Dry oil sump and engine questions
Posted: Sun Feb 19, 2012 4:26 pm
I would like to seek learned opinions from you guys about a couple of
things. First, I finished constructing a dry oil sump for my PSRU. I made
it out of 3" foam core ABS plastic pipe. My PSRU has an integral oil pump
and I have a pressure gauge in the cockpit that tells me that the max
pressure it sees is about 20psi and is usually closer to 10 psi. I'm not
sure if the oil outlet is subject to that pressure or is just in a
non-pressurized area of the unit but I would expect to see very little
pressure in my sump. A web search tells me that foam core ABS is for
non-pressure applications where the temp will not exceed 160F. I've seen
engine oil temps a bit over 200F but I think I can get those to stay under
200F. The PSRU is not directly subjected to combustion temps like the block
so I would think that it would run cooler using it's own dry sump. (Might
have to see about fitting a temp gauge on it.) Especially since it is in
the front right behind two holes in the cowl for cooling air to enter. The
placement of my sump will put it right in the path of that cooling air as
well. ABS sump a bad idea? There's the issue about the ABS adhesive that
holds the caps on too. PVC is even worse with a 140F max temp
recommendation. Aluminum is impossible for me to make myself. Can't find
anything suitable off-the-shelf.
You might remember that my #8 exhaust valve seems to be leaking. Leak down
test shows low compression and I hear air leaking out the exhaust pipe. I
double checked the leak down with the rockers removed to be sure the valves
were closed. Very low hours on the engine since rebuild (after my burned
piston). Maybe 10 hours total, ground and in-flight. Tried smacking the
valve with a plastic hammer to see if some carbon or something was holding
it open with no luck. I had a very good engine shop disassemble, inspect,
and reassemble the heads after the burned piston event just to be sure
everything was OK. Is there any chance of improvement with more time on the
engine or should I just dive into pulling the head to check out the valve?
Or is there something else that can be tried before pulling the head?
Another somewhat related question. When I first built the engine, and again
after the rebuild I am getting lower compression readings on all the
cylinders than I would expect. Inputing 80 psi I get low 60s on all
cylinders (except #8 which gives me low 30s right now). I tried two
different testers (one automotive and one from Aircraft Tool Supply) and get
the same readings. I am very careful finding TDC and even try to get the
numbers up a bit with a bit of nudging on the prop (I've had luck with this
on Lycomings). I am careful to come up to TDC in one direction and then not
reverse to try and seat the rings on one side of the groove. Is there
something about my Chevy V8? Do the rings need more time to fully seat?
The engine is running great and developing good power.
Thanks in advance guys.
Mike
-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
-----------------------------------------------------------------
things. First, I finished constructing a dry oil sump for my PSRU. I made
it out of 3" foam core ABS plastic pipe. My PSRU has an integral oil pump
and I have a pressure gauge in the cockpit that tells me that the max
pressure it sees is about 20psi and is usually closer to 10 psi. I'm not
sure if the oil outlet is subject to that pressure or is just in a
non-pressurized area of the unit but I would expect to see very little
pressure in my sump. A web search tells me that foam core ABS is for
non-pressure applications where the temp will not exceed 160F. I've seen
engine oil temps a bit over 200F but I think I can get those to stay under
200F. The PSRU is not directly subjected to combustion temps like the block
so I would think that it would run cooler using it's own dry sump. (Might
have to see about fitting a temp gauge on it.) Especially since it is in
the front right behind two holes in the cowl for cooling air to enter. The
placement of my sump will put it right in the path of that cooling air as
well. ABS sump a bad idea? There's the issue about the ABS adhesive that
holds the caps on too. PVC is even worse with a 140F max temp
recommendation. Aluminum is impossible for me to make myself. Can't find
anything suitable off-the-shelf.
You might remember that my #8 exhaust valve seems to be leaking. Leak down
test shows low compression and I hear air leaking out the exhaust pipe. I
double checked the leak down with the rockers removed to be sure the valves
were closed. Very low hours on the engine since rebuild (after my burned
piston). Maybe 10 hours total, ground and in-flight. Tried smacking the
valve with a plastic hammer to see if some carbon or something was holding
it open with no luck. I had a very good engine shop disassemble, inspect,
and reassemble the heads after the burned piston event just to be sure
everything was OK. Is there any chance of improvement with more time on the
engine or should I just dive into pulling the head to check out the valve?
Or is there something else that can be tried before pulling the head?
Another somewhat related question. When I first built the engine, and again
after the rebuild I am getting lower compression readings on all the
cylinders than I would expect. Inputing 80 psi I get low 60s on all
cylinders (except #8 which gives me low 30s right now). I tried two
different testers (one automotive and one from Aircraft Tool Supply) and get
the same readings. I am very careful finding TDC and even try to get the
numbers up a bit with a bit of nudging on the prop (I've had luck with this
on Lycomings). I am careful to come up to TDC in one direction and then not
reverse to try and seat the rings on one side of the groove. Is there
something about my Chevy V8? Do the rings need more time to fully seat?
The engine is running great and developing good power.
Thanks in advance guys.
Mike
-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
-----------------------------------------------------------------