Need answer

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Model T Ford Forum: Forum 2015: Need answer
Top of pagePrevious messageNext messageBottom of page Link to this message  By Craig Scott Fancher on Saturday, March 14, 2015 - 12:16 am:

I got a spark knock when I pull the spark rod about halfway down I read that you ground out each spark plug to find out what rod needs shims takin out but I got a true fire ignition so if I ground out a spark plug will this mess up the true fire any help will be greatly appreciated thanks craig my email is

Top of pagePrevious messageNext messageBottom of page Link to this message  By George n Los Angeles CA on Saturday, March 14, 2015 - 01:34 am:

I have heard(read) that it might on some of the older units. I don't know about the newer units.
Geo n L.A.

Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Coiro on Saturday, March 14, 2015 - 02:36 am:

Yeah, I get that when I advance the spark too far. -When we do that, the power impulses are driven straight down into the bearing caps instead of off to the side where the crankshaft throws can "roll with the punches" by swinging away. -Remedy: Don't over-advance the spark timing.

Top of pagePrevious messageNext messageBottom of page Link to this message  By Hap Tucker in Sumter SC on Saturday, March 14, 2015 - 06:26 am:


First, welcome to the forum. From your profile it looks like this is your third posting and all of them have been in Mar and two of them are looking for parts for a 1922 Roadster (body, and other parts close to central Illinois ). I’ll try to remember to post a note on your other question later today. A little bit about yourself and your car would help folks know how to better answer your questions. I.e. are you a certified auto mechanic and this is your 10th Model T you are working on or have you mostly driven newer cars and not done much mechanically with cars in general and this is your first Model T. Most of us are between those two book ends somewhere.

If the problem is spark knock as defined by the timing being too far advanced for the load the car is pulling then you don’t need to short out the spark plugs to find the problem (assuming everything else is close to sorted out correctly) you only need to retard the spark some. See for a short description of that and why it is harmful to the engine. For a T that is NOT running the normal magneto ignition, but is running a distributor and I think but I do NOT know for sure that the True Fire is similar – you have more choices for the ignition advance when you are moving the spark lever. For an explanation of why the stock magneto ignition has fewer actual choices of timing (but the ones it has work great) go to go to the “ choose a technical document” and from the drop down choose “The Model T Ford Ignition System & Spark Timing By Ron Patterson & Steve Coniff.”

Note that if it is a detonation caused by the timing being too far advanced switching to a higher octane gasoline can help. That is why the old 60’s cars with the higher compression engines used premium gas.

The problem can also be caused by “pre-ignition” which can be caused if there are carbon deposits on the cylinder head. They glow red hot after the engine has been running and they can ignite the fuel air mixture prematurely. See: and click on the 1921 Ford Instruction Manual for information on removing the carbon from the head. At the end of that same manual it has a trouble shooting chart. One item it covers is:

ENGINE KNOCKS (typical causes)
1. Carbon deposit on piston heads.
2. Loose connecting rod bearing.
3. Loose crank shaft bearing.
4. Spark advanced too far.
5. Engine overheated.
Any of those or a combination of those can cause the engine to knock.

Again welcome to the forum. If you are new to Model Ts (that is my guess – but it is only a guess based on very little information) I would recommend joining one of the local Model T clubs (see: and ).

And of course if you are new to Model Ts – please read the safety items I try to share with new owners pasted in below.

When I was a teenager I didn’t care what year the car was or if it had any safety issues etc. I was concerned about could I drive it. If I could, then it was great car. And besides you don’t really need good brakes or brakes at all for that matter as long as the horn works.

While it doesn’t matter what year or for that matter what make parts you use, it is important that you enjoy your car. And there are some known safety items about the Model T that you should check out before you start driving it. (If you are driving slowly on a farm where it doesn’t matter if the brakes fail, the spokes fail, car turns over, etc. – then you can ignore them all). If you have been around Model Ts for while you probably already know about the pitfalls. But if not, I would recommend you review them so you learn about those issues second hand rather than first hand experience. Getting an experienced Model T person to help you learn about your car can save you lots of frustration and possible expense. For example if you fail to retard the spark and you push down on the starting crank at the front of the car to start the car, you could easily break your arm. That is a known safety issue with Model Ts. And it isn’t dangerous as long as you understand what causes it [spark lever advanced [that is the left hand lever on a left hand drive car] it should be pushed up], commutator adjustment rod installed wrong or bent improperly so that even with the spark lever up, the spark is still too far advanced, shorted wire on the commutator, etc. . And if you use the electrical starter that your car should have – if the spark is advanced and the engine back fires – it can damage the starter and/or bendix drive. For additional details please see:
and there are other related threads.

Some other safety related items:

And be sure the car is in safe working order. An engine that burns oil is not a critical safety issue (at least not in my book) but the front end castor if it is set up negative can flip the car. If the rear axle still has the original babbit thrust washers you can lose your normal service brake. Those and similar items are well documented "oops" for the T. But if you have never been around one -- they are probably new "data points" for you. Some of them are listed below – not to scare you but to let you learn from others rather than discovering all the lessons on your own.

Safety Glass is nice:

Use safety wire and not lock washers or cotter pins on the two studs holding the wishbone to the underside of the engine.

Lots of safety items

Over center steering – shouldn’t happen on the later Ts (Ford added a stop inside the steering gear housing. The change was approved Oct 28, 1921 and would have taken a little while to be put into regular production. Ref: )– If the steering gear is original to the car – that can also be used to establish it was before or after that change. Note there would have also been a period of overlap when both designed were used as the old stock was used up. If someone replaced the steering gear housing or rebuilt it without the lock pin – or installed the wrong length drag link etc. the over center steering might happen: as well as:

Types of safety wire:

Example of loss of brakes caused by drive shaft failure:

Top T tips – many of them are safety related also:

Tour safety check list:

And if you have a gas hot water heater in the garage – be very very careful. The float in a Model T Carb will sometimes stick (or trash in the valve) and the carb will leak gasoline. Not too bad if there are no sparks – several homes, garages and cars have been lost when a gas hot water heater was near by and someone started the dishwasher other item that caused it to turn on the burner at the wrong time. Note gas fumes tend to be heavier than regular air …. so they tend to hug the floor. If you adjust your garage door to let the mice in and the air out – that is a temp work around. But replacing the gas fired hot water heater with an electric heater or having the gas one relocated away from the garage is the best thing

Even with a perfectly good and properly adjusted front steering system – if you back up quickly, the front wheels can go full left or full right and pull the steering wheel out of your hand – so remember to back up slowly. It is caused by the caster of the front wheels similar to the casters on the front of the shopping cart – designed to be stable in one direction but not so stable in the opposite direction. Since you have already been driving the car you probably do not have the following problem – but you might still want to check. If someone rebuilt the front axle and it is was really difficult to keep the car going straight they may have inadvertently swapped the front spring perches. There is a left and a right spring perch that tilts the axle so the bottom of the axle is slightly ahead of the top of the axle (5 1/2 degrees positive caster – although there is some discussion that it is a little less but still positive for the balloon tires like you have). If it has negative to neutral caster it can cause a wild ride and also could cause the car to flip even at a slow speed see: that shows the spring perch installed incorrectly and how the front axle looks then. Also see: Note even with the spring perch installed correctly a bent or shortened wishbone could cause neutral to negative caster.

Also the rear axle thrust bearings if they are babbitt (originally bronze in the 1909-1915 cars and then switched to babbitt on the cars during 1915 ref: see part number 2528 ) can fail with minimal warning leaving the driver without the normal transmission brake (the main regular brake on a stock Model T). See the discussion at: If you loose the brakes and you are on a flat area with minimal traffic – it is not nearly as bad as loosing them while going down hill towards a busy intersection. See the rear axle babbitt discussion part way down in the following thread:

Wood spokes work fine – but they need to fit tightly, not be split or wood rotted, made of quality wood (pine is not a good choice and yes some folks have offered pine spokes for sale) and the bolts etc. need to be tight without too much wobble in the wheel. see:

Again a T is a faithful servant but it has some known issues that the driver needs to be aware of and to take proper precautions about.

I would also encourage you to check out the local Model T Ford club(s) near you. (Did I say that already – yes, and that is because I think it will be a big help to anyone. Please See: and They can be a real source of encouragement and help you as you learn to maintain the car. Steve Jelf has an excellent set of books he recommends for new owners on his web site at: with the T section at: and the recommended books listed at: Note there are also free “how to books” on the internet such – see: 56bbT2W68C&hl=en&sa=X&ei=tdpWVMi4PMOjgwSAhoC4Ag&ved=0CBcQ6AEwAA#v=onepage&q&f=fa lse and there are others – but I didn’t see a 1926-27 one. And the Ford Service is online at: and does include the 1926 -27 “Improved car” features.

Good luck with your project and welcome to the forum.

Respectfully submitted,

Hap l9l5 cut off

Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Saturday, March 14, 2015 - 09:14 am:

I'm with Bob. If it only happens when you advance your advancing too far causing the noise. Use it to learn how to correctly operate the spark lever.

Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Saturday, March 14, 2015 - 10:19 am:


The typical 'knock' for a loose connecting rod occurs on down hill with throttle closed a bit, the knock is a loud rattle from the motor.

A 'spark knock' is more muted rattle, and occurs when the timer is advanced too much for the engine speed.

If you are having 'spark knock' at such a limited position of the spark lever on the quadrant, the first thing to check is the timing setting, that is adjusted by bending the timer rod from the steering column to the timer case.

First set the timer case to the right spot, which is approx. 15 degrees past top dead center of #1 piston on the compression stroke. Or easy way, turn over with crank handle to just TDC on #1, and then turn a bit more so that the crank shaft pulley is just past 3:00-9:00 as on a clock's face.

Disconnect the timer rod, and rotate the timer case so that the coil will buzz at that spot, hold it there. Retard the spark lever at the quadrant, and then re-bend or shape the timer rod to reach that fixed position of the timer case. That will set the timing.

Good luck! Have fun!

Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Saturday, March 14, 2015 - 10:33 am:

If you're getting an unhappy banging noise when climbing, you may have the spark advanced too far AND the carburetor needle turned in too far.

Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, March 14, 2015 - 11:29 am:

I will add to the confusion a bit. There are other knocks which occur when the spark is advanced too far. One is main bearing knock caused by a loose main crankshaft bearing. This will knock whenever the engine is pulling hard and will make less noise when the spark is retarded.

Another is piston slap. This knock is caused by the piston being too loose in the bore or a bent connecting rod. This knock will also be louder when pulling and will decrease when the spark lever is retarded.

Both the loose bearing and the piston slap will decrease as the engine warms up, but the true spark knock will get worse when the engine is warmed up.

It would be very rare for a Model T to need premium gas. The compression is just too low to cause pre-ignition, however heavy carbon deposits in the cylinders can get hot and cause pre- ignition. This will be most likely when the engine is very hot. A test for carbon caused pre-ignition would be that the engine continues to run on after the ignition switch is turned off. This run-on usually only lasts for a few seconds.

Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Bennett - Australia on Saturday, March 14, 2015 - 11:02 pm:

I had the same thing with my True-fire fitment on my Haighs chocolate van. Easily fixed. Just alter the length of the rod linking the timer unit to the rod on the steering column.
Hope this helps.
Allan from down under.

Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Sunday, March 15, 2015 - 12:24 am:

If you short out one plug wire on a truefire you lose only the spark to that cylinder, but if you pull the wire off you lose 2 cylinders.

(Message edited by kep610 on March 15, 2015)

Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Sunday, March 15, 2015 - 09:04 am:

I second Allan's comment, I had to fabricate a longer timer rod to achieve the proper timing with my Truefire unit. See this post:

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