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1950 buick straight 8 missing


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My engine devoloped a miss and you can hear it and feel it in the exhaust. Before this happened I have changed the coil, converted it to electronic ignition. the distributer cap, plug wires and plugs are newer. Not sure what else could cause it except a sticky valve. I'm going to put seafoam in the oil and drop the pan and put a new gasket and clean out the pan of sludge and put fresh oil in it next. Any thoughts?

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I'd first isolate which cylinder is misfiring by grounding out one plug wire at a time.  Then I'd ohm out that plug's wire.  I'd also watch in the dark for arcing among the plug wires.  Inspect the cap and rotor for cracking, burning, etc.

 

Then I'd do a compression test.

 

Always a good idea to drop pan and clean pan and oil pump fairly soon after acquisition.

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I have new plugs to install delco 45rs. I purchased a new cap and rotor just to be safe. I put about 1000 miles on the car last year and this just devoloped yesterday after a short run. I'll try your method next thank you.

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4 hours ago, Grimy said:

I'd first isolate which cylinder is misfiring by grounding out one plug wire at a time.  Then I'd ohm out that plug's wire.  I'd also watch in the dark for arcing among the plug wires.  Inspect the cap and rotor for cracking, burning, etc.

 

Then I'd do a compression test.

 

Always a good idea to drop pan and clean pan and oil pump fairly soon after acquisition.

Do you believe my issue is electrical or more valve train related?

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1 minute ago, Mr. Reed said:

Do you believe my issue is electrical or more valve train related?

That's what the protocol described above will find out.  We all *hope* it's electrical as that's much more easily fixed.  However, having owned a number of flathead engines over many years, to me it *sounds* more like a exhaust valve that is either (1) sticking open or (2) burned and needs grinding.  The idea is to rule out electrical with less than an hour's work.  The compression test will show whether you have a sticky or burned valve.

 

Some possibly good news:  On two inline flathead engines I had, the first tour in the spring, after the car was essentially laid up over the winter, would disclose a hanging valve after perhaps 10 miles.  Because those engines used large (7/8) spark plugs, I was able to insert a slender brass drift through the plug hole and gently tap the valve down--AFTER pulling the side pan to ensure that the stem had a large gap between its base and the lifter--that is, don't be banging on a valve when the cam lobe is holding that valve open.  Some here will disagree, but on my flathead engines to this day, I add 4 oz of Marvel Mystery Oil (aka MMO, about $25/gallon at Walmart) to each 10 gallons of gas about every other tank (pour the MMO into tank before inserting the nozzle), and for sure to the last tank before stopping the car for the winter.  This is especially useful if you're using ethanol-laced gas as we have only that in California.  Once I began that practice, in more than 25 years I've never had a valve hang up again (knock on wood).

 

First, find the offending cylinder by grounding each plug wire in turn.  When the idle does NOT slow down or get rougher, you've found a weak cylinder.  Then check for a bad plug wire by connecting an ohmmeter to the ends (pull the ends off the plug and out of the distributor cap).  If you have stranded copper core plug wires, you should get a reading of 5 ohms or less.  If you have resistance (carbon core) wires (I wouldn't use them unless you have a high-end stereo), any reading above 5,000 ohms is suspect.  Look inside the distributor cap at the condition of the contacts, and inspect for any carbon tracking, especially near the contact that feeds the offending cylinder.

 

Then do the compression test, paying special attention to the reading of the offending cylinder in comparison to the others.  15-20% variance is OK for almost everyone, but consider a variance of much more than 10% a warning that a valve job is somewhere in your future.

 

To see if the valve is sticking open, determine whether the inner RF fender panel is removable.  If so (we hope), jack up the front end, remove right front wheel and inside fender panel to gain access to the valve side pans.  Remove the side pan associated with the weak cylinder.  Watch the valves associated with the bad cylinder as a helper bumps the starter (disconnect the coil wire).  The happiest thing you can find is that a valve stays open when the lifter has gone back down--the valve is sticking against spring pressure.  Then spray your favorite penetrant around the stem, but you mostly need penetrant through that spark plug hole.  tell your neighbors they are now protected against mosquitos for the next month 🙂 .

 

Last gasp before having to do a valve job:  Add a double or triple dose of MMO to your fuel and drive the car.  There's some risk in a stuck-open valve burning from this, but otherwise you gotta do a valve job anyway.

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Diagnose the issue......don’t start guessing and swapping out parts. Start with the basics. Compression check. Wet and dry. Cylinder power balance test.......with a scope or DVOM to determine the actual  contribution each hole is making. A five gas exhaust analyzer and a ignition oscilloscope are also necessary. You wouldn’t want your doctor to guess what’s wrong with you and start cutting things out of you because it might be the issue.......why would you want to do the same to a car? I understand it’s hard to find help, and people with right equipment. Usually doing it right is expensive and time consuming. Jumping around trying to make a quick and easy fix rarely happens. 

Edited by edinmass (see edit history)
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Where Ed and I differ is that I suggest methods that can be done at home without equipment more specialized than a DVOM, vacuum gauge, and compression gauge.  If you have the more advanced equipment available to you, by all means use them.

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10 hours ago, Grimy said:

That's what the protocol described above will find out.  We all *hope* it's electrical as that's much more easily fixed.  However, having owned a number of flathead engines over many years, to me it *sounds* more like a exhaust valve that is either (1) sticking open or (2) burned and needs grinding.  The idea is to rule out electrical with less than an hour's work.  The compression test will show whether you have a sticky or burned valve.

 

Some possibly good news:  On two inline flathead engines I had, the first tour in the spring, after the car was essentially laid up over the winter, would disclose a hanging valve after perhaps 10 miles.  Because those engines used large (7/8) spark plugs, I was able to insert a slender brass drift through the plug hole and gently tap the valve down--AFTER pulling the side pan to ensure that the stem had a large gap between its base and the lifter--that is, don't be banging on a valve when the cam lobe is holding that valve open.  Some here will disagree, but on my flathead engines to this day, I add 4 oz of Marvel Mystery Oil (aka MMO, about $25/gallon at Walmart) to each 10 gallons of gas about every other tank (pour the MMO into tank before inserting the nozzle), and for sure to the last tank before stopping the car for the winter.  This is especially useful if you're using ethanol-laced gas as we have only that in California.  Once I began that practice, in more than 25 years I've never had a valve hang up again (knock on wood).

 

First, find the offending cylinder by grounding each plug wire in turn.  When the idle does NOT slow down or get rougher, you've found a weak cylinder.  Then check for a bad plug wire by connecting an ohmmeter to the ends (pull the ends off the plug and out of the distributor cap).  If you have stranded copper core plug wires, you should get a reading of 5 ohms or less.  If you have resistance (carbon core) wires (I wouldn't use them unless you have a high-end stereo), any reading above 5,000 ohms is suspect.  Look inside the distributor cap at the condition of the contacts, and inspect for any carbon tracking, especially near the contact that feeds the offending cylinder.

 

Then do the compression test, paying special attention to the reading of the offending cylinder in comparison to the others.  15-20% variance is OK for almost everyone, but consider a variance of much more than 10% a warning that a valve job is somewhere in your future.

 

To see if the valve is sticking open, determine whether the inner RF fender panel is removable.  If so (we hope), jack up the front end, remove right front wheel and inside fender panel to gain access to the valve side pans.  Remove the side pan associated with the weak cylinder.  Watch the valves associated with the bad cylinder as a helper bumps the starter (disconnect the coil wire).  The happiest thing you can find is that a valve stays open when the lifter has gone back down--the valve is sticking against spring pressure.  Then spray your favorite penetrant around the stem, but you mostly need penetrant through that spark plug hole.  tell your neighbors they are now protected against mosquitos for the next month 🙂 .

 

Last gasp before having to do a valve job:  Add a double or triple dose of MMO to your fuel and drive the car.  There's some risk in a stuck-open valve burning from this, but otherwise you gotta do a valve job anyway.

 

 Grimey, we are talking about a BUICK, with  overhead valves, or more correctly, valves in head.

 

  I have had, on two occasions, a plug gap close. All the way.  Bet it is ignition related.

 

  Ben

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10 hours ago, Grimy said:

Where Ed and I differ is that I suggest methods that can be done at home without equipment more specialized than a DVOM, vacuum gauge, and compression gauge.  If you have the more advanced equipment available to you, by all means use them.

 

I agree..........problem is 80 percent of the time, you can get away with not having the proper equipment and fix the car. The last 20 percent you need the correct stuff, and 95 percent of the mechanics have no clue as to properly use the equipment. By the time I get to working on something it's almost always "I know this guy who can fix it after every tractor mechanic in the state had his hands on it". I'm usualy that guy if you in the pre war car hobby.....not post war. The last five cars I worked on were in the previous category. 

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3 hours ago, Ben Bruce aka First Born said:

 

 Grimey, we are talking about a BUICK, with  overhead valves, or more correctly, valves in head.

My bad!  Had a Pontiac L-8 in mind for some reason.  Thank you, Ben!  OHV makes it much easier, and much less likely to have a sticky valve.

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Ed hits the nail on the head. See my thread on General forum about Stalling Studebaker. Problem probably started with a coil going bad. I made it worse by thinking it was probably points and/ or plugs. Switched them out, problem persisted. Changed coil, problem persisted. Changed wires, problem persisted. Changed cap, problem persisted.  Rebuilt carb, problem persisted. Ed came to the rescue, problems solved!  Sent him the distributor, coil and wires, he tested and found new coil was bad, new points were junk. He is sending me back the distributor and other parts so should be back up and running soon. 
As Ed the magician (in my book anyhow) says research the problem before changing anything, try to test each part first then fix!  
When I grow up I hope I can have the tools and a portion of the skill and knowledge Ed has regarding these old cars. I better do if fast, I’m older than he is by a lot!  
Have fun

dave s 

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On 4/12/2021 at 4:36 PM, Mr. Reed said:

My engine devoloped a miss and you can hear it and feel it in the exhaust. Before this happened I have changed the coil, converted it to electronic ignition. the distributer cap, plug wires and plugs are newer. Not sure what else could cause it except a sticky valve. I'm going to put seafoam in the oil and drop the pan and put a new gasket and clean out the pan of sludge and put fresh oil in it next. Any thoughts?

 

I'm a bit confused. This happened after the coil and electronic ignition as put in place of the point system?

 

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Yes. When I purchased the car it didn't run so we installed a new coil because the previous owner put a 12 volt jump pack to the car which fried the coil. We did a lot of work on the car to get it road ready. I drove it 1000 miles trouble free. It sat all winter.The car didn't miss before. The previous owner zip tied the spark plugs wires together and I'm thinking they may be our issue after all. We separated them but will look for any arching at night.

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Start it... then feel each exhaust port on manifold... as it warms you can find which one misfires.... gives you a place to start diagnosing from... if you find a cold cylinder... swap a plug.. repeat when cold...

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I've had problems with regular plugs and modern gas w/alcohol, they work ok for a while and then start missing.  I'd try a set of NGK XR5 with the 'projected' tip developed for modern fuels.

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14 hours ago, Mr. Reed said:

Yes. When I purchased the car it didn't run so we installed a new coil because the previous owner put a 12 volt jump pack to the car which fried the coil. We did a lot of work on the car to get it road ready. I drove it 1000 miles trouble free. It sat all winter.The car didn't miss before. The previous owner zip tied the spark plugs wires together and I'm thinking they may be our issue after all. We separated them but will look for any arching at night.

 

Good possibility a valve got stuck as a result of sitting all winter. 

 

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