67 GMC

Trying to make a compression tester. Got a gauge and looking to make a fitting to fit the spark plug hole. Just wondering if it's a metric thread or NPT and if anyone else has done this.

A friend lets me borrow his compression tester but I wanted something that you can attach and leave on for "1 man" operation.

Thanks

RenegadeT

I doubt its NPT or metric, probably standard SAE threads. I'm not sure what you're trying to do, a typical $40 compression gauge has a valve to allow one man operation. You can even borrow one from the parts stores for free (refundable deposit required)

mike mike

I made a fitting so I could put compressed air in spark plug hole to hold valves closed when changing valve seals. I knocked the porcelain out of the metal end of a sparkplug and welded a fitting on.

ETexas XJ

The rubber whip ends of my compression gauge set allow for the same thing.

Another handy tool I built is a low side a/c (R-134) coupler with an air fitting on it to put shop air into an empty a/c system. Finds leaks much better than adding dye and wasting refrigerant. Just be sure you have dry air and vac it down real good after repair.

DFlintstone

U changing seals? You can feed a length...small nylon is good, a length of cord into the hole, then bring the piston up with a wrench to hold the valves up.

Best to make sure that you don't loose the end in there!

ETexas XJ

Also a good way to break a crank bolt loose (or reinstall) if you don't have air tools handy.

67 GMC

I'd like to leave the gauge hooked up to the cylinder to see what's going on for the 4 cycles. The compression gauge only shows the max compression and you have to hold it to the plug. I want to see what's happening when it's running. I've got a no combustion going on. Got spark, got fuel and compression is 140. I'm trying to see if I can tell what the valves are doing. Is my exhaust valve closed? Can't figure it out and I don't want to take the head off at this point.

I've got a guage that does pressure and vacuum.

cruiser54

Ever thought of using a vacuum gauge to accomplish your task?

cruiser54

Ever think about using a vacuum gauge? Check out this link.

http://www.classictruckshop.com/club...ts/vac/uum.htm

Turbo X_J

If you have fuel vapor
+ O2
@ 140 psi
and you add a spark, it's gonna go,
no if's,
and's,
or but's.



ETA:
You do realize when doing a compression test, all spark plugs are removed & the throttle plate is blocked wide open, right? As far as making your own tester, probably easier to either borrow one from the autopart stores or they are like $20 from Amazon.
Thread should be 14mm x 1.25

cruiser54

Yep. What kind of spark? Is it blue or orange? Where are you checking for spark?

67 GMC

Still the same. All new plugs. New Cap, New Rotor, switched working plug to #1, no difference. Change #1 wire, no difference, Changed #1 injector, no difference. Injector wire on, no difference (but fuel smell) and fuel on plug. I have a new Borg Warner injector to try but didn't have time this week to get to it.

When I did the compression check, I had all plugs out, fuel pump relay out and coil to distributor wire off. I didn't "block the throttle plate open" as the other poster mentioned. Would that cause higher compression readings? During compression, the intake and exhaust are both closed, so I don't see what it does to have the throttle plate open as far as measuring highest compression. That's what the compression gauge is doing, stopping at the highest setting.

Good news is that I got the radio working! I also discovered a remote car starter (or something like that) is present. There's a switch under the dash that say temp Cold, off, temp warm. When I first got the Jeep, nothing happened when I moved this switch around. Now that I've found two or three blown fuses and replaced them and a few inline fuses, the clock in the Jeep started to work and so did the radio. Then, I switched this switch to temp cold and the fuel pump primed a about 2 seconds later, the jeep started up with the key not in the ignition! Not too thrilled with this development (I don't have the key fob). I'm thinking about taking this out but it's got a lot of wires coming out and a lot of splices. Why do people do this????!!!!

67 GMC

I do have one (I use if for adjusting my Quadrajet carb on my '67). Would I just pick any vacuum line or is there a specific spot?

67 GMC

This is a good idea (breaking a spark plug is cheap!)

cruiser54

On the intake manifold. Might have to T it in with the main line that runs over to the passenger side for the "ball".

So only #1 is dead?