REAL Push Rod Tube STC
Forum rules
You must be a member of the Cessna 120-140 Association in order to post new topics, reply to existing topics, or search for information on this forum. Use the "Join" link in the red menu bar.
You must be a member of the Cessna 120-140 Association in order to post new topics, reply to existing topics, or search for information on this forum. Use the "Join" link in the red menu bar.
-
- Posts: 25
- Joined: Tue May 01, 2018 7:00 am
- Location: Watts Bridge Memorial Airfield
- Name: Michael Sheppard
- Aircraft Type: 1948 Cessna 140
- Occupation-Interests: Mechanical and Structural Designer.
- Contact:
REAL Push Rod Tube STC
I have a C90-12F and changed the push rod tubes over to the REAL gasket type a while back. I have been trying to eliminate oil coming through the air box, dripping onto the inside of the cowl and then running back and getting blown onto the belly. I assumed it was because of intake valve guides having too much clearance but have eliminated that cause. I am wondering if the REAL push rod tube being slightly smaller internal diameter than the original Continental tubes are holding up the flow of oil back to the sump and filling up the rocker hats and then going down the guides and through the induction tubes. Has anyone else had this oil through the airbox problem after changing to the REAL pushrod tubes?
Michael
Michael
- 5099
- Posts: 40
- Joined: Tue May 01, 2018 7:00 am
- Location: Southeast Arizona
- Name: Ramp Rat
- Aircraft Type: C-140
- Occupation-Interests: Semi-Retired A&P
- Contact:
Re: REAL Push Rod Tube STC
Wow! You must have an oil pump from a Chevy 350 to pump enough oil to fill a push rod tube and force oil pass a valve guide.
From what I was reading, you are getting oil from Inside the airbox and not from the outside????
If you've already “dealt” with the valve guides (interested just what you did) and are sure you don’t have an oil leak there. . What about oil getting pass the piston oil rings?
Next time you have the urge, take the upper spark plugs out, run the pistons down and using a bore scope, look at the area just above the piston and the lower part of the cylinder. Do you see a puddle of oil just above the piston? You may have an oil ring problem that won’t show up during a compression test. Of course, some oil in this area is normal but what you've described, it sounds like a lot.
JMHO, Steve.
![Wink ;)](./images/smilies/icon_e_wink.gif)
From what I was reading, you are getting oil from Inside the airbox and not from the outside????
If you've already “dealt” with the valve guides (interested just what you did) and are sure you don’t have an oil leak there. . What about oil getting pass the piston oil rings?
Next time you have the urge, take the upper spark plugs out, run the pistons down and using a bore scope, look at the area just above the piston and the lower part of the cylinder. Do you see a puddle of oil just above the piston? You may have an oil ring problem that won’t show up during a compression test. Of course, some oil in this area is normal but what you've described, it sounds like a lot.
JMHO, Steve.
America, Love it or Leave IT!
- 6643
- Posts: 2383
- Joined: Tue May 01, 2018 7:00 am
- Location: KLCI, NH
- Name: John C
- Aircraft Type: 1946 C140/C90
- Occupation-Interests: A&P, semi-retired
- Contact:
Re: REAL Push Rod Tube STC
Easy enough to test your theory. Run the engine then pull one of the rocker box covers.
-
- Posts: 25
- Joined: Tue May 01, 2018 7:00 am
- Location: Watts Bridge Memorial Airfield
- Name: Michael Sheppard
- Aircraft Type: 1948 Cessna 140
- Occupation-Interests: Mechanical and Structural Designer.
- Contact:
Re: REAL Push Rod Tube STC
Thanks for the replies
I have done that, run the engine and then quickly pulled a rocker cover, my theory was wrong, no excess oil in the rocker hat.
I had a couple of inlet valve guide replaced which were worn, but still seem to be getting oil coming down the induction tubes to those cylinders.
The oil rings on those pistons are fine.
I cannot see that it could be coming from anywhere but the valve guides when the engine is at idle and the carb butterfly is closed allowing the suck from the cylinder to pull oil through the guide. Unless there is somewhere else?
Thanks
Michael
I have done that, run the engine and then quickly pulled a rocker cover, my theory was wrong, no excess oil in the rocker hat.
I had a couple of inlet valve guide replaced which were worn, but still seem to be getting oil coming down the induction tubes to those cylinders.
The oil rings on those pistons are fine.
I cannot see that it could be coming from anywhere but the valve guides when the engine is at idle and the carb butterfly is closed allowing the suck from the cylinder to pull oil through the guide. Unless there is somewhere else?
Thanks
Michael
- 6643
- Posts: 2383
- Joined: Tue May 01, 2018 7:00 am
- Location: KLCI, NH
- Name: John C
- Aircraft Type: 1946 C140/C90
- Occupation-Interests: A&P, semi-retired
- Contact:
Re: REAL Push Rod Tube STC
How much oil are you talking about?
-
- Posts: 25
- Joined: Tue May 01, 2018 7:00 am
- Location: Watts Bridge Memorial Airfield
- Name: Michael Sheppard
- Aircraft Type: 1948 Cessna 140
- Occupation-Interests: Mechanical and Structural Designer.
- Contact:
Re: REAL Push Rod Tube STC
Not sure how much, but enough to drip out of the air box run down the inside of the cowl and spray onto the firewall and belly.
Michael
Michael
- 6643
- Posts: 2383
- Joined: Tue May 01, 2018 7:00 am
- Location: KLCI, NH
- Name: John C
- Aircraft Type: 1946 C140/C90
- Occupation-Interests: A&P, semi-retired
- Contact:
Re: REAL Push Rod Tube STC
Not to be a pain, but are you sure it's dripping out of the airbox? Could it (e.g.) be coming from the spine of the case?
-
- Posts: 25
- Joined: Tue May 01, 2018 7:00 am
- Location: Watts Bridge Memorial Airfield
- Name: Michael Sheppard
- Aircraft Type: 1948 Cessna 140
- Occupation-Interests: Mechanical and Structural Designer.
- Contact:
Re: REAL Push Rod Tube STC
Any dialogue is good to help me solve or accept the oil leak.
No definitely the airbox. I can put my finger into it and feel the pool of oil. Also when I take the induction tubes off I can see oil lying in the spider above the carby.
Michael
No definitely the airbox. I can put my finger into it and feel the pool of oil. Also when I take the induction tubes off I can see oil lying in the spider above the carby.
Michael
-
- Posts: 243
- Joined: Tue May 01, 2018 7:00 am
- Location: California
- Name: Randy Thompson
- Aircraft Type: Cessna 140
- Occupation-Interests: Work on airplanes and engines
- Contact:
Re: REAL Push Rod Tube STC
Do your rocker arms have holes in the upper end? Later engines went to undrilled intake rockers because it was determined that the intake didn’t need the extra oil. The exhaust side did because it runs much hotter than the intake. Since the intake valves suck air into the cylinder, the also suck oil in. The intake elbows are below the cylinders and some of the excess oil ends up traveling down to the carburetor and the airbox.
Randy Thompson A&P IA Pilot
Hold STC SA547EA for installation of O-200 engine in Cessna 120/140 and 140A"s
Overhaul small Continentals
Hold STC SA547EA for installation of O-200 engine in Cessna 120/140 and 140A"s
Overhaul small Continentals
-
- Posts: 25
- Joined: Tue May 01, 2018 7:00 am
- Location: Watts Bridge Memorial Airfield
- Name: Michael Sheppard
- Aircraft Type: 1948 Cessna 140
- Occupation-Interests: Mechanical and Structural Designer.
- Contact:
Re: REAL Push Rod Tube STC
Hello Randy
Thanks for your input.
Yes they do have holes at the upper end. I know that because when we have pulled a cylinder in the past we noted that the input and exhaust rockers were the same, both with a hole at the upper end. From what you are saying it would be OK to change those input rockers to later models with no hole at the top! I think you may have found my solution.
Cheers
Michael Sheppard
1948 Cessna 140 VH-TMO
Thanks for your input.
Yes they do have holes at the upper end. I know that because when we have pulled a cylinder in the past we noted that the input and exhaust rockers were the same, both with a hole at the upper end. From what you are saying it would be OK to change those input rockers to later models with no hole at the top! I think you may have found my solution.
Cheers
Michael Sheppard
1948 Cessna 140 VH-TMO
Who is online
Users browsing this forum: No registered users and 17 guests