Oh No...this could be bad. HELP please!

[Ironmike]

Well, it's always something. Took a nice long ride the other day and 1 mile from home my '71 340 began running real bad. Didn't have time to look at it so in the garage and off to work.
Decided to check it out today and found something really bad. Coughing, backfiring thru the carb, the pipes....a real mess. Idled ok though.
Get the thing to TDC(dead on) and find the rotor pointing to about the #6 position on the cap. What the #$%^%.
Off came the drivers side valve cover and #1 valves are right where they should be, both closed. Looks like #7 intake is just beginning to open(or close).
So I figure 1 of 2 things happened, either the timing chain jumped a tooth or 2..or my distrib jumped a tooth or 2. Haven't pulled the distrib yet, what's my next move?

 

[rumblefish360]

Timing chain. It is unlikely the distributor jumped. It is very likely the chain jumped. A replacement chain is easy and will take a Saturday to do. Easy enuff!
While your at it, look at your plugs, they may need a changing now.

 

[moparker]

I think you're on the right track. I guess you will have to just start searching. Sorry.

 

[Ironmike]

Thanks. I'm thinkin' chain, too. Never heard of a distrib jumping before. But....can't I be absolutely certain it's the chain by what the valves are doing on the other cylinders, while at TDC?

 

[alsdemon]

compresstion test will show something i think or cam lubes or going away. vac. readings. als

 

[w2360Duster]

Well, it's always something. Took a nice long ride the other day and 1 mile from home my '71 340 began running real bad. Didn't have time to look at it so in the garage and off to work.
Decided to check it out today and found something really bad. Coughing, backfiring thru the carb, the pipes....a real mess. Idled ok though.
Get the thing to TDC(dead on) and find the rotor pointing to about the #6 position on the cap. What the #$%^%.
Off came the drivers side valve cover and #1 valves are right where they should be, both closed. Looks like #7 intake is just beginning to open(or close).
So I figure 1 of 2 things happened, either the timing chain jumped a tooth or 2..or my distrib jumped a tooth or 2. Haven't pulled the distrib yet, what's my next move?

FYI #1 and #6 are piston pairs and would be on either with the crank at TDC,With a hydraulic cam i wouldn't be 100% positive that its on compression stroke(even though it looks like the valves might be closed) unless you take the #1 plug out and see if it blows coming up to #1 cyl. Very doubtful it jumped timing.

If it has points id start there (check if their burnt or closed up), check for fouled plugs? it is possible it could of wiped a cam lobe but i think it wouldnt happen so quickly. my 2 cents worth

 

[Ironmike]

#1 and #6 pairs makes sense, but before I did anything I threw a timing light on it and it was OVER 50 degrees BTDC. I cranked my light all the way to 50 and the mark just came into view. Man! I couldn't believe the thing was idling. I CAN see the piston, but honestly don't know if it came up on the compression stroke or not. If your damper shows TDC and the piston is at the top of it's stroke, it's gotta be the compression stroke, right?
No points. Accel 52 series distrib with an Accel box and coil.

 

[demon seed]

Pull the fuel pump and with your finger reach in and around the inner corner for the timing chain. First crank the engine over by hand a little bit this will put the slack side of the chain towards the hole you're about to put your finger into. Now how loose is the chain 1/4" 1/2" 3/4".

Terry

 

[fishy68]

If your damper shows TDC and the piston is at the top of it's stroke, it's gotta be the compression stroke, right?

No because there is 2 top dead centers for each cycle. There's TDC compression stroke and TDC exhaust stroke. In both cases the piston will be at the top and the mark on zero. When #1 is on TDC compression stroke #6 is on TDC exhaust stroke and vice versa.

When you checked the timing did you have the vacuum advance unplugged? I have also seen the mechanical weights stick in distributors causing them to get stuck in the fully advanced position.

 

[Cudafever]

This is how i check for a loose time chain.......before i pull the timing cover.
Turn you eng over in a clock wise direction until you hit TDC(does not matter if it compression stroke or exh stroke for this exercise) when you get to TDC, remove your distributor cap. Now while looking at the rotor, TURN the crank in the opposite direction,(Counter Clock wise) until the rotor turns..................How many degrees did the crank turn? 10, 20 30....More


If its 16 or more degrees, it has jumped or is about to jump and is in need of replacement

I'm with rumblefish on this one, and this simple test will prove it, one way or the other.

 

[green1]

This is how i check for a loose time chain.......before i pull the timing cover.
Turn you eng over in a clock wise direction until you hit TDC(does not matter if it compression stroke or exh stroke for this exercise) when you get to TDC, remove your distributor cap. Now while looking at the rotor, TURN the crank in the opposite direction,(Counter Clock wise) until the rotor turns..................How many degrees did the crank turn? 10, 20 30....More


If its 16 or more degrees, it has jumped or is about to jump and is in need of replacement

I'm with rumblefish on this one, and this simple test will prove it, one way or the other.

I agree; and why compare #1 and # 7??

 

[340_833 dart]

How many miles are on the timing chain and gears?
If you replace the chain and gears make sure to install the MP timing chain tensioner.
For $35 you won't go wrong.

 

[Ironmike]

Not really comparing #1 and #7. Just wanted to know what #7 SHOULD be doin' at TDC cause 7 is the only cyl on that bank with valves in motion. Plan to dig into it tomorrow and get to the bottom of it.
I really love the car and the performance but so far ain't real fond of some of Mopar's quirky engineering. Think it might cost too much to drop a small block Chev in there, so I gotta just deal with it and learn the in's and out's.

 

[moparker]

Not really comparing #1 and #7. Just wanted to know what #7 SHOULD be doin' at TDC cause 7 is the only cyl on that bank with valves in motion. Plan to dig into it tomorrow and get to the bottom of it.
I really love the car and the performance but so far ain't real fond of some of Mopar's quirky engineering. Think it might cost too much to drop a small block Chev in there, so I gotta just deal with it and learn the in's and out's.

Don't say the "C" word on here. Don't go to the dark side Luke.

 

[MOPARJ]

Oh, I have seen my share of GM's bite the dust.

Sounds like a chain to me. Have a look at it and replace it with a quality double roller setup with steel gears. Get it timed right once it is installed on the motor.

Mopar technology really isn't too difficult to master; it just takes time. The timing chain is just something that wears over time, especially if it is poor quality, or a link type chain with nylon coated gears. Once it is back up on its feet and tuned right, that 340 will run just as well, if not better than any 350 ever could (stock for stock). Lol, a 350 wouldn't look right in a Mopar anyways.

 

[Ironmike]

I know. It ran really great before this issue. Apples to apples...better than a SBC with the same mods.
Worked late tonite and all week. I plan to have it running again by Saturday evening. I love it when a plan comes together.

 

[340_833 dart]

Question for the group; didn't all 340s come with double chains and steel gears? Every 340 I've opened up had them.
Wouldn't the chain have to be really, really stretched in order to jump some teeth?
Just thinking out loud.

 

[Cudafever]

Question for the group; didn't all 340s come with double chains and steel gears? Every 340 I've opened up had them.
Wouldn't the chain have to be really, really stretched in order to jump some teeth?
Just thinking out loud.

Yes, the only way it would have fiber teeth is if it had been replace with the wrong one.

The chain that jumped on me was a 318 with fiber teeth......at 16* of play"..........it jump a tooth, the vary next day after i tryed the test, i posted aboveops:

 

[fishy68]

IronMike I owned several small block chevy's when I was young cause I didn't have much money and they were always cheap. I have to say I'd take working on a small block Mopar any day. The only drawback I can think of to a sm. Mopar is if your running headers they are a real pain to work around. The few small block mopars I owned when I was young held up better than the chevy's except I did have one real stout 350 that just seemed indestructible. Just my take on them but to each his own.

 

[redfastback]

Did you try to bring the the timing back to about 15-20 BTDC? what happens?