The Murphy Builders Site

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

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






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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

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

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.

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

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

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

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

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

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

on Lycomings). I am careful to come up to TDC in one direction and then

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

Thanks Ken and Drew. I managed to forget about the proximity to the
headers. And the info about the PSRU oil temp on Ken's plane clinches it.
I hadn't run across that expansion tank in my web searches Drew. That just
might work. Also, I was doing compression checks on a cold engine. Very
good point. I'll check again on a hot engine. How do you lap a valve in
place? Thanks again guys.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Ken
Sent: Friday, February 29, 2008 4:08 AM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Dry oil sump and engine questions

Mike Kimball wrote:

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.

Hi Mike
Oil can burn! Your exhaust headers glow very brightly. There is no place
for low temperature plastic under the cowl IMO. I even went to teflon
tubing (500*F) for my psru sight gauge and mine only has about 9 ounces
of oil in it with no pressure. I'd suggest welding up a custom tank if
necessary. You want a good margin of safety here for hot day climbs or
other issues that might raise the temperature. I only have air blast
cooling but I have seen 212+F psru oil temps. A couple of percent of
engine power is being converted to heat in the psru.

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?

I'd defer to anyone with experience with that particular engine but I
can't think of any scenario where it might improve. More likely is
further degradation perhaps on multiple cylinders if there is a common
cause.

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.

I think you know this and it is not relevant but an actual COMPRESSION
reading depends on cranking speed somewhat and throttle fully open.
Usually I see higher readings than the compression ratio would suggest
because in the real world the charge is also heated when it is
compressed. Adding a bit of oil will raise the pressure if it is ring
leakage of course.

However it sounds like you are actually doing a LEAKAGE check with
compressed air here. Sure sounds like you have had a valve problem with
#8 since new. Based on what you've said I would not suspect a ring
issue. Ring leakage is usually quite audible with your ear to the oil
filler. It can sometimes be tricky to get a leakage checker to seal in
the spark plug hole but again you can hear that leakage. Sorry but
there is a definite problem here.

I like to do a very light hand lapping of valves so I can see the
sealing surface or at least confirm the valve seating with some
machinist blue. That also checks for bent valves or mis-aligned valve
guides. Everybody has a bad day though and another possibility can be a
bent valve after installing the heads on engines with interference
pistons and valves. Doesn't take much to do damage before getting the
camshaft timing correct...
Ken

Thanks in advance guys.

Mike

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Thw rope trick for lapping valves in place. It occurred to me after I wrote
that it might be really hard to do with only 1 18mm spark plug hole I've
only done it on lycoming engines but I'll explain it anyways.
safety first remove all the spark plug wires then remove the spark plug
and turn the engine till the piston is near the bottom. push as much of a
peice of rope ( 1/2" cotton is ideal but anything will work ) as you can
into the cylinder. Now turn the prop to bring the piston up and squish the
rope up into the head. Now you can take off the rocker arm. For lycomings
there's a neat tool to compress the valve spring enough to remove the
keepers. I guess on your chevy you'll have to figure that part out
yourself. Basically you need a lever about a foot long that presses on the
spring on both sides while leaving enough room to get the keepers out. Some
sort of a fork that bolts on where te rocker arm came off. After you get
the valve spring off you can attach your lapping tool then turn the prop
back enough that you can pull the rope out of the cylinder then push the
valve down far enough to see and paint the lapping compound on through the
spark plug hole then lap the valve and reassembe using the same tecknique.
Oh yeah I never had much luck with those lapping tools that just turn the
valve back and forth a little bit so I just use my cordless drill with a
peice of rubber hose attached to a drill bit and the valve stem to spin the
valve.