Knocking When Engine Decelerates

[Its_Always_T_Time]

My engine has a rapid, loud knock which has gotten worse recently. It started a little while ago and I only put a few (maybe 4-5) miles on the car since it started due to me being away for the summer on the TS Empire State. It seems to happen when the engine has been ran for a few minutes and can be made to happen when the engine is decelerating (or I put it into neutral after moving and decelerate the engine to keep it from racing).

I’m going to do the plug-shorting test to isolate the knock and drain the oil and drop the inspection plate and check for play in the rods. I’m imagining I’ll need some new rod cap bolts as reusing them probably isn’t the best idea. They appear to be one of those castellated nut and bolts with the hole in them, I just put a pin in them and bend it well to secure it like the other castellated nuts once I torque them down to tighten the caps? The pin won’t fall out inside the crankcase? I’m going to read my T books about fixing loose rod caps, I’m just wondering what I should look out for, how to actually check for play (I just try to move them with my hands and measure the movement with calipers?), and common mistakes to avoid and whatnot. Any help is appreciated.

I'll post some pictures of the inside of the engine and the inside of the inspection plate when I pop it open on Friday.

[Scott_Conger]

Though it could be one of several more obscure causes, you are describing a classic rod knock. Before doing anything else, you need to isolate it to the correct cylinder so you do not embark on a snipe-hunt. If no single shorted plug nets you the results you're after, try shorting out #2 and #3 simultaneously and have someone try to induce knocking...if the knocking largely or completely goes away, you have a worn out center main for sure, caused by a nearly certainly worn out 4th main at the back of the transmission.

you will find nothing out by fiddling/sliding the rods around. They all will. That is not the knock. The knock is excessive diametral clearance between the rod ID and the crankshaft throw. Read your books and evaluate how you wish to verify that. Calipers will not play any part in measuring anything. If you must measure something, you need a 1" micrometer.

I'd advise that you isolate the knock to a rod, then remove the cap, inspect for obvious trouble and when you find none, reassemble with a piece of (.75 x 1/25") newspaper clamped between the rod-cap and the crank. Tighten down. If you can turn the engine over by hand, you have excessive clearance (see? told you you need not measure anything.) Disassemble cap, remove newspaper and peel off one shim from one side of the rod and reinstall a fresh piece of newspaper. Bolt together. Is engine too hard to turn? Disassemble and remove newspaper...you're done. Engine still turns? Disassemble, remove a shim from the OTHER side and repeat the newspaper trick, etc.

If you get talked into using plasti-gauge on an older engine, well, good luck to you...cranks wear out of round, tapered, all sorts of things, and what is good tight fit at one angle of the crank can be a different measurement in another. This can lead to great frustration and no measurable headway.

[Art M]

In addition to Scott's thoughts, I would measure the crank journal for out of roundness and taper. I chased talking rods until I gave up tighting rods and finally measured with a micrometer. A caliper is probably accurate enough.. Reground crank and rebabbited and 6000 smiles later the rods are,still quiet. Hope you are luckier than I was.
Art Mirtes

[Allan]

How common are laminated shims which allow the selective removal of same to adjust rod clearance? I have yet to pull down an engine fitted with them. Are they a more modern fitting?

Allan from down under.

[Joe Bell]

I had one years ago that did this, some one had replaced the cast iron pistons with aluminum ones, the bore was to large from years of the cast running, the cast have a lower oil ring to keep the piston from slapping, the aluminum do not and that is where the noise come from at least on this engine. Worth a check? Hope this helps.

[Mark Nunn]

If you need to separate shims from rod caps, this is one way to do it.

By Dean Yoder on Monday, November 28, 2011 - 04:10 pm:
Heat the shim pack with propane or mapp gas torch. The heat destroys the glue.

Others suggest a sharp knife or single edged razor blade.

[Norman Kling]

One thing about a rod knock. Usually it is first noticeable when you just slightly decelerate. As you would do if you just want to slow down a little but not when you are going downhill on compression. The knock comes when the rod is running slack on the crankshaft. As it gets worse, it might be heard at all speeds.
One other thing mentioned above, was a loose center main. If it is loose, you are safer to pull the engine and, rebuild because the wear in the center main is usually upward toward the block and if the weight of the transmission and flywheel pulls the rear of the crankshaft down and the center goes up, eventually your crankshaft will break just like a wire which you continually bend back and forth.
Norm

[TWrenn]

If it has Tru-Fire i don't think you can do the "short-test" as it may ruin the electronic coils. Just sayin, as you didn't mention what type of ignition.

[R.V.Anderson]

To answer Allan's question, the laminated shims have been around at least since T days. They were likely more expensive than plain ones, so most home mechanics probably didn't use them. They were almost certainly more of a shop item, since to a rebuilder, then and now, time is money.

[Its_Always_T_Time]

If it has Tru-Fire i don't think you can do the "short-test" as it may ruin the electronic coils. Just sayin, as you didn't mention what type of ignition.

I have a stock ignition system with rebuilt coils.

[Its_Always_T_Time]

One thing about a rod knock. Usually it is first noticeable when you just slightly decelerate. As you would do if you just want to slow down a little but not when you are going downhill on compression. The knock comes when the rod is running slack on the crankshaft. As it gets worse, it might be heard at all speeds.
One other thing mentioned above, was a loose center main. If it is loose, you are safer to pull the engine and, rebuild because the wear in the center main is usually upward toward the block and if the weight of the transmission and flywheel pulls the rear of the crankshaft down and the center goes up, eventually your crankshaft will break just like a wire which you continually bend back and forth.
Norm

The knock has been steadily getting worse, at first I thought it might be ignition knock because I switched over to burning 93 octane for easier starting in cold weather as per my Dad's advice, but playing with timing settings did nothing to stop it. If it is indeed a center main bearing, my garage is downright miniscule and I have barely a foot of space on any side of the car, so pulling the engine, let alone rebuilding it, will be nigh-on-impossible for me to do. I'll probably have to get Lizzie towed to a T engine rebuilder and have them do the babbitt work for me.

[Scott_Conger]

The knock has been steadily getting worse

gives me the feeling that you may be the latest cautionary tale for all newer owners of these cars that when you first hear the knock you STOP and fix it. A slight rod knock immediately detected means 1 hour removing a pair of shims. A rod knock pondered over for 4 miles that gets steadily worse is a pulled head and a new rod and lapping...good for an 8 hour day and $100 for a custom bored rod.

Four miles is a huge difference in the amount of work and expense.

I think you're going to find the noise almost immediately by shorting plugs and it will likely be #1 or #2, and you're going to find babbit in the pan and be replacing a rod. Let's hope not, but not hopeful after reading/rereading your posts.

[Norman Kling]

The knock getting worse could be due to the type oil used in the crankcase. Most of the newer oils are multi-grade and don't change much in viscosity with temperature, however, the older single grade oils will get thinner as the temperature rises leaving a thinner film in the bearing. The multi=grade oils will run just fine in a T but the thicker ones will cushion the worn bearing so it might be quieter when the engine is cold. Either way, the cause of the knock needs to be found and fixed. The sooner the better. If you have room in front of the car, or a good beam overhead, the engine can be pulled out from the front even in a small garage. you could even pull it outdoors and then roll the car inside to park it. It CAN be done!
Norm.

[Its_Always_T_Time]

The knock getting worse could be due to the type oil used in the crankcase. Most of the newer oils are multi-grade and don't change much in viscosity with temperature, however, the older single grade oils will get thinner as the temperature rises leaving a thinner film in the bearing. The multi=grade oils will run just fine in a T but the thicker ones will cushion the worn bearing so it might be quieter when the engine is cold. Either way, the cause of the knock needs to be found and fixed. The sooner the better. If you have room in front of the car, or a good beam overhead, the engine can be pulled out from the front even in a small garage. you could even pull it outdoors and then roll the car inside to park it. It CAN be done!
Norm.

I use 5W-30 synthetic oil, I figured it would be good since it won't be too thick when she's cold. When I was driving Lizzie back home before I parked her pending repair, the low pedal seemed to not engage properly, even though previously it seemed like I had my low band adjusted well, the planetary gears would only do their characteristic "groan" intermittently and power in low was similarly intermittent.

I have thought of pulling the engine and putting it inside the garage to be worked on over the winter...but unfortunately that leaves Lizzie without a home during wintertime as that's the only available garage bay for her. My garage has about 1.5 feet of space on any side of Lizzie when she's centered inside of it, there's only just barely enough space in there for her and not much else. The only place I could put her while the engine is inside the garage would be under a cover in front of my Dad's house, but then she would get salt all over her as the sanitation department here in NYC loves to throw enough salt on the roads to make one wonder if there's any salt left on the Earth after a mere dusting of snow. I also don't think parking her on the street without an engine under a cover is legal in NYC.

Work and school have once again gotten in the way of me being able to have some wrench time with Lizzie, so I have yet to diagnose the knock issue. I've taken off Friday morning to get my hands and coveralls thoroughly dirty. I'll have to see what I'll be doing depending on the severity of the damage, if it's a matter of pulling the head and repairing a bad rod I'll repair it myself. If it's a disaster scene inside the engine (like bad mains or severely out-of-round crank journals) I will be "treating" Lizzie to the works for her 100th birthday coming up next September, getting her engine, transmission, and rear axle completely rebuilt by a trusted T shop.

[Scott_Conger]

There are adherents to 5W-30 oil, but I believe those folks using it successfully are running somewhat fresh engines. If you search for that extremely light oil within the forum, you will find that it has wreaked significant havoc in older engines on multiple occasions. There are known and well understood reasons for this, but I'm fairly certain that this post will bring enough negativity anyway, without listing them.

[Art M]

In previous postings, some have reported that when they tried synthetic oil, the bands slipped so severely that the car wouldn't move. I have added synthetic when a certain oil made the bands very grubby. About 1 quart in 3 quarts. It eliminated the grabbiness but never used yesterday brand of oil after that..
Also, some people have experienced excessive oil consumption in a more modern car with a worn engine.
I use synthetic oil in my modern cars.
Art Mirtes

[TXGOAT2]

10W30 synthetic oil with a pint of STP, the synthetic goop version, works well in my engine It was 95 F here yesterday, and I ran the car about 20 miles at speeds up to 50 MPH. The engine used to smoke at idle, but restricting the flow of the Texas T oiler put a complete stop to that. I believe it was flooding the troughs with too much oil for regular road use. I guesstimate I reduced its flow rate by about 1/2. I'm still getting oil thrown off the cam gear and the engine sounds great. I can start the car with the crank on mag without difficulty and it does not creep. That may change with cold weather. If so, I will simply add a pint or two of Marvel Mystery Oil.

[Its_Always_T_Time]

So I’ve got my coveralls on and I’m going to be firing Lizzie up and diagnosing the knock in a few minutes. I’ll post some pictures with questions as I go in case I run into any snags.

Edit: Shocked myself and dropped the screwdriver. OUCH! Doesn’t seem like I’m leeching enough current off the plug to make it not fire, maybe I should just take the plug wire screws off and then remove the wire with an insulated wrench? Then again I wasn’t able to manipulate the throttle enough with one hand and put the screwdriver in the right spot at the same time. I think I’ll need my Dad to help so one of us can race the engine to lure out the knock and then the other to short the plug or remove the wire while doing so.

[Its_Always_T_Time]

Should I just hold the points down on the coils instead?

I accidentally shorted #4 coil while the engine wasn’t running I think I fried it. Edit: it seems to work fine still.

No matter how fast I run the engine and what coil I hold down, I can’t get her to knock.

Edit: Seems to be when #2 and #3 coils are held down she knocks loudly. Bad mains I’m imagining.

I’m guessing I should call someone near me a little more experienced in all things Model T for some advice.