what's up with my engine?

[kyle_22r]

here's the background:  got off the freeway and stopped at the store today.  went to start the truck up, and it starts making a loud rattle like the timing chain or valves are loose.  tach is also jumping around like crazy.  truck seems like its running fine, just noisy as hell and the problem with the tachometer.  i also notice that the sound abruptly shuts up and sounds like it normally does and the tach stops tweeking out if i rev the engine to a hair under 2500RPMs and beyond.

i figured it was the coil, so i replaced that and the problem's still there.  took a look at the cap and rotor, the cap had 2 pickups that were pretty badly chewed out?  replaced that, still no improvement.  the engine only has 2000 miles since i built it.  somebody on the pbb thinks the timing chain could've jumped -- but if it did why would my tach be acting like it's got a bad coil?  i wouldn't think valve timing would affect the ignition like that.

any help?  i'm 100% stumped on this one.  could a signal coil in the distributor be the cause of my woes?  igniter?

[BigMike]

My buddy changed his timing guides and tensioner on his '83 22R and when he put everything back together he couldn't get it running.
I came over to see if I could help out, and we found out that he was off by one tooth retarded. It would only start if you had WOT and the second you let up it would die. Then we reset his timing but I messed up and it was 1 tooth advanced. When we tried to start it, it was backfiring and trying to spark on the compression stroke, +1 advanced.
So my point is that his truck wouldn't run UNLESS the timing chain was nuts on. One tooth off in either direction and it wouldn't even start up.

Only 2000 miles, I hate to mention it, but what about a piston? Did you hone your wrist pin bushings?
Otherwise if its going away at a certain rpm then it sounds like its something is resonating and then becomes harmonic.. But the tac? Was it raining and you got some water or moisture some where? The coil and/or igniter are really about the only electric devices on your whole truck, what could it be?

Stay with me, I'm brainstorming here..

Maybe the tac isn't even related and its just a 2nd problem that happened to occur at the same time? What about your clutch? Is it pretty old? Well I guess if the disk because loose it would get worse at higher rpms so can't be that..

Pull out each spark plug and check how each cylinder is burning.
You know what it could be, a low impedance issue with the igniter. Maybe one of your spark plugs lost its electrode so there is an extreme amount of resistance in your ignition system and its not able to develop enough spark until it gets the rpms up to develop enough energy to push the spark past the huge gap of a bad spark plug. Then the spark could be jumping over to the cylinder head or causing some other sporadic issues with a lot of charge and no where to go..

Hopefully you've got a dead cylinder at lower rpms because of a bad ignition system. Then once it gets moving it is developing enough energy to cover up the issue.

[kyle_22r]

i really wish i had more daylight today.  this whole thing is like a monkey on my back and i'm gonna lose sleep on it, and not going to be able to think at work tomorrow. 

i'll pull the plugs tomorrow and see how they're looking.  the thing that really boggles my mind is that the engine seems to be running fine, it's just making an awful racket at lower RPMs and the tach is acting strange.   i've wanted to check the plugs lately as i probably ran the engine out super lean a few times when the old fuel pump was going out(had it cut out on me with my foot to the floor)

but then again, even a messed up spark plug wouldn't cause the tach to go crazy would it?  it's all over the place until i hit that magic spot  a bit above 2000 then the tach smooths out, and the engine shuts quiets down.

[Duffil]

did you replace the distributor when you built her?  pull the cap and check to see if the shaft moves...you said 2 nodes on the cap were toast?  maybe bad bushing in it????but i doubt it...let u know if i have any other ideas

[oddball]

My samurai did that after I replaced the timing belt, so naturaly I thought I fawked up on the belt or valve adjustment. Everything was cool except for the bottom of the dist. housing was all gouged out and there was a ton of metal shavings. There was also quite a bit of play in the shaft ( up and down) I cleaned the shavings out and the tach stopped jumping around but the idle got rough and it died constantly in the lower RPMS. Like yours it ran fine above 2000 or so. It was rattling and making a wierd humming vibration. The new owner replaced the dist and said it is fine now. Try changing the dist. if nothing else works

[kyle_22r]

well, i've got some good news and some bad news.  i swapped distributors and the problem didn't go away, so i pulled the valve cover.

the good news - i figured out what the problem is.

the bad news - while turning the engine over by hand, i noticed something rather strange.  my timing sprocket was walking back and forth, and the distributor drive gear had some serious slack, like it wasn't fastened to it!  i pulled the cam bolt, tapped off the distributor gear and 2 pieces of the dowel pin fell out(into my timing cover of course )  there's still a piece in the camshaft but its countersunk and i have no idea how to get it out.  looks like i might be screwed as far as this top end goes -- it's probably not coming out unless i pull the head and do the head gasket.

on the bright side, it's probably a good thing that i stopped driving it, since any more and the cam gear probably would've spun on the camshaft, and the valves would've hit my pistons -- destroying the rest of the engine.

i'm back at the crossroads again -- replace the top end on my nearly new engine(i wasn't wild about my cylinder head in the first place) or swap in something better...

[Duffil]

you could try a propane (NOT acetylene) torch and an EZ out...maybe force in and loctite a small bolt and(with a rag in your timing cover!!)  try to pop 'er out...have fun!!   Lotsa luck!!

[oddball]

Well like you said at least you caught it before major engine destruction, good luck

[kyle_22r]

i think i'm just gonna yank the head tomorrow, to avoid any "what ifs" involved with just popping the nuts off the head studs and pulling the rocker assembly.  toyota sure made the camshaft a pain in the butt to get to didn't they?