my first compression test. please advise how to

So the engines coming out of the TT over christmas.

Last thing to do before it happens is a compression test.
Just wondering how to do it exactly. Ive done a bit of reading but still unsure about a few things.

Is this the correct process? Few questions along the way.

1.Go to supercheap auto and buy a generic compression tester for 30 bucks

2. Remove the injector connectors, coilpack connectors, coilpacks.
I dont need to remove the fuel relay or anything do I? Injector plug removal will stop engine from flooding?

3. Do I remove one single spark plug at a time? Then replace when I do the next cylinder?

4. Wide-open throttle. Crank the motor about 5 revolutions. Should reach a stable reading. Record reading.

5. Motor will be cold as it doesnt have intakes or anything on. Hasnt run for about 6 months. This ok?

6. I just do this once for each cylinder? Thats it? Then I can note down the values and strip the car down?

 

Compression test

Correct

Remove all the spark plugs
Not applicable.

 

Get a leakdown tester if you can afford it.

Itll tell you alot more about each cylinder..

As the battery drains your reading will drop.

 

Wrong, don't even bother........... Ask Shane, His cheap tester says his engine is an NA


LOL

BTW, I test with all plugs out and good battery..

 

what kind of tester would do the job and from where?

Considering i only plan to use it once....

 

Do you have an air compressor??

This is the tester that gets around stores...

http://www.ebay.com.au/itm/LEAK-DOW...=AU_Car_Parts_Accessories&hash=item2c68a615f4

I have one and it works well, just the connection is charged air style, not nitto, so some fiddling needs to be done to connect it to a compressor but they work.

 

lol, no, my 'cheap tester' is actually quite a good one, just it's 20 years old and has decided 0 is now 50. Subtract 50 from the reading and it's still accurate

 

Using a leak down tester is quite a bit more complicated and to get accurate readings you need to spend $300-400+.

The cheap eBay ones (like I have ) provide a relative figure for each cylinder once you get them setup, which if you're testing the health of an engine is all you really need, but if you're doing it to post values to sell, it's probably not really accurate enough, imo.

 

I bought a repco branded one. Seems OK. Was under 100

 

Id still take a cheap leak tester over a cheap compression tester anyday after the problems ive recenlty had with them.

The deal with the leak tester is you have to SET the needle by turning a valve on the unit.

If its cheap it will be hard to get the needle exactly on set, and once you have it will still wander past the mark if you leave it too long.

So get it as good as you can, and don't change it, then test all your cylinders and find the best one.

Start with cylinder 1, at TDC with all timing marks aligned and work your way thru 2,3,4,5,6 in that order, rotating the crank clockwise to bring each cylinder up to TDC. Check with a skewer or something

Don't rotate counter clockwise as it loosens the timing belt and you'll have to do a fair few revolutions clockwise to fix it.

Once you have your best cylinder connect the leak tester to it and tune the gauge to the SET position. Its much more accurate with air flowing thru it and wont jump around.

Now retest all your cylinders.

 

Tip, take your top left timing cover off, then mark your intake timing gear from the TDC mark equally in 6 increments. Now as you move from cylinder to cylinder simply line up the next mark on the timing gear. Much easier than sticking something down the plug hole

 

Key thing as you've pointed out with these cheap testers, they will creep, but don't reset it again between cylinders, otherwise the relative comparison will be all out. Set it once and then don't touch it until you've tested each cylinder. The figure won't necessarily be accurate, but each cylinder will be accurate to each other.

A used engine around 15-20% is good. A new engine you should see around 10%. But again you're looking for consistency across cylinders of around 5% variance, 10% max.

 

Agree, if you know what you're doing they'll tell you a lot more than a compression tester. ie a hairline crack in a valve will still show good compression, but it'll stand out like dogs balls with a leak down tester.

 

Gauges

can be repaired & recalibrated.
Alternatively, the damaged gauge could be replaced with a quality digital gauge.

 

https://www.alltools.com.au/shop/index.php/560/2476_Cylinder_Compression_Tester_

You don't need to spend a lot. Just be selective. This ABW one is quite good.

Should be easy to find

 

Agree, their gear's generally pretty good.

 

Why are you doing a comp test? If it hasn't been run in 6 months, chances are the numbers will be low anyway.

Remove efi fuse beside brake booster
Remove balance tube
Remove all spark plugs
Crank to get highest reading on each cylinder

No need to hold throttles open as balance tube is off, no need to disconnect injectors or cas, make sure battery is fully charged.

 

Disconnecting CAS disables fuel & spark

 

So does pulling the fuse, easier than fiddling with a probably already dodgey cas connector

 

dont know which fuse that is, or if it is printed on my fuse box.

So I can just disconnect CAS, remove balance tube, and away I go


Ok I think ill get one of those ABW ones.
Im doing the test as im parting out my car this christmas, but have left the engine intact so I could do a comp test on it. I know its in good nick, just want some numbers showing it to help sell the engine.

Id say most people are aware comp test results vary a fair bit, and not to rely on the actual numbers. I mainly want to ensure theres no cylinder creeping away from the rest, or if there is find out how much by so i can pass that onto a potential buyer.


Thanks for the tips guys.