STRANGE ENGINE NOISE

[Bill Robinson]

I’ll try to make this description short. The engine goes in a ’27 Tudor. Numbers match.
• The engine was rebuilt 11 years ago.
• Scat crank was installed, as well as a .280 cam, bored, new pistons, Z head, etc. nothing was spared. Transmission and rear-end were also totally rebuilt at that same time. After quite a few tours and lots of local driving- no breakdowns.
• It runs great and pulls hills better that any of my 4 other Model T’s.
NOW the PROBLEM-> The engine has a noise. Not a knock (not a hollow sound), but more of a rattle. When? When accelerating at speed in excess of 25mph or going up a hill.
• Over the years, 2 well known Model T mechanics have disassembled/reassembled and both had the same opinion “it’s not a knock- it’s detonation”.
• Recently, my friend John Z and I have checked shim clearances, end play on the crankshaft, camshaft, and generator. No endplay. I just installed a rebuilt generator. The noise is still there.
• A few days ago, John and I took the car for a ride after the above adjustments were made and the same noise is still there.
• John was driving and listening, and after a few miles on the way home, he came to a stop sign with a mild/slight grade at take-off. He took off and held the trans in low to approximately 25-27mph, which is unusual for him. Then we both looked at each other rather strangely, and we both grinned and said, “NO NOISE on this hill!”. After another 2 similar tests, there is no noise if running in low, but shift to high, it returns.
At this point we both came to the conclusion that the noise may be coming from the transmission and NOT the engine.
Have any of you experienced this problem? If so, how did you correct the problem?

[TXGOAT2]

I'd investigate the possibility of detonation. It could be caused by a plug firing out of time, perhaps due to a frayed timer wire, a hot running valve, an intake leak, or a head gasket issue, among other things. A thin spot in the head casting might lead to a steam pocket and a hot spot. Does the sound occur when the engine is cool, or just when it is fully warmed up? Does richening the mixture make any difference? Have you tried using 93 octane gas? A spark plug running hot could cause detonation. Is there any chance a plug could be touching the piston? If it's a mechanical sound, running 10W oil and pulling one plug wire at a time with the engine hot might reveal the source. A loose wrist pin or piston slap could cause a knock. A misaligned rod might or tapered crankpin might, also. Timing gear problem? Crack in frame, loose rivets, loose motor mounts.... ? Could the Scat crank be touching something under certain conditions?

[Erik Johnson]

Years ago, my dad's '17 touring suddenly developed a strange engine rattle.

It turned out that one of the transmission bands was extremely loose - for whatever reason the nut had backed its way off almost to the point where it was close to falling off completely. I can't remember exactly which band but I'm thinking it was the reverse because I don't recall shifting or braking was an issue when the noise suddenly developed (if the low or brake band were loose, I would have noticed it right away via operating the pedals while driving).

[TRDxB2]

Just wondering....
If you didn't get noise in Low gear at 20mph but get it in Hi at 20mph what's different?
Low gear tightens the band & high gear locks the clutch, could it be a slipping clutch needing adjustment?
Do you get the noise in reverse too?

[bobt]

Bill. I have the EXACT same problem in my 26 Roadster. I call It "CLATTER" I don't like it but I'm just driving. bobt

[Bill Robinson]

Thanks for the replies. Most of the replies are great possibilities that have already been explored and checked out. Example- An engine miss- this was one of the first possibilities checked out. While driving, idling, hills, flat roads or any other conditions, there is never a miss or power surge that will indicate a missing cylinder or spark plug or slipping clutch. The car runs well at all times. I live in the edge of the Appalachian mtns, just a few miles from Tennessee, and at no time does the car have a problem pulling hills or loss of power. Missing cylinders or power surges due to slipping bands or clutch plates are not the problem.
Here is a possibility that John and I discussed. See the photo of the 2 gears, which for all practical purposes are new, due to the rebuild. Note that the dimple in the brass timing gear and the alignment mark on the Scat crank are aligned, as they should be. Have any of you ever run into the situation where one of the spots got “mismarked” during factory production which could put “perfect timing” “one notch away from perfect timing”? A single notch could possibly effect TDC to the point of a "misfire", but not one that a human can feel. Has anyone ever had that situation? Not me, that I know of anyway.
I’m fortunate in that I have access to an exact replica ’27 Tudor (but the replica has a stock crankshaft) that runs very well and with me being a parts swapper, if a defective part is suspected, such as a timer, I simply borrow a known good part from the other car. Timers have been swapped, BTW.

[Poppie]

My suggestion FWIW, .... Try switching back to Battery as most trembler coils are now adjusted with the new type of testers for ease instead of using the era tester, "The HCCT", The HCCT uses alternating voltage which varies the current draw and timing of the coil to keep the coil set (4) on the same foot for different engine speed, frequency and current draw. Coils set up with D/C rectified or (battery) current could be out of step while running on Fords preference of electrical power, "The Magneto", The engine (Combustion) may not know which foot its on. Switch to Battery for a full days test. Keep safe....n

[Ruxstel24]

Just throwing this out there.
Could the noise be coming out of the rear axle and transferring up to the transmission ?

[speedytinc]

My 27 RPU has point of harmonic vibration that seems to add enough vibration to create a rattle.
My noise seems to come from the gas tank. Like a loose baffle or tank mount.
The tank rattle seems more noticeable with a lower fuel level.

[Jerry VanOoteghem]

Drive it with the floorboards removed. Keep an eye on the clutch bell crank, (or, have someone else look, so you don't run into anything). When the noise begins, look for side-to-side movement of the bell crank shaft. As the bronze throw-out bearing wears, it can allow a lot of side-to-side play and make a pretty good rattle. When you're in low gear, the throw-out is loaded up with the force needed to compress the clutch spring so, no noise then.

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[Mike Silbert]

Bill,

It is possible that any part new or original could or can be made incorrectly.
Sometimes the reason an NOS part still around today is because it was made defective originally.
I operate on the thought of trust nothing, verify everything.
Parts are only right after they are proven right.

If you think the timing gears are marked or made wrong then do a check called "degree the cam"
It takes some effort and is a lot harder on a complete assembly than doing it during the rebuild.
If the camshaft timing is off it will effect performance which you said was good.
I am not thinking this is not likely the issue but check it to eliminate it off the list.

You describe the noise as "Not a knock (not a hollow sound), but more of a rattle."
My gut is telling me from reading your posts it likely is not coming from deep inside the engine and it is related to RPM and maybe load on the engine.
As the engine goes through the speed range it has continuously changing harmonics and there may be a specific RPM range that sets off a vibration.
Rattles can come from many internal and external places like crank belt pulley, fan, body parts, mounts, loose fasteners and a lot more.
If it were my problem I would "strip" the car of loose easily removed parts like hood, fan belt, anything else that is quick and easy to make a rattle.
Then go for a test drive and see if the noise is still there or changes.
You can also bump things with your hand and see if anything rattles.

To me there is still a question as to whether it is an internal or external noise issue.
If you could find the key RPM noise range then maybe you could narrow things down with a stethoscope in the driveway.
I see lots of tests to get to the bottom of this issue.
I also see lots of good suggestions posted by others.
Mike

[TXGOAT2]

Lightly pressing each pedal in turn when the rattle is occurring may reveal something. Pulling back a little on the hand lever might do the same. The entire exhaust system is always suspect when odd noises crop up. Brake rods and other chassis parts can produce unusual noises due to the range of vibration produced in the T. Tying rubber tarp straps around these items one at a time might be revealing. Fan hub, crank pulley, coil box, engine splash pans, even throttle or spark linkage can be the culprits.

[TXGOAT2]

When trying to pin down elusive sounds or transient malfunctions, it sometimes happens that what you know is right is what's wrong.

[TXGOAT2]

Shutting the car's doors against foam rubber might be revealing.

[Bill Robinson]

As Jerry VanOoteghem suggested, I was able to manually move the bell crank shaft side to side (Langs calls it a clutch lever shaft), by hand .157” or 5/32”. The bell crank shaft movement was by-hand, not while driving as he suggested. Mainly because I’m waiting for some RTV to dry before I drive it. Maybe tomorrow. I’m hoping that his guess is a good prospect.