70 Bronco 302 - Oil Blow Back? Piston Ring Replacement?

[tonytony9]

Hi Everyone,

The past few months I have been going through essentially a gasket overhaul/chasing down leaks. This included, intake manifold gasket, valve cover gasket, replacing the rear main seal, oil pan gasket, rebuilding the carb/extension place gasket. Overall, my Bronco is running excellent ever since the autolite 2100 2b carb rebuild. I might have minimal smoke out the exhaust (potentially on acceleration, although, with the new cold weather moving in, I cannot confirm). Replaced all the vacuum lines, PCV valve, oil fill cap and vacuum advance.

I am dealing with what appears to be a fully original Bronco. In terms of leaks, what seams to be left is a transmission seal & transfer case seal leak. As well as a slight leak from the oil pan plug. Bottom end health looked great, no scoring on the main bearing.

Here is the issue, I am getting oil seeping out the oil cap and from the gasket on the PCV. Oil pressure on all the cylinders looked good on a compression test. I was told that the oil blow back could be caused by worn piston rings.

What is the process I should be going through to ensure piston rings are good and valve seal are good?

1. I replaced the spark plugs and will be able to check if I am getting oil build up.
2. I have tried to seal up as many leaks as possible to see if I am burning oil.
3. I have attached my compression test.
4. Oil pressure on my stock gauge cluster seems consistent. 40lbs after a few moments of running. Goes up to about 55lbs after significant time driving at highway speeds and then drops back to about 40lbs on the same trip when traveling off highway at reduced speeds around 40mph or lower.

 

[73azbronco]

I'd just replace the rubber parts your arrow points to. Honestly if original, that is not a leak, more of a marking it's territory.

Compression looks fine. Oil pressure is good. Drive it. Keep check on fluid levels.

 

[Timmy390]

The rubber grommet on the valve cover is wasted....old hard brittle and cracked......I would replace it and get a new breather cap.

Tim

 

[tonytony9]

The rubber grommet on the valve cover is wasted....old hard brittle and cracked......I would replace it and get a new breather cap.

Tim

Would you recommend getting a breather cap in this style? From my understanding, abandoning the plastic right angle that connects and runs via a tube to the aircleaner.

https://www.cjponyparts.com/ford-performance-oil-breather-cap-push-in-open-element-chrome-with-ford-racing-logo/p/OC44/

 

[tonytony9]

I'd just replace the rubber parts your arrow points to. Honestly if original, that is not a leak, more of a marking it's territory.

Compression looks fine. Oil pressure is good. Drive it. Keep check on fluid levels.

Looks like I only replaced the PCV valve itself (not the gasket), the oil cap and gromet (not the right angle plastic piece).

Ill replace the valve/gasket, oil cap/gromet/right angle

 

[Johnnyb]

X2 replace the rubber. Also, it looks like there is a gap at the bottom of the hose attaching to the breather. Not a pressure or vacuum (much) port, but a hose clamp won't hurt either.
-JB

 

[tonytony9]

X2 replace the rubber. Also, it looks like there is a gap at the bottom of the hose attaching to the breather. Not a pressure or vacuum (much) port, but a hose clamp won't hurt either.
-JB

Thanks for the feedback.

Definitively, what would worn/blown piston rings/valve seal symptoms look like? I am trying to gauge my overall engine health as I move deeper into the restoration process.

 

[Broncobowsher]

Would you recommend getting a breather cap in this style? From my understanding, abandoning the plastic right angle that connects and runs via a tube to the aircleaner.

http://[URL]https://www.cjponyparts...-element-chrome-with-ford-racing-logo/p/OC44/

[/URL]

View attachment 935281

No. That is more likely to have oil drooling down the valve cover.

Your engine appears to be good. If not perfect, still a fine unit in its current condition. Keep up the refreshing of aged, but not wore out stuff.

 

[DirtDonk]

Those compression numbers look pretty great for an old engine. Basically indicating that the rings are still in good shape.
But has the engine been sitting unused for an extended period of time? Sometimes just driving it regularly will help to "re-seal" rings a bit more.
Did you do the compression test both wet and dry? I think that would be a definitive answer as to whether it's rings or not.

Make sure that the PCV is sucking good. See how the engine reacts when you pull it out of the grommet while it's running. How much vacuum is there when you put your finger over the end?
Where is the other end of the hose going? Looks pretty factory, so it should be going to the base of the carburetor. Usually to a fitting on a carb spacer, at least for most years I've seen.
Aftermarket carbs usually have a 3/8" hose barb for the PCV valve, but your setup looks pretty factory, so it's probably a spacer. Can't tell for sure with the air cleaner on though.

If you do buy that filter element, don't throw away your old one just yet! Those filters just do the same thing. Fill up with oil and ooze it all over your valve cover.
Maybe take a look-see inside your existing filler cap and see if there is a filter media still in there. Not really a "filter" as much as a vapor recovery setup that allows the oil to condense and drain back into the engine.
It was never a very clean or efficient design, and for '71 Ford changed it around completely. But even the '71-'77 version was not immune to the ooze.

Paul

 

[tonytony9]

Those compression numbers look pretty great for an old engine. Basically indicating that the rings are still in good shape.
But has the engine been sitting unused for an extended period of time? Sometimes just driving it regularly will help to "re-seal" rings a bit more.
Did you do the compression test both wet and dry? I think that would be a definitive answer as to whether it's rings or not.

Make sure that the PCV is sucking good. See how the engine reacts when you pull it out of the grommet while it's running. How much vacuum is there when you put your finger over the end?
Where is the other end of the hose going? Looks pretty factory, so it should be going to the base of the carburetor. Usually to a fitting on a carb spacer, at least for most years I've seen.
Aftermarket carbs usually have a 3/8" hose barb for the PCV valve, but your setup looks pretty factory, so it's probably a spacer. Can't tell for sure with the air cleaner on though.

If you do buy that filter element, don't throw away your old one just yet! Those filters just do the same thing. Fill up with oil and ooze it all over your valve cover.
Maybe take a look-see inside your existing filler cap and see if there is a filter media still in there. Not really a "filter" as much as a vapor recovery setup that allows the oil to condense and drain back into the engine.
It was never a very clean or efficient design, and for '71 Ford changed it around completely. But even the '71-'77 version was not immune to the ooze.

Paul

Hi Paul,

I am the second owner and not sure how long it sat. It has driven frequently enough by me that sitting would not be an issue since my purchase in March.

Done both Wet and Dry?: I believe only dry, I am going to try and run the test again this week with my buddy who is a mechanic. Can you explain the wet process? I know it involves putting oil on top of the piston head?

So we are talking apples to apples; the PCV valve is the one on the passenger side and jingles when you shake it. The other one, in the oil fill cap, driver side, is a a breather?

To test the vacuum, do you mean to put my finger on the bottom end of the PCV or on the hole in the grommet?

The other end of the hose is going to the carb spacer, back side of the carb. To my knowledge, I brought all vacuum lines back to the original factory setup. I have the original, Autolite 2100 2b carb.

I am clear photos, see below. I noticed that oil is starting to appear on the carb now. And, where the oil fill cap tube runs to the air cleaner, there is some dry up oil around the tube that is apart of the air cleaner:

Carb was rebuilt less than 250 miles ago. It was completely clean.

 

[DirtDonk]

I am the second owner and not sure how long it sat. It has driven frequently enough by me that sitting would not be an issue since my purchase in March.

That's good news. When they sit for a long time, things tend to take longer to diagnose and fix.

Done both Wet and Dry? Can you explain the wet process? I know it involves putting oil on top of the piston head?

Correct.
They should usually be done when the engine is at least warm, and with all plugs removed and throttle held wide open.
Doing it "dry" means it's done as-is. Just the plugs out and the engine spinning.
Doing it "wet" is done by squirting a little oil or other such stuff into each cylinder. I think motor oil is the go-to still, but there may be easier things to spray into the plug hole. But better? I figure oil is probably still best.
It's almost not needed at this point, in your case, because your numbers already look good. But if you want to take the time, at least you'll know for sure.

So we are talking apples to apples; the PCV valve is the one on the passenger side and jingles when you shake it. The other one, in the oil fill cap, driver side, is a a breather?

Correct.
The PCV valve sucks the "bad air" out of the entire engine, through the intake vacuum, and re-burns it in the combustion process.
The plastic elbow fitting with hose to the air cleaner housing is the breather that lets clean, filtered air from inside the air cleaner housing get sucked back into the engine to replace the air sucked out by the PCV.
Stands for "positive crankcase ventilation" and actively sucks, as opposed to the old methods.

Speaking of clean air in and all that, I noticed something on your carb that I'll touch on later.

To test the vacuum, do you mean to put my finger on the bottom end of the PCV or on the hole in the grommet?

The hole at the bottom of the PCV valve itself. Sometimes the hoses and tubes get gunked up over the years and won't let the full manifold vacuum do it's job. Might just need a good cleaning. But if it's sucking like a big dog, then you know it's clear.
And while these are not scientific fact tests, you can gauge different things by how the engine reacts to your finger. For example, when you pull the PCV valve out of the grommet while the engine is running, does it raise the idle, or does it stumble and maybe even die? When you put your finger over it to check the suckage, does the idle go up or down or get rough.
You get the idea.

The other end of the hose is going to the carb spacer, back side of the carb. To my knowledge, I brought all vacuum lines back to the original factory setup. I have the original, Autolite 2100 2b carb.

That's the spot. Gets full vacuum at high volume, and spreads it out as evenly as possible to all cylinders.
Make sure to keep the pictures of your distributor advance control system so if you ever have to unplug the hoses, you can get them back in the correct orientation on the modulator valve thingy mounted to the back of the intake.

I noticed that oil is starting to appear on the carb now. And, where the oil fill cap tube runs to the air cleaner, there is some dry up oil around the tube that is apart of the air cleaner:

Kind of typical. But does seem to be building up quicker than normal. It might just be vapors coming out of the valve cover, condensing up in the air cleaner housing. Not sure, but that's a reasonable explanation for now. And it's not a horrible amount.

View attachment 935875

As far as I know, that's not the original location for the ignition coil. Broncos usually had them laying down at a slight up-angle on the passenger side of the intake, just in front of the carburetor and to the side of the distributor. I mention it only because, being there against the head, it might get hotter than normal.
Your location is actually slightly more optimal, especially for aftermarket coils, because it's in a vertical position. Which is better for keeping the heat transfer oil inside covering all the wire windings. So I'm up in the air as to recommend anything different than you have, or not.
The factory coils lived long hard lives on top, laying down. Aftermarket coils might not live as long unless they're upright.
Just so you know more "stuff" about this vehicle.

View attachment 935876

That's the blue thingy that controls the ignition timing. It's also what contributes to "rpm hanging" when you let off the throttle.
It takes a mixture of ported vacuum and full vacuum and, through the spring and diaphragm inside, figures out what is needed for lowest emissions.
It's one of the few emissions related devices that I always removed. Funny, but I keep things like air pumps and EGR valves, but hated the way these things worked. Kept mine for several years like that, but finally removed it when I bought a distributor with a single vacuum fitting on the front, rather than the usual dual fitting vacuum advance canister.
If yours is working, just leave it. But if you ever replace your distributor and can't find a dual-port vacuum version, you'll have to punt...

View attachment 935877

Yep. Original ones (and some replacements still are) were plastic. But the metal ones can be legitimately correct replacements. Depends on the inner spring and "pill" setup inside.

View attachment 935879

View attachment 935880

And speaking of vacuum...
Notice in that first pic, the heat-barrier fiber sleeving covered metal tube, that's threaded to the choke housing of the carb? That is your choke pre-heater that sucks warm exhaust air into the choke to keep it warming up. This was utilized before they went to electric chokes in '73. Not sure if they kept it anyway after that, but with your '70, this was part of the whole "choke stove" arrangement.
But it's missing half of it's complement. Notice in the second pic, the angled tube coming out of the bottom of the carb. Originally there was a second hard line coming up from the exhaust manifold, right next to the heat-sleeve covered one. If yours is like normal, the old one is probably rusted and broken off. Might want to check that out, because you may need to change some stuff without it.
If the other tube is missing, then your other one is sucking dirty air into the engine. It's a small vacuum leak too.
So if your "cold air" tube is missing, then you should disconnect the "hot air" tube from the choke housing and then block the threaded fitting on the housing with a threaded cap. Used to be easy to find the right ones at the local parts store if they had a supply of fittings.

Might not be a huge deal now, but in the long-term you need to make sure that only clean air is getting into the engine. It's a tiny hole, but still...

Paul

 

[tonytony9]

That's good news. When they sit for a long time, things tend to take longer to diagnose and fix.

Correct.
They should usually be done when the engine is at least warm, and with all plugs removed.
Doing it "dry" means it's done as-is. Just the plugs out and the engine spinning.
Doing it "wet" is done by squirting a little oil or other such stuff into each cylinder. I think motor oil is the go-to still, but there may be easier things to spray into the plug hole. But better? I figure oil is probably still best.
It's almost not needed at this point, in your case, because your numbers already look good. But if you want to take the time, at least you'll know for sure.

Correct.
The PCV valve sucks the "bad air" out of the entire engine, through the intake vacuum, and re-burns it in the combustion process.
The plastic elbow fitting with hose to the air cleaner housing is the breather that lets clean, filtered air from inside the air cleaner housing get sucked back into the engine to replace the air sucked out by the PCV.
Stands for "positive crankcase ventilation" and actively sucks, as opposed to the old methods.

Speaking of clean air in and all that, I noticed something on your carb that I'll touch on later.

The hole at the bottom of the PCV valve itself. Sometimes the hoses and tubes get gunked up over the years and won't let the full manifold vacuum do it's job. Might just need a good cleaning. But if it's sucking like a big dog, then you know it's clear.
And while these are not scientific fact tests, you can gauge different things by how the engine reacts to your finger. For example, when you pull the PCV valve out of the grommet while the engine is running, does it raise the idle, or does it stumble and maybe even die? When you put your finger over it to check the suckage, does the idle go up or down or get rough.
You get the idea.

That's the spot. Gets full vacuum at high volume, and spreads it out as evenly as possible to all cylinders.
Make sure to keep the pictures of your distributor advance control system so if you ever have to unplug the hoses, you can get them back in the correct orientation on the modulator valve thingy mounted to the back of the intake.

Kind of typical. But does seem to be building up quicker than normal. It might just be vapors coming out of the valve cover, condensing up in the air cleaner housing. Not sure, but that's a reasonable explanation for now. And it's not a horrible amount.

As far as I know, that's not the original location for the ignition coil. Broncos usually had them laying down at a slight up-angle on the passenger side of the intake, just in front of the carburetor and to the side of the distributor. I mention it only because, being there against the head, it might get hotter than normal.
Your location is actually slightly more optimal, especially for aftermarket coils, because it's in a vertical position. Which is better for keeping the heat transfer oil inside covering all the wire windings. So I'm up in the air as to recommend anything different than you have, or not.
The factory coils lived long hard lives on top, laying down. Aftermarket coils might not live as long unless they're upright.
Just so you know more "stuff" about this vehicle.

That's the blue thingy that controls the ignition timing. It's also what contributes to "rpm hanging" when you let off the throttle.
It takes a mixture of ported vacuum and full vacuum and, through the spring and diaphragm inside, figures out what is needed for lowest emissions.
It's one of the few emissions related devices that I always removed. Funny, but I keep things like air pumps and EGR valves, but hated the way these things worked. Kept mine for several years like that, but finally removed it when I bought a distributor with a single vacuum fitting on the front, rather than the usual dual fitting vacuum advance canister.
If yours is working, just leave it. But if you ever replace your distributor and can't find a dual-port vacuum version, you'll have to punt...

Yep. Original ones (and some replacements still are) were plastic. But the metal ones can be legitimately correct replacements. Depends on the inner spring and "pill" setup inside.

And speaking of vacuum...
Notice in that first pic, the heat-barrier fiber sleeving covered metal tube, that's threaded to the choke housing of the carb? That is your choke pre-heater that sucks warm exhaust air into the choke to keep it warming up. This was utilized before they went to electric chokes in '73. Not sure if they kept it anyway after that, but with your '70, this was part of the whole "choke stove" arrangement.
But it's missing half of it's complement. Notice in the second pic, the angled tube coming out of the bottom of the carb. Originally there was a second hard line coming up from the exhaust manifold, right next to the heat-sleeve covered one. If yours is like normal, the old one is probably rusted and broken off. Might want to check that out, because you may need to change some stuff without it.
If the other tube is missing, then your other one is sucking dirty air into the engine. It's a small vacuum leak too.
So if your "cold air" tube is missing, then you should disconnect the "hot air" tube from the choke housing and then block the threaded fitting on the housing with a threaded cap. Used to be easy to find the right ones at the local parts store if they had a supply of fittings.

Might not be a huge deal now, but in the long-term you need to make sure that only clean air is getting into the engine. It's a tiny hole, but still...

Paul

Paul,

I hate to make this post more complicated than it already is; my Bronco is now running pretty poorly and I am assuming it has to do with the fuel system. First, let me reply to your comments in the previous reply...

1. I am going to try a wet test after the Holidays. Compression & leak down test results to follow.

2. I did not hear or see any noticeable change to my engine's idle when either pulling the PCV valve from the grommet or sticking my finger on the bottom of the PCV valve. My finger was actually pulled into the valve, so suction seems very strong. No change in idle and great suction, if I understand you correctly, means I am good to go in terms of PCV? Or does this indicate a potential issue with my distributer dual port vacuum advance? It is brand new and was advancing the timing not long ago. Timing was set, of course, with proper procedure in regards to the advance.

3. Coil: I was under the impression my coil was original (really, this was an uneducated, not researched opinion). I only kept it because it is working and I have read the original Ford oil filled coils were very reliable even 50 years later. If it is a replacement, I was thinking of replacing the points and coil with a Petronix Flame Thrower/Ignitor system simply for reliability and peace of mind.

4. Sleaved Choke Housing Tube: I am getting lost here. Are you referring to this port that is plugged in the first picture below, circled in red? I also currently do not have the bottom of my air cleaner attached to the exhaust manifold. I hear this is essential in the winter. Although, my carb guy told me this can actually damage the carb. So, I am not sure how to proceed. Not sure how to test if the air cleaner will open to receiver air rather than air from the exhaust manifold on the passenger side.

I also took some additional photos to assist.

 

[tonytony9]

I am going to create a new thread for the potential fuel system troubleshooting:

70 Bronco 302 - Fuel System Trouble Shooting

Hi Everyone, I bought my Bronco back in March of this year and am diving in as the second owner. She is an East Coast survivor, all original, and I have adopted the philosophy of fixing/replacing only if it is broken or beyond refurbishment. As a result, I have not touched the fuel system. This...

classicbroncos.com

 

[DirtDonk]

Back in a bit to add some details to your previous post. But in the meantime, I don’t remember if you’ve done this, but have you run any testing for vacuum leaks? When the engine is running, have you sprayed carburetor cleaner or even water around everywhere on top of the engine? You’re looking for any change in idle quality. Not just speed, but any change at all. If you spray something near a component or a gasket, and the idle changes, you have a vacuum leak.
What made me think of that, other than the rough running, is that you saw no change when you plugged the PCV valve. Yes, seeing a lot of vacuum signal is a good thing. But having no change in the idle quality when you plug it up seems wrong. I just can’t remember all the poesies

 

[DirtDonk]

And I’m not sure if you heard your carburetor guy correctly, but if that is an accurate description of what he’s saying, I think you need to find a different carburetor guy.
Unless he’s speaking of the flapper valve in your air cleaner, being rusted shut, then there’s nothing to worry about by connecting it.

If heat hurts a carburetor, then what’s it doing bolted to the top of an engine?
If exhaust heat hurts a carburetor, then why do millions of vehicles, most still running around, have their exhaust system plugged into the carburetor?
So a blanket statement makes no sense. But if there are some pertinent details that we’re not hearing, that could be the difference.