smoke at idle

[martin_t]

Hi Martin,

Manual or Auto ?

GM 180 box has a modulator on the box that when the internal diaphram goes bad allows the engine to suck gearbox oil in

just a thought

Cheers John

Hi John

Thanks for the reply. Its an LT77 box from a Sherpa but rebuilt.

Regards

Martin

[sidecar]

I built all the engine actually from a box of bits..........bottom up!! No one was more suprised than me when it fired first time!!!
It doesn't seem to be using oil, but then again, as I mentioned earlier, I have only done 1500 miles.
One thing, the smoke doesn't smell of petrol, more just like exhaust fumes.

Cheers

Martin

Hi Martin,

It certainly does not sound like you are burning enough oil to make smoke. In fact the oil consumption of your engine sounds very good. (As in you are not using any!)

Regards,

Pete



My lump would have used 'an amount' of oil in 1500 miles, are you saying that you have not had to top up the oil in 1500 miles, if so then it ain't burning oil!

I changed oil at 1000 and hadn't topped up at that point. It may have used a little but not enough to warrant topping up. I tend to keep it at about half way between low and High on the dipstick.
Since the oil change I have done another 500 miles and not topped up as there has been no significant fall (maybe a tad but negligeable).

Cheers

Martin

[DEVONMAN]

Martin,

Have you got a PCV valve on the engine?
If so then check that it's not sucking oil into the mixture from the rocker cover.

The vacuum at the PCV will be higher at idle (and overrun) so it may not suck oil all the time.

Same goes for most breather set ups.

If not PCV, what breather system have you got?

As said earlier, 1500 miles is not much so if it's rings them they may well
bed in more and improve the situation. Given that you have already done an oil change I don't thing you have done enough miles to gauge the oil consumption of the engine.

However, in your first post you said you had smoking due to valve seals on the engine before the rebuild. Maybe it was something else, so I would look at things that were not changed in the rebuild such as the breather system.

Regards
Denis

[ramon alban]

One thing, the smoke doesn't smell of petrol, more just like exhaust fumes.

Hello Martin,

The good news is you dont seem to have a fuelling issue if the plug colors are good and the exhaust only smells of ( Er? ) exhaust. No surprise there then?

So! I would say you have a couple of things going on.

Anything wispy and white is gonna be steam and at this time of the year its quite noticeable until the combustion efficiency/process reaches full running temperature and the production of water in the exhaust gasses lessens.

Also on load and driving at speed any bits of steam are much less likely to be easily seen

As to the blue smoke content which disappears when driving - the perceived wisdom is that its generally valve stem oil seals or worn stems.

A bit of seeping or the ever present suction in the inlet manifold at idle is drawing small amounts of oil into the combustion chambers, which of course does not happen so much when cruising and on full load, anyway.

However if you can get an observer to eyeball for the blue smoke symptom when on overrun, that would be a definitive test - due to very high vacuum thereabouts!

On both counts I think the worries are few!

Still worried? - Read this self-diagnosis treaty:

http://www.vintagemodelairplane.com/pag ... oke01.html

[mgbv8]

I think Ramons and Denis's comments are going to be the answer now we have seen the background info.

I seem to remember a mate having similar issues that went away when he fitted rocker covers with splash guards inside.

And another mate had the same issue which I fixed because he had fitted a PCV system and his hoses to the carb had no filters fitted and were drooping so they filled with oil. This gave him occasional blue smoke in gobfulls at idle and over run and then not again for a good few miles of running.
The hoses were acting as traps and eventually got enough oil laying in the low section of pipe that when on idle at max vac the oil got slugged into the inlet manifold. Its surprising just how much smoke a few drops of oil can make !!

I just fitted shorter pipes that ran downhill from carb to rocker cover and the problem was gone

Perry

[martin_t]

I think Ramons and Denis's comments are going to be the answer now we have seen the background info.

I seem to remember a mate having similar issues that went away when he fitted rocker covers with splash guards inside.

And another mate had the same issue which I fixed because he had fitted a PCV system and his hoses to the carb had no filters fitted and were drooping so they filled with oil. This gave him occasional blue smoke in gobfulls at idle and over run and then not again for a good few miles of running.
The hoses were acting as traps and eventually got enough oil laying in the low section of pipe that when on idle at max vac the oil got slugged into the inlet manifold. Its surprising just how much smoke a few drops of oil can make !!

I just fitted shorter pipes that ran downhill from carb to rocker cover and the problem was gone

Perry

Hi Perry

Thanks for the advice, will deffinately take that on board.

Impressive performance figures by the way!!

Martin