Hello:
I have a 1989 F250 with 7.5 liter engine and 102K miles. Just recently the initial timing slipped from the usual 10 degrees BTDC to 6 degrees (Always measured with the spout disconnected). It was still 10 degrees about 10K miles ago. Could this be timing chain wear, and should I replace it? Love my F250. Thanks.

 

I doubt the timing chain slipped a tooth on the gear. If slipping a tooth changes the timing 4 degrees, then that would mean the gear has 90 teeth on it. It could be timing chain stretch but I doubt it would stretch 4 degrees in 10K miles. Just re-time it and you're probably OK. Your chain is probably stretched somewhat and when you last timed it that same stretch was already there. You can check the play in your timing chain and gears by putting tension on it in one direction and then turning it back the other until you see the distributor move. First set the camshaft pulley mark at zero and then see how many degrees it moves. My old 72 F100 has a couple degrees of slop in it and it still runs fine.

 

Man, If you look in my gallery at the timing chain pics, My timing chain was a little loose, but it wasn't the chain causing all my problems, it was the woodruff key on the crank that was wore almost in half! changed my timing by 40deg. at times, and other times it ran just great!
just a thought to consider, but it is relatively easy to change the timing chain. it took my about 4 hrs start to finish, and my truck has a/c p/s anf all the other accessories. cost about $80.00 all told, too!.
packrat


edit: I really shouldn't type and eat dinner at the same time! Sorry for the spelling errors

 

Thanks gman and packratF350. I think I'll just retime and keep an eye on it.