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MG MGA - Smokey Start
|Well, i just startd my newly rebuilt engine and I am finding a lot of whiteish smoke blowing thru the exaust. I am going to test and tweak the rebuilt carbs this weekend. The smoke is a heavy white smoke, but this could still be all the lube used in the rebuilding. I ran it for 20 min but it still is there. It did however diapate when I removed the #4 plug wire and ran on 3 cylinders. Any comments on weather this is normal?|
|White smoke is almost always water. After 20 minutes any assembly lube, etc should be well gone. Check the radiator level and perform a compression test. This has the indications of a bad/blown head gasket or a crack in a water passage in the head or block|
|Not what I wanted to hear, the radiator is low so I will try again. What other test can I do to norrow it down?|
|Well, after holding my hand to the exaust it is spuing water on my hand. (Bummer). Do you think it might just be a head gasket? Is there any way to narrow it down?|
|While it quite possibly may be a head gasket, don't forget that water is a normal byproduct of combustion. Water in the exhaust is not necessarily a "smoking gun". I'd rerun the test with a fresh refill on the radiator, maybe after re-torquing the head nuts.|
|As Chuck states water is the largest component of car exhaust. In a perfect burn a hydrocarbon plus oxygen equals H2O and CO2. The white smoke in the above guess would be the antifreeze burning not water. It burns with a sickly sweet smell. Once you have smelled it you will always recognise the smell. There is a different smell between oil and coolant burning. Visually they can appear the same. I suspect oil is burning in that cyl. May go away with time. Complete your set up and drive it. If there is a coolant leak it will use coolant and or pressurise the radiator continually and become obvious.|
|R J Brown|
|Well that is somewhat comforting, I have no antifreeze in it yet, only water, as it is just the completed chasse at this point. I am jut trying to test everything and work out the quirks before I set the body. Should I do a compression check? Could the white smoke be the unadjusted carbs running rich? Also, how about adding food dye to the water?|
Thanks for the help!
|Modern oils, even the cheaper ones, are so efficient that they can affect the bedding in of piston rings. Factory bores/rings are so well produced that no such issues arise but this does not always apply to "after market" components. I had no choice but to use non-factory items with my prewar MG OHC engine and, after dismantling my meticulously assembled engine, am now on my second set of rings (which are better, but still bedding in after some thousands of miles).|
|Lots of white smoke is normal with a new engine as it burns off the assembly oil, but it should subside after 5 minutes to be only a tiny wisp of white smoke only visible immediately at the end of the tail pipe. Still spewing white vapor after 20 minutes means the engine is ingesting either water or oil in substantial quantity. In a newly rebuilt engine it is unlikely to have that much oil getting past the piston rings or down the valve guides.|
The problem is most likely to be a leaky head gasket passing coolant from water jacket into a cylinder. Some of the water is boiled to make visible white vapor during combustion. Disconnecting the spark wire on the offending cylinder stops combustion and vaporization, so the white vapor stops and the exhaust blows out liquid coolant instead.
Fill the radiator to the top with no air space, and do a pressure test on the cooling system. See here: http://mgaguru.com/mgtech/cooling/cool_106.htm
If the head gasket leaks the radiator will not hold pressure for long. The pressure drops as coolant is lost into a cylinder bore. This could result in hydraulic lock in a cylinder. Remove spark plugs and crank the engine over to see of coolant is blown out of the spark plug port.
A less likely possibility might be a cracked head leaking coolant into the combustion chamber. Far less likely is a cracked cylinder wall.
|You didn't say who rebuilt your engine but if you did, did you put any sealer on the headgasket before installation? They tell you not to use anything and some will fight over it, but imho if you need to replace it spray both sides with Coppercoat spray sealer before installation. Use several coats untill you have a nice copper colored surface. I have had uncoated head gaskets leak but never one treated with coppercoat.|
|Pull your spark plugs. If you have 3 brownish/tan ones, and one that looks brand new ( well, its been steam cleaned) that will be the offending cylinder......|
This thread was discussed between 21/05/2008 and 23/05/2008
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