My T is making a kind of sound between a knock and a thunk when there is a light on no load on engine under load don't seem to do it as much I found if I retard the timing it seems to get a little Better at first I thought the sound was coming from transmission but not really sure
Try turning by hand, gas and ignition off and listen. Note your lever settings then try premium non-ethanol gas.
Just went thorough this with my 27. Similar symptoms. Turned out that crankshaft pulley was loose on crankshaft. Cranks are often slightly worn. Pulley had been loose long enough that movement had also worn the holes where the pin went through allowing significant movement and a "knock" that telegraphed right through the engine. New pulley from Bob Bergstrom and problem solved. The new pulley was .002 undersize so you can hone it to fit a worn crankshaft. Another common problem is a broken or weak spring in the hand crank allowing it to bump against the crank pulley under certain conditions. Good luck!
I had the same thing with no load on engine. Topping a hill and starting down or steady speed on flat ground. Retard timing helped but still there. I pulled oil pan cover and tightned the adjusted rods and no more knock.
Vern, I think you're implying "octane ping" or detonation is the problem. I don't know what kind of compression ratios the "speedster" heads available can yield, but I'm pretty sure that would never happen in a stock engine. Have you had octane issues with your T ? I'm curious, not nit-picking your post.
Wouldn't matter what head is used, if you advance the timing just a tad to much, the engine will ping-knock.
Even in the Ford manual when trouble shooting knocks.
OK Frank. ?!?
Yes Rich, the 4:1 compression is not indicative of detonation unless there is a hot spot. My suggestion's purpose is to isolate whether it is a 1) mechanical problem with the moving parts or 2) the combustion of gasoline, including the timing.
Vern, thanks for your reply - then, higher octane will eliminate detonation from a "hot spot" (I usually figured that meant enough carbon built up to become incandescent) ?? I don't understand how octane is related to a "knock" caused by a spark timing issue. Again, not being an oaf here, I don't understand and would like to learn.
Sounds like a rod knock.
Use a screwdriver and short out each plug one at a time and isolate which rod is knocking. You can also use a stethoscope or a broomstick to listen while she's idling.
Your crank may be out of round there or your babbit bearing might be worn. Sometimes you may find a certain road speed that the noise goes completely away, and one or two MPH on either side will start it up again.