MTFCA Forum

Hi,

Thanks to the previous replies to a separate post about my loud puffing exhaust, I've tried to short out the spark plugs one by one (still waiting to get the compression tester). I've taken a short video showing what happens and hope someone can help me diagnose what the problem is at this point and what next steps I should take even before the compression testing.

Here's the URL to the video: https://1drv.ms/u/s!AoOCcCJSc1JlioNhgt9 ... w?e=IEqK8n

This may be a lot to ask, but would appreciate any advice at this point. I'll report more once I do a compression test.

You'll see on the video (and I'm not sure of the how you number the spark plugs/cylinders. But, I went with #1 being at the firewall, and #4 at the fan end of the engine. Here's a synopsis of shorting each spark plug (see video):

#1 (front of engine): Engine slows down and loud exhaust stops. Per previous posts, this would seem to be where the valve is sticking, right?
#2: Can see an arch from the screw driver to the spark plug, but there is little noticeable difference in the sound of the engine.
#3: Can't even see an arch from the screw driver to the spark plug. I guess there is no firing going on at all in this cylinder, right?
#4 (back of engine): Engine slows down considerably, but loud exhaust continues.

I would certainly appreciate any help on what to do next. As you can tell, I've got a lot to learn about my Model T (but love it). I'm not afraid to tackle repairs.

Any guidance would be greatly appreciate from anyone willing to assist.

Thanks, Steve

Firstly get the engine established, it appears that the two cylinders in the center have no reaction, one with no spark and one with spark but no reaction when shorted. Start with turning the engine with ignition on and confirm that all coils are buzzing, if one is not then trace the wiring from that coil or change the coil. If all coils are buzzing and #2 ie second from the front still has no reaction when shorted, remove the spark plug and look down in to the cylinder at the valves (may need a flashlight) and see if a valve is stuck open. If a valve is stuck open and with the piston TDC on compression stroke you can tap the stuck valve closed with as mall hardwood stick. Oil the valve stem firstly then turn the engine over until the valve is forced up again, if it stays up repeat the process until it moves freely. With all cylinders firing and there is still popping out the exhaust put some drops of water around each spark plug and check for bubbles. A spark plug may be leaking and sucking air causing an uncontrolled lean condition that will manifest itself with popping out the exhaust. Start here then we will go from here to the next level.

Altair,

I appreciate your patience with me.... I turned the key on, and cranked slowly. It buzzes at 10:00, 4:00, 10:00, and not again at 4:00. Repeated that several times. How do I know if it is the coil vs. wiring? I took the cover off the coil box. Is there a secret to getting a coil out, or is it just that I'm not pulling up hard enough? Not sure what I'd even look at when I do get the coil out.

I felt the metal terminals at the top of each coil (ignition off), and all were warm except the one that coincided with the spark plug that was not arc-ing.

Thanks, Steve

You don't have a problem. You have several problems. You're going to get lots of help, all sending you in different directions. If David will stick it out helping you, then stick with him, or chose the next guy...in any event, be methodical, don't start taking things off until you KNOW what is going on and why...and NOT just to take a peek. I'd give advice as to where to start, but that'd be breaking my own rule right away . Good luck.

Hint: some of your trouble can be diagnosed or aleviated without lifting a wrench.

I suspect you have several problems going on here at the same time. To check the coil health, swap coils 3 and 4 and see if the problem with #3 cylinder moves to #4 cylinder, that would indicate a problem with the coil. I agree valves could also be problem.

Stupid question, how do I get the coils out to swap them? Do they just lift out?

Lift, tilt top toward you, away from firewall, withdraw. You might need to lift wiring harness out of the way and WILL need a little patience if they're initially stuck in there

Good choice for first start at diagnosis.

Scott's right and makes me hesitant to post. Yet I blab.
Sometimes the coils can be a REAL snug fit in the coil box.
Perhaps a pair at time to initially lift them from the box. Works here sometimes.
Steve, when it's time for the #3 coil (3rd from the left inside the coil box) to buzz, wiggle/nudge/fiddle-with the movable point to try to wake that coil up. The big round steel flap on the top of the coil, that's the movable point. Fiddle with it.
No, you won't get zapped. That has worked for me on a friend's truck.
You might simply need four, hot rebuilt coils.
Follow David's lead.

Steve, if you have trouble getting the coils out of the box, DON'T be tempted to pry on anything on the top of them. That would most likely mess up the adjustment of the points which is very important. Also, if you live in a high humidity area, try to lower the humidity somehow or catch a day when it is low. Humidity can make the coils swell a bit, making them harder to remove. If you feel you have to pry on them, pry on the side of them gently with a screwdriver or something similar. Don't get in a big hurry, work them out slowly, they will come out with a bit of work. Dave

I forgot to say, sometimes the wood cases warp over time making them hard to get out. Once you get them out, they can be sanded a bit on a flat surface to square them back up, just don't get too carried away. Usually, it doesn't take much. Keep us posted. Dave

I find it easier to start with the 2 middle ones. Rock them gently back and forth while lifting up. Try not to put any pressure on the points them self while you do this. If push comes to shove, mark the wires and remove the coil box.

Mark Gregush wrote: ↑

Mon Jun 01, 2020 9:53 am

If push comes to shove, mark the wires and remove the coil box.

Good point Mark. Rather than wrestle stuck coils out of the coil box, just swap two wires from the commutator. Mark them first so you know which wire goes where. You will know if it's a bad coil if the problem moves to a different cylinder.

With apologies to Scott.

OK.... traveling down the path of checking coils as a first step. I was able to get them all out. I cranked until I had a solid buzz on one of the other coils in position where there wasn't a spark. Then I put each in the position in the coil box that corresponded to the lack of spark in the original test, and turned on the ignition one-by-one. Three of the four buzzed (but not the original that was in this spot in the coil box). Therefore, seems it can be concluded that the lack of spark in the original short test, can be explained due to a defective coil. Here's the link again to the original video and now a photo of the coils (the defective coil to the far left is the defective coil): https://1drv.ms/u/s!AoOCcCJSc1JlioNhgt9 ... w?e=r1fa3b

Per earlier advice, I need to get this fixed first before moving back to the possibility of a stuck valve.

Is there a way to fix the coil myself (seems too complicated)? If not, what's the consensus on coil replacement? Buy new, buy refurbished, get this one rebuilt, or another option? I'm fussy about the car and keeping it original to the point that I purchased it (e.g., I'm not replacing the original upholstery or top - which are pretty worn from 1923).

Thanks for hanging with me and allowing me to learn along the way.

Steve

Seems I have a defective coil (see string of messages). Do I buy new, rebuild one or all that I have, or another option? Or, try and fix myself?

Thanks, Steve

Send the original to one of many on the forum that rebuild them. A proper tuned set of coils are a must for a good running T.

If the coils haven't been rebuilt in the last 20 years, send them all to one of the folks who rebuild them. The paper wrapped capacitors go bad with age and they likely all need replacement leith possibly new points and adjustment/tuning. I use Ron Patterson "Coilman" but there are several other fine folks that do a great job.

Best to get all of the coils rebuilt. I sent mine to the coil doctor and he did a great job. Probably been the problem all along. Good luck.

Not all coils can be rebuilt some may have open or shorts in the winding's. While there is plenty of info on the web to rebuild them, more then likely you are not going to have the equipment to set them up after rebuilding. (even just replacing the points you need this setup equipment) There are several rebuilders, see the list in services on the home page. Contact one of them and talk to them. Tell them what you need and what you have re the coils. YOu might want to get a total of 5 so you have a ready to go spare.

Thanks everyone! I’m getting them rebuilt (and getting an extra too). I’ll likely be back to the forum once I see how things are running (or not) with rebuilt coils. I’m curious to see what changes with suspected open valves with good functioning coils.

Steve

Shoot, I might be more excited than you! Itchin' to see how you fare!