Exhaust Valve - dollar bill trick!

I've been trying to find out why my car won't idle well for quite a while. Lately the engine has a "tick" as well - even after adjusting the rocker clearances.

Finally did the dollar bill trick. I held a dollar bill with both hands stretched across the tail pipe - and sure enough it "pops" back and forth against the pipe. I assume this means my exhaust valve is burned and is causing my idle rough.

I checked the compression and it's good as far as I can tell. On a hot engine, I propped the accellerator down, removed all plugs and disconnected the coil to the distributor. Cranked the engine for a while to test each cylinder. Results are 150-160 psi. I cranked it pretty good and took the test a few times - these are my highest readings. Some of my readings were as low as 142 if I didn't crank it over a lot. I assume you crank as long as you get the highest reading? Can you get a false reading if you crank too much?

Does this mean I need a valve job - absolutly? Or is there something else that can cause my dollar bill test to "pop"?

Would seafoam work in this problem and what is the best way to use it? Down the crank case, or through the carbs, or should I let it suck it through the intake vacuum line?

Thanks for the help!!

I've never heard of the "dollar bill trick" and doubt that it's a reliable way to diagnose a burned exhaust valve.

Your compression readings appear reasonable and if the range is 142-150 there's not likely to be a bad valve & I'd suggest looking for another reason for your rough idle.

I have never used Seafoam but recommend against using it or anything like it except in certain rare instances.

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I've never heard of the "dollar bill trick" and doubt that it's a reliable way to diagnose a burned exhaust valve.

Your compression readings appear reasonable and if the range is 142-150 there's not likely to be a bad valve & I'd suggest looking for another reason for your rough idle.

I have never used Seafoam but recommend against using it or anything like it except in certain rare instances.

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I agree, the compression readings are telling you to look somewhere else. I have been fooled before by the dollar bill test. I used to just hold my hand in front of the tail pipe and feel it suck on one cylinder. I believe you can get that indication from a perfectly healthy cylinder that just has a miss. So look at easy stuff first like plugs and plug wires. I have even looked at carburation before and found it to be just in need of a good tune up other than carbs then had to straighten the carbs back out when I corrected the miss fire problem. Also check vacuum.

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Would seafoam work in this problem and what is the best way to use it? Down the crank case, or through the carbs, or should I let it suck it through the intake vacuum line?

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If you have a bad carbon buildup on the valve seats the Seafoam is supposed to help get rid of it. Whether that's your problem or not is another matter. Use a small funnel with a hose and feed it through the carbs, as directed on the can - half in each carb. If you haven't done it before be prepared to smoke up the neighborhood.

Incidentally, Mazda has their own version of "seafoam" they recommend for cleaning the intake/valves/etc (for the Miata, Protege, etc). Their instructions are almost identical to seafoam.

Thanks guys. My points, condensor, wires are all new. Timing is about 20 degrees BTC, and the dwell is 60. The carbs are rebuilt this spring by me, including the shafts (but didn't rebush). Lately it's running rougher and the engine developed a new "ticking" noise. I readjusted the rockers and set them at a slightly tight .014 (they were already pretty close to specs). No effect on the ticking.

I do find it strange that my compression is good, yet I still suspect a burnt or sticking lifter. The tick almost seems in tune with the dollar bill slapping against the tailpipe - but it's going fast enough to make it difficult to be sure.

I am a novice at this, so I could use all the advise I can get!!

I'm still trying to find out why my idle is so rough lately. I'll recap what's been done and some of the symptoms.

About two weeks ago an oil line to the pressure sending unit blew. Not sure how much I drove it that way (maybe 15 minutes or an hour), but she was over 2 quarts low with very low oil pressure. After the oil problem: A noticible ticking noise developed which doesn't sound consistant on all rockers.


Symptoms:

1) ticking noise at all RPMS (not the usual consistant clatter of the MG's)
2) rough idle and misses on all RPM's (still smooth enough to drive but it's not right)

Checked or replaced items:

1) new points, condensor and cap (this spring)
2)New wires (last fall)
3) Checked rocker clearances (and set to a tight .014 to try to clear up the ticking)
4) Dwell is steady as a rock at 60 - no fluctuations or vibrations while running
5) Timing is about 20 degrees btdc and is steady. (tried different settings high and low, but rough idle isn't affected)
6)rebuilt carbs including shafts this spring (didn't rebush)
7) Checked vacuum - vibrates the needle. (not sure what is normal, but it clearly shows vibration)
8) Compression is good. 155 on 1 and 2, and 160 on 3 and 4. These are my highest readings on a hot engine (took it about 3 times)

Here's what I think and I really hope I get some solid opinions on this. As noted in my last thread, the old dollar bill test against the tailpipe fails. The bill flaps and makes a distinctive "pop" sound. The car was dangerously low on oil a couple of weeks ago and since then the "ticking" noise never went away. And my idle has progressively gotten worse. The vacuum gage vibration is not good. Adding all the above up, I'm suspecting a worn valve, cam or bushing somewhere. At this point do I need to remove the head to see what's going on?

Thanks again. I just want to get this thing fixed and enjoy my summer! At this point, the car runs good enough to drive, but I'm afraid I'll damage it further if I keep driving it.

Jonny, it sounds suspiciously like you may have partially wiped a lobe off the cam.
Pull the plugs and the valve cover, and turn the engine over slowly by hand, while watching to see if all the rockers move the same amount. Ideally, do it with a dial indicator setup on each rocker individually, but you can probably do it by eye.
Jeff

Being somewhat lazy, my approach is usually to try the easy stuff first.

In this case:

1) Try to determine exactly where the ticking is coming from. The best way is with a stethoscope or even a piece of rubber tubing.

2) How much is the vacuum needle fluctuating? Is it a very regular fluctuation or intermittent? You can get some good info on reading vacuum gauges by keying "vacuum gauge reading" into Google.

3) Any indication of oil burning from the exhaust or plugs?

Jonny, by all means do the easy things first. That's what "Strategy based diagnostics" is all about.
Jeff

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Jonny, it sounds suspiciously like you may have partially wiped a lobe off the cam.
Pull the plugs and the valve cover, and turn the engine over slowly by hand, while watching to see if all the rockers move the same amount. Ideally, do it with a dial indicator setup on each rocker individually, but you can probably do it by eye.
Jeff

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This is exactly what I was thinking when I read your description of what you found, then I read the above by Jeff. The compression check shows that the valves aren't leaking and are closeing all the way but with a cam partially worn off on one cylinder you could be getting what you said. Of course, there is no guarantee that we are for sure right, but based on our experience and what you said at least what Jeff suggested is worth a try.
I had a lobe break off on a VW once and it wasn't just a ticking noise but a loud banging. I had to completely loosen that rocker and drive on three cylinders until I could replace the cam shaft. If you do end up having to replace the cam shaft, definitely replace the lifters also.
Bob

Bugeye, I adjusted the rocker clearances yesterday and didn't notice anything unusual with the distances the rockers moved. I will check again. I'll try to measure the travel with something to make sure.

ColdPlug,

1)I did try to determine where the ticking was coming from with a stick placed on various parts of the engine a few days ago - but it's tough to determine. It sounds like it's coming from the front of the engine - but it's tough to be sure.

2)Basically the needle vibrates at idle and smooths out above about 2000 rpm. The vibration isn't wild - it's pretty tight and definite. Should there be any vibration at all on the needle - is it suppose to be perfectly smooth? Is a little vibration OK? Mine vibrates back and forth about an 1/8 (maybe 1/4) inch on the guage (trying to remember?). It isn't intermittant, but I notice there are slight changes intermittantly. The vibration I'm concerned about is constant and consistant.

3)No oil burning - plugs look tan except the #1 is whiter than the rest.

Mr Bassman, I'll try to check the rocker travel to see if they are the same. Am I looking for extremely obvious difference or will it be slight which requires a measuring device?

Thanks guys!!

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2)Basically the needle vibrates at idle and smooths out above about 2000 rpm. The vibration isn't wild - it's pretty tight and definite. Should there be any vibration at all on the needle - is it suppose to be perfectly smooth? Is a little vibration OK? Mine vibrates back and forth about an 1/8 (maybe 1/4) inch on the guage (trying to remember?). It isn't intermittant, but I notice there are slight changes intermittantly. The vibration I'm concerned about is constant and consistant.

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It isn't unusual to have some pulsation in the intake system (valve timing overlap) & thus in the vacuum gage. The longer the connecting hose the more the needle is damped. I sometimes plug the gage connector & drill a .040" hole through the plug. This stops the quick vibrations & keeps the gage from buzzing like a mad hornet.
D

Do you have a worn timing chain slapping against the timing chain cover?
Put a hose or stethoscope against the cover (watch the moving belts!) and see if you hear anything.
Could also be a worn rocker arm, rocker arm bushing or those little springs that keep the rocker arms spaced properly.

As Dave said, some movement of the vacuum gauge needle is normal. I think you might be able to isolate the location better with a hose & would give that a try. (And yes, watch the fan blades & belts).

A reasonable next step (assuming the noise comes from the top of the engine) is to pull the rocker cover and look closely at things in there. Look for a rocker that wobbles (bad bushing), a broken pushrod, etc. Check the clearances again to see if any have changed dramatically from your settings.

You can probably check the lift without a dial indicator if you make up a template or gauge of some sort that measures lift from a reasonably flat surface, like where the valve cover seats.

Dave, As far as the Vacuum guage. I read John Weimer's article on Vacuum Guages here https://www.theautoist.com/vacuum_guage.htm . I recommend reading this, it was very interesting. First of all, I need to put a "T" in the line rather than disconnect the vacuum advance from the distributor. He said that can affect the reading. Second, based on what YOU said, there is a fitting that is included which looks like what you described. I assume this fits on the hose and buffers the line to the guage so the vibration might be a false reading at this point? I need to retake and see if it still vibrates.

Coldplug: I'll try a hose, or I might even buy one of those car stethiscopes (sp??). I'll probably use it again - as long as it's cheap enough. Didn't think of checking "wobble" in the rocker arms. I'll do that when I check the travel. I don't think my push rod is broken - it doesn't run that rough and the noise isn't that bad (don't think so anyway). It's a "tick" which gets louder from time to time and is always there.

Thanks!

I just happened to think about that ticking. No one has mentioned this because you said you replaced the wires but it might be a good idea before you get too far into the motor to look it over in the dark while it is running. There might be one of the wires arcing somewhere or the coil and you will kick yourself later if that is what it is.
Bob

Great suggestion! I did that last week in the dark - no sparks that I could see. I learned that trick on my first car (an old 67 mustang!) Like I said, this may be two problems or it might be a single problems - I'll look at it all until I find a solution.

Today, I ordered the "Colortune" spark plug gas analyser from ProperMG for $42. I want to see something regarding the combustion on each cylinder - thought it would be a good tool to have. I also ordered a tune up kit (on sale) for $34. It includes plugs, wires, condensor, cap and points - pretty complete! I figured having an extra tune up kit in my trunk for emergencies isn't a bad idea - and I get a chance to double check all these parts at the same time. $34 for all that seems like too good of a deal to pass up. /ubbthreads/images/graemlins/smile.gif

I checked for the tick noise using a $9 stethiscope today. The ticking is coming from the front. I placed it on the valve cover, but it's too noisy to figure out what is what. I then placed the steth right next to each spark plug - and it definitly helped isolating the tick. Loudest right next to plug 1 and plug 2. Tough to tell excatly which is loudest - but it narrows it down a little.

I checked the rockers for play - nothing that stood out. I also tried to check the travel - again kind of tough to do without a proper guage - but they seem normal. Checked all clearances - all a tight .014.

One thing I have noticed is when I take off the vacuum line to the manifold - it's like she opens up and runs much better! Idle is much smoother (but not perfect), and took it out for a drive which seemed smooth as well. Not sure what that means! Once I put either the pressure guage or the line to the distributor - the idle drops dramatically (which I beleive is normal) and the idle gets rough again. Is this a sign of something? One other thing I should mention is the car runs better cold - when it warms up to normal temp the car varies from a little rough to very very rough at idle.

Sounds like the mixture is a little rich, but that doesn't explain the ticking. Your description of where the noise is makes it sound like a valve. Did you take a good look at the valve springs when you had the cover off?

Which point makes you think I'm running a little rich? I think I was a little rich on the 3 and 4 cylinders. But the #1 appears to be a very different story.

I took the car out for a quick spin around the block - shut off the car and coasted in my driveway. Pulled the plugs and found 3 and 4 were a little dark. But #1 is pretty white. #2 looks tan. I leaned out the rear carb (which I fiddled with a few days ago and probably enriched too much) and the plugs look more tan now after a drive. But why is my #1 so white? This is something I asked another forum several months ago and was told this is pretty normal and the "white" will change from time to time to another plug. But I notice Plug #1 is always the one which is much whiter than the rest. Which tells me it's lean (or coolant leak). I don't see any coolant in my oil, and I don't see white smoke. So I assume it means #1 is running leaner than #2 - which means what? A valve is letting too much air into cylinder #1? I wonder if it's gotten worse since my oil problem. The tick is related to cylinder #1 or #2 ( tough to tell for sure which). But that might explain what's going on?

I'm also curious why my car idles much smoother and healthier when the vacuum line is disconnected? Any ideas? I'm going to try it again to make sure, but it sure seemed much smoother.

To answer your question, I didn't notice anything unusual about my springs. Everything under the valve cover looked normal as far as I could tell.

The reason I suggested it might be running a bit rich is that by disconnecting the hose you let some additional air into the manifold, which leans the mixture. It sounded like the engine is happier with the leaner mixture.

Re the plug colors, it sounds like #1 may have a problem somewhere. What year is your car? If it's one with air injection, is it still connected? If it has had the injection removed, is the port for #1 well plugged?

I've never used a Colortune on a "B" but have used it on other cars and found it especially good for balancing carburetors.