396 Stroker - Burning Oil & Extreme Crankcase Pressure
08-14-2016, 04:37 PM
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396 Stroker - Burning Oil & Extreme Crankcase Pressure Quick summary: 396 stroker, low miles on the block and new H/C/I 1,500 miles ago.
Earlier this year at the track I blew my dipstick out of my dipstick tube and sprayed oil out the top of the tube. I worked with MightyMouse on my catchcan setup and upgraded my hose barb fittings to -12AN fittings and that seemed to stop the tube from blowing out. The guy I was racing let me know that I was "smoking" about half way down the track...I attributed that to the oil spraying onto my heads and headers. That leads me to where I am now...last week I ran into another fbody and we ended up doing a few pulls from a 40or so roll, after the first pull I looked in my rearview and saw tons of blue smoke and smelled oil burning. I assumed I blew the dipstick again, however when I looked under the hood I had oil coming out of the breather on my catch can. Also I have tons of oil in my intake manifold, it is pooled in the back corners near the runners as well as right behind the throttle body.
From the research that I have done so far my guess is something wrong with my rings, since that would explain the extreme crankcase pressure, but havent ruled out a PCV issue.
My long term plan would be to pull the block, have that honed out and reassembled. Thinking I might be able to reuse most of my rotating assembly since its relatively new and all forged Scat.
Any thoughts and ideas about what could be wrong would be greatly appreciated.
Earlier this year at the track I blew my dipstick out of my dipstick tube and sprayed oil out the top of the tube. I worked with MightyMouse on my catchcan setup and upgraded my hose barb fittings to -12AN fittings and that seemed to stop the tube from blowing out. The guy I was racing let me know that I was "smoking" about half way down the track...I attributed that to the oil spraying onto my heads and headers. That leads me to where I am now...last week I ran into another fbody and we ended up doing a few pulls from a 40or so roll, after the first pull I looked in my rearview and saw tons of blue smoke and smelled oil burning. I assumed I blew the dipstick again, however when I looked under the hood I had oil coming out of the breather on my catch can. Also I have tons of oil in my intake manifold, it is pooled in the back corners near the runners as well as right behind the throttle body.
From the research that I have done so far my guess is something wrong with my rings, since that would explain the extreme crankcase pressure, but havent ruled out a PCV issue.
My long term plan would be to pull the block, have that honed out and reassembled. Thinking I might be able to reuse most of my rotating assembly since its relatively new and all forged Scat.
Any thoughts and ideas about what could be wrong would be greatly appreciated.
Last edited by abern310; 09-30-2016 at 08:52 AM.
08-14-2016, 07:09 PM
#2
What pistons are in it?
With that much stroke, the piston design and debur of the bottom of the cylinder are very important. You could have an issue where too much of the piston skirt is exposed below the cylinder at BDC causing the piston to rock and oil to escape past the rings into the chamber on the intake stroke and exhaust gas to escape into the crankcase on the exhaust stroke.
With that much stroke, the piston design and debur of the bottom of the cylinder are very important. You could have an issue where too much of the piston skirt is exposed below the cylinder at BDC causing the piston to rock and oil to escape past the rings into the chamber on the intake stroke and exhaust gas to escape into the crankcase on the exhaust stroke.
08-14-2016, 09:36 PM
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What pistons are in it?
With that much stroke, the piston design and debur of the bottom of the cylinder are very important. You could have an issue where too much of the piston skirt is exposed below the cylinder at BDC causing the piston to rock and oil to escape past the rings into the chamber on the intake stroke and exhaust gas to escape into the crankcase on the exhaust stroke.
With that much stroke, the piston design and debur of the bottom of the cylinder are very important. You could have an issue where too much of the piston skirt is exposed below the cylinder at BDC causing the piston to rock and oil to escape past the rings into the chamber on the intake stroke and exhaust gas to escape into the crankcase on the exhaust stroke.
Would that be an issue that would always happen or would that develop over time?
08-14-2016, 09:57 PM
#5
I agree that long of stroke has been know to cause excessive oil consumption over time but I never heard of it causing excessive crank case pressure especially at that low of mileage.
Not apples to apples, but Back in the day I had a procharged LT1, that was basically stock with 8lbs of boost. I started noticing it was blowing the oil dipstick out of the tube and oil was coming out of the breathers. After tear down it had a cracked ring on the #8 slug. The car still rand and drove fine, just had excessive crankcase pressure.
Not apples to apples, but Back in the day I had a procharged LT1, that was basically stock with 8lbs of boost. I started noticing it was blowing the oil dipstick out of the tube and oil was coming out of the breathers. After tear down it had a cracked ring on the #8 slug. The car still rand and drove fine, just had excessive crankcase pressure.
Last edited by kinglt-1; 08-15-2016 at 10:18 AM.
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08-15-2016, 09:10 AM
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4.125 stroke and 6.125 rod = 1.48 rod/stroke ratio, that's not so good. Those pistons are getting rocked in their bores and oil control is an issue. It's making more crankcase pressure than you can control and blowing oil out where ever it can. Total seal rings with a Napier second if you haven't already.
08-15-2016, 09:56 AM
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4.125 stroke and 6.125 rod = 1.48 rod/stroke ratio, that's not so good. Those pistons are getting rocked in their bores and oil control is an issue. It's making more crankcase pressure than you can control and blowing oil out where ever it can. Total seal rings with a Napier second if you haven't already.
I really don't want to bail on the block yet, I would like to dive into it and see if the piston rocking is definitely the cause (which I am assuming it is).
With a relatively tight budget...is it worth sinking the money into this block for a hone and rebuild, or building a 408 short block
08-15-2016, 11:28 AM
#13
IMO if the goal is 500rwhp or less.... use a stock engine, and a turbo. Its like you keep 'trying to build' for mediocre output that a stock engine will handle for 1/10 the cost?
08-15-2016, 11:43 AM
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Just looking to get my car running again...buy it, build it, break it - rinse and repeat
This is the first build so I'm not quite sure what "keep trying to build" entails. I've got $4500 into the full long block which I would consider a pretty good build for the price. So before I call it quits on this block I want to make sure that I completely understand the problem with it.
08-15-2016, 12:12 PM
#15
Not disagreeing with you on that at all. This just happens to be a big question mark on my build.
Just looking to get my car running again...buy it, build it, break it - rinse and repeat
This is the first build so I'm not quite sure what "keep trying to build" entails. I've got $4500 into the full long block which I would consider a pretty good build for the price. So before I call it quits on this block I want to make sure that I completely understand the problem with it.
Just looking to get my car running again...buy it, build it, break it - rinse and repeat
This is the first build so I'm not quite sure what "keep trying to build" entails. I've got $4500 into the full long block which I would consider a pretty good build for the price. So before I call it quits on this block I want to make sure that I completely understand the problem with it.
08-15-2016, 07:04 PM
#16
The skirts on a piston are barrel shaped, with the widest part being the "major diameter". This major diameter is what a machinist measures to hone the block for the correct piston-wall clearance. If the piston is not designed correctly for the stroke, the major diameter of the skirt will come out below the bottom of the cylinder and the piston-wall clearance increases. This is what allows the piston to rock. What makes it worse is on the way up, the edge of the cylinder can start slicing material off the major diameter, making the excess piston-wall clearance constant and not just at BDC. The aluminum being trimmed off the skirt will show in the filter.
That's why I think you're problem keeps getting worse and worse.
08-15-2016, 07:08 PM
#17
Sorry about that. Yeah, I didn't mean "you" specifically you. I guess I was thinking about the forum as a whole slice of those dead-set on N/A 'builds' underachievers. "the underachiever N/A build folks" will throw 5k at an engine and it will last 1/10 as long as a stock engine and make 100 horsepower less than a stock engine on boost, basically because 'if you want something done right, do it yourself' they didn't do that part.
-Keith Duckworth, co-founder of Cosworth
08-16-2016, 10:18 AM
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Sorry about that. Yeah, I didn't mean "you" specifically you. I guess I was thinking about the forum as a whole slice of those dead-set on N/A 'builds' underachievers. "the underachiever N/A build folks" will throw 5k at an engine and it will last 1/10 as long as a stock engine and make 100 horsepower less than a stock engine on boost, basically because 'if you want something done right, do it yourself' they didn't do that part.
08-17-2016, 02:50 PM
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Aluminum slivers.
The skirts on a piston are barrel shaped, with the widest part being the "major diameter". This major diameter is what a machinist measures to hone the block for the correct piston-wall clearance. If the piston is not designed correctly for the stroke, the major diameter of the skirt will come out below the bottom of the cylinder and the piston-wall clearance increases. This is what allows the piston to rock. What makes it worse is on the way up, the edge of the cylinder can start slicing material off the major diameter, making the excess piston-wall clearance constant and not just at BDC. The aluminum being trimmed off the skirt will show in the filter.
That's why I think you're problem keeps getting worse and worse.
The skirts on a piston are barrel shaped, with the widest part being the "major diameter". This major diameter is what a machinist measures to hone the block for the correct piston-wall clearance. If the piston is not designed correctly for the stroke, the major diameter of the skirt will come out below the bottom of the cylinder and the piston-wall clearance increases. This is what allows the piston to rock. What makes it worse is on the way up, the edge of the cylinder can start slicing material off the major diameter, making the excess piston-wall clearance constant and not just at BDC. The aluminum being trimmed off the skirt will show in the filter.
That's why I think you're problem keeps getting worse and worse.
