MGB Excessive Oil Loss

[68sebring]

Got a problem with my MGB at the moment in that I'm loosing excessive oil through the road draft tube, any ideas on where to start?

The car is running a Weber 45 so I can't route the vent into the carb

Two things spring to mind a) the oil seperator is no longer doing it's job as oil droplets are getting past the wire mesh and being vented b) the road draft tube is creating to much suction and its literally pulling oil out of the engine?

I really do mean excessive too, after a 400 mile trip it had used about 3 litres (!!) and the bottom of the car was covered in oil

Any help appreciated

Neil

[Huntsman]

Are your piston rings and valve guides shagged so the engine is pumping its oil out?

[68sebring]

Hope not as it was only rebuilt 5000 miles ago but I guess its possible.

I'm getting good pressure (70psi when warm) and dont appear to be burning oil either as no blue smoke.

[wildoliver]

Do a compression test, it isn't unheard of for piston rings not to bed in, I assume you used a crap oil to run it in?
Is it worth pulling the breather off and soaking it in petrol over night then giving it a good clean out?

[68sebring]

OK, compression test done but I'm not sure if its that conclusive?

Cyl 1 Dry 150psi Wet 160psi
Cyl 2 Dry 165psi Wet 170psi
Cyl 3 Dry 175psi Wet 185psi
Cyl 4 Dry 150psi Wet 160psi

Now obviously the range between 1/4 and 2/3 isn't correct but the Wet tests dont really show it up as a piston seal issue? or do they?

Any thoughts?

Cheers

Neil

[wildoliver]

Theres nothing wrong with those readings, I'll admit they aren't perfect but it's a b-series none of them are perfect new or not.

So it has to be valve stem seals or it is blowing the oil out of a breather or dropping oil somewhere. Get a white cloth over exhaust and see if any oil is being burnt, then put a white sheet under the car after a hot fast run and leave overnight and see if anything is dropped.

[68sebring]

Well after much head scratching we decided to pull the head today and found that the cylinder bores are glazed so its engine out time for a quick rebuild :-( it looks like during the running in period the owner at the time made a few fatal mistakes a) took it easy for 1000 miles b) changed the oil at 500 miles for Castrol 20-50

So, after the rebuild can anyone recommend some good running oil, then some better quality oil before switching to Castrol/Penrite???

[wildoliver]

You shouldn't need to pull the engine.

Deglaze the bores, either using a honing tool available even from halfrauds, or even a bit of wet and dry paper and elbow grease (obviously moving the piston down to lowest point first).

You will clearly leave a very small amount of glaze lower down the bore but to be honest this area rarely glazes anyway it is usually the top half of the swept bore, and also if the upper half is deglazed the rings will soon scrub any glazing remaining off.

Then go and buy the cheapest nastiest oil you can find, some of that "motorway" brand stuff is my favourite.

Take the car out and give it a little bit more stick than you would a normal running in car to clear out the bores then try as normal to run in, you don't need to show as much care this time as obviously the bearings are all run in already, it's only the bores your trying to bed in and to be honest kicking it's arse is probably the best way of doing that.

Also sounds daft but try setting your mixture a little on the rich side for the first couple of hundred miles just to make sure your bores aren't going to get oil sat on them.

Pulling the engine will achieve very little.

[pikeyboy]

Look on peter burgess's web site for info on running engines in, but basically give it some in first and second to say 5K and dont let it labour is the trick this beds the rings in a treat you can feel it start to free off after say 50 or 60 miles. running in oil i use a comma oil from pete i think its made by esso and is a straight 30 grade, to be honest though for my race egnine i dint even bother running it in...just kept it below 6500 in qualifying

[68sebring]

Well the engines back in, the real reason we pulled it was because the over pressurization had caused oil leaks from most of the engine seals and the only real way to sort them all out was going to be to pull the engine and sort them, the additional cost to do this was negligible.

First impressions are good even though I've only covered about 50 miles, just another 450 or so to 'run it in', any excuse to get it out on a road trip when the sun is out. A trip from South to North Wales and back sounds tempting for this weekend, all on B/A roads of course!

[wildoliver]

Just remember to be harder on it this time, it's fair to assume the bearings will be run in which is one of the reasons to be slightly gentle on the first run in of an engine, the bores can take a lot more hammer, so don't be pussy footing around this time, crap oil and a good few bursts of revs in lower gears, don't labour the engine and don't sit at the same engine speed for long periods.

And do change the oil after 500 miles.