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1991 400 oil in crankcase

S
Nov 28, 2010
167
9
18
Saskatchewan, Canada
I have a 1991 indy 400 that I rebuilt the engine in last year. I rebuilt everything including crank and pistons. It was running good until it seemed to loose some power. I noticed the wiring that goes to the gauge pod fell from the hood onto the exhaust and burnt a couple wires. Being it was the last ride of the season, I decided to leave it and fix it next year. I thought that maybe that was the cause of the power loss. I pulled it into the garage this year and fixed the wire and then started it up. When it started it was smoking badly. I noticed alot of oily residue where the exhaust hooks to the exhaust manifold. I removed the muffler and a bunch of fluid poured out of the muffler. I thought it was antifreeze because I could see some signs of sepage around the head gasket, but it wasn't green and seemed more like oil. I then removed the 2 small drain bolts in the bottom of the crank case and oil poured out of them. I then did a compression check and I got 120psi on each cylinder. I removed the head to check the pistons as I had to fix the head gasket leak anyways and the pistons and cylinder walls are fine. There didn't seem to be an excess of oil in the cylinders just the exhaust and crankcase. What could be causing this.
 
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Jay

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Nov 26, 2007
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Was it maybe fuel/oil you drained out of the crankcase? If you had a leaking needle/seat in a carb it would fill the cases. I don't remember where the 400 engine had the oil feed into it, could it actually leak oil thru the carbs into the cylinders? 120 psi on both sides sounds good to me, and if you don't see any obvious damage I would suspect fuel related issues for the power loss. As long as the rest of the sled is ok, like a bearing going south, melted hyfax, 2013 mainshaft twisted off. :face-icon-small-win sorry couldn't resist
 
S
Nov 28, 2010
167
9
18
Saskatchewan, Canada
It may have been oil/fuel but it was definatly more on the oil side than the fuel side. The oil is injected into the boot between the carb and the crank case so it cant drain through the carb but if it can drain through the oil pump with out it pumping, it may fill the crank case. But that doen't explain the oil in the muffler unless it was pushed in there from the full crank case while I was pulling the engine over. That would make sence, IF the oil can drain through the pump.
Kinda has me stumped, I have never heard of this happening before. I guess I will put the head back on and see what happens.
 
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S
Nov 28, 2010
167
9
18
Saskatchewan, Canada
I wonder if the vent for the oil tank was plugged and with the summertime temperatures in the high 20c to low 30c, if it would pressureize the oil tank and push oil into the crankcase. I will check the vent line tomorrow.
 
V

volcano buster

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Nov 26, 2007
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Stayton Oregon
I think I would drain the crankcase and clean up what you can. Once done, if you have good gas and oil in it fire it up and let it run until warm. Shut down and start watching for where issues could be coming from. I'm wondering if you don't just have a summer storage issue.
 
S
Nov 28, 2010
167
9
18
Saskatchewan, Canada
Yeah thats exactly what I am going to do. It is obviously getting lots of oil. LOL
It wouldn't be a summer storage thing because all I ever do for storage is shut the gas off and let the engine run intil it runs out of gas, pull the plugs and squirt a little 2 stroke oil in the cylinders, install the plugs again and pull it over a few times slowly to spread the oil around. The oil that I squirt in the cylinders is nowhere near the amount that was in the muffler and crank case. I will put it back together and try it out.
Thanks
 

m8magicandmystery

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the oil line often has mini housing with a tiny check valve that can let oil drain if its malfunctioning..but often they reseat ok once regular running resumes.
 

Jay

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I believe he means the small brass 90 degree oil fitting by the carb. It opens at very low pressure, 2 or 3 pounds, if it fails it could let the oil just flow and fill your cases.
 
S
Nov 28, 2010
167
9
18
Saskatchewan, Canada
Sorry guys for the very late reply but it slipped my mind to do a follow up of my problem. All I did was drain the oil out of the crank case and the sled has been great. Not sure what caused it but it's good to go. Thanks for all the help.
 
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