Where to get tool to check engine compression ?

DeBordEngineMan

DeBordEngineMan

Senior Member
I have seen and heard guys on this forum talk about a gauge that threads into the sparkplug holes to check how much compression a engine has I think the plugs are 7/8 thread? This freaks most guys out at the local parts stores! Just like to have one to check my old stock engine. Is this something a local parts house would have or Do I need to order one from an A model supply house? Thanks for the help Robert DeBord
 
I do not think I have ever seen an adaptor available at a regular parts house. May be a Model A parts Supplier may have one BUT I just made one using an old spark plug.

Chris
 
that spark plug hole is exactly the same thread setup as standard gas, water, and emt fittings, works well with pneumatics too, i found all that under one roof of the shop. a hose, clamps and a decent gauge , vacuum and compression . just for kicks.
 
You need any compression checker that has 14mm plug threads plus an adapter made to use 14mm plugs in a 7/8 hole. This adapter is $6.50 at Snyders.
A12405ADP-8019-xl.jpg
 
NPT - National Pipe Thread


I bought an adapter from Snyder's.

If you're handy, you could make one up from the shell of an old spark-plug.

Still haven't gotten around to actually CHECKING the compression yet... :rolleyes:
 
another easy comp check is to see if it will run on 1 cylinder before you go out to the store and get all this stuff. Start your car up, bring the throttle down a little, pull the spark all the way down. Then grab a screw driver, and slowly take each spark plug wire off one at a time, utill you get to the last one. You may have to give it a little more throttle as you go. But if you get it running on one cylinder and it stays running, you comp is good, at least you valves are in decent shape and your rings are sealed. then do this test to every single cylinder. If you get one cylinder that just will not run like this, or runs way worse than the others, that is your problem cylinder. Most people dont beleive a model a will run on one cylinder, but it will lol ive done it mulitiple times. try it, see what happens. BTW, dont take of the cylinder wire, untill you have the next cylinder wire already hooked up, because then it really wont run lol. It wont take more than 5 minutes and it sure beats 30 minutes on phone calls with part suppliers, or 15 drive to the store to get guages.
 
Logan said:
another easy comp check is to see if it will run on 1 cylinder before you go out to the store and get all this stuff. Start your car up, bring the throttle down a little, pull the spark all the way down. Then grab a screw driver, and slowly take each spark plug wire off one at a time, utill you get to the last one. You may have to give it a little more throttle as you go. But if you get it running on one cylinder and it stays running, you comp is good, at least you valves are in decent shape and your rings are sealed. then do this test to every single cylinder. If you get one cylinder that just will not run like this, or runs way worse than the others, that is your problem cylinder. Most people dont beleive a model a will run on one cylinder, but it will lol ive done it mulitiple times. try it, see what happens. BTW, dont take of the cylinder wire, untill you have the next cylinder wire already hooked up, because then it really wont run lol. It wont take more than 5 minutes and it sure beats 30 minutes on phone calls with part suppliers, or 15 drive to the store to get guages.
Click to expand...

You're better off to SHORT each plug terminal rather than make an OPEN. When you make an open you make the coil work harder, plus the high voltage will seek the path of least reistence to ground, and that may be through the coil internally, or through the rotor to the distributor shaft, or it may be through the distributor body to an another plug. Once a path is established, it makes it easier for a misfire in the future.
 
"buy a rubber tipped compression tester" I have an old SUN unit since high school but the rubber is smaller than the 7/8 hole for the plugs.
 
i just use mine with the big rubber end . works fine . hold it in the hole & activate the starter . no biggy ...................... steve
 
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