Compression test

[Sandun]

Hi
Today i test the compression of my engine (948cc) Because it has some oill leak on 2nd sparking plug (come out oill from the plug hole , so i have to clean it always )

This is the result

1 plug ( i count from rediator side ) 140
2 plug (the oil leak one ) 150
3 plug 160
4plug (near the battery ) 165

How i do this test

1st i start the car (5 minutes ) , then stop and rest for cool some , remove the all plugs , fuel pump wire, ignition coil wire.
Then i test one by one (dry test )

Any wrong ? ,Please let me know , and please tell me next step to repair my car .The pic show my meter (i read red color numbers ) - Sorry i am new for this test actually 1st time.

Many Thanks
Sandun .

[Sandun]

This is 1 plug when i got result 140

[simmitc]

Hi Sandun, it sounds as if you have completed a dry compression test correctly. We would normally prefer to see readings that were within a few PSI of each other on all cylinders, whereas yours vary from 140 - 165 which is a range of 25. However, if the engine is running well then I would not worry too much for now. What we need now is a wet test as a comparison. Leave all the plugs out. Take some light oil, around SAE30, perhaps some sewing machine oil, and put about a teaspoon full in through the plug hole. Wait for a moment and then repeatg the compression test. Do this one cylinder at a time as otherwise you will force the oil out of other cylinders whilst testing the first.

Note the new readings and then we can compare with the dry ones that you already have.

After completing the tets, spin the engine a few times before refitting the plugs.

Just to re-cap, if I recall your other thread correctly, the engine is fine, but oil appears to be collecting around the plug for number 2 cylinder, but this is the only problem. If the "gasket" or sealing ring is in place and the plug is tightened correctly, then I don't really see how the oil can come from within the cylinder. Are we certain that it is not dribbling down from the rocker cover?

[Sandun]

Many Thank to you for Come to help me .

No it is no any leak from drop down oil to the sparking plug holes ,

I notice today , usually when i start the car without run( just start) , lot of carbon and oil deposit on the plugs , specially Number 2 plug lot of oily , (others also like this but not more ) - (if i run the car no problem - but after this oil come out problem i am not going to run the car )

So i thought (think ) , when i going to compression test lot of oil come out from the hole , - But it not happend like that , no oil i can see on the plug hole when i remove the compression tester .

Befor the test i remove the fuel pump wires - Please attention , is it fuel overload problem ?

As you said , Today I got wet compression test result .

1. Plug Dry 140 wet 150
2. Plug Dry 150 wet 170
3. Plug Dry 160 wet 180
4. Plug Dry 165 wet 180

What is the next please ?

[philthehill]

Sandun
Whilst the compression figures are not the best they are not that bad.

I am of the opinion that the bores are worn (born out by the increase in compression when the bores are oiled).

I personally would leave the bore wear problem well alone unless you are desperate to do something about the compressions.

What I would do is remove the head and fit new valve guides with the facility to install top hat seals (both short valve guides and top hat seals are available from ESM). Only fit the top hat seals to the inlet valve stems.. Cut the valve seats and face off the valves and lap them together.

When the head is removed you can check the condition of the bores and if necessary review and revise the way forward.

Phil

[oliver90owner]

What next? Change the plug washers. Nothing should get past the plug threads if the plug washers seal correctly.

[Chipper]

Try the test again, but jam the throttle wide open (as you are supposed to when doing a compression test), either by placing a suitable length rod between the throttle pedal and driver's seat, or making an arrangement at the carburettor throttle spindle to jam it open.

[philthehill]

Whilst holding the throttle open may make a few pounds difference in the compression poundage it will not alter the relationship between the four compression readings - they will still remain relative to one another.

Phil

[simmitc]

I'm mostly with Phil on this; and as I wrote originally, although the dry readings are not optimal, they are by no means the worst. The comparison with wet indicates that there is some wear in the engine, but nothing with which it cannot cope. I would leave the bulk of the engine alone for now and plan to recondition it when time and funds are available. After all, it's running OK.

Compression tests are really useful to diagnose certain faults, but you probably already knew that the engine was a bit worn, so what we have really done is to confirm that there is no catastrophic failure, which is good.

If I understand correctly, this still comes back to the oil collecting around the outside of number 2 plug, and I regret that I am struggling to see where it can be coming from. Even if the plug was cracked or porous, anything in the cylinder is going to be either burnt or pushed out through the exhaust valve. number 2 is not the worst bore, number 1 is, so why is there no oil there?

Can you humour me: Thoroughly clean and dry the engine. Cover the head and rocker cover with talcum powder and then run the engine. Hopefully the talc will not all be shaken or blown away. Run the engine until the oil appears. The talc should reveal a path showing where the oil has travelled. If the oil still appears around the plug without any other trace then I will have to agree that it's coming out via the plug, but I do not see how it can.

If I've got this wrong, and it's not the oil problem then please ignore these suggestions.

[pgp001]

Just to add to the above.
To either eliminate or prove that the actual plug and it sealing washer could be leaking.
Try swapping N°2 plug with one of the others and see if the problem moves with the plug to its new position or stays at N°2 cylinder.

Phil

[philthehill]

As regards the oil around No: 2 plug.

I would suggest that the plug is not seating correctly on the cylinder head because carbon at the bottom of the plug threads is not allowing the plug to go fully home and therefore not allowing the plug sealing washers to do their job. A common fault on engines that produce an excess of carbon in the combustion chamber.

When the plug is tightened it feels as if the plug is fully home and tight but it is not so allowing oil to seep past the threads.

The plug threads need to be fully run through with a greased (the grease will catch most of the crud) 14mm plug tap to clean any carbon from the threads. The plug sealing washer seat needs to be fully cleaned to remove any crud.

Once the threads are run through - spin the engine to blow out any remaining crud from the cylinders.

Phil