Which oil for Wet Compression test

[Dante]

Hi all,
I am about to do a compression test and was wondering about the 'wet test' sequence where I am to inject some oil into the cylinder.

My research indicates that I should use Grade 30 oil and I was wondering if I shouldn't be using the usual oil (in my case 20W/50 for the 2a).

If have to use a Grade 30, can I use my 4 stroke Lawn mower Grade 30 oil

Thanks,
Dante

[JohnE]

Mate
not that i am an expert,but i believe any engine oil will do, just squirt it in with an oil can, the pump type, all it does is take up the slack hydraulically in the rings etc.



john

[DEFENDERZOOK]

yep.....what he said.......engine oil......

just make sure to use the same amount in each cylinder.......
eg if you use 3 squirts in the first cylinder.......then use the same amount in the others as well.......

[harry]

all it does is take up the slack hydraulically in the rings etc.

isn't that what you want to know about?
you need to know about leaking rings and leaking valves, and that is why you are doing the test.
personally i consider cranking type compression tests as 'battery capacity' tests.
anyway, if you have a lower cylinder pressure than the others [or multiple cyl's] then put a couple of squirts in, this will assist the rings to seal, and retest the cyl's, if the bad one's go away then the problem is assumed to be rings. note - all the cyl's comp pressures should improve when you add oil.
if the problem doesn't go away assume valves.
of course if the engine hasn't been running for some time then you may be wasting your time, go and run the engine and drive it hard for a while then try the comp check.

[Dante]

all it does is take up the slack hydraulically in the rings etc.

isn't that what you want to know about?
you need to know about leaking rings and leaking valves, and that is why you are doing the test.
personally i consider cranking type compression tests as 'battery capacity' tests.
anyway, if you have a lower cylinder pressure than the others [or multiple cyl's] then put a couple of squirts in, this will assist the rings to seal, and retest the cyl's, if the bad one's go away then the problem is assumed to be rings. note - all the cyl's comp pressures should improve when you add oil.
if the problem doesn't go away assume valves.
of course if the engine hasn't been running for some time then you may be wasting your time, go and run the engine and drive it hard for a while then try the comp check.

Nope .. just wanted to know if I can use the engine oil (for now). Want to learn how to check the overall condition of an engine and this is one of the tests I want to know how to do. The 2a is becoming my project vehicle to learn all about trucks, regardless if the 2a needs it or not. (For example ... I have never changed oil or spark plugs).

I did think about the battery capacity testing and was wondering about that.
From my problem with the bad earth I learned (new for me, obvious for others) that the starter motor will turn with less strength the weaker the battery goes. I'd assume that this affects the compression.

In order to learn on how the battery effects the test I have planned to run the test twice.
First with the same battery load all 4 cyls, then repeat just with recharging the battery to full after every cyl.

Thanks for the pointers, Dante

[UncleHo]

G'day Dante

To do a compression test on your 2a I would suggest that you first remove all the plugs, then starting from the No1 cylinder with a screw-in type tester wind the starter so that you get approx 5 full compression strokes, note the pressure (new engine=145 PSI, 7:1 compression ratio) anything over 125 PSI is OK, then repeat with other cylinders, if you have some below that, then try the "Wet" test, 3 squits of engine oil then 5 full compressions, if there is an increase in pressure , the rings are worn, if no increase (and if the cylinder has low comp)then it is a valve problem , if there is low compression on 2 adjoining cylinders, then it could be a head gasket, this will also be noted by a miss in the running, that can be checked by shorting the spark plugs across to the head with a screwdriver, and checking for bubbles/oilsmear in the radiator ( not always detectable) all Australian Landrovers were only fitted with the low 7:1 compression motors with the exeption of the Station Wagons as they were fully imported.

cheers

[JohnE]

Now we all know what you are doing,
Maybe i am reading it wrong or its the way you wrote it, but can we assume you have never changed oil or plugs in a vehicle. or just that vehicle.
If its the former and seeing you are not 'au feit' with oil or spark plug changes, I would suggest,
you start off with the easy stuff first, then work your way up gradually to the harder stuff, like doing the compression test, or the valves etc.
And go the way you have started here, ask lots of questions,
as you have seen you get the same answer, some expanded for your questions.

I am sure if anyone lives near yu they would be only too happy to show you as well.

But if its the latter, still ask the same questions.


Happy mechanicking



john