gauges for the 270 engines than it is to the part number for the 216 engines.

Perhaps a test is in order to determine the actual range.

When the switch was made to individual gauges, both 216 and 279 engined vehicles used the same round gauge with part number 1506359. I presume the gauge had sufficient range to accommodate both types of engine.

Thanks Colin, that's a ton of research and very helpful. You may be right about the Fox gauge given the number ranges. The cluster and gauge was in a NOS Fox dash and didn't looked messed with (for instance, the temp gauge was electric and had the instrument cluster been civilian or from a 216 Chev it would have been mechanical).

Here is the information for the Otter oil gauge.

I bet the Otter and Fox gauge not only adjusted for pressure but allowed for a larger diameter line. Jordan, is the Otter line 3/16" or 1/4"?

Bruce/Jordan,

I have done some more reading.

Oil pressure gauge pipes and fittings can be found at group number 1.519 in the Chev/GM parts lists.

Attached are two examples of the listings for 216 engined vehicles.

Pipe Assy 592818 started to be used upon the transition to individual round gauges.

The other tubing, union and nipple were used with the early instrument cluster.

The mentioned “Tubing unit” seems to be a parts listing of bulk coils of tubing for workshops. ( image attached)

Info regarding C60X to follow.

While the listings for the 216 engined CMPs were easy to follow, the listings for C60X are not.

C60X-01 (October ‘42) lists 1/4” (upper) and 3/16” (lower) tubing. None of the listed fittings are the same as those for 216 engined CMPs.

C60X-04 ( January ‘45) lists 1/8” tubing, but the other fittings have the same part numbers as those for the larger tubing (a mistake?)

I am not sure what conclusions to draw, but please have a look at group 1.519 in your Fox and Otter parts lists.

Here is the group 1.519 from the Otter parts listing.

It’s 1/4” OD tubing to the gauge. I suspect the line in my Otter is original. I can’t prove it but all the rest is still very much original and unmucked with.

I also found the below picture from the internet. It was a page that identified differences between Chevy and GMC dashes. The gauge on the left was for Chevy and the gauge on the right is for GMC. The difference was the Chevy 216 vs GMC 270.

Here is an NOS glass (GM 1566971) for the Otter and others that shared the same part number along with the box it came in.

This confirms the 80psi for the oil gauge.

"QTY. 2" They just KNOW you are going to break one installing it...