I bought my first T about a month ago. I drove it about 80 miles home and it ran pretty well the whole way. A couple of days later the trouble started. It started with loss of power and running bad. I had black flakes in the fuel line so pulled the tank and cleaned out the old 35 year old sealer. I put new sealer in and cleaned out the fuel line and sediment bowl. It still did not run right and has developed what seems to be a vibration in the engine or drivetrain above 28 mph. I swapped out the NH carb with a newly rebuilt one, but no change. I replaced the New Day Timer with a new one and set the timing, no change. I swapped out the coils with newly rebuilt ones, no change. A friend suggested a stuck valve, so I added Marvel Mystery Oil to the fuel and crank case, no change. I get a good spark at each plug, and am now out of ideas. It is looking like I may have a more serious problem but I have no idea what it may be or where to turn for help. The vibration actually seems to be getting worse and I am now afraid to drive it for fear of causing additional damage to whatever is going on. Any ideas would be greatly appreciated. Thanks! Paul A.
I think you would benefit from someone in your area who has experience with Model Ts. Is there a club in your area?
You know you have spark and fuel, do a compression check. If one is lower than the others you can zero in on the problem.
Paul, I feel your pain. I was there 2 years ago, learning, thinking, trying. To me it sounds like a timing issue, are your spark plugs good?
This is my first advice on this forum, but Iíve spent many hours, figuring out the same issue. I replaced my timer with new rebuilt coils, spark plugs, and problem was solved. I also reseated and timed the valves. The other potential issue is the carburetor.
Kudos to you for buying a T and driving it 80 miles home rather than trailering it home and going through everything like I did. You the man.
I see you have a 1927 touring. Congratulations. Sorry you have been having trouble. Owning a T is certainly a challenge and the more you learn the happier you will be.
Improperly adjusted coils can have a devastating effect on the smooth operation of the engine, so You may want to consider sending your four coils off to be adjusted. I sent mine to Ron Patterson and it made a world of difference. Did you clean out the fuel filter? Maybe you need a new fuel filter. How are your spokes? Walk around the car and look for loose spokes or brown powder on the metal hubs. Loose spokes are very dangerous and could result in wobbly wheels, causing a bad vibration.
It is possible that all your NH needed was a float adjustment and a new set of gaskets. For proper operation, the tang on the opposite side of the float hinge should be adjusted so that the float is 15/64Ē from the machined flange. Also, check to be sure your float has not sprung a leak.
When you close the choke knob and set it, how many turns does it take to attain the proper fuel to air mixture on your carburetor. You may have it too lean or too rich. Jim Patrick
There is no club close to me. I did meet a great T guy from this forum who lives close by. He has been helping me with the problem, but we are not sure what the problem is or where to look next. I did replace the plugs early on, but no change. I am new to this, so a compression check is above my pay grade. What do I need in order to do that? Also, I am wondering if the problem may be drivetrain/transmission related? I just can't tell where the vibration is coming from.
Might try cleaning the plugs. I use a broken spring hook to clean the carbon from around the porcelain and dump it in my hand to see how much there is. If it is set to run too rich this will cause too much carbon.
I did take my carb apart and cleaned and adjusted the float. The float does not leak. I then swapped mine out for a professionally rebuilt one, with no change. I also cleaned and checked the adjustment on the coils. Again, I swapped out mine for newly rebuilt ones from the coil Doctor. No change. I have not checked my spokes, but will do so. Mine are the wire wheels and appear to be in excellent shape. I have played with lean and rich on both carbs. Also I have played with advancing and retarding spark while it is vibrating, but I can't make it stop.
Does it vibrate when parked or when going down the road or both?
Does it vibrate in low or high or both?
Paul, if your car will reach a speed of 30 to 35 mph try this- while at speed, reach down and pull the brake lever to neutral and push the throttle up to idle. If the vibration is still there it is most likely in the drive train.
Paul, you say that it vibrates while driving above a certain speed, does the engine run smooth without vibration while just sitting still and adding RPM?
Great questions. Sorry, I should have mentioned. It starts well, idles smooth and runs great to about 26 - 28 mph. Then the vibration starts. I will try neutral and idle at 35 to see what happens
I commend you for having the courage to drive your T 80 miles, before getting to know it, but it may have been a better idea to haul the T home where you could learn how to drive it on short runs instead of driving it so far and possibly damaging it, or overheat it by driving it so far with the incorrect settings, low lubrication fluid levels, or operating the pedals incorrectly. There is so much that can go wrong within a Model T engine if one does something as simple as pressing on the pedals too long or too hard. A set of band linings that can last for years can be shredded or charred in one mile if operated incorrectly. I have had my T for 48 years and am still learning about different ways to get the most out of it and I spent 2 years doing a complete restoration and knew it inside and out before I ever took it for a drive. If your T ran well during the trip while it was hot, but started running bad a couple of days later after it cooled off. It is possible that the long trip and constant vibration may have dislodged buildup in the engine and gas tank that is causing the problems you are now experiencing. There is also the consideration of fluid levels and lubrication and the damage that could result if the levels were low during the 80 mile trip. Jim Patrick
PS. Have you taken off the head to check the valves and pistons for excessive carbon buildup?
The man that I bought it from was a long time T owner. It was well maintained and all fluid levels were good as well as full grease cups. He gave me lessons on driving it and I felt pretty comfortable. I don't see the difference between 1 long trip and many short ones? I watched the temp closely along the way and it never got hot. It did not vibrate on the way home. If it had, I would have called AAA and had it hauled. If driving it caused buildup to dislodge, it was going to happen sooner or later anyway. I forgot to mention. The fuel filter is in perfect shape. I did clean it as well as the entire sediment bowl. I drove it the day after I got it home and it ran fine, so I don't think I damaged it the previous day.
I have not looked at the Pistons. I will add that to my list, thanks
Paul, you probably did nothing wrong, T's are pretty rugged machines. On a side note, if you have a good sediment bulb with a clean screen as you described, i would ditch the additional fuel filter as it usually causes unwanted fuel flow problems with a gravity feed system.
Make sure you order a new copper head gasket. They are usually damaged in the removal and canít be reused and if you donít have one on hand to install, your diagnostic tests will be held up until you get one. Get some spray on copper gasket sealant to seal both sides of the head gasket. When removing head bolts, donít start on one side and go across, stagger the removal by removing a front bolt, then a back bolt, then a right and a left, until they are all out. Put them back in the same way. Head bolts should be torqued at about 50 ftlbs. Jim Patrick
Before you go to the trouble of pulling the head, do the 35 mph at idle test and figure out if it is something out of "kilter" in the running gear.
It could be something very simple, or it could be something serious. my money is on simple!
Paul, you mentioned that you purchased your car from a long time T owner. I would suggest you contact him concerning your problem as he likely knows more about this particular Model T than anyone. Maybe he would be willing to drive to your place and drive the car and provided advice. Wish you good luck and keep us posted.
Man don't start pulling the head ! The problem you describe WILL NOT be addressed by doing that. You stated it runs & idles good in your later post. Which is it? Running poorly at first then running OK. DO NOT pull the head with out doing a dry/wet compression test.I've re-read your postings & they seem to contradict each other.
It sounds like you have done all the right stuff and know what you are doing. The vibration and rough running are probably related.
Do the compression check as Scott recommended. You may have burned a valve or have a stuck one. The compression check will tell. You can do a quick check using the hand crank to see if one cylinder has no resistance when cranking.
It may be something in the drive train like the universal joint. Pulling the brake lever half back as John suggested will tell.
It is easy to pull the head. You can remove the radiator for easier access but it is not necessary.
You may have a bad bearing. Really bad bearings can develop a "half speed whirl" that will vibrate and add a lot of drag. You can remove the inspection cover off the bottom of the pan to take a peek.
Depending on what your plans are for the car you may want to remove the engine from the car and take it apart for a good inspection. You can clean it up and paint it and fix all the oil leaks while you are at it.
I would highly recommend that you find someone in your local area who is very familiar with Model T's to come and check your car before you pull anything else apart.
It is very likely that something you did after you got the car has caused the problem. What you call a "vibration" could be normal for a Model T, or it could be a serious knock.
Don't pull the head until you determine that you need to pull it. If you install it incorrectly you could crack it, you could break off bolts or you could cause it to leak fluid or compression. You can determine much more about the engine if you do the compression test. Only pull the head if you have a compression leak or a fluid leak.
One thing that hasn't been addressed would be a carbon track in the coil box. If your car has been parked in the rain or driven in rain, or if you have washed off the engine with a hose you could have gotten the wood in the coil box wet. The high voltage from the ignition coils finds the easiest path to ground. If the wood is wet, it will burn a carbon path through the wood. If that happens, only way to fix it would be to re-wood the coil box. Before you try to do anything to the coil box. Try running the engine at a fast idle and take a screw driver and short the spark plug wire to the head at the spark plug. Do this one at a time and if the engine slows down you are getting good spark to that cylinder. If it runs the same, that cylinder is not firing. If one is not firing, you need to concentrate on why. It might not be getting spark from the coil, or the spark plug might be bad. Or you could have spark to that cylinder and have a bad valve or very bad ring or blown head gasket.
A bad valve or blown head gasket are found by a compression test and only if the compression in a cylinder is very low should you pull the head.
Another cause of burnt wood in the coil box would be allowing the coils to buzz without the engine running. Especially would be the case if they buzz without the spark plug connected.
Anyway, before you "fix" anything else which is not broken, find a local to look at your car. Good luck
If your car has coils and a timer, lets check them. The easiest way to check them is to; put the car in the start position, ie emergency brake on, spark up (left rabbit ear up) For this test we don't want the car to start, so fuel off. Turn the ignition on Batt, then turn the engine slowly, 1/4 of a turn at a time. You should feel compression as you turn the crank, and then you should hear each coil buzz and stop as you turn the engine. I once had a problem with a timer and it was easily singled out doing this. In my case I had one coil that continued to buzz. It was caused by one of the terminals on the timer that was grounded by carbon. If the coil don't buzz it also could be the coil or wiring. You can check the coils by grounding grounding the upper terminals at the box. Something else that happens to the 26/27 is the coil cover will ground out the coils. I usually leave mine off. If the coils are loose in the case you can use Popsicle sticks to wedge them toward the engine side. Hope this helps and good luck.
Well I always say I'm no expert, but am learning while I lurk all the time. Seems you've covered all the bases..carb, coil, plugs, clean fuel tank. Maybe. How can you be certain virtually all of the "old gunk" is gone? Or none of the new sealer didn't come loose? Plus, why the fuel filter? From what I've read/learned, Model T's don't need a fuel filter. Their use usually requires a fuel pump to subsequently get enough fuel into the carb. Which now brings up my thought...fuel starvation at the higher speed..maybe due to this filter? I don't know. Worth trying it without it wouldn't you say? What else is left? Short of a new engine!! Just my lame brain thoughts.
Thanks for all of the great suggestions. I am making a list of things to try. I should clarify, by filter, I am referring to the cylindrical filter inside the sediment bowl. I do not have an additional in-line filter. My initial problem was the fuel issue. Once I cleaned the tank, sediment bowl, filter/screen in the sediment bowl, the fuel problem seems to be gone. I am reasonably sure it is not the carb or coils as swapping good ones did not change anything. I have tested the spark by grounding each plug and they all spark well. It appears a compression check is in order as well as perhaps rebuilding the coil box. I recently met a great fellow with a number of T's who is willing to come and take mine for a drive. However, his time is limited and I am not sure when he will get to it. Thanks to all for the ideas. I can try a few on this rainy weekend.
Wow! There is a lot of great advice accumulating on this thread. Paul, is your T being kept in a garage? The best way to shorten its' life is to keep it parked out in the weather.
A lot has been said about the importance of doing a compression check, but no one has told Paul what parameters the compression check should be. Please tell him what an acceptable compression reading is and what an unacceptable reading is. While you are at it, since he said it is beyond his pay grade, you may want to describe the technique on how to do a compression check on a Model T. I have done one the 350 of my 1974 Camaro, but have never done one on my T as it has never given me reason to do one. Paul, you need to research it online to find out as much as you can about the test and what it will accomplish.
You can get a compression gauge at any Auto parts store, but you will need an adapter for it to fit the spark plug opening, which is much larger than modern spark plug openings. Take a spark plug with you to the auto parts store to see if the attendant can help you with the adapter.
Lastly, you need to get the following books to study. I would say the Model T Service Manual and Model T Service Bulletin Essentials are necessary to your education on the mechanics of the T and the Model T Restoration Handbook, if you plan on restoring your T. The best features of the Restoration Handbook can be found on the last few pages, where it lists the names and contact information of all of the current suppliers of Model T services and parts providers. This was crucial to me when I first got my T in 1970, before there was an internet and a newcomer had to wing it, use trial and error and use his common sense and of course, the valuable information in the below books, during the restoration process. Jim Patrick
My 27 was restored about 35 years ago and is still in really good shape. It has been stored indoors and will continue to be. You are correct, I do not know how to do a compression test. However, I have learned a lot about T's this past month and will learn ASAP. I must admit, I would have been lost without this forum and my newly found T friends, Dale and Ray. Thanks to all.
How to do a compression test:
1) Buy or borrow a compression tester. Get one with a conical rubber tip that can be pressed onto the spark plug hole. If the only one you can find is designed to be threaded into the spark plug hole, buy an adapter from one of the vendors:
2) Once you have the tester, invite a helper over. If the engine runs, start it up and run it long enough to get fully warmed up, then shut the engine off and remove all of the spark plugs. If the engine doesn't run, you can still do the test cold.
3) With all of the spark plugs out, have the helper open the throttle all the way. Attach the tester to the #1 spark plug hole and have your helper crank the engine over with the starter while you watch the tester. Tell him to stop cranking when the needle on the tester reaches its peak value. It should only take three or four pulses of the tester for the needle to reach its peak value. Write down the cylinder number and the peak tester pressure value.
3) Move the tester to each cylinder in sequence, repeating step 2) above, except try to crank the engine for the same number of pressure pulses that you used for cylinder #1. Write down each cylinder number and its corresponding peak pressure value.
4) Take a look at the table of cylinder numbers and peak pressures. A good peak cylinder pressure for a stock T is around 40 - 50 psi.
All the cylinder pressure numbers should be within 5 - 10 psi of each other.
5) If all cylinders are at least 40 psi, all is well. If all are close but low, like below 25 psi, the rings may be worn. try squirting a bit of oil into each cylinder and repeat the test. If the peak pressures jump up to near normal, it means that the oil helped the rings seal and confirms that the rings are worn.
6) If two adjacent cylinders are low compared to the rest, it may mean that the head gasket is blown between those two cylinders. If only one cylinder is low compared to the others, it may mean that one of the valves in that cylinder is not sealing properly, allowing pressure to leak away.
If you do take the compression test, please post the results here so that folks can comment and make further recommendations. Good luck!
Thanks, I need to find a compression tester
Mark. Thank you for taking the time to write that thorough tutorial. Very useful to anyone who has never performed a compression test on a Model T. Jim Patrick
One more thing, if you were able to warm the engine up for the test, let it cool down completely before re-installing the spark plugs.
If you tighten the spark plugs with the engine hot, you may tighten them too much, making it very difficult to remove them later.
Thanks for the tip
On of the posters recommended pulling the engine for a complete tear-down. DO NOT DO THIS!! You have a restored, running T with a problem, likely a minor one (but maybe not, just don't just assume it's a major problem). If you do a full tear-down you WILL find something worn and you will have to spend $$$$ fixing it, and won't have a T to drive while that is happening. Don't be like the kid who gets a new toy and immediately tears it apart "to see how it works" and then no longer has a new toy, but a project, seldom re-assembled!
There are a FEW things you should ask the former owner: 1) Most important: were the Babbitt thrust washers in the rear axle replaced with bronze. I would not recommend driving around in a car with Babbitt thrust washers. 2)Are the engine valves one piece, not original two-piece ones (you might be able to check this with a light through the spark plug holes). The two-piece are known to return to their two separate piece state; not good! Hmm, that's all I can think of right now, the rest of the questions you can easily observe (spokes tight, etc. )
OH, and welcome to the affliction!
Paul. Since it is a dynamic problem occurring above 28 Mph. You might want to get with Your buddy and run a static test. Jack back wheel / wheels off the ground. Bring the engine up to speed in high gear and see when and where the vibration starts and what part of the car it seems to be coming from.
Thanks for the advice. I don't intend to tear it down unless absolutely necessary. The previous owner said the valves are one piece. He rebuilt the rear end 20 plus years ago and does not remember about the washers, unfortunately. I jacked it up a couple of weeks ago and pulled hard on the wheels. I could only detect the tiniest bit of movement, but I am nervous about those washers.. I love the car, but sure wish it ran right.
The static test sounds like a good idea, but sounds a little scary!
Paul - Have read this entire thread carefully and you have been given a lot of very good advice. Some of the best came from David Dewey and a couple others who advised AGAINST taking any more of the engine apart than absolutely necessary, before thorough testing and "diagnosis". If my Dad taught me anything about engines, he taught me that most problems are almost always "something very simple".
All of the good advice in this thread has suggested many "possibilities" and for what it's worth, I'll mention one more that's worth considering, and I guess this comes to mind because it's a problem that I've actually experienced, and that is the possibility of a broken or weak valve spring. In the case of a weak valve spring, one cylinder could possibly be responsible for the vibration beginning at a higher rpm as you say, merely because the weak spring could not keep up with the more rapid valve action at the higher rpm. Again, just one more "possibility" but a hard one to identify because altho' you can actually SEE a broken spring, but you can't actually SEE a weak one!
Again, don't tear anything apart until you, and whatever experienced "T" guy you can find to help you, have made a very thorough "diagnosis". It'd be a darn shame to put a bunch of time, labor and expensive parts into an engine that didn't need it, and then, worst of all, to find that the "vibration" STILL exists!
For what it's worth,.....harold
Going to chime in here again with my opinion on the compression test: The T is a very low compression engine. The highest I've ever seen is 65 Lbs. per cyl. Much lower than a modern. This is why I prefer to check them cold. Warming up the engine usually accounts for higher pressures simply because things expand. Lower cold pressures more accurately represent trying to start a cold engine. Paul's engine starts/runs so this could not be that critical but still the cold pressures are more in line with the engine's condition.
Paul - Sorry for being so "long-winded" here, but one more thing, for what it's worth,....and this is something that I'll admit, took me a long, long time to learn:
Many times, I have made the mistake of trying to correct more than one thing at a time. When trying to overcome one particular problem, such as the vibration problem you have, if you make more than one change at a time, and, somehow manage to correct the problem, you probably won't ever know just exactly what the problem was!
Do one thing at a time, and then test run to see if it helped!
For what it's worth,.....harold
My 26 ran good when I got it 10+ years ago after sitting for 35 or so years so when I got it running at first a lot of stuff came out of the gas tank. It would run rough some times so I would open the drain on the sediment bulb and dump out dirt from time to time. One time I took out the screen filter inside to blow it out with the air hose and when I hit it with air the darn thing took off from my fingers like a rocket and hit the back corner of my shop near the work bench. That thing has found a good place to hide as it is still someplace in that corner after 10 years and the T runs just fine without it. I would take yours out and try a test run to see if this might solve the problem the easy way before doing a lot of work first. Wont hurt a thing but may not do anything either. Worth a try.
Bob, I must disagree with you on discarding the sediment bulb fuel filter especially if the gas tank has residue, dirt, rust or old deteriorating liner inside that can vibrate loose and clog the small jets of the carburetor. Paul, here is the filter for your 1926/27 cast iron sediment bulb. Jim Patrick
Just because you have spark at the top of the sparkplug, don't assume you have spark in the cylinders. I had a rough running engine and had spark at all 4 plugs as noted by shorting each one out. After crossing everything else off the list I went back to the plugs. I removed them and tested them in a vintage tester. 3 worked - 1 didn't. The dead one was a Champion 25. I couldn't get continuity through it with an ohmmeter either. I threw in all new Champion X's and took the racer out for a beautiful run just over 60mph, and smooth as silk.
Seeing spark at the plug terminal when shorting it out just means you have spark THERE.
I'm not saying this is your problem. I'm just pointing out that assumptions will have you chasing your tail all day long.
Are you SURE you're getting an adequate fuel supply?
If it was me, before I started taking things apart, I'd hook up a temporary "IV bag" fuel supply and try to run it off that....just to eliminate that possibility.
Just because you cleaned the old fuel lines, doesn't necessarily mean it's flowing well.
With the compression test that Mark Strange detailed above, at step 3, have the ignition off.
Regarding tearing an engine apart for an inspection on a newly acquired car. If you don't have a lot of mechanical experience and haven't rebuilt engines before, then the advice of others to leave it alone is probably correct. In my case, having worked on cars for 60 years, I was able to take my engine mostly apart to inspect thing and have it back in the car and running in 3 days. I did not take the engine completely apart, which when I finally did, took a month to have it running again, with lots of new parts.
I agree Don. I still think it's fuel. At least he clarified he doesn't have an in-line filter anyway. I like your IV bag idea! I'm not sure low compression would make it vibrate anyway. I would think it just wouldn't be able to pull itself up a hill. He still should check it anyway. O'reilly's has a nice one for around $49 but he'll need the spark plug adapter.
I had a vibration once, thought it was the universal joint. Turned out to be a chipped pinion.
Could a plugged up vent hole be the problem? How well was the gas tank cleaned out? Were measures taken to accommodate the baffles inside the tank? If not, it is feasible that there itís still debris hiding behind the baffles and possibly breaking loose and closing the gas outlet. Usually, a strong solvent or cleaner is used in combination with small river rock pebbles that are shaken and agitated around inside the tank to dislodge the lining and debris. What type of coating did you use to line the tank with? I used POR 15 when I cleaned and lined my tank in 2010 and it is still holding strong. Jim Patrick
Paul, have been following your instructors and looks like you have been given some excellent advice. The most important thing is once you find and fix the problem is to go out and enjoy your new toy. I am sure you know your last name translated is cute or adorable. You could name your new baby hejes or aranyos or sikkes to mean the same as your name. Don't be insulted if you don't understand anymore, it's all good. Frank ( Ferenc )
Wow, lots of great thoughts and advice. Jim, by vent hole, do you mean the one in the fuel cap? I did check that. I too, used the full POR system for cleaning, metal prep and sealer. I started the process by tumbling with 200 screws for hours. It was very clean when done. I have checked fuel flow at the bottom of the carb a number of times. It flows fast.
Frank, you must be Hungarian. You are the second one I have run into in as many weeks.
There are so many possibilities it is mind boggling. I managed to find a friend with a compression tester. I am hoping to get it tomorrow and see what happens. I am curious about my compression anyway. I will post when I find out. I found one at autozone today but it went up to like 300psi and the graduations were so large that accurate reading would be difficult. I will post when I find out the results.
I have been doing one change at a time and testing in between. Great suggestion.
Yes. The vent hole in the gas cap...
No one mentioned the wire harness from the timer to the coils. It once worked to smooth out an engine for me.
Whatever you do, try to avoid doing open heart surgery for what might be an ingrown toenail! Problem sounds like it's drive-line so check the simple things first. I once had a friend who bought a 27 Roadster that had been restored years ago and had been in long term storage. Same thing - I drove the car and there was a terrible vibration, almost a thumping at about 25-29 MPH, then seemed to smooth out. Turned out be flat spots on the tires.
While it's often difficult to trouble shoot things by remote forum postings, there is lots of good info here and experienced people trying to help - but start with the simplest things first. I'dlike to hear more about what you find if you jack up the rear end of the car, then run it and check as the tires rotate to see how smoothly things operate. When you jack up the T, don't use a floor jack under the center "pumpkin." Jack up one side at a time and put the rear axles on jack stands. There are indeed many possibilities but my suspicion is it's drive-train related. Let us know as you work your way checking things out.
Speaking of wheel balancing to address the excessive vibration, has anyone tried the glass balancing beads in their tires? If so, did they work to minimize the vibration and would you recommend them to Paul? Jim Patrick
You've got a lot of suggestions, but one thing that came to mind was your coils and you saying you checked their adjustment. If you messed with the point gap, even a little bit, that can affect the running of the car, especially on magneto. I know you say, you put in a set of rebuilt coils, but did you do any tweaking of them yourself before trying them? I've known it to happen more than once that someone gets a set of rebuilt coils and think they should readjust the point gap. Point gap is NOT critical on Model T coils, and trying to set it will throw off the adjustments that ARE critical
If you didn't try adjusting the points, then please disregard. I just know what it's like to get a new car and start going over it to make sure everything is set right. Not a bad idea on most cars, but a real bad idea on Model T's when it comes to point gap.
Hal, I didn't adjust anything on my coils or the rebuilt ones. I just measured the gap. I am going out to the workshop today to test a few of the ideas. I was unable to borrow a compression tester today, but will get it in a day or two. Our weather is supposed to be bad for the next few days, so driving the car to test anything is out for now. I will just do some testing and no changing.
You can get an inexpensive compression tester at just about any auto parts store. Mark strange did an excellent job of 'splanin how to do the test.
Personally, I would take a hard look at the drivetrain. If you have bad compression in a cylinder it will show up at an idle. You said that the vibration came on at 28 mph or so; put the rear axle on jackstands (Block the front wheels) and run the engine in top gear until it reaches the speed where the vibration comes in, then pull back the handbrake (slowly) to stop the rear wheels from turning and putting the car in neutral. If the vibration stops, it's in the torque tube or rear axle. if it doesn't stop it's in the engine and or transmission.
Had a similar issue with a friends 1926 T truck. We tried all the usual things (which you have tried) to fix it but it still had a miss when under power (idled perfectly).
Put a coil box rebuild kit in her and problem solved! Seems that no matter how good they look they can STILL hide cranky wayward little bolts of electricity!
I checked everything I could. Spokes, plugs, fuel flow, coils firing at each cylinder. All good. Did the static test. Same amount of vibration with wheels spinning or not. I did hear a pop, pop, pop coming from the engine at high rpm's that I was not able to hear going down the road before. Probably too many rattles going down the road. I am assuming that is a miss?
Compression Test: 1 - 47, 2 - 41, 3 - 40, 4 - 41. What do you all think?
Fire it up in the dark with the coil box lid off and see if you have any arcing taking place from the coil box or insulators around the plug wires.
Dan, I did that already. Nothing.
Comp is OK. Move on.
John Codman's advice is dead-on. IMHO I think it is drivetrain related.
Compression is good. Because you have the vibration without the wheels turning it is in the engine. Because you hear the pop, pop, pop at higher rpm you have a miss. Although you have done everything to the ignition there is probably something you missed there. John Aldrich suggested a coil box rebuild. Someone else suggested new wires.
I think it was mentioned before, what about a weak valve spring.
Popping from where? carb or exhaust?
Paul, this certainly is puzzling. I know you said you checked the plugs, but can i ask what plugs you are using? You would not believe the problems some here have had with bad plugs.
Intake/exhaust manifold leak ?
I am rebuilding the coil box today. I guess wires are next. I have a set of motorcrafts and autolites. Both test ok with meter. I could not tell where the pop pop was coming from, exhaust I think.
Paul, a valve spring could be the problem. If you pull the cover to inspect, make sure all the valves are opening enough, also.
Have you been able to isolate what cylinder is missfiring by pulling one plug wire at a time and looking for a change ?
Be patient, you'll get there.
Where is it popping from; carb or exhaust?
Paul, you may be on to something with those plugs. Toss them and get some Champion X. I've seen those "modern" motorcrafts especially develop leaks around the ceramic. As has been mentioned before though you can't tell if a plug is any good by testing it ok with a meter. You need to test it under compression. At least changing the plugs might help reduce the number of things you're chasing. I also recently looked on while some folks were helping on a 12 T on a recent tour. Poor T struggled and seemed to have little power. and was surging once it was going a bit faster. Sounded like it was gasping for air or something. Some timer adjustment improve it but I heard a distinctive hissing sound while it was at idle. Sure enough, at least one spark plug took almost a full turn before it was properly seated into the head. Check the simple things first.
I rebuilt the coil box today. It does seem to have a little more power, or is it just my imagination? However the vibration did not go away. I recently met a long time T guy with a lot of experience working on them. He graciously volunteered to take a look at it. I am hopeful he will be able to find something. I will keep posting as things develop. Thanks to all!
Paul - Please do! We can all learn from each other, right? Don't become discouraged,....between the two of you, you'll find it.
Paul, Any new news on this? Just wondering. George
Have you ever tried to run the car without the lid on the coil box. A short drive that way won't hurt anything. Since you have opened the box and swapped coils and you have a '27 - it is very easy to accidentally bend the "spring things" on the underside of the coil box lid. Those could be interfering with the coil point operation. Whatever test shows you the vibration is THERE then run that test without the coil box lid in place. Not all day run but just one short test run. Push all 4 coils down good after you take the lid off and be aware if you hit a big bump a coil might just up a bit and start missfiring but if the engine runs smooth at the higher RPM then you have found the issue. Those "spring things" on the underside of the coil box each hold down a pair of coils but if they are bent up and deformed they then touch the coil point vibrator (lower part of the coil point assembly). This is a quick test and totally agree with others that say it is something simple. If one of the first things you did before you had this problem was to take the lid of the coil box - you might have installed crooked or did do that once and bent those springs. Nothing evil happens if you take a short ride without the coil box lid installed unless you drive through somebody's swimming pool. Your compression looks "normal enough" to me.
One question I forgot to ask. HOW did you determine you had "good spark" at each plug? Often when I hear that statement of "good spark" at the plug it turns out the test method proved no such thing. I am thinking over what you have done and the most often made oversight when all has failed has to do with how something was tested.
Clean and oil the timer.