Compression Test on Rebuilt engine - FAO Tom, Mark, Steve, etc

[Doug_RS2]

I have just done the compression test:

Cyl-1st--2nd
1--12.0--12.2
2--12.0--12.2
3--11.2--11.5
4--12.2--12.4
5--10.8--11.0

Bit of a difference

I used a Gunson tester - It has done 6387 miles since the rebuild - bit ****** off with no5.

Anyone else got any comparisons?

These should be low compression, 8.7:1 CR, so what difference, if any, should I see?

[Mihnea]

Cold or warm engine???

[Doug_RS2]

cold

[Anees786]

hiya mate i had a compression test done on my rebuilt engine the results were as follows

1- 140 psi
2- 130 psi
3- 140 psi
4 130 psi
5 120 psi

[Mark Halligan]

cold

Supposed to be hot with throttle open AFAIK?

Doug, forget those 9 bar readings I told you about, I just went and tested my comp tester by hooking it up to my 'JoeBlow' stirrup pump, and its fecked, its a bit beat up as I have had it for years and the needle is bent and catching on a rivet on the gauge face (no glass, all the good gear me ).

So for the moment the last 'accurate' readings I have were done at 150 miles into the run in and these were all 12.1 bar for all five cylinders, with engine hot.

I'd like to know what pressures we should be getting with these low comp pistons too, mind you had no real problems with knocking the other night whilst mapping as far as I can remember...Mihnea??

Mark.

[Doug_RS2]

OK - I will do them again with it hot - Is this as close to operating temps then?

And I didn't know you were supposed to open the throttle

I'm glad your car is not 9 bar Mark - because one of us would have had something seriously wrong

Where's Tom's numbers?

[audiman]

I havent done them yet. Been really busy at work unlike you and MArk who get afternoons off, or are on holiday at the moment :@

[SteveH]

I did mine shortly after the rebuild. I'm going to do them again this weekend to check for any change since running the engine in.
I got 12.3 - 12.5 Bar on all cylinders. The engine should be at a minimum of 80 degrees IIRC.

[SteveH]

Are you using low compression pistons??

140 psi = 9.5 Bar
130 psi = 8.8 Bar
120 psi = 8.1 Bar

Looks low all round

hiya mate i had a compression test done on my rebuilt engine the results were as follows

1- 140 psi
2- 130 psi
3- 140 psi
4 130 psi
5 120 psi

[Anees786]

Not that im aware of i had the test carried out by the garage. Who told me they were fine.

[Audi Parts Guru]

Gents, this may be of interest to all of you

How To Do The Compression Test,
Run the engine until it reaches normal operating temperature. Tests done on a cold engine usually show lower readings. Remove the HT leads and take out all the spark plugs. The ignition system MUST then be disabled. If this isn't done it will continue to generate high tension voltages into the HT leads which will have nowhere to go with the plugs out. These high voltages will find another route to earth and can damage the ignition system or even the car's ECU. Unplug the low tension connections to the coil or to the distributor. If you aren't sure how to disable the ignition system on your own car then check with a dealer before you start. It is also good practise to unplug the fuel injectors or disable the fuel pump, especially on cars fitted with a catalytic convertor. This prevents unburned fuel getting into the exhaust system during the test.
Screw the gauge into cylinder 1 and rest it somewhere you can see the dial while you crank the engine. Open the throttle fully either by pressing the accelerator or wedging the linkage open under the bonnet. If the throttle isn't open then air can't get into the cylinder and the readings will be far too low. Crank the engine until the gauge stops rising and count the revolutions while you do so. It should normally take no more than 10 engine revolutions (5 compression cycles) to get a full reading. You can count the cycles by watching the gauge too - each jump of the needle is one compression stroke. Write down the final reading and also make a mental note of how quickly the gauge rose on the first few cycles. Then just repeat for the other cylinders. Make sure that each cylinder reaches its highest reading after the same number of engine revolutions. If all readings are good then the test can end there. If any cylinders are low then a "wet" test can be done. This involves squirting a few ccs of oil into the cylinder and repeating the test. The oil will help seal bad rings and increase the reading but won't affect it if the problem lies in the valves or head gasket

[audiman]

Good info Paul. Should help some of the lesser ppl here

[S2central.net]

'Lesser ppl' - you crack me up Tom

[audiman]