5 replies to this topic

[CBJ805T]

Hi All,

I've recently bought a new project mini which is a 1984, 1000cc Mayfair. The Engine runs (with a struggle) but the car is far from road legal so I've got no way of driving the car to access the Engine / Gearbox. I liked to do a quick health check on both but don't know what checks I should carry out. Any suggestions?

I'm intending to do a compression check - what pressure should I see in each cylinder? Do I check this by warming the engine, removing the spark plugs, fit the compression tester and turn the engine over on the ignition for a few seconds, check the pressure and repeat for the other cylinders?

I've heard people talking about how long the oil light stays on for - how long is too long? what does this tell me?

Soooo many questions!

[jaydee]

I'd see what colour water and oil are at first..

Before moving the car/testing i'd treat the engine with a basic service: reset tappet clearance to 13 thou, flush the oil and fill up with 20w50, new spark plugs, points, condenser, HT leads and fresh fuel in your tank .

The oil light is vague, no use for telling you the health of an engine, its a 'safety' light, when it goes on, you have a problem.
You need a capillary oil pressure gauge to see whats the actual pressure. As a rule of thumb, when engine warm pressure should never fall below 25 psi on idle, never below 55 psi when under load. When starting from cold, pressure should rise almost immediately, should reach at least 60 psi. Pressure have to raise when load applied to engine. Those vaules are a bit 'borderline', i have 40 psi at idle warm, 60 psi idle cold, 70 psi under load.
With 20w50 oil you souldh see plenty of pressure on your gauge..

Compression results..140 psi is low, 160 is quite fine for a road engine, 170 and above are good. What yo really want, is same compression at each cylinder. Dont forget throttle wide open while doing the test, do a dry test on each cylinder, then repeat dropping few drops of oil in the cylinders.

[yellowmonster]

I think Jaydee's figures are a bit too shiny..
The manual states that at idle anything above 15 psi is normal and ok, and under load anything above 50 is fine really.
The safety pressurevalve opens at around 72 psi, this figure is what you'll reach on coldstarts.
Compression testing always with fully opened throtte.

I have an '82 998 which idles warm @ 25 psi and shows a fair 55 psi under normal (warm) driving, it has little oilconsumption and still does 85-90 mph.
I haven't tested compressions yet, but for now I think it's quite fine and happy.

I know it's not ideal, but for a short test I'd remove the frontwheels and let the body rest on some wooden beams.
This way you can start the engine and "have a go" to test the gearbox for (synchromesh-)grinds and unusual noises.
First make sure all fluids are fresh and the engine has had a mini-service.
I think it's pretty safe to test it like this, as long as it's firmly supported and can't move.

But perhaps others may have other and better solutions..

Edited by yellowmonster, 07 September 2011 - 02:44 PM.

[CBJ805T]

Thanks for you're advice but as always answers prompt more questions )

With regard to the cylinder pressure test - when you say throttle fully open - do you literately mean put the accelerator to the floor and I turn the engine over?

yellowmonster - are all your figures relating to oil pressure?

Using a capillary oil gauge, where do I measure the oil pressure from?

[yellowmonster]

You want the best figures from your compressiontest, which means best cylinderfilling.
This can only be accieved with a fully opened inlet, aka full throttle or carb completely removed.
So yes: 'pedal to the metal' and then turn the engine over a couple of turns.

My figures are indeed oilpressure-related.
Remove the oilsender (next to the dizzy) from the engine and put your gauge in.
Now you're plugged into the main oilduct, from oilfilter to crank and that's where full pressure will be.
If your readings are low, make sure the oilpressure-reliefvalve is working properly.
Here's a link to an older simular thread-> http://www.theminifo...post&p=2194631]

Edited by yellowmonster, 07 September 2011 - 05:33 PM.

[dklawson]

To summarize for the compression test, all spark plugs labeled and removed after the engine is warm, throttle wide open, have an assistant turn the engine over on the starter while you watch the compression gauge. Turn the engine over until the gauge stops climbing, this may take several seconds. The actual value of the compression is not as important as the compression being "uniform" from cylinder to cylinder. If there is more than 10% variation from cylinder to cylinder your engine has a problem.

If you have access to an air compressor, I find a much more helpful tool is a leak-down test. (Google for how to build your own or places that sell them). With the leak down tester you will get an idea how/where the engine is worn. The leak-down tester can find problems that a compression test misses.