I just had the engine for my 84 F250 rebuilt. Engine builder has me using break in oil and running for 20 min. My question revolves around the timing since everything has been apart. I can get close to TDC without starting the vehicle, but my concern is the timing not being correct during the break in and screwing something up. Am I over thinking this or will being close to TDC work for this 20 min cycle? This is my first time doing this and I want to make sure I don't screw it up. The distributor is just sitting in there. It's has not been adjusted yet.




Thanks!

 

No harm in running the engine at 0 degrees +/- during the break in. While it is running you could tweak it to what ever is suggested as the base timing for your new engine. Just be careful to not get your finger or hands around the fan blades.

 

What you actually want to do is run it at about 25° or 30° BTDC for your 20 minute camshaft break-in run. There is no danger of "ping" or engine knock, as there is absolutely no load on the engine in neutral. When you hit 2000 RPM or so, rotate the distributor till it reads 25° BTDC or so on your timing light.

(Of course, you have previously verified, before even thinking about starting the engine, that the crankshaft balancer weight hasn't slipped, and TDC indicated at the crankshaft balancer "0" mark & pointer coincides exactly with the #1 piston at true TDC on the compression stroke. Nod your head "yes"...)

What an advanced ignition timing does, is allow the engine to run much cooler than a more retarded ignition timing does. And a freshly rebuilt engine already tends to run a bit on the hot side. When you hear people talking about glowing red hot exhaust manifolds and things like that, it's because of a slow or "late" ignition timing setting. The fuel is still burning, and the excess is burning in the manifolds and exhaust, instead of the combustion chamber where it belongs. Hard on valves too.

It's important that the engine starts right away. That means have everything ready to go. Battery fully charged, carburetor bowl primed with fuel. Ignition timing verified and set. Can start it up at say 8° or 10° bring it to 2000, then advance the distributor to a healthy lead timing for the duration. A lot of guys will run straight H20 in the radiator and keep a hose running, with no glycol engine coolant, on account of any possible small leaks that need addressing. Less messy that way.