Oil smoke

[abri]

Trying to get opinions and hoping for good news here.

When running at cruising speed and putting my foot down slightly/increasing load, there is a slight blue smoke puff at the rear. Similarly, when going up a hill and putting load or at high revs blue smoke appears.

There's no sign of oil on the plugs and no smoke at idle or when not under load.

Could it just be valve guides/stem seals? The typical symptom of a puff of smoke after decelerating down a hill and putting your foot down does not seem to appear, which has me a bit worried that it is not valve stem seals and could be more serious.

I've done a compression test and the cylinders hold pressure fine, so I'm really hoping it's not rings.

[Spider]

Typically worn guides will give a puff of smoke when say after coasting down a hill, then opening the throttle, if it puffs then and goes away, that's usually guides.

If it smokes on under some load to a lot of load, then it's likely rings and / or worn bore.

Could also be a gummed up ring from old or poor quality oil, you could try giving it a flush with diesel lube oil (fill and run for about 200 km) and see if that helps.

[Smiffy]

Does it smoke at first start up in a morning ? If not I'd be more inclined to think it's bore washing and a not tuned correctly.

[abri]

It doesn't smoke at startup, only when under quite a bit of load.

The motor apparently sat from 1978 to 2012 when it was put back in the car (original speedo read 56000 miles). The head was taken off at the time and someone confirmed that the original pistons were in there, so 56k miles is likely genuine. Could it be rings/bores with mileage that low? Could be gummed up rings then I guess. I have noticed that the new oil I put in went darker quite quickly - is that due to bore washing?

Smiffy, could you elaborate on your "not tuned correctly" comment? What have you got in mind that could cause these symptoms?

[Spider]

I know the 1275's we got out here (which were fully imported from the UK) in the 78 to 80 period did have a ring problem (or actually incorrectly honed) from the factory, they'd smoke after about 30 000 - 40 000km.

[Smiffy]

It doesn't smoke at startup, only when under quite a bit of load.

Smiffy, could you elaborate on your "not tuned correctly" comment? What have you got in mind that could cause these symptoms?

If it's running rich it will be washing the bores and burning the oil thats left on the bores. Running rich running can be down to a number of things and not only the adjustment of the carb. For instance incorrect ignition timing can result in the engine seeing a rich mixture, a weak spark or even incorrectly adjusted valve clearances do can all do the same thing.

Imho if it doesn't smoke at first start up, especially first thing in the morning after been left over night. It's not the valve guides and you should be looking at the overall tune of the engine.

I'd start by checking the valve clearances and the state of the jet, especially if it's the original carb. Check that it's still round and not worn oval, which again would result in a rich mixture.

[abri]

I redid the compression test today and got:

Cylinder 1: 1220kpa = 176psi
Cylinder 2: 1250kpa = 181psi
Cylinder 3: 1250kpa = 181psi
Cylinder 4: 1260kpa = 182psi

The motor was run for about five minutes at a fast idle speed prior to the test and all cylinders held their pressure for approximately one minute before I released it.

Are these readings what one should expect from a healthy stock standard Mk1 1275 S or are they too low?

[Smiffy]

I redid the compression test today and got:

Cylinder 1: 1220kpa = 176psi
Cylinder 2: 1250kpa = 181psi
Cylinder 3: 1250kpa = 181psi
Cylinder 4: 1260kpa = 182psi

The motor was run for about five minutes at a fast idle speed prior to the test and all cylinders held their pressure for approximately one minute before I released it.

Are these readings what one should expect from a healthy stock standard Mk1 1275 S or are they too low?

Nothing wrong with those figures. Whats the tail pipe colour look like, black and sooty ?

[Lord Croker]

We had this happen on my nephew's Mini, which was essentially a Cooper S engine in a 1300 A+ block, totally rebuilt & after a lot of investigation & an engine strip-down, it turned out to be a problem with the closed circuit breather system. Admittedly, it's the only time I've ever known this, but if you are running such a system, try disconnecting it & running the breathers into a catch tank.

[66S]

A compression (ring) test does not show much about oil rings. It sounds like oil rings to me and if the engine has done 50K or more, I think the life of the original rings is past it's best.

Regards
Al

[abri]

@ Smiffy, Thanks. The tailpipe is dark grey...I'd say a bit darker than my other cars. But the plugs are burning the right colour.

@ Lord Croker, thanks for the tip. I will try that. I have noticed that there is a very substantial drop in rpm if I remove the oil filler cap at idling speed. Does this tell you anything about the condition of the breathing system?

@ 66S, the motor has done 56k but was standing in someones garage between 1978 and 2012. Perhaps it is time to pull it and have a look. I'm just trying to eliminate all other options.

[carbon]

Abri,

How much oil are you typically getting through in miles per pint?

[abri]

Carbon, I haven't calculated. I was alarmed to see that it needed two pints after about a week of driving here and there (less than 150km) but then I thought I may have been mislead. When I got the car, one of the first things I did was change the oil. I emptied the oil cooler as well. I'm thinking when I put oil in after draining the old oil there may have been a bubble in the oil cooler or something that caused the dipstick to read fuller than it actually was. I was just looking for explanations for going through two pints of oil in such a short time without big plumes of smoke behind me.

So short answer to your question, I don't know for sure

[Lord Croker]

Your engine slowing down when the oil filler cap is removed shows that the breather system is not blocked & is what I would expect. Unfortunately we never found out why my nephew's engine was throwing so much oil around & sucking it through the breathers, the system was removed in the process of elimination. The only thing I could think of was that it was a highly tuned engine creating immense inlet depression, possibly because it could have used bigger carburettors.
I've had a few oil burning engines, but they always smoked at idle, or when accelerating away after slowing down with a closed throttle. The only other circumstances I've had oil smoke under load, is on my own Mini, which has an oil cooler & if I drive away with the oil cold, it floods the rocker cover & goes down the guides.
This is a challenge, but if I can come up with any more ideas, I'll let you know.

[Spider]

so much oil around & sucking it through the breathers

One cause for this is the Oil Separators not having any or the right gauze in them.

[carbon]

Abri - just to check, what grade oil are you using in the motor?

Compression results would suggest rings and bores are not excessively worn. Other question is what type of seals are fitted to the valve guides, and are there seals on both inlet and exhaust? If there are no seals on exhaust this can increase oil consumption quite a bit, depending on valve stem to guide clearance and possibly also down to type of rockers used (if they are forged type with oil hole then there is likely to be more oil going towards the valve stem than with the sintered type). I fitted exhaust guide seals on my 1293 recently, and this made quite an improvement - previously it was kicking out a bit of smoke when hot on tickover.

If the new oil went dark pretty quick after changing then other suggestion would be take it for a good long blast and then changing oil again for new 20W50. Fill to max line on level ground and then keep close track of how much oil you are getting through over the next 500 miles or so.

[abri]

Thanks again for sharing your thoughts. It seems a theme is emerging - valve stem seals/guides and possibly PCV.

I took the car to a local ex-BMC Blackheath (Cape Town) mini mechanic and racer yesterday. He looked at the amount of sucking at the oil filler cap, disconnected the PCV to feel for blow by at the same place and had me rev the motor to see how much/when it smokes. Together with the history and symptoms that I provided him with (standing motor from '78 to 2012, "restorer" who did take the head off and saw the pistons were still the originals and ok, previous owner who only spend money on cosmetics so he could sell at a large profit, rather heavy oil use, smoking under load but not in the typical stem seal manner, etc.), he asked me whether I knew if the stem seals were changed when it was put back on the road. I wouldn't be surprised if they weren't, so it is possibly a set of seals from 1978 that's in there. That is going to be the first thing I do. He said he's also going to modify the PCV so that it doesn't work as well...apparently it is not good for the motor to suck in all those bad gasses and vapours - better to blow them out into the atmosphere

It provides some support (from someone who could see the car) for some of the thoughts raised on here, so I think I'm happy to tackle the issue with a conservative approach and just make sure I get new stem seals on there.

The car is running its original forged rockers. It currently has Castrol GTX "High mileage" 20W50 (http://www.castrol.com/en_za/south-afri ... l-gtx.html) in it as I've been told this oil is the closest available one to oils used when these motors came out of the factory. I have no proof of that though.

The guy I saw yesterday also recommended I switch to Castrol SAE 40 http://www.castrol.com/en_za/south-afri ... ae-40.html. It is apparently gentler on the early Mini gearboxes (ie. Mk1 3 synchro gears).

It'd be interesting to hear your thoughts on the oils.

I'll report back when the stem seals have been replaced.

[Smiffy]

GTX High milage oil is 10/40, all GTX used to be 5/50 which I always used to use until the change. Don't remember it smoking, but mine started using more at this time and stopped again when I changed to Comma Sonic 20/50 and now comma's gone bust/discontinued that. I use Millers 20/50.

[carbon]

Abri,

Interesting to see in SA you have Castrol GTX in 20W50 flavour, not available in UK.

If you are replacing valve stem seals would recommend fitting 4 shiny new seals on the inlet guides, and then put the used seals from the inlets on the exhaust guides.

[abri]

Carbon, what is the thinking behind fitting the used seals on the exhaust guides? Shouldn't I just fit eight new seals?

The guy who looked at my car also asked me whether I want seals on all eight guides and said it's "up to me". Are there any benefits to not having seals on the exhaust guides?