14 replies to this topic

[oltonlad]

hi everyone, i put a post on here last week with a problem that ive got with my engine, sometimes it seems to be burning oil but sometimes it doesent, anyhow a couple of the chaps on here told me to do a compression test so here are the results (the car is a mini 1100 special 1979 with a 295 cylinder head fitted)

cylinder 1 150 psi
cylinder 2 170 psi
cylinder 3 190 psi
cylinder 4 190 psi

then i did the test again after putting a bit of oil down the bores

cylinder 1 160 psi
cylinder 2 190 psi
cylinder 3 210 psi
cylinder 4 205 psi

as you can see cylinders 1 & 2 are quite a bit lower in compression than 3 & 4, when the car is revved on light throttle up to about 3000 rpm there is no blue smoke from the exhaust but if i rev it hard there is a bit of blue smoke from the exhaust, dont get me wrong ..... not like a smoke screen or anything but i just dont want it to smoke at all, any help or suggestions would be most appreciated, thanks.

[MRA]

No1 cylinder is outside of the 10% rule, 2,3 & 4 are all within the 10% rule and as such are ok.

However to fix the issue with No1 you are probably going to have to go down the route of a strip down.... it could be as simple as a head gasket failure or a more complex head strip recut valves & seats and rebuild to a full engine rebuild.

Start with the head first as its not a bad idea to recut the valves and seats occasionally, look for grooves or damage on the valve seat in the head and the corresponding valve faces before you condem your engien though.

[100ev8]

did you test comp with all plugs out ? like mra says looking like a strip down or another engine

[oltonlad]

did you test comp with all plugs out ? like mra says looking like a strip down or another engine

yes, i did the test with all of the plugs removed and with the engine warm, the engine has been rebored by 20 tho' at some point already and is showing 90,000 miles, i'm hoping that it is head gasket or cylinder head related, i dont want to replace the engine with another 1100 as they are all old now and i might buy one that is just as bad or even worse, i will have to rebuild the engine if it needs it and keep the engine numbers etc all original.

[MRA]

Looking at the figures again....

the difference between the 1st set and the 2nd set of data.....

1 10
2 20
3 20
4 15

I would say that you have some valve & valve seat wear, possibly down to regression caused by using unleaded in a leaded head ?

I would suggest that although you could perform a full head rebuild you may still find that you need some more work on the engine.

[oltonlad]

Looking at the figures again....

the difference between the 1st set and the 2nd set of data.....

1 10
2 20
3 20
4 15

I would say that you have some valve & valve seat wear, possibly down to regression caused by using unleaded in a leaded head ?

I would suggest that although you could perform a full head rebuild you may still find that you need some more work on the engine.

thanks for the advice, i will take the head off at the weekend and have a look, i have used a lead fuel additive in the engine but thats not to say that the previous owner did, i'll check the bores while the head is off to see if there is any wear etc, i may as well have the 295 head rebuilt and converted to unleaded as i think its worth it.

[bmcecosse]

Nothing too serious there - sure, it's not perfect - but it's far from serious at this stage.. I would RUN it! And - make sure one of the breathers is connected to the little brass stub on the side of the carb to draw away any internal pressure in the crankcase.

[oltonlad]

Nothing too serious there - sure, it's not perfect - but it's far from serious at this stage.. I would RUN it! And - make sure one of the breathers is connected to the little brass stub on the side of the carb to draw away any internal pressure in the crankcase.

thanks for the info, does this bit of oil burning affect the emissions for the mot as i need to get the car mot'd soon or should i just get the head done anyway??

[mk3 Cooper S]

Nothing too serious there - sure, it's not perfect - but it's far from serious at this stage.. I would RUN it! And - make sure one of the breathers is connected to the little brass stub on the side of the carb to draw away any internal pressure in the crankcase.

thanks for the info, does this bit of oil burning affect the emissions for the mot as i need to get the car mot'd soon or should i just get the head done anyway??

Wouldn't worry about the emissions on the MOT as it is old enough not to be of too much concern.

Why do 1100's burn oil? remember my orange clubman in the 80's !!

Is the fuel mixture ok and you are not washing the bores with too fuel?

I have a 567 CAM that will suit that engine and head if you go for the rebuild but persobnally I would run it until it gets really bad.

[sx_turbo]

You could do a leak down test, this is more time consuming but.gives much more accurate results and you should.be able to pin point the fault better before stripping anything down

[Ivor Badger]

Nothing too serious there - sure, it's not perfect - but it's far from serious at this stage.. I would RUN it! And - make sure one of the breathers is connected to the little brass stub on the side of the carb to draw away any internal pressure in the crankcase.

thanks for the info, does this bit of oil burning affect the emissions for the mot as i need to get the car mot'd soon or should i just get the head done anyway??

Wouldn't worry about the emissions on the MOT as it is old enough not to be of too much concern.

Why do 1100's burn oil? remember my orange clubman in the 80's !!

Is the fuel mixture ok and you are not washing the bores with too fuel?

Never worked it out exactly why around 79 the engines suddenly started burning oil. They would even do it on a single long distance run. Reringing and new valve stem oil seals used to fix the problem. The bores always looked unworn, in fact it looked like the engine never ran in, just put some sort of skin on the bores. I always wondered if it came about as they closed Wellingborough foundry and made the blocks elsewhere.

[dklawson]

You could do a leak down test, this is more time consuming but.gives much more accurate results and you should.be able to pin point the fault better before stripping anything down

I agree. A leak down test gives you a much better idea where the problem is and will help you decide what (if anything) you want/need to work on.

But I also agree with Roy. The numbers may not be great with #1 being a bit low, but I suspect the engine still runs well at this point and could be used until you are ready to invest in a complete tear down and rebuild.

[MRA]

That may be true, however a head strip and rebuild is not the end of the world, but will help to avoid the all too common burnt out valve that the small bore engines suffer with.

ANd it will also allow you to evaluate the bore wear if any. which will allow you to organise your next build more accurately.

[Joe555]

1275cc Metro engine.

oltonlad has a highest compression test of 210psi, mine is only 1: 158psi, 2: 160psi, 3: 155psi and 4: 158psi this is after having it honed and new rings. Before I fitted the new rings it was slightly higher, the highest being 170psi. What should it be and what is a leak down test?

Joe

[dklawson]

The values from a compression test are not necessarily as important as the "spread" between the measured values. As Martin said above, you want the values to be within a 10% spread of each other.

A leak down test involves pressurizing the engine with compressed air while each piston is at TDC. The gauges allow you to determine a rough "percent" leakage. In addition to measuring the percent leakage, you also "listen" for where the air is coming out. If you hear air leaking in the carb throat you have leaky intake valves. Air leaking in the exhaust... exhaust valves. Air leaking/bubbling into the radiator, head gasket failure or cracked head/block. Air leaking into the crankcase, worn rings.

More info is available in the links below:
http://autos.yahoo.c.../ques057_1.html
http://en.wikipedia....eak-down_tester