110 compression/gas in oil

R

RandyMettler

Senior Member
I am getting gas in my oil. All cylinders have good cylinder compression at 110. I did a leak down test at 100 psi resulting in approximately 10 pounds of compression loss in all cylinders, except #6. #6 had 40 pounds loss. I heard air escaping inside the 8BA block out of the oilfill tube and dipstick. Could all the valve guide seals at the intakes need to be replaced? If so, would that cause gas to contaminate the engine oil?


Regards
 
Usually, gas in the oil sump is caused by a leaking carburetor. Check the fuel bowl in the carb after it has been running......wait a few hours to see if it is leaking down. You should not run the engine with any load on it.......gasoline will dilute the lubricating ability of the oil and ruin the bearings.


The gas-in-oil is most likely independent of the bad cylinder compression.
 
"The gas-in-oil is most likely independent of the bad cylinder compression."


It is my understanding that 110, 115 and 120 is stock from ford dealer out the door. This changes of course depending on the year of the 8BA. 110 on all cylinders would be good then? Great advice on not running with diluted oil. I have changed it after each short test run. If by bad cylinder compression, you were referring to #6 having 40 percent loss, I am not sure what would cause that if the compression reading for number6 is 110.

This probably is a stupid question, but does the gas from a leaking carburetor simply collect on the top of the pistons and slowly make its way pass the rings? I am planning on doing a bench test with the carbs off. Filling the float bowl to a set mark, bolt upper carburetor body back and let is sit over night.
 
Last edited:
Bad diaphragm on the fuel pump. Gas gets into the crank case via the oil fill tube. When running gas constantly runs into the crankcase. If it were the carb, you would have to leak a lot of gas to get into the crankcase.
 
Bad diaphragm on the fuel pump. Gas gets into the crank case via the oil fill tube. When running gas constantly runs into the crankcase. If it were the carb, you would have to leak a lot of gas to get into the crankcase, probably enough to kill the engine from running so rich.
 
I think I have a leaking power valve as well as bad diaphragm. When taking off the primary carburetor I noticed fuel in the throttle body. I also have air bubbles in my fuel lines when running. Not sure if the air indicates a bad diaphragm but because of the quanity of gas in the oil makes sense and sounds dead on. I didn't know a bad diaphragm could cause the contamination issue.

Thanks for all your time and information

Regards
 
Last edited:
Sounds like you are running a dual or more carburetor setup.


I'm also guessing the carburetors are Holley 94s.


A leaky fuel pump diaphragm will let fuel leak right down the rear "oil fill", also why you shouldn't run a full time electric fuel pump through a old mechanical fuel pump.


Seems like you have good fuel pressure? If the diaphragm is leaking pressure will suffer but you can't rule it out totally.


Keep at it.
 
Thanks Tinker. Dual 94s is correct. Those are my current projects. I do have and inline electric fuel pump but use it only for 3 or 4 seconds to prime. I am taking apart my fuel pump tomorrow. I am hoping it is the cause for the oil contamination. When I get it functioning will I be able to remove the electric unit I use to prime with? It sounds like by your post that the electric pump is hard on the diaphragm. Also is a bad diaphragm easy to spot visually? I have gone through 3 oil changes in diagnosing my drivability problems. I have always put expensive racing oil in for this an ruined the oil in a few miles. Can I run normal oil for testing until I get is worked out. I understand the fords need zinc in the oil. I don't know, but guess running normal oil for 10 or 20 miles won't damage the motor. I may need to change oil a few more times. Once the problems solved switching back to the racing oil.
 
I'd just run 5w-30 on a new rebuild. 30w if you want better pressure on a older engine. Maybe some lucas zinc additive if you prefer.

You don't have to have a electric pump with a dual. A good mechanical pump will handle it just fine. Every "vaperlock" situation for me has been a bad coil/condensor. Fl to Mn driving.

Another thing to replace is the check valves in the pump. Might be part of the bubble issue. Think charlieNy rebuilds these pumps. Not a ad, just a fact. last couple pumps i bought was from macs. Served me well so far (5yrs). Bubbles could also be bad connections letting in air. But the check valves are a overlooked component and very important.


94's have issues with new PV seating. Making them leak gas. There are also guys that rebuild these correctly also. Depends on what you want to do. I'm a fan of Strom 97s.


Everyone has a different experience.

Once you get it straight, run the crap out of it. It'll help the valves/rings and everything else.
 
Last edited:
Regular oil will be just fine. That's all I've ever run in my engine for over 20 years now, Pull the pump and rebuild it.
 
I pulled to fuel pump and pulled it apart. My models check valves may not be serviceable. It does not have the retaining plate with the two bolts that hold the plate in place. It also does not have the two hole gasket for the check valves. The two valves are press fitted, no gasket, no bolt holes. Taking them out appears to be a one way mission. Not problem if I can replace them. The aftermarket kits may be slightly sized different.

Also my oil fill adapters bottom mating surface to the intake manifold was badly warped. (The fill, not the intake) I belt sanded it as flat a I dared. It is my knowledge (Just from recent research, may be incorrect) that people have stacked or used thicker gaskets at this junction between the oil adapter and intake to change the pumps actual fuel pressure output. Slightly increasing the arms throw by about 1/16" should increase the pumps pressure output, but by how much. It probably doesn't matter as I plan to install an adjustable inline regulator. The Dual 94s seem to be tricky enough. Might as well take the fuel pressure out of the equation.



Definitely going to mount the pump and turn the motor by hand to make sure the pump arm and fuelpump rod can handle increase throw.
 

Attachments

  • Flathead_Engine_fuelpump1947to48[1].jpg
    Flathead_Engine_fuelpump1947to48[1].jpg
    40.8 KB · Views: 18
  • 100_7696.jpg
    100_7696.jpg
    107 KB · Views: 13
Last edited:
FYI, I was running dual 94's and Charlie NY advised me to block off the PV"s. I purchased the plugs from him and was really pleased at how they did the job. No more PV size concerns or issues.
Charlie explained the reasoning much more technically than I can remember many years later. Chap
 
chap52 "block off the PV"s"

Thanks for your input.

What year block did you have when you did that? Was your distributor vacuum controlled? Did it affect acceleration? The problem with the power valves and dual 94s is the available vacuum the engine produces is spit between the two valves and is effectively cut in half. This causes the power valves to open early when not needed. So, any carburetor system with any vacuum advance and retard controlled distributor would not function as designed, at least that is what I have been able to determine.

To take it a step further. If you only plugged one power valve and left the other open, the pv would receive the proper vacuum and should function as designed and provide the correct amount of fuel when required. The problem I see with this scenario is the fuel would not reach all cylinders equally as the seat position with two carbs are not centered on the intake.

I thought about purchasing the plugs and running without the powervalve assist during high load demand situations. I have heard of people doing so. My concern would be at times the engine may run lean. If that is true and the engine would run leaner, what I haven't been able to find out, could that cause engine damage over time?

Regards
 
Last edited:
Two carburetors do not affect engine vacuum. They see the same vacuum with one, two or three carbs. The proper power valve will work just fine. Charlie and I have talked about this several times, he prefers to block them, I prefer to keep them.
 
You should at least put in 3.5s in each dual (unless it's progressive linkage). Make sure they seat well.
 
Last edited:
I don't have progressive linkage. I did a leak test yesterday and although the fuel level did drop a bit the throttle body was dry when I separated the main carb body containing the pressure valves from it. It sounds like you are against plugging the power valves when you say at least 3.5. Do you agree with flatjack9 that multiple carburetors will receive the same vacuum pressure as one carb set up? Not trying to insult anyone, When it comes to flatheads you could tell me the earth is flat and I would believe you. There are people that say vacuum affects multiple carbs and the choice of power valves is important for proper fuel delivery. Most people will not run multiple 94s because of the vacuum control. They prefer the Stromsburg's mechanical power valve control. What I am getting at is I'm still trying to figure all this out an appreciate all input that is available.

Drive fast and take chances!
 
If you have one carb, there is a set vacuum for the pv to open. If there is two carburetors, they share the vacuum. hence the pv's should equal the same as a single carburetor. Or they dump gas too early.


Engines are a air pump. More holes open, vacuum suffers. Same with any engine outside of an electric "motor"


To my limited knowledge on a dual setup, for ease of use, it's better to not have progressive linkage.


You can use a thinner gasket or tack weld a dot on the push rod. Both "fixes".
 
Last edited:
I think we are all saying the same thing in different ways.

When doing the gas leak test over night in the float bowls, both carbs leak gas exactly to the top of the spring on the power valves and stopped. I find this odd. No gas visible in the throttle body below. I covered the top of the carbs and the gas inlet barb on the carbs tight with surrand wrap and rubber bands to stop evaporation. Why did they leak to the exact same level? Does this mean no gas is leaking through the power valves gaskets?
 
Last edited:
You must log in or register to reply here.
Back
Top