Hello Model T Friends!!!
I was doing some thinking about a problem Model T engine I’m working on. It has a knock that has been narrowed down to No. 2 cylinder. The piston, near the top of the bore, appears to be tight in the cylinder. My first thought was a bent rod. It may be bent (it has yet to be removed) but could it also be a problem with how the engine was bored? If the shop that bored the engine sat the block on a level bed that was perpendicular to the boring bar it should be fine. However, if the shop used a “portable” boring bar that attached to the cylinder head, is there a possibility of it not being perpendicular with the crank? Actually, the loudest noise I heard came from No. 2 cylinder but I’d say the others were talking a little too. At first I thought it was the fact there was so much sideways clearance at the large end of the rods on the crank (they varied from 0.020” to 0.060”) but now I’m thinking about the bore not being perpendicular. I had an engine that was “decked” by a shop one time. The deck of the block and the centerline of the crank were off by about 0.030” from the front to the back end. Any thoughts on this problem?
You are correct about "portable" boring bars. They work just fine if the deck is parallel with the pan surface. But if the block HAS been decked, it depends on how that was done. The Storm Vulcan mill I used to use when I worked at P-M auto parts in Dallas could easily true a block deck and ensure it was parallel with the pan surface because we set the block up ON the pan surface for milling. The owners brother also had a parts business and offered machine shop services but they used a grinding wheel set in the middle of a table where you would slide the block or head or whatever across that wheel to try to skim it. There was no way to ensure the end result would be parallel to the pan surface. If the deck surface were parallel to begin with then the quality of that job became very much operator dependent.
As for your specific question, if the bore of your engine is not 90 degrees to the crank centerline I would expect you would see some scoring in the cylinder/s due to the piston running a little cocked. Question: how did you narrow it down to #2? If you pulled the spark plug wire and the knocking stopped then you most likely have a rod big end with too much clearance. That could have resulted from a bore not perpendicular to the crank centerline since the load on the rod is not centered.
All just speculation until you take it apart and inspect everything. Still, not wasted thought as you'll have those things to check out.
I have not pulled the rod/piston yet. When the engine was turned over, the piston got tight at the top. I'm assuming either the rod is bent or bore is not perpendicular to the crank. The rod has a lot of sideways clearance but I think it perhaps was still not enough for the out of alignment problem it has. A screwdriver was used to listen and find the knock while the car was running. I think the others might be talking to but this one was louder.