my 25 open express has a knock that comes and goes. can improperly adjusted spark advance cause this? i use regular gas with a lead additive, is that ok ?
The octane of today's fuels almost makes spark knock impossible in a stock model T, no matter where you have the advance lever. And a lead additive is not necessary given the low valve spring pressure used in a T.
Please elaborate on the specifics of how the knock comes and goes.
Some knocks come when you slack off the gas and just go along at an even speed. Usually a rod knock. The knock which comes when the engine is pulling hard is usually either a main bearing or a loose piston. A constant double knock is quite often a loose wrist pin. A knock which usually happens at idle can be a loose pulley or the pin through the front crankshaft pulley. Some knocks are caused by the cam bearing or loose valves.
Some knocks are noticeable in a cold engine and go away as the engine warms up.
So you need to describe the knock a little better to be able to pinpoint it.
In addition to what Norman mentioned; if you are running a re-ground cam shaft you could have excessive end-play causing the front lobe of the cam to hit the notch in the front cam-bearing now and again This is a relatively easy fix by installing a kit designed for the purpose. The major vendors carry it. Just some thoughts.
I just shimmed my crank pulley. It was making a knocking sound.
thanks so much. i will provide more info as i monitor it closer.