19 replies to this topic

[hoggy]

Ive recently put a 1275 spi engine in my mini and have converted it to run carb.

I have driven it about 20 miles max and it's smoking really bad when driven, it is oily blue smoke. It is using loads of oil too (about 4 litres) in those 20 miles.

I had the head skimmed and ground in the valves and put on new stem seals aswell.

My first thoughts were knackered piston rings, but i have just removed the manifolds and there is oil in the inlet ports in the head and it looks like possibly in the exhaust too but has been burnt off.

Any ideas what's wrong?

[Guess-Works.com]

Your choice's are, head gasket is letting oil into the bores ( this would occur on no1 cylinder as that's where the oil feed to the head is )

Your valve guides are completely knackered

you have a bust head

And 4 litres in 20 miles, make sure you havn't got a hole in the sump !

[The Matt]

Valve guides could be shot, but that is ALOT of oil to have used. Did you fit new head gasket and torque it all up correctly?

Also, when the head was skimmed, was it pressure tested? Is there more oil in one inlet port than the other, or are both equal?

As GW said, the oil consumption may not be just down to the head, to have used that much you may have oil leaking out somewhere!

[dklawson]

The amount of oil you're missing is more consistent with a major leak than could be addressed by the smoking exhaust alone. Are there pools of oil under the car after you park it?

As others have suggested, if the guides were badly worn, you've wasted your time and money lapping in the valves. The guides and valve stems need to be in good shape to justify the lapping. With new seals though I wouldn't expect even the worst worn guides to account for the volume of oil you're loosing.

It could be a combination of faults causing your problem. Add to the list you already have to check your PCV valve/system. If it's allowed to pass vacuum all the time, and if your rings are shot and the engine has lots of blow-by, you could be getting a fair amount of oil drawn into the intake manifold like you're seeing. Still, I don't think that alone explains what you're experiencing.

[Bungle]

is there any oil in the water ?

[Dan]

Add to the list you already have to check your PCV valve/system

Oooh, showing your age a bit there DK. The PCV valve was ditched years ago and the brethers have been permantly connected to vacuum for a very long time now.

Trying to lap unleaded valves and seats by hand is pretty futile anyway I'm lead to believe, they're far harder than the grinding paste is. Three angle cutters are needed to clean the seat up properly.

[dklawson]

I guess I am too old. So... if the breathers are directly connected to vacuum, would it not be possible that excessive blow-by is pumping lots of oil and oil fumes into the intake?

No PCV... what is the world coming to?

[Guess-Works.com]

It would, but not 4 litres... mind you when I ran my 1330 at over 8k rpm, that ditched a fair amount of oil out the breather on the transfer case, but that wernt a little puff of smoke, that was BIG CLOUD down the 1/4 mile strip.

[hoggy]

Yeah a new headgasket was fitted and torqued correctly. There are definitely no leaks that i can see and no drips of oil under the car, and no water in the oil or vice versa.

The engine oil was drained then i put in about 4litres and it was left overnight and then the disptick read about halfway between max and min. now after running it for a bit it doesn't even register on the dipstick?

The timing cover breather is connected to the carb and the crankcase has a breather on it. i modified the timing breather to clear the duplex chain, do you think the inlet could be sucking oil out from here? It was smoking excessively when you put your foot down and a little at idle.

Any ideas what to do about this? I was going to take the head off and have it pressure tested, to rule out any cracks in the head? then have new guides fitted if the pressure test was ok, is this the best place to start?

[Dan]

Having a half and half breathing system won't help your engine much, you should either have it all ventilated or all PCV to keep pressures and flow properly regulated. Personally I think you should stick with PCV on a road car for many reasons I have been into many times before.

Doesn't take all 4 litres to go for the oil to disappear off the dipstick. It's about a litre from the bottom of the dipstick to the mid point I think and remember that a good half litre will have disappeared into the engine's guts after an oil change. Stick half a litre in and I think you'll find out that you haven't lost as much as you think.

I have to say that dodgy guides usually shows as smoke at startup only because there isn't enough running through them for it to smoke continously and it needs the oil to pool up in the ports while the engine is off before there's enough for a smoke screen. Permanant smoke under light load ususally points to a broken piston ring in my experience.

Edited by Dan, 19 December 2006 - 12:24 AM.

[hoggy]

When i removed the manifolds the oil was in a pool in the ports? Going to do a compression test to try and determine whether it's rings before i remove the head. Praying it's not rings and i have to take the engine out again!

[hoggy]

Just did a compression test. readings are

DRY

1= 160 2= 170 3= 165 4= 180


WET

1= 210 2= 200 3= 210 4= 250

Does this look like a ring problem then? I really hope not!

[The Matt]

The engine oil was drained then i put in about 4litres and it was left overnight and then the disptick read about halfway between max and min. now after running it for a bit it doesn't even register on the dipstick?

Hmmmm, from memory a mini engine takes more oil than that (I seem to recall more like 5 litres, but I really could be wrong so double check that). The 'doesn't even register on the dipstick' doesn't mean that all of that 4 litres has gone, it could be just below dipstick level, so it may not have used anywhere near 4 litres. Also bare in mind (as Dan has said) that the dipstick will read lower after you have run the car, than when you freshly re-fill.

If you are getting crankcase compression and pushing oil through the breather system (and lots of it, but not as much as we originally thought) then you will have nice yukky breather pipes. Are they full of oil?

It does seem possible/probable that you have ring problems though.

As Dan has said, valve guides, or stem oil seals usually allow some oil to trickle down to the crown of the piston whilst standing, causing big clouds on startup, then it usually clears. If you are getting snoke all the time, I guess you have 'problems down below'.

[hoggy]

Can i take that from the compression readings it is definitely a ring/bore problem. Just want to be sure before i strip down the engine and remove it as it's only just been put in!

[Dan]

Compression tests don't reveal much. They only show massive, engine killing problems really. To find a cracked ring, scored bore, leaky head gasket or similar you need to do a leakdown test which shows how badly they are leaking. For example the last time I changed the head gasket on our Mini it had just had a leakdown test done which showed 51% leakage in a cylinder that was still reading very healthy compression. A good leakdown result is about 7 to 12 % on an A series I seem to remember. The oil that is being forced into the leaky cylinder (wherever it is coming from) during your compression test is of course effectively reducing the unswept volume available for the charge to compress into and so raising the compression to compensate for the leak so long as it isn't being burned off. Or something like that.