Could use some advice for a possible burnt valve

[spitfire]

Hey everyone,

my 50 Windsor may have a burnt exhaust valve. It has new plugs, wires, cap, rotor, points, condenser, etc. The car actually runs good when cruising or accelerating, but has a rough idle and you can hear a miss in the exhaust. I don't know if anyone here has heard of this test, as many haven't, but I read about a trick where you hold a dollar bill or a small piece of paper over the exhaust pipe, at the outlet, and see if it tries to suck it in. Mine does, I get a few puffs and then it snaps the paper right into the pipe. I did adjust the valves, which didn't solve it.

Do these symptoms sound like a burnt valve? Is there a sure way to find out which cylinder it's on, apart from a leak down test? I usually rent tools like that, but no one has one to rent around here, and I don't really need to have one on hand.

I did a compression test when I purchased the car and found that all were at 110, except for number 3, which was at 100. The car had maybe 20 miles on it since it was out of a 40+ year storage at the time of that test. The car had a visibly leaky head gasket, so I went ahead and replaced it. I didn't notice any warpage of the head at the time. Now, I forgot the exact numbers of the last recent (about 5K miles later) compression test, but the funny part was the way they were varied. Cylinder 1 had around 117, 2 had maybe 115, 3 had 105ish, 4 was around the same, 5 had maybe 110, and 6 had about 115 again. I remember the test making me thing maybe the head was warped or not properly torqued. I used the same tester for both tests.

I was kind of curious about what your opinions are. I'd be willing to do the head gasket over again, however I don't want to pull it again if it needs a valve too. I'd rather do everything at once. Any suggestions on what the issue could be?

Thanks,

Dan

[austinsailor]

Compression test should tell you everything. More conclusive than the dollar bill test.

[Adam H P15 D30]

You really don't need a fancy leak tester. Just hallow out an old spark plug and weld a air fitting onto it. Turn your compressor air down to about 50psi, run each cylinder to TDC on the compression stroke and listen at the carb and tail pipe for the leak. Compression seems pretty good for a leaky valve though. How is the state of tune? Was it all gummy inside when you had the side covers off??? Did you do a wet compression test? What is the vacuum at idle?? Put a vacuum guage on it at see if it bounces around a lot at idle.

[spitfire]

Thanks, austinsailor. So, if I re-do the compression test, the cylinder with the lowest number would be the one with the biggest issue. I think that was still no. 3. I just want to make sure that it's a valve before I take apart the whole top end for a valve job.

Thanks,

Dan

[spitfire]

Hey Adam, thanks as well. I didn't do a wet test, but I do remember attaching a vacuum gauge to it at one time and finding that the needle vibrated very rapidly a small amount. I remember the vibration moving within one or two inches of mercury, very fast.

The valve covers did have plenty of goop blocking up drain holes and I did my best to clean everything out.

As for the state of the tune, everything is maybe 6K miles old. Plugs, wires, cap, rotor, condenser, points, carb rebuild, and the timing was correct. Seems the car has always done this to an extent, but it seems to have become worse as time goes on.

I'm not doubting that the rings/cylinder walls have plenty of wear at 94,500 miles, but being it doesn't blow a bunch of smoke, runs quite well when driving around town or at 55, and carrys 54 or so psi oil pressure at high speeds (20-25 at idle while in gear), I figure I can get around for a while longer without a rebuild, as long as it doesn't start knocking. Plus, I don't have 3-4K for a rebuild at the moment, which is what I've been quoted. The dollar bill test just kind of told me that possibly the valves are the biggest culprit, which is something that I could do for now. I'm no expert though, so that's why I turn to you guys .

Thanks again,

Dan

[Kudzuking]

You really don't need a fancy leak tester. Just hallow out an old spark plug and weld a air fitting onto it. Turn your compressor air down to about 50psi, run each cylinder to TDC on the compression stroke and listen at the carb and tail pipe for the leak. Compression seems pretty good for a leaky valve though. How is the state of tune? Was it all gummy inside when you had the side covers off??? Did you do a wet compression test? What is the vacuum at idle?? Put a vacuum guage on it at see if it bounces around a lot at idle.

Fancy leak tester? and I thought i was old skool ! ! !

[austinsailor]

Maybe I'm misunderstanding - was the last compression test some time ago or after it started this miss? I read it to be some time ago. A burned valve should cause a substantially lower reading on that cylinder, particularly if it's failing the dollar bill test. Lower, as in a reading of zero to maybe 20 or so, and little change when you squirt oil into the cylinder and check it again wet.

If you have one low, wet and dry, it's probably a valve. If 1 and 2, or 3 and 4, or 5 and 6 are low it's almost certainly a head gasket.

If your head gasket is leaking somewhere besides the thin web between the above cylinders it'll most likely be loosing enough water you'll know long before you have to worry about tests.

[austinsailor]

I guess we have it good here - a rebuild is about $1500 - $1600.

Everything you say leans towards a pretty good motor and a bad valve. $10 or $15 for a valve and $35 or so for a head gasket should put you on the road. And an afternoon's labor, of course.

[spitfire]

Maybe I'm misunderstanding - was the last compression test some time ago or after it started this miss? I read it to be some time ago. A burned valve should cause a substantially lower reading on that cylinder, particularly if it's failing the dollar bill test. Lower, as in a reading of zero to maybe 20 or so, and little change when you squirt oil into the cylinder and check it again wet.

If you have one low, wet and dry, it's probably a valve. If 1 and 2, or 3 and 4, or 5 and 6 are low it's almost certainly a head gasket.

If your head gasket is leaking somewhere besides the thin web between the above cylinders it'll most likely be loosing enough water you'll know long before you have to worry about tests.

Austinsailor, sorry for not being more clear. I guess it's been a long day . The second test was after it started missing. I didn't see any numbers lower than 105, which is why I had trouble telling which cylinder was the problem cylinder. I always thought if any had an issue, it was cylinder number 3, as it originally had the lowest compression out of the six. It has always missed at idle a little, as long as I've owned it. What I thought was peculiar was that 12456 all had 110 psi even and 3 had 100 when I first checked it, at time of purchase. After I did the head gasket, it kind of went all over the place. 1,2, and 6 all went up, while 3, 4, and 5 lost compression. That makes me think that either the rings seated and revealed that some cylinders have better compression than the others, or that maybe I did something wrong when I reinstalled the head.

I guess we have it good here - a rebuild is about $1500 - $1600..

Everything is ridiculous here. I thought 4 grand was pretty high for a rebuild on this motor, then again I've never rebuilt one and I don't know what it involves. This includes disassembly, full machine work, parts, and reassemble. I wouldn't mind getting out of here, though.

Everything you say leans towards a pretty good motor and a bad valve. $10 or $15 for a valve and $35 or so for a head gasket should put you on the road. And an afternoon's labor, of course.

This leads me to another question. Would it be worth it to do the extra work and do a full valve grind? A shop told me that they would grind all twelve valves for about $20 and I figure I could lap the seats. A full Felpro top end gasket kit from rock auto is around $36 or so. I originally wanted to do a full valve job, as I thought my guides needed replacing as well (smoke upon high-speed deceleration), but since I cleaned the valve galley, I haven't actually noticed any smoke. So, assuming I don't have to replace the guides, I could do all of the valves for an extra $20. Is it a whole lot more work? If I can make the motor a little happier for the rest of it's life, maybe even extend it's life a little, I may be willing to do the extra work.

Thanks,

Dan

[Don Coatney]

If you have a burnt exhaust valve there would be a noticible misfire as the engine would be running on 5 cylinders. When you adjusted the valves what gap did you set them to. Did you do it with the engine up to temperature and running?

You last mentioned smoke on deceleration. That is a sign of worn valve guides. Worn valve guides may also be the cause of failure of the dollar bill test.

[austinsailor]

If I've got it right now, all cylinders are over 100 now, I doubt aburnt valve is involved. Don may be right.

I don't have any experience with a worn guide causing that, but I can see it's possible. It most certainly will cause smoke on deceleration with worn guides. Been there!

A burned valve will smooth out at higher speeds if it's not too bad.

I once had a Ford 289 with very worn guides. guide seals stopped most of the smoke, but at low speeds it ran real bad at low speeds. I had done a valve job on it myself, seats and valve faces were in excellent shape but I think they'd just seat at different angles and leak. Put some good junkyard heads on it and it ran real nice. But that was all 16, maybe one in real bad shape cause one cylinder to miss. You should be able to pull the valve cover and tell if it's that loose.

Edited January 7, 2013 by austinsailor

[suntennis]

One test you can easily make is have the engine at idle and short out one spark plug wire at a time to see if it effects the running of the engine. For normal operation, shorting out a spark plug wire by either disconnecting the plug wire or by any other means, you should have a noticable missing in the engine. If you do this and find that it does not affect engine idle, then you have found a cylinder where the problem is. Problem could be caused by a number of things.

[spitfire]

If you have a burnt exhaust valve there would be a noticible misfire as the engine would be running on 5 cylinders. When you adjusted the valves what gap did you set them to. Did you do it with the engine up to temperature and running?

You last mentioned smoke on deceleration. That is a sign of worn valve guides. Worn valve guides may also be the cause of failure of the dollar bill test.

Hey Don, thanks for your help. That would make sense. The car usually billows smoke coming off the freeway, right about the time I hit 40 mph or so.

I adjusted them with the engine at operating temperature, factory service manual specified .008 for intake and .01 for exhaust. I think I may have set them for .009 and .011. I read that a little too much clearance is better than too little. The miss was there before the adjustment.

If I've got it right now, all cylinders are over 100 now, I doubt aburnt valve is involved. Don may be right.

I don't have any experience with a worn guide causing that, but I can see it's possible. It most certainly will cause smoke on deceleration with worn guides. Been there!

A burned valve will smooth out at higher speeds if it's not too bad.

I once had a Ford 289 with very worn guides. guide seals stopped most of the smoke, but at low speeds it ran real bad at low speeds. I had done a valve job on it myself, seats and valve faces were in excellent shape but I think they'd just seat at different angles and leak. Put some good junkyard heads on it and it ran real nice. But that was all 16, maybe one in real bad shape cause one cylinder to miss. You should be able to pull the valve cover and tell if it's that loose.

Interesting. The high vacuum of deceleration causes oil to be pulled up through the guides and into the combustion chambers, correct?

One test you can easily make is have the engine at idle and short out one spark plug wire at a time to see if it effects the running of the engine. For normal operation, shorting out a spark plug wire by either disconnecting the plug wire or by any other means, you should have a noticeable missing in the engine. If you do this and find that it does not affect engine idle, then you have found a cylinder where the problem is. Problem could be caused by a number of things.

This reminds me of one thing I failed to mention last night. It doesn't miss with every revolution. It will make a few revolutions and then "cough" once or twice. Rev-rev-rev-rev-miss-rev-rev-miss-miss-rev-rev-rev etc. I've had a car with a badly bent valve and it missed with every revolution. Maybe that's a sign that it's really bad guides and not necessarily a burnt valve.

Thanks,

Dan

[TodFitch]

This reminds me of one thing I failed to mention last night. It doesn't miss with every revolution. It will make a few revolutions and then "cough" once or twice. Rev-rev-rev-rev-miss-rev-rev-miss-miss-rev-rev-rev etc. I've had a car with a badly bent valve and it missed with every revolution. Maybe that's a sign that it's really bad guides and not necessarily a burnt valve.

Mine does that too. Might be a sticking valve or badly worn valve guides but I think not. For one thing, the old "short out a plug" test shows its not specific to one cylinder. That, along with good compression in all cylinders, pretty much rules out an problem inside the guts of the engine. So in my case I'm guessing it is more ignition related. Maybe worn bushings in the distributor allowing a wobble on the shaft that irregularly changes the point gap and timing.

Hard to tell exactly as when it misses the RPM changes slightly and that, in turn, affects manifold vacuum and advance timing. So when I watch things with a timing light, dwell meter and manifold vacuum gauge everything seems to change at once. A bit difficult to sort out causation from correlation.

I figure I'll get around to rebuilding the distributor and putting in new bushings one of these days and if the occasional miss is still there after that start looking more closely at the carburetor.

Edited January 8, 2013 by TodFitch

[spitfire]

Mine does that too. Might be a sticking valve or badly worn valve guides but I think not. For one thing, the old "short out a plug" test shows its not specific to one cylinder. That, along with good compression in all cylinders, pretty much rules out an problem inside the guts of the engine. So in my case I'm guessing it is more ignition related. Maybe worn bushings in the distributor allowing a wobble on the shaft that irregularly changes the point gap and timing.

Hard to tell exactly as when it misses the RPM changes slightly and that, in turn, affects manifold vacuum and advance timing. So when I watch things with a timing light, dwell meter and manifold vacuum gauge everything seems to change at once. A bit difficult to sort out causation from correlation.

I figure I'll get around to rebuilding the distributor and putting in new bushings one of these days and if the occasional miss is still there after that start looking more closely at the carburetor.

Thanks for the info, that's interesting. Whenever mine misses though, or "coughs" (as I put it), it takes the dollar bill in with it, which tells me that for a split second, something is allowing a vacuum effect to take place in the tail pipe. The only thing I could think of would be something in the valve train. If it wasn't doing that, I would think it would be something electrical. Maybe I'm way off base here. I haven't paid enough attention to the distributor, though.

I think I will pick up a vacuum gauge (borrowed the last one) and read it again, paying closer attention. However, I'm 90% sure the car needs valve guides, so it may get a valve job anyway.

Btw, Tod, generally speaking, where are you in the SF Bay Area?

[Jerry Roberts]

[quote=spitfire

... I think I will pick up a vacuum gauge (borrowed the last one) ...

Don't buy one from Harbor Freight , I had one of those and threw it away . Get an American made vacuum gauge . I have one for sale on ebay , item number 330854156203 that works well . You might find one cheaper though .

[TodFitch]

...

Btw, Tod, generally speaking, where are you in the SF Bay Area?

Other end from you in "The Valley of Hearts Delight" as it was once called when it was filled with orchards and fields. Much more prosaic "Silicon Valley" nowadays.

http://archive.org/details/valley_of_hearts_delight

[spitfire]

[quote name=spitfire

... I think I will pick up a vacuum gauge (borrowed the last one) ...

Don't buy one from Harbor Freight ' date=' I had one of those and threw it away . Get an American made vacuum gauge . I have one for sale on ebay , item number 330854156203 that works well . You might find one cheaper though .[/quote]

Haha, thank you for telling me. Harbor Freight's stuff is pretty hit-and-miss. I worked there a few years ago, while I was a full time student. Working there was about as nice as their vacuum gauges evidently are. I took a look at your gauge, seems pretty reasonable for any good tool.

Other end from you in "The Valley of Hearts Delight" as it was once called when it was filled with orchards and fields. Much more prosaic "Silicon Valley" nowadays.

http://archive.org/details/valley_of_hearts_delight

Ah, ok. Just curious if there are any on here that live in this area. There is a guy that seems to live here in town with a beautiful '48 or so Chrysler Windsor. I've yet to talk to him. I'm sure he's seen my car, but I'm probably just the scabby looking kid in the spot-primed '50 with a noisy speedometer cable haha.

Take a look at gauge #8. That describes exactly what I remember seeing when I did the vacuum gauge test. I guess that just about confirms it....

[spitfire]

Now, I have a question on the guides (bear with me here)....

I found that Rock Auto and other retailers sell valve guides made by "Sealed Power", a Federal Mogul company. Rock Auto states that the Intake guides are 0.3425" ID, while the exhaust guides are .3445" ID. However, the service manual states that the guide inside diameter "ream installed" is .3425" to .3435" for both intake and exhaust, which would mean that the exhaust valve that Rock Auto lists is .001 out of tolerance. I am a cnc machinist by trade and some of the parts I make are medical, where a thousandths might be unacceptable, however, I don't know if it will make a difference on an old flathead. That's half the width of a piece of paper. Would the ones that Andy Bernbaum or Roberts sell be any different? Do they compress enough once installed to be within tolerance? Seems like a bit too much to me.

The next question I have is are the guides themselves actually any different, intake from exhaust, other than the fact that the intake valves are installed counter bore down? Also, could you freeze the new guides to make them contract and install easier? Do I need to ream the guides to size once installed? How would I do that? I can’t imagine that reamer and an electric drill would be acceptable for anything within an engine….

Sorry for all the questions guys, but I really appreciate all the help,

Dan

Edited January 10, 2013 by spitfire

[wallace66]

My 47 Dodge was brought out of a 10 year storage, I changed the fluids and put some Techron in the gas. It developed a miss on one cylinder, had leak down and popped out the tail pipe at idle. I remembered from years ago that carbon can come off the top of the pistons or the combustion chamber and get stuck in a valve. So I fired it up, it was missing bad, took off the air cleaner and brought the rpms up. Then I slowly trickled water down the carb. Within about 20 seconds the engine started running smooth as silk and the miss was gone. So it had a chunk of carbon stuck on the valve face. I then went back and did a compression check on that cylinder again, all good and the leak down was gone as well. So I got lucky this time..... I always start with the simplest remedy and work my way up to the wrenches if needed. On another engine, Jeep F134 it did have a burnt valve, part of the valve head was missing! So on that one I bought a new valve for $13 bucks, the seat was still perfect, so I hand lapped them to each other with a suction cup tool and lapping compound, put it all back together and it ran great, and still does, that was 4 years ago.

[Don G 1947]

Look for a broken valve spring.

Don

[Kool48]

On 1/7/2013 at 10:03 AM, suntennis said:

One test you can easily make is have the engine at idle and short out one spark plug wire at a time to see if it effects the running of the engine. For normal operation, shorting out a spark plug wire by either disconnecting the plug wire or by any other means, you should have a noticable missing in the engine. If you do this and find that it does not affect engine idle, then you have found a cylinder where the problem is. Problem could be caused by a number of things.

This is exactly where I'm at with mine.   #1 is my issue.