Not your average "knock"

[James_Lyons-WV]

Anyone ever had a knock that you only hear when the engine is cold, and only when you advance the spark?

So, my 15 touring has 20 years with me in the seat. This is a tour proven car. Anyway, I spent two years sick and the car never moved. My health has improved so I took it out a few times this summer. I seem to have a knock that is a bit odd. It is much lighter than a main bearing, and a little bit lighter than a rod knock. It only does it when the engine is cold and as it warms up, it goes away, mostly. Also, it only does it when you advance the spark lever at least half way.

I shorted each cylinder and it does not go away like a rod noise would. And again, it's too light for a main.

It makes me wonder about the following:
- Cam bearings
- Wrist pin
- Piston slap

Happy to hear opinions and suggestions.

[tdump]

my guess is wrist pin,

[Craig Leach]

Hi James,
I have no idea of anything that sitting will cause a knocking? Unless coolant is involved as in leaking into a cylinder & rusting something. I have found loose rods because of an out of round crank that did not sound like a rod but was bought in time. Being a mechanic by trade I have very good listening equipment & believe they are indispensable when it comes to these problems. A stethoscope is your friend, an electronic one is indispensable. Find where the noise is most prevalent & start looking inside. If you don’t find anything keep looking.
Craig.

[Moxie26]

Have you checked the initial timing with the brand of timer you have?... Chances are your initial timing has to be retarded a bit, and the control rod lengthen in relation of spark lever in full up position.

[TXGOAT2]

First guess: If it goes away as the engine warms up, I'd suspect a piston slap, especially if it has aluminum pistons. Second guess, a wrist pin, again, especially if it has aluminum pistons. Be sure you are suing a suitable oil.
Other possibilities include engine mounts and the exhaust system.
*Bearing knocks almost always get louder as the engine warms up. (Almost) Noises related to pistons, especially aluminum pistons, often get quieter as the engine warms up.
You might pull the transmission cover plate and look for evidence of anything loose, and look for evidence of unusual or excessive band lint or other debris that might obstruct the oil pipe.

[Jerry VanOoteghem]

Other possibilities include... the exhaust system.

Excellent thought Pat. A loose exhaust pack nut will allow the pipe to rattle until the pipe heats up and elongates, putting pressure on the joint and stopping the rattle.

[TRDxB2]

Anyone ever had a knock that you only hear when the engine is cold, and only when you advance the spark?

So, my 15 touring has 20 years with me in the seat. This is a tour proven car. Anyway, I spent two years sick and the car never moved. My health has improved so I took it out a few times this summer. I seem to have a knock that is a bit odd. It is much lighter than a main bearing, and a little bit lighter than a rod knock. It only does it when the engine is cold and as it warms up, it goes away, mostly. Also, it only does it when you advance the spark lever at least half way.

I shorted each cylinder and it does not go away like a rod noise would. And again, it's too light for a main.

It makes me wonder about the following:
- Cam bearings
- Wrist pin
- Piston slap

Happy to hear opinions and suggestions.

Just wondering. After the T being in hibernation for two years what maintenance did you do to wake it up? I'm thinking more about fuel degradation.

[TXGOAT2]

Old gas is a possibility. It doesn't always smell bad or look bad. It could cause a sticky valve or increase the drag on a piston. As far as that goes, a little rust on a valve stem or cylinder wall from condensation could do the same. I'd pay attention to the noise, and if it gets worse, I'd want to find out why.

[James_Lyons-WV]

All... thanks for the replies.
It is a completely factory engine with cast iron pistons, and std bore. 13 years ago, I re-ringed the engine and installed stainless vales with oversized stems.
The noise is internal and can be heard with a long screwdriver to the ear. When the car was put into hibernation, the gas and coolant was drained. During its slumber, the engine was turned over every 3 or 4 months, stopping in a different spot for the pistons to rest each time. Waking it up consisted of the typical springtime wake up.

The investigation will continue with the engine in the car. I'm leaning toward a wrist pin. I'm not pulling it until I figure it out, or at least narrow it down to removal required. I'll keep everyone posted.

[TXGOAT2]

I'd drive it for several 5 to ten mile runs, paying close attention to the engine's sound and performance. The noise might go away. Another possibility is that a piece of carbon is causing the light knock. Carbon can loosen, flake off, and stick again where it hits a piston at TDC. A ring might have become stuck, changing the drag on the piston. If the noise has any relation to the period in storage, driving the car for a few miles may eliminate it. I would add Marvel Mystery Oil to the gasoline as directed, and add a pint of it to the crankcase. It won't hurt anything, and it might help. It also smells pretty.

[J1MGOLDEN]

I recently woke up a 1925 engine that had been in storage for 90 plus years and it had no knocks at all.

Changing the spark advance did make a big difference in the sound level when running.

[Mark Nunn]

James, my '26 Runabout has the same symptoms that you described. Mine is in cylinder 3 (shorted sparkplug method). I have about 20 miles on the engine since adjusting rod bearings. That points a finger at the wrist pin end. I wasn't planning engine work this fall but that may change.

Thank you to all of the previous responders for your input.

[Norman Kling]

If you are driving the car and the knock begins, try retarding the spark lever. If the engine does not slow down but the knock goes away, you could have the spark too far advanced. Does it happen in both low and high or is it dependent on the rpm and also how hard the engine is pulling. Usually in high gear at a very low rpm, the engine is pulling quite hard and the strain on the wrist pins and rod bearings is at it's greatest. So it could be related to either the spark position, or how hard the engine is pulling for the rpm.
Norm

[TXGOAT2]

Mark, if you just adjusted the rod bearings, it could be that one is just a little tight, which could cause the piston to rock or slap, especially when cold.
You might pull the plate and see that all the rods are free to move forward and back a bit on the pin. If you adjusted them to quiet a knock, one may still be a little loose, or you may have a tapered of flat crank pin. From here, I'd guess that one rod is a bit tight.

[Wayne Sheldon]

You guys have covered this quite well! For myself, I have had a couple model T engines that developed wrist pin knocks, so that was my first impression when I first read the few beginning post. Other comments have also been very good.
One thing I feel compelled to add. The wrist pin bolts are very important, and take a much tougher beating than most people realize. Thirty years ago, I ran basically out of original Ford wrist pin bolts. A few phone calls to friends found nobody with an abundance of extras that I would considered getting a few (I was offered several spares by good friends, but since they didn't have an abundance of them?). I chose instead to take the advice of a few "experts", and used modern high strength grade eight bolts (I will hopefully never do that again!).
I had gotten my first boat-tail running with a tired old engine I had in order to build everything around and get everything fitted the way I wanted it. I drove the car with that tired engine for almost two years, and on several tours, with that old engine while I slowly reworked the proper engine for it. I got it all put together in time for the MTFCA's 25th annual Endurance Run! It was a special two-day Run, and somewhat longer than the usual 200 miles.
I had put maybe a hundred easy miles on the engine before the start of the Run. The Run began fine, and the car ran great for quite a ways. But then I began hearing something, something quiet, like a soft knock. I eased off a bit, but continued driving and listening. The knock continued to get worse, and depending on driving conditions, would be very quiet at times. It didn't get worse in the way I would expect a rod to do, but did continue to get a little worse as the miles went by.
One other mistake I had made, was since this wasn't intended to be an Endurance Run car, the boat-tail's engine did not get added oil delivery to the front of the engine, and a few of the hills had been steep! As the day's run was getting close to halfway point, on a particularly steep hill, I thought I got my answer about the knock, number one rod bearing tossed it's Babbitt.
That Run had been unusually brutal. My cell phone call told me that about ten cars had broken down ahead of me (we had seen and stopped for I think four of them?). So my next call was to AAA for a five mile lift to the night's motel parking lot. The only time I ever carried a spare connecting rod was the only time I ever threw a rod bearing on a tour! So I tore into the engine within minutes after AAA dropped me there. It didn't take long to find I had a bit bigger problem than just a thrown rod. I started out planning a difficult (but I had done it before?) under the car change without pulling the head. However, I soon discovered that the number one modern grade 8 wrist pin bolt had stripped! There was no getting it apart the hard way underneath the car. So I carefully removed the head (to preserve the head gasket), and removed the piston and rod out the top. In the parking lot, I didn't have anything like a Dremmel tool and small cutoff disc or drill press to cut the stripped wrist pin bolt out of the way. So it took more than an hour to finesse the stripped bolt out of the rod. Fortunately, my spare rod had one of my last Ford wrist pin bolts, so once I had it apart, it didn't take long to get the car put back together. I was concerned about the grade 8 bolt having stripped, but hopeful that I was good to go for the next morning.
The next morning began okay, but wasn't long before I knew I still had a quiet knock. And like the day before, it was slowly getting worse. We were technically DNF due to not completing the first day, so we looked ahead at the map, and chose a couple places to take short cuts, and reduced our speeds. We crossed the finish line as an incomplete, but early enough to watch others as they finished.
I considered the Run a great success! One of the best I ever ran on, and I made it back under my own power in spite of a major breakdown. I parked the car in a friend's driveway for a few days until I retrieved it with my trailer.
The following weekend I pulled the head and pan cover from the engine, and pulled all four rods and pistons. Number one was fine, just as I had installed it in the motel parking lot, with the Ford wrist pin bolt doing exactly what it was supposed to do. One of the other three grade 8 bolts had stripped just as number one had, apparently the second day's knock. Another had stripped partially, and was also difficult to remove from the connecting rod. Of the four modern grade 8 bolts? Only one survived the first three hundred miles of driving.
I scrounged the couple more Ford wrist pin bolts I needed and never had any trouble from that engine again, driving for a couple thousand miles before selling the car to buy our first real home.

Whether the grade 8 bolts were defective or not? Or is the better tensile strength of grade 8s leaving them weak in the material strength necessary to prevent stripping of the threads? I will likely never know for sure.
But I still tend to not trust grade 8 bolts.

[Art M]

Wayne,
The grade 8 bolts that you talk about might not have the right alloys or not have been properly hardened and tempered. Years ago many bolts from a hardware store were lacking the correct metallurgy.

Art Mirtes

[TXGOAT2]

Grade 8 bolts have their uses, but they are not suited for some applications, such as head bolts, rod bolts, motor mount bolts, main bearing cap bolts, and some others. Another possibility is that the thread profiles and clearances may be slightly different than the Ford rods.

[Wayne Sheldon]

Art M, Yes, that was one of my thoughts about the bolts.

Pat McN, Also part of my point. Way too many people, I have heard comments a hundred times (probably not an exaggeration) telling me that many people almost worship the grade 8 bolt's superiority for all uses.

The fact is that Ford's metallurgy in its day was second to none. And today with such poor quality control in nearly all aspects of our world, original Ford bolts for most uses on a model T are about as good as one can get and use (provided of course they have not suffered some significant damage).

Strength comes in many forms. Hardness and tensile strength are two entirely different things, and require different metallurgies. Tempering, both planned and unplanned, also makes a critical difference in the types of strength.
My experience more than anything illustrates that the wrist pin bolts are under much greater stress than most people understand, and not just any bolt should be used there.

Thank you both for your comments.