7 replies to this topic

[Tinkerbelle]

Hello All,
I don't seem to be able to get to the bottom of my grey smoke on my 1275 engine. A little history, the engine was originally an Ebay special late unleaded MG Metro 1275 with small inlet valve . It was rebuilt recently (1000 miles ago), bores were marginal but I had not got the budget to get it rebored and new pistons etc, so I got it honed lightly and got new rings. Head was stage 3ed if that if a real word!! by Rob Walkers (atually Dennis at Rob Walkers).

After build the engine was worn in gently using the method on MiniSpares website and set up on r/road, but always smoked. Does not seem to get any worse when hot or cold. But gets worse after idle when accelerating and changes colour from light to dark grey randomly.

List of checks done and smoke still present:

May be new rings not seating - It runs fine and compression is 155 -160 across all cylinders.

May be valve seals - renewed with rebuild so are assumed to be ok.

Carb floats did not seal causing overflowing fuel and overfuelling into engine - float valves replaced with rubber tipped ones, problem irradicated

Remaining possibles

Damaged head allowing oil into inlet or exhaust (do I need to get it pressure tested)

Rings (oil control) not sealing correctly.

Another carburettor fault - unlikely as they are brand new twin HS2s.


Can I tell from exhaust gas emissions analysis if it is engine oil or fuel, i.e. HC and CO ratios?

Any help would be very appreciated with any more diagnostic ideas before I spend the next month of spare time removing stripping and fitting the +40 pistons I got at the weekend, as I really need to get the welding done on the wife's Sidewalk!

Thanks

Matt

[Carlos W]

Is. It using any coolant or oil?

[Tinkerbelle]

I haven't noticed any. The car only gets used rarely so it is hard to distinguish between oil use and that that has dripped onto the floor! Coolant I have no idea, actually I have needed to top it up before!

Sorry i meant to mention that.

[Carlos W]

Would you describe the smoke as off white, or dark grey?

[Tinkerbelle]

Hard to tell, it is light grey not dark, but goes dark when reved after idling for some time.

I hate people like me who don't have nice clear diagnostic aids!

[IainR]

White or light grey smoke usually means water is entering the combustion chambers due to a blown head gasket - I just diagnosed this on my car earlier this week

[Tinkerbelle]

Head gasket is something that I had not checked due to good compression. Would really like to not have to rebuild the engine with the running in time etc all over again, head gasket gone would be good, not just too worn bores.

I haven't actually considered if the engine is actually duff, it was an Ebay special!

There is no oil in water or water in oil (mayo) though.

[Tinkerbelle]

Anymore ideas anyone.

I just fired it up and warmed it up on the way back to the office and noticed that the free to air breathers all have grey fumes coming from them, more than i have noticed before.

Is this blow by from combustion? Which would help the worn bores theory.

IainR - Pressure tested the rad and there was no increase in pressure when reved up as you would see if head gasket was gone into water column and it held pressure happily!