MTFCA Forum

I have a “Sun” 300 psi compression tester. I use it to check my T’s and at 50 psi it barley moves the gauge. I have looked and had no luck finding a 100 psi gauge. I’ve tried putting a 100 psi gauge on my tester, but it doesn’t hold the reading. Does anyone know if there is a 100 psi compression gauge made, or any ideas so I don’t have to use a 300 psi gauge. Thanks

You're looking for a pressure gauge to replace the "300" one

my internet search for "100 lb pressure gauge" brings up hundreds of gauges of every npt, dial diameter and brand imaginable

Hi Mike there are almost no compression gauges with a gauge lower than 300 psi. to take a compression test you need a good check valve to hold the pressure and a way to release the pressure. Most gauges use a shraider valve type set up to do both. not sure what you tried? from what I can figure out the sraider valve is not the same as a tire valve. and do not last very long. ( may be the heat ) Most screw in compression gauges will accept the 100 psi gauge in place of the 300 psi one. If the have a sepporate valve. ( you will need to adapt the 14mm to 1/2" pipe )
Carig.

What Scott said. Google 100 psi pressure gauge and take your pick. Take the 300 psi gauge off your tester and replace it with the 100 psi. You will probably need to make an adapter with 1/2" npt thread.

My tester had a tire fitting, so I soldered the business end of a Schrader valve into a 1/2" pipe plug.

Craig

as an aside, I put together a dandy compression tester just as you described. I love it...and at the time I made it, I loved it so much, I made 6 more and tried to hawk them. The whole project was entirely unsuccessfully. No one else shared my enthusiasm, even at cost. I eventually gave them all away, and at $0 there was great enthusiasm among each of the 6 new owners. No entrepreneur wants to be known for just making door-prizes, so the entire venture was those 7 original units and that was it.

Scott,
That looks like a very good idea. Most gauges don't have a pipe connection. The one I use has the valve and as you say doesn't hold for long. And since it just has a tapered rubber fitting to jamb into the holes I just hold it in my hand while someone else pushes the starter button and I look at the gauge while it is in.
Norm

this compression tester: https://www.amazon.com/Engine-Compressi ... 6651&psc=1

with a 100lb gauge swapped out, and a 1/2 npt end grafted on is a terrific tool.

After 3-4 compressions, all of the tubing volume is accounted for, and ultimate compression is reached and measured. Lots more cranks will not increase the compression. After the ultimate pressure is attained, it is held for review until released with the button and is an ideal one-man-band tool, and especially handy on a stem-winder.

Thanks for the info. I removed the 300 psi gauge from my tester which is above the valve. I replaced it with a handful of different 100 psi gauges and the gauge itself leaks down by the time I want to read it. Any suggestions on where I should find a 100 psi gauge? I see the gauge for fuel injection is 100 psi. Not sure if a gauge used for liquid can be used for air. Thanks

Just go to any hardware store and go into the plumbing section. Get a 60 or a 100 psi gauge. Water or air doesn’t matter.

The best choice is to buy a cheap one from Harbor Freight, remove the 300 psi gauge, and buy a 100 psi tree sprayer compression gauge from Tractor Supply.

The most accurate area of those gauges is the center third dial area and 50 psi is the most likely reading.

The device also has a valve to hold the pressure and a button to release it.

You will also need a 14 mm to 3/4th inch pipe thread adapter, like is used for modern spark plugs in the Model T engine.

The adapter is available from many of the model t suppliers.
The size I've 1/2 pipe thread.

Art Mirtes

The adapter is available from many of the model t suppliers.
The size I've 1/2 pipe thread.

Art Mirtes

The adapter is available from many of the model t suppliers.
The size I've 1/2 pipe thread.

Art Mirtes

You will also need a 14 mm to 3/4th inch pipe thread adapter...

14mm to ½" NPT

My 60's vintage gauge has the rubber nipple to fit that era plugs. I took an old Champion spark plug apart, scrapped the porcelain and put the collar back in it. Screw the plug in the head and then use my original gauge and it works just fine.

Art, you are right, the size is measured on the inside of a pipe and outside of tubing.

I get mixed up, it is called dyslexia and old age.

I had the dyslexia first.

I did get have an adapter that was welded in to an old two piece spark plug that worked good for a long time.

This would probably be the period correct one to use, it's a K R Wilson and the tip fits into the plug hole and expands when the lever is brought down against the stem it most likely had different rubber tips for other applications. Jim