33 replies to this topic

[tomtic]

Mini has been off the road for a good while, have had to resort to buying a brand new car to get me from A to B in the meantime.

It's smoking very heavily at times when accelerating. Revving while stationary fills the car behind with a cloud of blue smoke :/ At idle it's not too bad, barely noticeable. It is using quite a bit of oil too.

After so many headgaskets going, even after having the headskimmed, found there was a low patch on the block which managed to level it off. Managed to get level compression through all the cylinders for once, 11 bar through all the cylinders. When the head was last taken off, it was not stripped and rebuilt, as the seals had not long been replaced, and the valves were lapped on the previous rebuild.

Even with the heavy smoking its still getting 11 bar, is there anything that's likely to be causing this? I really don't want to take the head back off after getting it to seal properly for the first time

[ginigwunkle]

blue = oil

could be many things, seen as youve recnetly changed the oil seals on th head it could be the valve guides themselves that are worn or worst the piston rings themselves.

whats the bores themselves like honed or shiny?

[tomtic]

Yes its oil, as I said I was going through a LOT of it

Can it really be piston rings/bores if I'm still getting a good compression? I was hoping the good compression would mean its not leaking past the pistons. But in any case, the bores are good yes.

[ginigwunkle]

its either the piston rings or the head thats leaking it.....

did you notice valve play in the guides last time it was off?

you say youve just changed the head gasket so i doubt its that!

[tomtic]

I didn't take the valves out, so couldn't say. But if a piston ring had gone, would I not notice the loss of compression?

[yorkshirechris]

I was under the impression that there's the compression rings as well as piston rings, which leads me to believe that if your piston rings have gone or are on their way out, you will still get good compression.

[tomtic]

I was under the impression that there's the compression rings as well as piston rings, which leads me to believe that if your piston rings have gone or are on their way out, you will still get good compression.

Well, what are the symptoms for a piston ring 'going' ?

[yorkshirechris]

Blue smoke under acceleration... because that means oil is passing through the piston rings and being burned off, hence the blue smoke. It could be the valve stem oil seals but I'm guessing you replaced those when you replace the head gasket. And if it's really bad smoke it sounds like piston rings to me... although before you go dismantling the engine, wait and see if anyone corrects me I'm fairly sure thats what it is though.

[minorconfusion]

all the oil your slopping in there every other day coupled with worn valve guides will let oiul into the bore's.. this will flod out the rings giving them plenty of make shift sealant wich will up the compression.. try a compression test after not putting oil in it for a couple of days.

[T.Harper]

I was under the impression that there's the compression rings as well as piston rings, which leads me to believe that if your piston rings have gone or are on their way out, you will still get good compression.

yes compression rings do make up one or more rings on the piston

[tomtic]

It's been off the road for 3-4 months, and compression tested it yesterday. That's when I got 11 bar in all cylinders, not put any oil in.

[T.Harper]

As mentioned above, there are many reasons for oil burning. If you are confident it is not worn rings or bores then the valve guides are probably to blame. These do wear from the "not entirely vertical" arc of the rocker arm. Bronze valve guides wear particularly faster than cast iron. If you find it is these, then replacing them with cast guides (and making sure you ream them first) is perfectly adequate for the road.

I will just say that valve guides leak most oil - produce most smoke when the engine is experiencing high vacuum behind the carb butterfly, i.e. Idling and Decelerating.

Worn rings/bores produce blue smoke a lot more often, also noticeable when accelerating.

Leak down testing will be able to identify where your engine is losing compression, (if any).

You can also try disconnecting the breather from the carburettor to see if this makes a difference, (may make it worse, depending on breather condition, but it is rare that these are the cause of oil burning).

[T.Harper]

On second thoughts, I have just looked up bar: psi and your 11bar is just under 160psi.

I attended a tune up session at MLMotorsport where 150-175psi is quoted as low. Best do a leakdown test to see if this is your rings. A good road engine should have over 200psi-220.

Hope this helps

[tomtic]

On second thoughts, I have just looked up bar: psi and your 11bar is just under 160psi.

I attended a tune up session at MLMotorsport where 150-175psi is quoted as low. Best do a leakdown test to see if this is your rings. A good road engine should have over 200psi-220.

Hope this helps

Since I've had the engine the compression has never been above 11.5 bar and its run fine. Haynes manual iirc quotes 10.5 bar for a high compression 998 anyway?

The majority of the bluesmoke is when revving, on lift off the smoke goes. There is a slight amount of 'white' smoke when idling.

I've actually just run it upto temperature and tested compression...

11 11 12 11.5 across the cylinders, measured in bar.

Edited by tomtic, 28 April 2008 - 07:45 PM.

[T.Harper]

oh, does it? I must be wrong then. You could try asking on http://www.mlmotorsport.com/ maybe they might be able to diagnose this. If you are confident it's not the rings it's probably valve guides and/or stem seals though