Blue Smoke from exhaust

[NEG]

Hi all, Yesterday took our Sprint (1350) out for a good run and noticed a puff of blue smoke from the exhaust pulling away after running down a long hill with the throttle closed. I.E. Roundabout at bottom of hill come to a stop then pull away.....the car was up to temperature and I only noticed it twice, it seemed fine during normal driving and there's no noticeable smoke starting her up from cold. At idle it's fine. The engine has done about 1200 miles since it was rebuilt so I'm not sure what the issue is.

Normally I would suspect oil rings and possible worn guides or guide seals...any ideas guys?

[PETROLHEAD]

Normally blue smoke OFF the throttle or a puff of chuff in between gear changes is indication of worn valve seats/guides as the oil escapes through to the combustion side on the vacuum strokes.

Is it notably cleaner under sustained open throttle?

[NEG]

Thanks Shrew, it's seems fine normal driving but I've not been able to get out today to check...

[PETROLHEAD]

you could try an engine flush and fresh oil and filter.

sometimes carbon deposits can build up on the guides and seals, and gum up the oil scraper ring.

For the price of a tin of flush, oil and filter, say £50, it's sometimes worth a try, but good practice in my opinion every now and then anyway.

[NEG]

Took The car out again today and there was some smoke as before pulling away after a downhill run with closed throttle but it seems to have cleared so I'm not sure what is going on. A few WOT blasts and no smoke I could see, I think I'll just have to keep an eye on this one.

She did throw a bit of a strop though as the boot release cable decided to snap! Grrrrrrr, means driver seat out....I think I may just about have enough cable to remake the end and get it fixed. PIA though.

[Veesix75]

Is it definitely blue ?

If you have closed throttle, it could be running very rich on closed throttle / tick over and that might induce a black puff.

Let the car tickover on the drive with tsomething behind the exhaust, a sheet of cardboard and give it a few blasts. Of you get a lot of black crap on the cardboard it could be over rich.

I assume you don't see any grey/white puffs of smoke as well? Both could be sign of over fueling, carb imbalance. I had similar when one float wasn't closing fully.

[NEG]

Yes, blue.

Tested using kitchen paper close to the exhaust with a few blasts an all it seems to produce was water vapour....

On the plus side I fixed the rear hatch release cable!

[Marlow Sud]

I would put my money on valve stem rubber seals.

Brgds
Simon

[NEG]

I'm thinking the same thing...

[Spacenut]

I agree - the valve gear on a boxer is horizontal rather than vertical, and the cam boxes are half-full of oil...