Did boost blow out my rear main, or just a coincidence?
01-12-2019, 12:03 AM
#1
Racer
Thread Starter
Did boost blow out my rear main, or just a coincidence?
Just finished putting the LS3 in my C5 with an A&A T-Trim...
Ran it for about 20 min without the charge tubes hooked up, no issues...
Water pump decided to start leaking, so I replaced that, hooked up all the charge tubes, ran it for another 15 min or so, just tweaking idle and stuff in the shop.
Took it outside and ran it for about 30 min. Got into boost a little bit, about 5 PSI, but was taking it easy while sorting out the tune...
Noticed a big cloud of smoke behind me... brought it back into the shop... rear main seal is leaking like a sieve (or possibly something else in the bell housing)...
I had the check valve hooked up in the little line between the valley plate and the intake, but NOT the breather line that's supposed to be tapped into the oil filler cap and run to the filter.
I was considering hooking that line to the passenger valve cover port (which is just capped with a rubber cap at this point) because I have the different style oil cap with the big "handle" on it.
Engine is out of a wrecked Camaro with about 10k miles on it, didn't replace the rear main.
What are the chances that this is just a coincidence? Or did I over-pressurize the crank case and blow that seal out by not having that breather installed in the cap?
It's weird that it didn't start leaking right away when I was running it, but waited until I got into boost. Then again, you would think if I was pressurizing the crank case, it would blow the dip stick or one of the rubber caps on the valve covers.
What do you guys think?
Ran it for about 20 min without the charge tubes hooked up, no issues...
Water pump decided to start leaking, so I replaced that, hooked up all the charge tubes, ran it for another 15 min or so, just tweaking idle and stuff in the shop.
Took it outside and ran it for about 30 min. Got into boost a little bit, about 5 PSI, but was taking it easy while sorting out the tune...
Noticed a big cloud of smoke behind me... brought it back into the shop... rear main seal is leaking like a sieve (or possibly something else in the bell housing)...
I had the check valve hooked up in the little line between the valley plate and the intake, but NOT the breather line that's supposed to be tapped into the oil filler cap and run to the filter.
I was considering hooking that line to the passenger valve cover port (which is just capped with a rubber cap at this point) because I have the different style oil cap with the big "handle" on it.
Engine is out of a wrecked Camaro with about 10k miles on it, didn't replace the rear main.
What are the chances that this is just a coincidence? Or did I over-pressurize the crank case and blow that seal out by not having that breather installed in the cap?
It's weird that it didn't start leaking right away when I was running it, but waited until I got into boost. Then again, you would think if I was pressurizing the crank case, it would blow the dip stick or one of the rubber caps on the valve covers.
What do you guys think?
01-12-2019, 09:04 AM
#3
Team Owner
If you had a line from a pressurized source to the valve cover, you easily blew it out.
01-12-2019, 06:46 PM
#4
Racer
Thread Starter
Technically, the valley cover to intake line won't help when in boost. There's a check valve installed there to prevent the boost from the intake from pressuring the crank case. It should only be drawing crank case fumes into the intake during vacuum situations.
01-12-2019, 06:53 PM
#5
Racer
Thread Starter
In theory, there wasn't any boost running into the crank case. So the only source should have been blow by... and that seems pretty unlikely on a 10k mile motor at 5psi. 🤔
The more I think about it, it's probably just a coincidence. That engine sat for a while, and even though the rear main was low-mileage, it could have dried out from not being exposed to oil.
01-18-2019, 10:51 AM
#7
Racer
Thread Starter
OK, little update on this guys;
Replaced the rear main seal the other night. (Holy **** what a pain in the *** with headers!)
The seal that came out looked fine, was seated up against the crank properly, flexible, no tears that I could find, and the plate seal looked good as well.
Was really hoping to find a smoking gun in there...
Anyway, put the new seal in, got her all back together and ran it for a while on the lift to see if something else back there was leaking.
No leaks that I could see. I ran it without the oil filler cap on to assess what kind of pressure/vacuum was there.
At idle with my boost gauge reading like 15in of vacuum, my oil fill had a little bit of pressure coming out of it (measured by capping it with my hand).
I took the little PCV line off from the valley cover, it definitely has vacuum coming out of it (which means my check valve is in correctly).
I'm assuming that little line just doesn't flow enough volume to pull the pressure out of the crankcase?
Where is all the pressure coming from at idle?
It's gotta be blow-by right?
Why does a 10k mile engine have so much blow by?
A couple of the cylinders had some water in them that sat for a while, you guys think that the rings got messed up (rusty)?
Next step compression and leak-down test?
I have the oil cap vented to the air filter with that big line that A&A supplies with their kit now, so it's not an immediate concern.... right?
Replaced the rear main seal the other night. (Holy **** what a pain in the *** with headers!)
The seal that came out looked fine, was seated up against the crank properly, flexible, no tears that I could find, and the plate seal looked good as well.
Was really hoping to find a smoking gun in there...
Anyway, put the new seal in, got her all back together and ran it for a while on the lift to see if something else back there was leaking.
No leaks that I could see. I ran it without the oil filler cap on to assess what kind of pressure/vacuum was there.
At idle with my boost gauge reading like 15in of vacuum, my oil fill had a little bit of pressure coming out of it (measured by capping it with my hand).
I took the little PCV line off from the valley cover, it definitely has vacuum coming out of it (which means my check valve is in correctly).
I'm assuming that little line just doesn't flow enough volume to pull the pressure out of the crankcase?
Where is all the pressure coming from at idle?
It's gotta be blow-by right?
Why does a 10k mile engine have so much blow by?
A couple of the cylinders had some water in them that sat for a while, you guys think that the rings got messed up (rusty)?
Next step compression and leak-down test?
I have the oil cap vented to the air filter with that big line that A&A supplies with their kit now, so it's not an immediate concern.... right?
Last edited by sydneyACE; 01-18-2019 at 10:53 AM.
02-28-2019, 09:44 AM
#8
OK, little update on this guys;
Where is all the pressure coming from at idle?
It's gotta be blow-by right?
Why does a 10k mile engine have so much blow by?
A couple of the cylinders had some water in them that sat for a while, you guys think that the rings got messed up (rusty)?
Next step compression and leak-down test?
I have the oil cap vented to the air filter with that big line that A&A supplies with their kit now, so it's not an immediate concern.... right?
Where is all the pressure coming from at idle?
It's gotta be blow-by right?
Why does a 10k mile engine have so much blow by?
A couple of the cylinders had some water in them that sat for a while, you guys think that the rings got messed up (rusty)?
Next step compression and leak-down test?
I have the oil cap vented to the air filter with that big line that A&A supplies with their kit now, so it's not an immediate concern.... right?
03-03-2019, 03:26 PM
#9
As far as plumbing goes I'd take a look at some of the catch can routing diagrams floating around along with the threads, very informative stuff and it's what I used to build my own pcv catch can.
03-03-2019, 05:20 PM
#10
Melting Slicks
Get a borescope down the bores where you believe water sat. Water can corrode for sure and will give a crappy ring seal that a leakdown will never show unless the piston is sitting at the corroded spot.
Compression test is often more useful than a leakdown. But a visual helps too.
And all engines will have some pressure in the crankcase, just because you think you can feel something with your hand, is not a technical measurement or indication of a problem.
Compression test is often more useful than a leakdown. But a visual helps too.
And all engines will have some pressure in the crankcase, just because you think you can feel something with your hand, is not a technical measurement or indication of a problem.
03-04-2019, 04:18 PM
#11
Racer
Thread Starter
Just didn't imagine it would be necessary for a few little half-throttle test drives under 5psi of boost.
It's been fine since I routed the line from the oil cap to the air filter as A&A's kit recommends. Been keeping an eye on oil-consumption as well as checking the line for excess oil and we're good there, so I don't see the need for a catch can at this point.
03-04-2019, 04:30 PM
#12
Racer
Thread Starter
Get a borescope down the bores where you believe water sat. Water can corrode for sure and will give a crappy ring seal that a leakdown will never show unless the piston is sitting at the corroded spot.
Compression test is often more useful than a leakdown. But a visual helps too.
And all engines will have some pressure in the crankcase, just because you think you can feel something with your hand, is not a technical measurement or indication of a problem.
Compression test is often more useful than a leakdown. But a visual helps too.
And all engines will have some pressure in the crankcase, just because you think you can feel something with your hand, is not a technical measurement or indication of a problem.
The pressure was pretty apparent at idle definitely something you could feel, and we put a rubber glove over the top to watch it fill. Maybe I'll get lucky and the rings will seat themselves better once I get some miles on the car.
I may do a compression test and leakdown if I get bored on of these days, but for now the car is running great and it's not burning oil.
03-11-2019, 08:26 AM
#13
I’ve noticed this blow by at idle on my car as well, one day when I had the vacuum hose disconnected on my PVC MM can. At first it scared the crap out of me, as I’m kinda paranoid about wrecking **** (since I’m pretty good at that). But I did a compression check and didn’t find anything obvious and the car was/is running fine and not burning oil etc.
I also could only feel the pressure if I put my hand over the breather outlet on the catch can. Once I connected the vacuum hose, that slight pressure was gone completely though, so it obviously isn’t anything significant. My car only has 5,000 miles on it too, so I was also thinking maybe the rings haven’t even worn in properly yet. Also, these LS motors (at least the LS2/3 motors) have fairly wide ring gaps, which is why the factory shortblock can handle boost/nitrous so well, but this would allow for some additional blow-by at idle. So, I’m assuming that it’s a normal thing, although it would be good to hear from others if they’ve seen the same thing.
I also could only feel the pressure if I put my hand over the breather outlet on the catch can. Once I connected the vacuum hose, that slight pressure was gone completely though, so it obviously isn’t anything significant. My car only has 5,000 miles on it too, so I was also thinking maybe the rings haven’t even worn in properly yet. Also, these LS motors (at least the LS2/3 motors) have fairly wide ring gaps, which is why the factory shortblock can handle boost/nitrous so well, but this would allow for some additional blow-by at idle. So, I’m assuming that it’s a normal thing, although it would be good to hear from others if they’ve seen the same thing.
03-11-2019, 01:12 PM
#14
Melting Slicks
They dont have wide ring gaps, and they do not suffer from blowby, and nor would a few thou difference in the ring gap make the slightest bit of difference to "blowby" at idle.
03-11-2019, 01:46 PM
#15
But I do know for sure that on older Chevy small blocks, using the amoung of nitrous that people regularly use on these LS motors nowadays would have resulted in the ring ends butting together and ripping the ring land off the piston. I’ve seen the results of that myself, a couple of times.
Are you saying that there is no discernable blow-by whatsoever at idle with these motors? If so, then I guess both my motor and the OP’s must be hurt, then? And I suppose that being the case, then there’s no need for a PCV system or a catch can that uses vacuum for PCV evacuation then?? I mean if the piston rings can hermetically seal the crankcase cavity from the combustion chamber, then all the OEMs were wasting their time and money with PCV systems all those years, just to satisfy EPA requirements?
03-11-2019, 02:03 PM
#16
Melting Slicks
Well, that’s what I’ve read and heard, from several sources, but I’ve never pulled a stock LS engine down to actually check the ring gap myself. I was speaking in relative terms to other GM OEM V8s. I’m pretty sure I could find that out easily enough though.
But I do know for sure that on older Chevy small blocks, using the amoung of nitrous that people regularly use on these LS motors nowadays would have resulted in the ring ends butting together and ripping the ring land off the piston. I’ve seen the results of that myself, a couple of times.
Are you saying that there is no discernable blow-by whatsoever at idle with these motors? If so, then I guess both my motor and the OP’s must be hurt, then? And I suppose that being the case, then there’s no need for a PCV system or a catch can that uses vacuum for PCV evacuation then?? I mean if the piston rings can hermetically seal the crankcase cavity from the combustion chamber, then all the OEMs were wasting their time and money with PCV systems all those years, just to satisfy EPA requirements?
But I do know for sure that on older Chevy small blocks, using the amoung of nitrous that people regularly use on these LS motors nowadays would have resulted in the ring ends butting together and ripping the ring land off the piston. I’ve seen the results of that myself, a couple of times.
Are you saying that there is no discernable blow-by whatsoever at idle with these motors? If so, then I guess both my motor and the OP’s must be hurt, then? And I suppose that being the case, then there’s no need for a PCV system or a catch can that uses vacuum for PCV evacuation then?? I mean if the piston rings can hermetically seal the crankcase cavity from the combustion chamber, then all the OEMs were wasting their time and money with PCV systems all those years, just to satisfy EPA requirements?
And of course the main reason for PCV and emissions systems are to satisfy the EPA. Only a fool would think piston rings offer a complete and utter seal.