Compression tester failed, need orings ?

[LeWidget]

Hi all,

I have a cheap Compression tester that I picked up some time ago. Went to use it, and couldn't get anything to happen. When I was testing, the needle would wiggle a little, but couldn't hold pressure.
A quick inspection, looks like a couple o-rings are dead (1 is now, broken). Question is, what's the more accurate way of testing to see what size o-ring you need?
I have a digital caliper, but figure, if they're broken/old/swollen/flattened etc.. then it likely wouldn't help a great deal using the calipers as the o-ring would be too deformed to get an accurate measurement ???
So is there an alternative way, or rule-of-thumb for finding out the size needed?

Just in-case, I did measure the smaller one, as it appears better condition than the other. I read (approx) ID = 2mm, OD = 5mm, CS = 1.7mm. Not sure if O-Rings come in specific sizes only, so I'm assuming a new one would be close to these specs ?

https://imgur.com/lqXMicu
https://imgur.com/edmbuzb
https://imgur.com/JrXdJ1w

Thanks in advance.

[edit] Can't seem to add pictures, but here's some links to them.
[edit 2] Taking another look, it looks like the pressure could be escaping through the connector that attaches to the gauge? Does anyone know how it suppose to seal off to hold pressure ?

https://imgur.com/2IN7JB1
https://imgur.com/9OWFKQd

 

[Wrench97]

Most hardware, auto parts stores have a assortment box take the old ones and match them up.

 

[American Locomotive]

That screw looking thing I believe is supposed to function like a check valve. It only lets air in one way. If that fails, you won't build pressure.

 

[CR888]

New Schrader valve.

 

[RedneckWelder]

If you take it to a hydraulic shop or equipment dealer they have oring cones and parts books for sizes, thicknesses, material types

Glue the broken back together and you’ll probably be able to pick it from an assortment at a hardware store but if you can’t take it to a place that specializes in them

 

[Legion Prime]

Just take the tester in with you. I had to do this last fall, they'll open up their box o' Orings and see which ones fit and you're done. It really is that simple. If they have a service dept you may even get a free schrader valve if you ask nicely. If not what's a couple bucks? Better than taking it home and then finding out it wasn't just the Orings.

 

[toplessHO]

New Schrader valve.

word of caution
all schrader valves arent created equal
IIRC the compression tester used a white band... or was that black?
You want one designed for compression tester not a tire valve or A/C

 

[LeWidget]

Thanks guys, I'll see if there's any Hydraulic places nearby and head over. Looking over this thing, how is it suppose to work?
I thought there would have been a one-way valve to prevent pressure backing out, so when you use it on an engine, every time it cranks, it pushes pressure into the gauge to give a reading, then suppose to lock it in to give a final reading ? I don't see a one-way valve anywhere, so how does it hold the pressure ?

[edit] In case any places don't have replacement schrader release valves, do they have a specific name? I did a quick google, but only came back with compression testers, no replacement valves... even ebay had nothing.. would have thought you could get one from there.

Thanks again, I'll hopefully get out there today and find a place.

 

[Legion Prime]

The schrader valve is the one way valve. Cylinder pressure overcomes the spring tension holding it closed and pressurized air enters through the valve and once the pressure in the gauge equalizes with the cylinder pressure the schrader valve closes.

 

[LeWidget]

The schrader valve is the one way valve. Cylinder pressure overcomes the spring tension holding it closed and pressurized air enters through the valve and once the pressure in the gauge equalizes with the cylinder pressure the schrader valve closes.

Oh ok, I was thinking it was the release valve to depressurise the tester. So the valve seems to be in the hose itself, closest to the bit that screws into the sparkplug hole..

https://imgur.com/LZnVuI7
https://imgur.com/CawtM7U
https://imgur.com/T7KzshY
https://imgur.com/bzbtpjm
https://imgur.com/iZou6ia

With the one-way valve, it seems loose. Shaking it, you can hear is moving about. If I blow into if, air moves through, but I have to **** a little to get it to close, so whether the spring is gone, or it's a different design, which closes as the piston goes down, creating a sucking force which closes this particular one ?
Not sure if it came like that (have only used the tool 1-2x), or it need replacement as others suggested. It looks like a cheapy from eBay, that I picked up as I like to tinker with mowers/trimmers, and do my own work on cars, but I don't think I've used it on a car yet....

Looking at the valve, looks like it's clamped on. Assuming the valve it buggered, might be cheaper to get a new hose piece, rather than pay someone to unclamp > replace > reclamp ?


Thanks again, much appreciated

 

[Legion Prime]

Yes you can just see the schrader valve in the very center in that first pic. It certainly sounds like all the spring tension is gone if not the spring itself. It should unscrew with a valve core tool and a new one sounds like it should get you going again. A tire schrader valve will work but it likely has a stiffer spring than the one your tester came with. It should work but give a low reading. If it starts working with a schrader from a tire at least then you know it's the valve that's bad and not the gauge. These guys ought to get you back up and running then.
https://www.ebay.com/itm/Compression-Tester-Replacement-VALVE-CORES-pack-of-3-for-gas-engine-testers-New/254355224763

 

[CR888]

If its a cheap'n'nasty China compression tester, it may be best to buy a new one, keep the gauge to make a pressure tester or something. Cheap CT's are hardly expensive. Personally I'd buy a good quality used CT with all the adapters from a company like OTC, SO, Matco etc that will be worth fixing when/if it breaks one day.

 

[LeWidget]

Thanks guys. I picked up a cheap valve stem remover from ebay, one with 2 sizes, but the smaller size is too large for the hole :/. I couldn't find a smaller tool (still looking)... is there a specific tool/size designed for this particular job? Still have yet to get to a local hydraulic place, who would likely have one, but wouldn't mind a spare for the toolbox for future use.
https://www.ebay.com.au/itm/2-Way-W...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

The hole for the valve on the compression tester looks to be about 3.5mm / 0.13' wide. The tool I picked up is approx 4.4mm / 0.18'.


Thanks,

 

[redmondjp]

I often use a small straight-blade pocket screwdriver as a schrader valve removal tool - have you tried that?

 

[LeWidget]

I often use a small straight-blade pocket screwdriver as a schrader valve removal tool - have you tried that?

Hey, thanks for the tip, I'll see if I can find one and give it a shot. Just a flat head ?
I did think about getting a small screwdriver, cutting the head off, then grinding a slot, essentially making my own mini removal tool.

 

[decableguy2000]

The schrader valves are white for compression testers. NAPA should have them.

 

[ihateminimumwage]

Milton 1251-2 is the schrader for gas compression testers. Best price I've found is through Tooltopia.

 

[redmondjp]

Hey, thanks for the tip, I'll see if I can find one and give it a shot. Just a flat head ?
I did think about getting a small screwdriver, cutting the head off, then grinding a slot, essentially making my own mini removal tool.

Yes, just a flat head, or two - one on each side of the valve on the flats. As long as the width of the blade is narrow. I've had this get me out of a pinch or two, maybe even on my own compression tester which uses two schrader valves (one for pressure release on the front).