My T will make a knocking noise proportional to engine speed that sounds like it is coming from the engine during deceleration in high gear, or very light load in low gear.

I suspect a rod needs a shim removed, but t is quiet at idle so I could not short plugs to see if one made it go away...

I decided to take the lower (3 dip) pan off and see what I could. All four of the rods move easily axially (back to front), however as hard as I push up and down or side to side, I could not feel any radial play in any of them. Any tips on what to look for? Should I just put it back together and see if it gets worse / easier to diagnose?

-Joe

Joe, the rod clearance is checked and adjusted by using a product called Plastigage. It's a hair sized strip of green material which you lay in the rod cap and compress in place between the crank journal and the rod. Look on YouTube to see it in action. Your target is a clearance of 1.5 to 2 thousandths of clearance. The shims are slivers of brass which will need to be separated using a razor blade.

Joe, don't rule out the main bearings, especially the #1, as it is often a culprit for oil starvation. I've read plenty of posts though about the center main knocking, as it has something to do with crank flex I think? Is this the '14 you bought from the guy in Wisconsin or Iowa or wherever it was that I was wanting?

Tim

Regarding the shims, the new ones are 15 layers of .002" brass, and you can peel off one layer at a time by heating it briefly using a propane torch. One layer will peel back by itself with a little heat. (Hold the shim with pliers while heating, not your hand.)

If your car's shims are old ones, they're solid pieces of brass or steel. You can't peel those. You'll need to use a micrometer to gauge their thickness and replace with a thinner one.

If you can't hear the knocking at idle, try revving until it can be heard, then short plugs for testing?
(Just don't stand in line with the fan..)

If it's only in high gear, put the rear axle on stands and try running it in high - check for other sources for the noise in the transmission..

Joe,
Is your car a pre-26 with the coil box on the firewall? If so, take the cover off your coil box and drive it without the cover. If you can duplicate the knock while driving, carefully reach down and push down on the points to stop the coil from working. That way you can short the cylinder while driving and determine if the knock goes away and identify which rod is loose. If it does not go away, you may be looking at a main bearing or some other component not associated with the rod bearing.

Joe,

The ability to move a rod fore & aft slightly is a popular test to judge rod bearing clearance. However, I believe it's a sort of worthless test. If you have any clearance at all, even .001, the rod will move fore & aft. If you don't want to do the Plastigage test, then remove one leaf of shim, (usually .002 thick), and see if the rod drags or locks up. If it's still free, you've got more than .002 clearance, which is too much.

Plastic gauge is a good tool, but it will only check clearance at one point on the circumference of the journal. How, exactly should the plastic gauge be used? I know that a piece of the correct type (usually by color) should be laid length wise with the crankshaft and the cap torqued in place. The cap is removed and the squeezed plastic is measured. Should the plastic gauge be used in at least two places? Once with the crank journal all the way down and once with it up, or will this give the same result? Should the plastic gauge be used near the junction of the cap and the rod. I think I'm asking how does the rod bearing wear? Mike

Mike,

I lay the plastigage strip across the bottom of the cap, reinstall the cap, retorque, remove, measure strip width. I believe it matters a lot if you have a thin film of oil on the crank & cap but I can't remember if that's advisable or something to avoid.

You probably would get different results with the crank rotated 90 degrees between two different tests. It would mean the crank is out-of-round. However, it's far easier to just measure the crank to determine that.

The rod bearing will wear most at the top & bottom.

Plastigage isn't necessary when taking up a babbitted rod cap, a piece of newspaper works just as good

Here's a quote from Jim Lyons:
"Put a small piece of newspaper that covers about 70% of the rod cap in place and tighten down the cap on the rod on the crank with the paper in place. If you can rotate the engine then it's still too loose. Keep grinding the cap face until the engine won't rotate with the newspaper in place but will when the cap is replaced WITHOUT the paper. It's old school but it works."

I've also tried it and I like it

Plastigage used, on Model A.

Model T should be .001-25 Minimum, and .001-75 Maximum.

Always use 2-3 drops of oil under the Plastigage.

Thanks Herm,

Should the mains have the same clearance as rods?

On a Model T, yes.

Herm.

I have very little experience with engine knocks. Last week on the way home from the 2015 Michigan Jamboree, I thought that I heard a knock from my engine. The engine was rebuilt about 5-6 years ago and I drive the car a lot, maybe 15-20K miles on it since the rebuild. The knock would occur when the engine was at a slow speed, a little more that idle and unloaded. I can not hear any knock at speed or under load. But the car is noisy and maybe it is being covered. So, a few days ago I decided to try and determine which cylinder was the problem, by setting up the knock and shorting each spark plug one at a time. Well, I could not get it to knock as it did. All I can figure is that during the test I had the hood off and maybe I was hearing the hood rattle. So, I'll keep my ears open (as much as these old ears will) and this winter when I check over the engine and drive train, I'll try what I learned here. Thanks Mike

Mike,

The difference between your test and what you hear on the road, is that during the test, the car is not moving. Think about your U-joint maybe? That is something you would hear with little or no load as you describe.

You might try jacking up the rear end and running it in gear while parked.

That's an interesting idea. I know that my U joint is worn, but I'm pretty sure that the sound is from the front of the car. That being said, my ears have deceived me before with where the sound comes from. I'll give it a try. Thanks Mike

Sometimes a knock toward the front of the engine is caused by the pin through the front pulley being loose and moving back and forth as the engine runs. Usually loudest at idle and not present with speed. Another cause in the front would be a loose camshaft bearing or a loose camshaft timing gear. The bearing might be more noticeable at low speeds but the gear would sound at all speeds.

I have a suspicion that your knock is in the connecting rods, but only testing will prove it. As above, a thin piece of newspaper should make the bearing tight but if it still turns, indicates too loose. Taking out one 2 thousand shim from one side and testing whether the crank will turn easily, then take the same amount out of the other side and test again. Do this alternating from side to side until you get it to turn hard. Then insert one shim on one side and tighten it up. The hardest rod to adjust on a 3 dip pan would be number 4 but don't ignore it. It needs to be adjusted too.
Good luck,
Norm

Mike,

If you've got a fiber timing gear have a close look at it. I had one that started making noise up front. I caught it just before it let go. You usually don't get any such warning.

Norm, the front pulley is one of the new aluminum split kind. Don't think that is it. I have a 4 dip pan and intend to check them all.
Jerry, My cam gear is aluminum. I had trouble with it a couple years ago. The front cam bearing was loose in the block and allowed the cam gear to be pushed away from the crank gear and then slammed into it causing a ringing sound. I repaired it with a steel shim. Hopefully once October comes around, I can pop the cover and try the paper test. Thanks Mike

That's great information. I am going to save it for future reference. Thanks

Thanks for all of the info! I am going to take a look at it again later tonight. To answer some of the questions:

1) Tim, yes this is the '14 from Iowa. It is a pretty nice car, but it has sat most of its life and was not really used. That combined with me never owning a T before, and only having about 15 min of T driving experience prior to buying it has made for a very fun journey.

2) Jerry, The car does not have a fiber timing gear.

3) I will be at OCF next weekend. If anyone wants to drive it there and help me diagnose, I would love the help.

-Joe

Joe,
A lot of info here on shims, but you say it's a 14 T with little use, that changes what you will need to do, IF still original it will not have shims so you need to set the clearances by filing the rod caps, might be best to get your self a workshop manual and go step by step in checking and setting.

The engine was rebuilt. I took the pan off and it has shims on the rods and mains.

Joe

If you can use plastigage while adjusting the caps with the engine IN the car, "then your a better man than me gunga din".

Either the Ford manual or the mtfca engine manual (can't remember which) has a method where you use a very light hammer to adjust the bearing clearance. If I remember right they should not slide axially with moderate finger pressure, but should move without problem when tapped with the light hammer.

Its an elegant solution to working in cramped quarters and works very well. Get the article - don't trust what I remember.

Joe, hope to see you there! I'm not much for diagnosing, but still like to go for a ride in her!

The rod caps in the pictures have center punch marks all the way around but i am not sure why.

Drilling, metal removal for balancing.

Bud's posting reminded me that rods shouldn't easily slide from front to back, it should be more of a tug & a snap. This is what the 'light hammer' test does. Been a while since I've had to lay under an engine and have oil drip on me.