View Full Version : Gas in the crankcase?

05-25-2007, 09:30 AM
Anyone ever have this problem? I recently brought my 1973 TR6 out of hibernation. When I went to check the oil (which I had changed before putting it to bed)I noticed that the level was way too high. I thought that very odd as I usually don't make that mistake. Then, I smelt it. It smelt like gasoline! Could this be my imagination?
I had leaky carbs last fall, mostly coming out the throat on the air cleaner side as well as the vent hole going to the float chamber. I removed the carbs over the winter and realized that I had been given, and had used, the wrong gaskets (4) between the carbs and manifold. They didn't have the cutout for the bypass valves, therefore the bypass was essentially blocked. I have replaced and hope that will rectify that problem. But could this be responsible for dumping that much gas into the engine?


05-25-2007, 09:52 AM
The fuel pump is another possible source for gas leaking into the engine sump. It sits well below the top level of the tank and connects directly in the lower part of the engine. A small leak in the diaphragm could lead to your problem.

For significant amounts of gas to get to the sump from the carbs, would mean at least one was leaking by the float valve, through an open intake valve, into the cylinders, past the rings then into the sump. While this is possible, even with a full tank, differential pressure is not much. A quick look down the throat of the carbs should show if they are the source of the leak.

05-25-2007, 01:32 PM
I agree with Ray, it's likely the diaphragm in the fuel pump.
I had the same symptoms last year when I first went to start my TR6.
It's amazing how much fuel can pass through the diaphragm, through the pump body and into the crankcase over a period of a few months.
Easy to fix at least.

05-25-2007, 02:44 PM
your rings might be stuck. Pull the plugs to see which cylinders have gas in them. Yes some gas will pass by the rings but sounds like you need to freshen that engine up. Maybe just a good long hot drive with some oil additive to loosen those rings up. If you haven't had the head off, maybe it's time to pull it and mike the bore diameters to see what kind of clearances you have. (you could also try a feeler gauge between the piston and cylinder for a crude estimate.) Remember that the front to back clearance will likely show the most wear and the cylinder will not be round, clearances will vary.Any verticle scores means at least a honing job but better, a full rebuild. a fresh tight engine will have .0015" clearance (roughly)maybe .002".

05-25-2007, 02:58 PM
Concurrence with Ray 'n Graham.

At rest, over a period of time with a leaky pump diaphragm the crankcase will be a bomb. Drain and fill with clean oil, change filter, R&R fuel pump. After a few hundred miles repeat the first two. A compression check or (preferably) a leak-down test at that point will tell you how things are internally. A diaphragm "kit" should be available at any NAPA store for pocket change, a replacement pump for little more.

05-25-2007, 09:33 PM
I recently had that problem. Last DEC after setting for 1 month. I took over 4 1/2 gallons of oil fuel mix out of my 250's crank case. I knew I had a speratic leak in the rear carb but refuse to believe that that much fuel could work it's way through the carbs and into the cylinders and past the rings. I have total seal piston rings too! Did find a very small hole in the diaphragm of the fuel pump. It did not go all the way through as far as I can tell. So I changed the mechanical fuel pump over to an electrical pump and it helped performance too. Problem with putting in just a diaphragm in the old pump is that the fuel will leak past the center shaft that connects the diaphragm to the cam and into the crankcase if you don't change the seal around the shaft. However I hear they are not available any more. Another benefit with the electric pump is that when the fuel pump is not running gas cannot go through it. Must be a check valve inside. Good Luck. Larry

05-25-2007, 10:21 PM
Think how clean the pan is know!