71 LA 340 timings moved!! how?? looking for help

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Shane pearce

Shane pearce

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Hi Guys... bit of a weird one for me at least and live in the UK so help is slim here.. my 71 418 stroker as covered over 1000 miles since full rebuild , but the other day I gave it some gas and it sounded like sh#t (like a quick popping banging from exhaust) so took it easy there after, I also noticed it was sometimes stalling while idling in drive at traffic lights. never done these things before

Anyway I checked the timing the following day to find it at 32 at idle!! I increased the revs and it advances as it should.... surely thats wrong lol!!

Forgive me but this is my first old Mopar, previously had a Charger 5.7 police cruiser and a 94 RT/10 Viper so my question is how has my timing moved?? checked the obvious and the dizzy is tight, doubt its connected but I've just replaced dizzy cap, rotor arm, ignition module and voltage reg after some electrical issues (which turned out to be a loose Amp metre cable causing all sorts of issues)

So its build is vast so will outline below, distributor is electrical and a 3656763 and vaccum advance line is plugged and not in use, I know guy who built it changed springs in dizzy as its very high revving and super quick up and down rev range.

What I'm asking and hoping for is an idiots guide to resolving this issue, where to start, etc the amount of money in the engine I'd be a broken man if it was to go bang!!! I would be so grateful for your help people.

People have asked if I've tried to twist dizzy and set it again, but I don't like that idea until I know wha tthe hell caused it to move in the first place.

71 340 block, now bored 40 over to 4.080,
new Scat 9000 series 4" cast crank,
ARP main bolts,
new Scat H beam forged rods with ARP studs,
Icon (Keith Black) 744 forged flat top pistons with valve reliefs,
Clevite H racing rod bearings,
Clevite full groove main bearings,
Clevite cam bearings, rotating assembly fully balanced (Pistons, rods, crank, balancer, bearings, pins and flex plate)
High volume oil pump,
hardened driveshaft,
Modified Moroso deep pan sump and high flow pickup.
Comp Cams XE274H cam.
Original 71 J heads 2.02 inlet valve, 1.60 exh, fully ported,
new exh valves, re seated,
new comp cams positive lock stem seals,
Mopar performance double valve springs,
tungsten retainers 4 groove,
stock rockers,
ARP head bolts,
Comp Cams 2103 Magnum double roller timing set
Mopar timing chain tensioner
Victor 340 single plane high rise drag inlet,
new Holley 750 vs elec choke, 14"x 4"
K&N air filter,
Mopar Performance Valve covers,
high flow water pump,
160f thermostat.
Carter high flow electric fuel pump with Holley regulator,

 
The places where timing could change would be the distributor housing, vacuum advance can or plate, cam moving back? Crank or cam Keyways broken .If the timing changed without you doing any thing, first check for a loose distributor hold down. If you reset the timing and power is down a lot, then cam timing moved, which would also change spark advance. Check to see if the vacuum advance is working properly.
 
I be looking at a bad/ slipped harmonic balancer

it might be two separate issues /just coincidence
 
How do you know it moved? Are you SURE of what it was ? My 408 runs at about 30 degree advanced. You did not state what you think it should be set at.
 
I think it is 32 degs initial after the onset of the issue. How much slop is in the timing chain? I'm not a fan of the tensioners. Mine had broken the guide on the spring side right at the pivot. The flat spring had slid down to the bottom of the cover.
 
My vote is right in the distributor, or you didn't have it where you thought you did
 
Normal slippage is for the timing to retard, not advance. So that makes me think distributor....

Maybe the wiring from the pickup in the distributor got reversed in the electrical fixes. If it was backwards to start with, then the ignition would trigger on the back edge of the trigger pulse, and you would have to advance the cam to get timing to a normal position. Then if this reversed wiring was corrected, now the ignition is firing off of the front edge of the trigger pulse (which is the correct edge) and the timing is considerably advanced.

The other thing is the damper ring slipping as mentioned; it will slip backwards and make the timing look advanced. But that would not make the car un any differently.

And the vacuum advance rod could be jammed up, keeping things far advanced.
 
I had a similar problem with a Mopar Electronic distributor, the vacuum advance was causing the plate to lift and jam, causing the timing to stick, making it look like the timing was advanced at idle. Took us a while to figure it out. I put in a new Mopar Electronic distributor and it ran perfect.
 
Thanks for all the input guys... been busy packing as going on a cruise tomorrow for a week... at least I've got a list of things to check now on my return....

Just to note though the vaccum part of the distributor is not set up, its unplugged and pipe is blocked with a bolt.
Also I'm assuming its not stuck as it advances instantly with a bit of a rev, I saw 40... but didn't risk anymore as I just dont know where it should be, I was thinking around 16 -18 degrees????

To be honest I have just figured it was too advance at idle and I was not the builder, that was the last owner importer.. but he has a giant chip on his shoulder and a real bad attitude so no chance of getting anything from him lol!! took 4 months for engine paperwork!!! All he's said to previous questions is "It was perfect when I had it" I'll give him credit he did build the engine and spend alot of money, but its far from perfect but he just blames anything on me lol!!

On a side note I had an electrical issue before where I had no spark at crank, turns out it was sharing supply with electric fuel pump and volts were dipping too much, we unplugged fuel pump and it fired up... so a auto elec guy seperated the two and run a relay on the ignition wire??? HOWEVER I still had electrical issue and I found a loose connection at the stock dash ammeter gauge, tightened that up and all issues gone Inc dim headlights and tail lights at idle.... so my question?? could that relay be causing an issue?? I'm just guessing here lol!!

But I'm sure I've booted it since then without issue, but can not be certain???

Thanks again for the info above.. I'm away as of tomorrow morning (to you guys) so not going silent but stuck on a boat for 7 days lol! I will update upon my return and hopefully the fix!!!
 
Shane pearce said:
Also I'm assuming its not stuck as it advances instantly with a bit of a rev, I saw 40... but didn't risk anymore as I just dont know where it should be, I was thinking around 16 -18 degrees????
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That is not what is being said. There are 2 advance mechanisms: mechanical and vacuum. What it being suggested is that the vacuum advance mechanism has broken on some odd fashion and is jammed and that is starting the total ignition advance at a very high number. That could happen, and the mechanical advance would still work... which is what you are seeing when you rev it some.

And yeah you had better back the way back down I would start in the 10-15 range with your high static CR; looking at your engine parts, SCR computes out to around 10.6 and could be more. And the DCR is in the mid 8's and that is pretty darned high for iron heads. No wonder it was carrying on... it was very, very likely to have been detonating, IMHO.
 
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nm9stheham said:
Normal slippage is for the timing to retard, not advance. So that makes me think distributor....

Maybe the wiring from the pickup in the distributor got reversed in the electrical fixes. If it was backwards to start with, then the ignition would trigger on the back edge of the trigger pulse, and you would have to advance the cam to get timing to a normal position. Then if this reversed wiring was corrected, now the ignition is firing off of the front edge of the trigger pulse (which is the correct edge) and the timing is considerably advanced.

The other thing is the damper ring slipping as mentioned; it will slip backwards and make the timing look advanced. But that would not make the car un any differently.

And the vacuum advance rod could be jammed up, keeping things far advanced.
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I have been down that road several times and now recognize it almost instantly. When it's firing off the back edge you can set the initial timing ok. But as soon as you rev it up a little, she starts randomly dropping sparks, and the timing light sees the damper marks jumping all over the place from retard to advance, or not there at all, or way up the ring and no index marks visible. This has never happened to me by itself. It was always occurred right after a new pick-up was installed. I cannot imagine a mechanism for this to occur on a good running engine.
If the hold-down is indeed tight (go twist the D to prove it, not the bolt, the housing) then I'll throw in with the guys that talked about the intermediate driveshaft or cam drives,or most especially a thrown advance spring. Basically nuthin else it could be? The crank drives the cam, that drives the intermediate shaft, that drives the D, that times the spark, that's connected to the ankle bone that's connected to the limb-bone, that's......lol, oh sorry, I don't know what came over me just then. Wilma! I need a beer.
 
Chebbys were notorious for the mechanical advance hanging up.
 
Well that whole design was just trouble as it got older and wore out.I've seen Mopar Ds still running with a quarter million miles, and the parts still working just fine. Well sometimes seized, so not quite fine. But a couple of minutes and back in action. I like GMs being on top tho.
 
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AJ/FormS said:
Well that whole design was just trouble as it got older and wore out.I've seen Mopar Ds still running with a quarter million miles, and the parts still working just fine. Well sometimes seized, so not quite fine. But a couple of minutes and back in action. I like their's being on top tho.
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470,000 on my power wagon distributor, changed engines a couple times, but dist is the original methinks.
 
I've had a couple of original distributors that would "stick" when revved up, then stall the engine when returned to idle.
Take completely apart, clean and lube as necessary. Remember that drop of oil we're supposed to put on the felt under the rotor?
Anyone ever do this?
 
Yup, if i recall its motor oil?
 
sccachallenger said:
I've had a couple of original distributors that would "stick" when revved up, then stall the engine when returned to idle.
Take completely apart, clean and lube as necessary. Remember that drop of oil we're supposed to put on the felt under the rotor?
Anyone ever do this?
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Naw I'm waiting for mine to seize.........since IDK when; a few decades I guess..... But then at 7000rpm, Ima guessing there is enough crankcase pressure for it to be self lubbed,lol.
 
nm9stheham said:
That is not what is being said. There are 2 advance mechanisms: mechanical and vacuum. What it being suggested is that the vacuum advance mechanism has broken on some odd fashion and is jammed and that is starting the total ignition advance at a very high number. That could happen, and the mechanical advance would still work... which is what you are seeing when you rev it some.

And yeah you had better back the way back down I would start in the 10-15 range with your high static CR; looking at your engine parts, SCR computes out to around 10.6 and could be more. And the DCR is in the mid 8's and that is pretty darned high for iron heads. No wonder it was carrying on... it was very, very likely to have been detonating, IMHO.
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Hey.. sorry about delay kinda lost interest sadly, bit like a sulking child lol!! anyway back at it as the issue is still there although alarmingly made 80% better by replacing Carter high volume elec fuel pump for a Holley Blue... fuel pressure now holding solid at around 7.5psi

Today I'm just in the middle of swapping back dizzy cap and rotor arm as noticed some play in the rotor arm on the shaft, but original one is solid..

I'm not running vacuum advance only mechanical. Oh and compression is 10.75:1

Checked timing with gun last week and checked for slack in timing chain, also checked it all lines up at TDC which it does, although waiting for piston stop tool to confirm 100%

to show the timing we are seeing its......
32 at idle
38 at 2.5k rpm
40 at 3k rpm
42 at 3.5k rpm

That was holding throttle and slowly increasing.

Was not going to hold revs any higher with that sort of timing, but blipped the throttle and saw 50!!!!!! so yeah something is well out..

Will update if I get anywhere after reading the above comments
 
Shane pearce said:
Checked timing with gun last week and checked for slack in timing chain, also checked it all lines up at TDC which it does, although waiting for piston stop tool to confirm 100%

to show the timing we are seeing its......
32 at idle
38 at 2.5k rpm
40 at 3k rpm
42 at 3.5k rpm

That was holding throttle and slowly increasing.

Was not going to hold revs any higher with that sort of timing, but blipped the throttle and saw 50!!!!!! so yeah something is well out..

Will update if I get anywhere after reading the above comments
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And this is with the initial set "where?" Have you pulled the dist. apart? Broken advance spring? PLEASE lose the word "dizzy." Thank you very much

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With no load on the engine it is common for the engine to want between 50 and 60 degrees of timing at cruise rpm. So you can't hurt it with a true 40/50 after 2500 rpm with no load.

This is also why the Vcan will someday have to be re-connected. The engine wants what it wants, and if you don't give her what she wants,she will complain about it, just not as loudly, or as often, as when it detonates.

I don't know what the big deal is, just put the power-timing back to where it's supposed to be, tighten the clamp and if it idles ok you're done. Then index the D housing to the block with a chisel mark,and keep your eye on it.
I mean 50 less 32 is 18 in the D. If you reset the power-timing to 34 then you will have 16 initial, And that is pretty close to perfect.
Now if it comes in too slow or too fast, well then some springing is in order. But your test shows only 6 degrees added from idle to 2500,and only 10 degrees added by 3500,and only 18* by blipping to guessing 4000; so that looks pretty tame.The curve appears to be pretty safe for the combo.
 
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Take a permanent maker and draw a line across the balancer, reset timing to 12 initial for now, tighten distributor and drive it.
Check balancer to see if line is straight across or if it shifted from the center, ring slip.

A distributor with mechanical advane will have some movement , depending on how light the springs are, large the bushing or slot is will determine how much.
It's also possible to reverse the polarity on the pick up wires, and end up changing the timing by a lot.

Key here is...did the idle rpm ever change from what it was before? or was it just performance that went away?.....32 idle would have it well above 1000 rpm at idle.
 
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