This is a follow-up over a thread a posted a few weeks ago. Here's how it went:
My '24 Touring has always had a disconcerting knock ever since I bought it. I believe that it's from excessive camshaft endplay, but I would like to see what you all think. Of course, it's very difficult to describe an engine knock, but I'll do my best.
The sound is loudest when its cold, and its more like a loud tapping/clacking sound.
It is very inconsistent as the engine is idling.
Lowering the throttle seems to help at idle. The knock also gets quieter when I'm driving it.
The noise disappears at 15-30 mph, and accelerating or decelerating doesn't cause it to reappear.
Shorting out any one of the spark plugs does not change it.
Now for things that I've replaced. The crank pulley is nice and tight on the crankshaft. I installed new bushings in the fan pulley, and that eliminated a separate knock that I was having. The generator gear is also good and tight on the generator shaft.
--Now for the update--
Today, I dropped the inspection cover and ruled out some possible sources of knocks. The rods had no detectable amounts of play radially. They were nice and tight. Unfortunately, I didn't have enough time to actually measure the clearances.
The camshaft has absolutely no noticeable amounts of play in any direction. That eliminates the possibility of a knock from the camshaft. The crankshaft also had almost no endplay.
I also checked the generator gear and the crank pin pulley. Both were nice and tight. No sources of knocks there.
This knock has me stumped! Could it be piston slap? I have the original iron pistons, and I've never measured the cylinders for wear. Any other ideas?
Probably cylinder wear resulting in piston slap. Bore the block and install a new set of aluminum pistons. The car will be more powerful, more responsive, and smoother.
From what you describe about your knock, it sounds similar to mine. I did all the same checks you did and mine seems ok. I believe my knock is piston slap. I also have iron pistons and have not taken cylinder measurments.
Here is a test for piston slap.
"First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder. Reinstall the plugs, fire the engine up again and listen.
If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back like a Marine Corps marching band coming toward you in the parade."
I have seen worn cam gears make a noise like that. I mistook it for a wrist pin noise. The gear teeth were worn thin on two areas, right across for one another.
Maybe centre main bearing?
Did you try the steel bar trick??
Just take a steel bar about 30cm long and 10mm tick. While the engine is running, put one end against several points of the engine and the other end against your ear. You will hear the noise. Where the noise is the best to hear there you should look for it.
Thought about something!!
Did the connecting rods have been changed recently.
The bolts on the camshaft side should be grind off on the outside. They can knock against the camshaft while running. You can best hear this while you put the steel bar just under the valve inspection cover on the engine.
If you're like me, you're a T owner on a budget. Also, like me, you have only one which you enjoy driving, also like me.
Anyway, before you pull the engine, take it apart and spend lots of dough on a "possible" problem, do everything you can to find out what's going on.
It could be piston slap, so try the test mentioned above. In my mind, it's always best to find out the source before you tear into the engine. If you can't, you may have to pull the engine.
I hope you find the source of the noise. Mine turned out to be a broken piece of rod babbitt that had been pounded flat by the crankshaft. But that noise had different symptoms than yours. I ended up just replacing the rod.
Thanks for that tip! I had no idea as to how to check for piston slap. I'll certainly try that.
I've also heard that a loose timing gear can cause a knock. Does anyone know what that sounds like? Unfortunately, I'm about 2 1/2 hours away from my T, so I can only theorize at this point.
It is most likely piston slap. If so it diminishes after the engine warms up. It is most noticeable when cold and running at low speed with the spark advanced. When you retard the spark it will either disappear or almost disappear, but you will also lose power. It might also be noticeable when pulling a steep hill at low speed. There too it will diminish with spark retard. Just run the engine with the spark as advanced as you can without a severe knock and keep on driving it. It is not likely to cause any severe damage to the engine. Then at some future time when you need to do more extensive work on the engine, you can re-bore and replace the pistons when you have the engine out.
Cam or generator gears with wear makes weird noises.
Is it louder when it's cold ?
It could be one or more slightly twisted connecting rods. They have an action that causes them to move forward & backward on their crankshaft journals each time the crank turns. They can be doing this for quite a very long time inside your engine until enough of the babbitt "thrust" on the rod is worn away that there is enough movement that they can be heard. This is one of the defects that I have frequently seen in the connecting rods that have been available from all the major vendors over the last several years that prompted me to start making my own rods (for my own use - I don't sell them). If you buy new, rebabbitted connecting rods, you have make sure they are straight before you use them. Over the last five years or so, about 50%-70% of them that I have checked do need to be straightened before use. Unfortunately, this is something many "engine rebuilding shops" can't do for you, because the fixture that most all of them have can only check rods with a bearing diameter of 1+1/2" inches or larger and the T rods are too small to get on their fixture.
If this noise in your engine is being caused by slightly twisted connecting rods, all you have to do to make the noise go away is take them out and send them with their caps, etc all attached to someone who has the fixture for straightening them. If the rods have issues with worn or poorly bonded babbit, or excessively worn "thrusts" then I would suggest they be replaced, but that you have the replacements checked for straightness before you install them (no matter how good the vendor or manufacturer claims them to be).
FYI... "Piston slap" when it first gets to the point that it becomes noticeable, generally is only present when the engine is up to operating temperature. (And that can be 30 miles on a 70 degree day). When piston slap becomes so excessive that it can be heard hot and cold, it is much louder with a hot engine.
One big possibility is a WRIST PIN that is too tight. I never get a new set of pistons from my supplier that doesn.t have at least one piston and often more that needs the WRIST PIN HOLE HONED!!!!If your wrist pins have not been honed it is only a matter of when not if you will crack the piston. The old theory that you install the rod in the piston, hold it horizontal and see if it will drop is hog wash, That is NOT enough clearance. You must be able to install your wrist pin in the piston, slap the piston in you cupped hand and see if the piston pin comes out. If the wrist pin will not move you are in deep trouble.
One of the fixtures that Adam Doleshal is talking about is as follows
One of the fixtures that Adam Doleshal is talking about is as follows. It checks not only twist but bend.
I thought about a twisted rod. If I find that my knock is not a result of piston slap, then I'll send the rods off to get straightened. I'm just a poor college student, so I hope that I don't have to get them rebabbitted.
Cameron, You might be able to visually see that one or more rods seem to have a lot of front to rear play on the crank shaft and if you look real close, you might be able to see that the babbitt "thrust surface" on those rods appears a little beat up, or maybe even is starting to crumble. If the noise only recently started, you might not see any evidence on the babbitt "thrust" which is a very good thing and is the result of immediately investigating a noise before it actually causes damage...
I have a rod alignment fixture like shown above with a set of mandrels for different size bearings that is for sale. A friends husband passed away and that is why it's for sale. Not sure what to ask for it....very heavy. Will take it to the Big 3 & Bakersfield swap meets. With the box of mandrels it's heavy. What would be a fare asking price? Anyone interested can contact be off line....don't really want to try and ship it.
I know that my rods have quite a bit of side play; at least 0.030". Certainly something to investigate.
I suspect you would like to eliminate the easy to fix (read less expensive things) first. The easiest way to gain good access to the timing gears for inspection purposes is to simply remove the generator AND THEN the generator bracket. I suggest doing it as two steps as it will make it a lot easier to reassemble and reduces the chance of damaging something.
Once the bracket is off you can;
1. Examine the cam gear all the way around.
2. Check gear backlash all the way around if you find any teeth that are worn.
3. Get a good check on the cam end play. It does not take much end play to get erratic noises. You can buy a "repair kit" that can correct excessive cam end play from the usual suppliers
4. With the spark plugs out get a helper to crank the engine fast (probably with the starter) while you watch and listen by the cam gears.
5. With a bright light you should also be able to get a bit of a look at the crank gear as well.
6. Check if the cam gear is loose on the camshaft.
You will either find your problem OR you will know that it is probably elsewhere. Either way it is progress.
I will also suggest ONE MORE TIME that I have encountered MANY loose centre bearings over the last 40 years in Model T's. Often on engines that have needed rod adjustments, the centre main also can use attention. Consider that the centre main is not much bigger than a rod bearing BUT it has two rods working on it.
It is suggested that you may have bent rods. A way to verify this possibility while they are in the car is as follows;
Remove the inspection cover. Using a bright light, have someone slowly crank the engine while you concentrate on the end gap of the connecting rod big ends. If the rods are sliding fore and aft as the crank is rotated then you may have found your problem. If they sort of just sit in one position axially then you probably don't have this problem.
Yes it is possible. But consider that it is not going to get significantly worse anytime soon. It can wait until you graduate and you can drive the car in the mean time.
A good inspection will not cost you much other than some time and maybe a couple of gaskets
I am assuming you would like to get a few more years of fun and driving from this car before you throw a whole bunch of money at it you don't have right now as a student!!!
A problem with adjusting the center main bearing is that often the wear is caused by sag in the 4th main at the rear of the transmission. When this is the cause, the wear will be mostly on the block rather than on the cap. So, try to pry upward on the crankshaft at the two adjacent rods. See if it moves upward at the main bearing. If it does, you have a problem that will take more to fix than adjusting the cap. In fact adjustment could cause the crankshaft to break. Best check of the second main would be to pull the engine and remove the transmission, then turn the engine bottom up and use prussian blue to check the contact pattern between the crankshaft and the main bearings in the block. It should wipe off the prussian blue on all three. If it does wipe #1 and #3, but not #2, you will need to repour the bearings and line bore the block. Anyway, enough said. I only adjust the mains when I have the engine out for some other reason.
Les is right on. Piston slap, although annoying, can go on for some time. Guess what, I have been told that all new GM engines have some degree of piston slap! Go figure!
Just keep at it before you resort to total tear down!
Thank you very much for your reply! I completely forgot to say that two years ago, I did a basic teardown and replaced the most essential parts, as well as tightened all the main and rod bearings. The cam gears also seemed fine, but I'll certainly take another look at them. I've driven it maybe 200 miles since then.
I'm still hoping that it's piston slap!
I usually pull the engine and remove the transmission to adjust bearings. That is just me, I hate oil dripping in my face and find I can remove the engine in about a hour and put it back in about 1 1/2 hours.
Anyway, if you have access to a dial indicator, it is easy to see if the centre main is worn on the top. Set up the dial indicator and then pry up on the crankshaft by the centre main. if you get more than about .001" of indicator movement (but be sure it comes back to zero before you panic, if not try the test again).
I have only encountered ONE engine where the wear was on the top of the centre main.
So yes, you want to verify that it is not worn in the block. I just have encountered way more instances of wear in the cap. And centre main wear causes kind of a erratic knock, really only noticeable at some throttle settings, and it disappears at others.
So Cameron, I hope it is piston slap too!! then you can drive for a bit longer. Just keep your ear tuned if the noise changes!! Maybe try a different weight of oil. It might help to fill the gaps!!
For years I thought my '19 had piston slap. Then one day, it suddenly got a lot louder!
I started tearing it down. At one point I moved the radiator aside and heard a "cling! cling!"
I found the top baffle was dangling loose in the radiator causing a terrible noise - much like the sound of piston slap - with which I am totally familiar!
I checked everything else and couldn't find another thing wrong, so I had the radiator repaired, and now I am piston slap free!
Incidentally, the engine had been rebuilt a year before, bored and new aluminum pistons fitted.
Give your radiator a healthy shake, Cameron!
Along with what Bob Robb has said, sometimes something other than the engine can make a vibration which sounds like a knock. I have one on a 26 Touring. The choke rod which comes through the firewall and dash panel rattles. If someone holds onto it, the knock suddenly stops. So you could have a loose hood, radiator baffle, choke rod, or something else vibrating which sounds like a knock.