67 Mustang - Oil leak and lack of power - Vintage Mustang Forums
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post #1 of 19 (permalink) Old 07-05-2019, 06:29 PM Thread Starter
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67 Mustang - Oil leak and lack of power

I have a 67 Mustang with an inline 6. This is my first rehab project. I recently replaced the seal on the engine valve cover because it was leaking and causing the engine to smoke. That is fixed, no leaks, all is good there. I still have the smoke from leaking oil in a different place

I now have oil pushing back out of the oil cap and onto the top of engine. It then is smoking. I have a push on style oil cap, so you can't totally close the cap.

The engine also running a little hard. I think the idle screw needs an adjustment. I recently rebuilt the carb but the car had been running fine.

I am also noticing a lack of power in first gear.

I am thinking there might be a problem with the compression or PVC system. I don't know much about how that all works

Any suggestions would be appreciated.
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post #2 of 19 (permalink) Old 07-06-2019, 08:21 AM
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The PCV valve should be stuck in the valve cover with a hose leading from it to the base of the carb so it can suck the fumes in. Here's a picture from the shop manual just for reference.
67-PCV.jpg

Make sure the valve itself isn't clogged, that the hose is tight on both ends, and that the hose isn't collapsing in on itself while the engine's running.

The oil coming out the breather plus the lack of power might be a problem with the rings not sealing though. It probably wouldn't hurt to check the compression just to see if all the cylinders are close to each other.
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post #3 of 19 (permalink) Old 07-07-2019, 09:02 PM Thread Starter
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Thanks fo the info. I checked the valve cover hose and it's working fine. It's not collapsing. I think you are right about the rings not sealing. I am gong to take the valve cover off and check the seals. I hope that is an easy job. I have never done that before. It would make sense. The engine seems to be pushing too much oil through and it's coming out the breather, causing the engine to smoke.

Any insight on how to check the rings and how they seal ?
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post #4 of 19 (permalink) Old 07-07-2019, 09:49 PM
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I think the quickest way to get an idea on how your rings are sealing is to test the compression in each cylinder. The rings in question are the ones on the sides of the pistons, so you can't actually see them without taking the whole engine apart. But checking the compression will give you (and the people who know what they're talking about and can jump in here) an idea of how they're sealing.

So you'll need a compression checker that screws into the spark plug holes and see what you get for each cylinder. Do a search for compression test, I'm sure someone's posted detailed instructions around here somewhere.
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post #5 of 19 (permalink) Old 07-07-2019, 10:08 PM
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First - get yourself a factory service manual for your Mustang... it'll come in handy in more ways that you can imagine.
https://www.npdlink.com/product/shop.../138040/124019

With it, you can do some research on what parts are located where, their proper function, how they integrate with one another, and how to test them...

The seals under the valve cover are located around the intake and exhaust valves, under the valve springs. Not impossible to change by any means, but it is a nuanced job with some specialized tools (and potential pitfalls).

The (piston) rings are located around the pistons, and they can't be seen without dissembling the engine. However, they can be checked relatively easily with simple tests outside of the engine. A compression test, dry and then wet, will give help you a good idea of their condition. After that, a leak-down test might make sense. This is done through the spark plug holes in the cylinder head.

However, long before I tore into an engine and started changing parts, I'd look for clues. What do the spark plugs look like? Are they oil fouled? 35 years old? Is the PCV valve the correct one? Is the car in proper tune, with proper engine timing? Is the ignition system functioning like it should, with good spark reaching the spark plugs? Etc.etc.

If the spark plugs are fouled (doesn't matter why, yet), then all of the carburetor adjustments in the world won't seem to make a difference.

Once you have details, we'll all be able to help you better. Right now, you'll get a lot of great suggestions but they will all be based on speculation and, worse case scenarios. It might be simple. It might not. But... it is better to approach a problem systematically, and learn along the way.


Edit - Put your location under your name - there could be someone local happy to help, lend tools, bring over beer or, just curse along side you for moral support... :-)

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Last edited by bbmach; 07-07-2019 at 10:11 PM.
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post #6 of 19 (permalink) Old 07-07-2019, 10:08 PM
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If it's valve seals it will usually smoke on start up and then slow after running. If it's rings in will smoke more when up to temp and the whole time it's running from the exhaust. Compression test will tell you. Compression good then more likely it's the seals. Sounds like your getting blow by and that would be rings.

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post #7 of 19 (permalink) Old 07-07-2019, 10:18 PM Thread Starter
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Thanks everyone. I did a compression test recently and had good results. They were in the guideline of the specs. I had a buddy that knows mustangs help me do the test. I am getting smoke in two places. One coming from the exhaust and two coming from the oil backing out of the breather valve/oil cap and spilling onto the engine valve cover.

I think my next step needs to be opening the valve cover and looking at the seals to see if they are bad. It would make sense that too much oil is pushing through the seals and then coming out the breather cap.

That is my next step. I will report back. Thanks for the help so far
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post #8 of 19 (permalink) Old 07-07-2019, 10:27 PM
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Oil would not push up through the seal. Oil would leak down from the seals into the cylinders and then burn in the combustion chamber then smoke out the exhaust. If the seals are real bad I imagine they could seal the pistons and show good compression. Could be both are bad and time to rebuild.
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post #9 of 19 (permalink) Old 07-08-2019, 07:33 AM
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Valve stem seals generally will not cause an engine to smoke continuously, nor do they hold oil from coming "up". Ford style seals are referred to as "umbrella" seals, which is exactly how they function. Like an umbrella, they keep excess oil off the valve stem, and from migrating down the valve stems into the ports where it gets burned.

From the symptoms you are describing, it sounds like a case of the crankcase being pressurized by blow-by, which is the result of poor piston ring sealing. An engine with bad valve stem seals will not push oil out the breather, but one with bad rings certainly will. My next step, since you technically have "good" compression, would be a leakdown test. That'll tell you the true condition of the rings.
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post #10 of 19 (permalink) Old 07-08-2019, 05:32 PM Thread Starter
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Hey guys,

I am stumped on this one. My friend, who is knowledgeable in mustangs took the valve cover off, checked the rods and oil flow. No issues there. We did remove the spark plugs and noticed several of them were pretty black and gunked. All the spark plugs are firing, we checked that. I plan on replacing the spark plugs to start. I will then do another compression test. When I did the test I was between 125 and 140 for compression.

We started the car up with the valve cover off and watched the rods in action. Everything was moving up and down and seem to be working fine. I have not put the valve cover on yet, but plan to put in new spark plugs and see if I continue to have the problem.

I still cannot figure out why the car is is pushing up back up through the breather oil cap and spilling onto my engine. The oil is then smoking me out in the car. The car also seems like it does not have any power in first gear especially. I also have black smoke in first gear coming from my tail pipe, like I am burning oil.

could this be from having too much oil in the car ? According to the dipstick it's full, but not way over ?

Any thoughts on what else this could be ?

thanks
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post #11 of 19 (permalink) Old 07-08-2019, 10:25 PM
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Originally Posted by jaredlgoldman View Post
I am getting smoke in two places. One coming from the exhaust and two coming from the oil backing out of the breather valve/oil cap and spilling onto the engine valve cover.
Pretty simple. Check to see whether the PCV is actually sucking crankcase gasses. If it is, you have excessive blow-by and the rings are allowing it.

Amateur restorer. Well, sometimes I have been paid for it. But not right now.
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post #12 of 19 (permalink) Old 07-09-2019, 02:42 AM
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Do you have an aftermarket valve cover?
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post #13 of 19 (permalink) Old 07-09-2019, 07:11 AM Thread Starter
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I have the original valve cover and it has never been a problem, this just started all the sudden. I rebuilt the carburetor a few months ago and the car was running great. All the sudden I have this oil leak issue and lack of power.

I did pull the PCV off the top of the valve cover to check that valve. You can hear that ball rattling around inside. I assume that means it's working. How do I check the PCV to make sure it's working ?
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post #14 of 19 (permalink) Old 07-09-2019, 07:37 AM
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The quickest thing that comes to mind is to pull it out of the valve cover when the engine's running and stick your finger over the end. It'll be pretty obvious if it's sucking.

A description of how the PCV valve works is on page 8-34 of your '67 shop manual. Though I don't see any official steps for testing it.
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post #15 of 19 (permalink) Old 07-09-2019, 09:59 AM
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I also have black smoke in first gear coming from my tail pipe, like I am burning oil.

Black smoke is unburned gasoline and means the carb is too rich. Burned oil smoke is blue/gray.
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