finally some action!
you could turn the engine over to get piston #1 at TDC and check to see if the rotor in the distributor is pointed at the #1 plug. be sure its on the compression stroke.
how many miles are on your jeep? how much slack was in the chain? and one favor, can you report back if you notice any difference in the way your jeep runs after doing the chain?
how do I know when #1 is at TDC? it sounds like I'd need to re-install the old gears+chain, reinstall the the timing cover and the HB, then point the HB timing mark to "0" on the cover guide, right? in other words: start over?
also, the jeep has 175K on it, the chain itself had about an inch of slack either way on it. I'll report back here how it goes
Oh boy, I see problems in your future...
"How worried should I be about messing up the timing?"
Very worried. If you are off by only one tooth, the engine will not run right.
I'm not worried about it not running right, I'm more worried about breaking things. If I have to open it back up and adjust the timing I will, after all, I'm learning here
"...since the crankshaft and camshaft ends are both keyed, it seems like it should be impossible: in other words, if the gears + chain are on all the way, does this mean the timing is correct?"
Nope. Think about it... True, the gears can go on only one way (because of the key.) But there is nothing to stop you from turning the crankshaft just a bit, and then installing the gears. Another way to explain it: it's the position of the gears relative to each other that is critical. There should be timing marks stamped into the face of the two gears, typically they look like big dots. Usually they point directly at each other, but not always. Were there any instructions that came with the chain & gears set? Good luck.
True, I could manually spin either of the shafts independently and my timing would go right out the window, but if I didn't do this, I should be good right? while torquing any of the bolts the gears+chain were installed, so both shafts always spun together. The cloyes instructions do show that the timing dots should be facing each other, so tonight I'll have to spin the shafts and see where they fall.
Wait a minute... I looked at the website you linked to, showing the Cloyes gear & chain set. According to that page, the crank gear has 3 keyways (for fine-tuning the cam timing.) Which keyway did you use? They are NOT all the same.
Forgot to mention that, I'm using the factory keyway
Wow! That is some SERIOUS stuff you're getting into. I dont think the engine would blow up if you miss by a bit, it just won't run and you'd have to take it apart... Since you're going with new gears, this is a all new game.
I'm not super worried about it actually blowing up (4.0 is a non-interference engine, meaning the pistons shouldn't eat anything if I'm wrong). I just want to make sure this will be a learning experience that doesn't end with my wallet empty...
I would put the old parts back on since they only have one key per gear and start over from TDC. If you mess this up it will be bad. You should have verified it was at TDC before you ever took it apart, if the Chiltons manual didn't tell you to do this first I would throw that thing in garbage. If you really want a quality repair manual you should buy yourself a Factory Service Manual for your year jeep.
yep, nothing mentioning TDC in the chiltons, only that 15 teeth thing and that the dots should face each other.
TDC #1 first. Replace chain and gears second.
live and learn!
I think I'm just going to verify the dots on the gears face each other, button it up, verify TDC #1 with it all together, and go from there. It's not easy working on this thing on city streets...
one of the few non rainy days this month: