cylinders compression test..how to?

Disconnect power to the ignition coil. Hold/wedge throttle wide open when cranking.

Don't recall what to do regarding carb setup, it's been 40 years since I touched one :D
 
Likely as good as you need.

The compression test is to do a few things but most importantly to see how consistent the cylinders are to each other. This kit will provide that. The exact number of lbs etc is nice to know but the similarity of all the cylinders is the big deal.

The compression is to some degree a function of the condition of your battery, your starter and then your engine.

You can also use it to get a leak down of each cylinder. So start a timer once you have reached a max compression level to see how long it takes each cylinder to leak down to atmospheric pressure.

If the leakdown is fast it usually speaks to the condition of your valve sealing and the longer times are related to the rings. I don’t know what a good target time is for leakdown but can look around for info.
 
Don't have to do anything to the fuel system. The float valve will work just fine even without a return line. You may smell a bit of fuel since the accel pump will squirt gas each time you open the throttle to full open as you crank the motor.
 
is a short video of how it's done... disconnecting the fuel pump is more for EFI cars as the injectors will keep spraying and that can become a fire hazard, but with carburetted cars the return line is going to feed the excess fuel back to the tank, and excess fueling isn't an issue.

It's not the number that is important, don't get hung up on this... it's the variance between the cylinders that the test determines, so a compression test simply tells you have a problem, it doesn't really tell you definitively what the problem is...

with plenty of experience however you can get a read of how quickly the gauge rises, i.e. what the readings are after 1 and 2 engine cycles etc and if the gauge "bounces" when heading upwards...and each of those indicate a particular issue... but that's not something I'm going to try and teach you as it will likely just confuse you.

A MUCH better test to actually determine the engines TRUE condition is a cylinder leakage test (leak down) but this requires a source of compressed air (and not just a small battery tyre pump) and a little bit more time, but tells you so much more. If you have a compressor available, I would say get a leak down tester instead.

SteveC
 
kmead said:
You can also use it to get a leak down of each cylinder. So start a timer once you have reached a max compression level to see how long it takes each cylinder to leak down to atmospheric pressure.

If the leakdown is fast it usually speaks to the condition of your valve sealing and the longer times are related to the rings. I don’t know what a good target time is for leakdown but can look around for info.
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actually that wont work at all, as the compression tester uses a schrader valve (like a tyre valve) in the gauge or the line to hold the pressure in the gauge, so measuring the leakdown of a compression tester simply tells you how fast the gauge is leaking air out, and has nothing to do with how quickly the cylinder loses pressure.

SteveC
 
fiatfactory said:
actually that wont work at all, as the compression tester uses a schrader valve (like a tyre valve) in the gauge or the line to hold the pressure in the gauge, so measuring the leakdown of a compression tester simply tells you how fast the gauge is leaking air out, and has nothing to do with how quickly the cylinder loses pressure.

SteveC
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Hmm. Sorry mine has a different solution, I apologize for neglecting to look carefully at the unit in the link.

Thanks for pointing this out.

Go with what Steve stated :)
 
thank you guys! @steve: actually i do have an air compressor (it's not a beast, but a small 25liter\2hp)..so try to teach me about the leakdown test!
 
I might have missed it, but all of the spark plugs should be removed for either test. In the case of a compression test it allows the engine to spin faster. And in the case of a leak down test it allows you to listen for leaks between cylinders.

The procedure for a leak down test is a bit long to describe (if all aspects are covered), but actually fairly easy to do. Might be easiest to search online for good tutorials in Italian? A small compressor should work fine. The test uses low pressure, just needs a constant supply of that pressure. So having some sort of "tank" (air reserve reservoir) on the compressor helps.

As to which test to do, it depends on what you want to find. If you are only looking to see if the engine is in relatively decent condition (not excessively worn or damaged internally), then a compression is fine and quick/easy to do. But if you suspect internal problems exist, and what to try and determine what those issues are, then a leak down test can offer more information. But a leak down test has a subjective component to part of it; if there is a leak and you want to determine the source of the leak, you need to do some detective work to listen for where the leak is and then make assessments as to why it might be leaking from there. So a little more understanding is required to benefit most from the test. Might depend on the experience and skills of the person doing the test. If you only use a leak down test to see if a leak exists, then it is no more beneficial than a compression test.
 
ghostdancing said:
i just want check how much the motor is stuffed
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If it runs fairly well and you want to see how worn the cylinders are, then a compression test is fine.
If it does not run and you want to know what is broken inside, then a leak down test is better.
 
In that case I'd just do a compression test. Easier to do, less chance of error, and the equipment is less expensive. Here in the USA many large chain stores for automotive parts will lend you such equipment. You pay a deposit that is returned when the tool is returned, so no cost. Not sure if something like that is available over there?
 
Then again. The motor runs fine, the owner is happy cruising along and enjoying his car. Then he does a compression test, finds one cylinder is out of spec...maybe something like 150-150-125-150 and gets totally upset, loses sleep every night, barks at the wife and parks the car and it sits there for 10 years.

Someone has to be the voice of common sense around here.

Just some Xweb humor, it doesn't hurt to know what's going on in ones motor...personally I like an oil pressure gauge.
 
So true. Or, the owner has not done a compression test and lays awake a night wondering if there might be a low cylinder. :confused: Then barks at the wife and is afraid to drive the car in case it has damage. :D
 
I find that when I get good compression or leakdown results, I stay awake at night wondering whether I did the test right...
 
And if you get bad results, you keep asking yourself maybe my readings were wrong and the engine is good. :confused:
 
Schroedingers compression, both consistent and inconsistent at the same time, both high and low at the same time until you actually check it...

Basically you are just damned unless you just go with, hey I am good with the way things are, finding out the reality of exactly what the way things are really does you very little good.
 
Good to see we are all neurotic. Back on topic, a compression test on an X is relatively easy, takes maybe 30 minutes and your results posted here will be wonderful for us to talk about.
 
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