LA small block timing is suddenly way off

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stillsteamn

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Hi, I have a 360 small block LA motor in my '67 Barracuda. MSD 6AL electronic ignition, MSD distributor with mechanical advance only, no vacuum advance, electronic points. Early this summer I set the timing by ear by rotating the distributor advanced as far as possible and it was running fine for 2 months. I had trouble seeing the timing mark with my timing light as it came around, so I did not bother noting what the actual idle timing advance was. Engine ran fine until recently started missing terribly (maybe after I revved it to demonstrate new mufflers?). Now I took a black Sharpie and blacked the timing mark on harmonic damper so I can see it with my timing light. From earlier static testing I know this timing mark aligns with TDC on cyl 1 compression stroke. Idle t.Timing now appears to be 30 degrees retarded and misses terribly!! I cannot rotate the distributor any farther advanced because the distributor cap mounting ear contacts the riser of the intake manifold. I think something may have slipped a cog?.. Sorry I don't know if the LA camshaft is driven by a chain or a gear. Is it possible my camshaft (chain) has slipped a cog? Or is there a way to remove some screws to advance the distributor rotor by about 30 degrees so I have some room to then adjust timing properly by rotating the distributor? I am stuck.
 
Bring #1 to compression tdc, verify timing mark on balancer is in right location. Pop the dist cap and make sure the rotor is pointing at #1 wire. Need to start with some basics.
 
Does it run the same as it did last week? Balancer slipped. Especially when you mentioned that you timed it by ear and it ran fine but the timing mark was buried. tmm
 
Did the outer ring of the damper slip?

That would mess with ya trying to set the timing, but it wouldn't run bad because of it.
I'm betting it jumped the chain (Especially if it was a plastic coated gear) and some evidence of this would be off white plasic bits in the oil pan.

Sometimes just draining the oil can make some of those bits come out so you can verify that is what the problem is.
Of course there are other ways also, like pulling a mechanical fuel pump and checking the chain slop, or see if it takes a bit of turn back and forth with the crank shaft and see how far it turns before the distributor rotor reacts.

( I know you know this 70aarcuda, I just posted for the OP) :)
 
Because you have no idea where the timing was ever set,, I wouldn't take the missing as a result of the timing,, I'd be pulling the plugs looking for a fouled plug, or bad/burned plug wire,, then once you find the miss,, set the timing properly,, and you will prob have way more power than when you "guessed"....

Re-read your post,, and timing chain jump is a possibility,, did you have the dizzy out, or change/install MSD dizzy, when you did the original timing by ear..?

hope it helps
 
Update based on your replies so far: I think the reason I could not see the timing mark earlier this summer was just because the harmonic damper is painted orange, the timing mark is orange with no contrast, and the lower radiator hose blocks most of my view of the timing mark so it's hard to see. Yesterday I marked it with a black marker to fix that. I did confirm back in spring that the timing mark was at 0°C TDC for cyl 1 on the compression stroke. By ear I would guess I set the timing 8° advanced or so, but can't be sure. Since the missing problem began I have verified the distributor rotor points to cyl 1 wire at TDC, checked spark plug wiring, pulled distributor cap checked rotor and weights and springs, verified strong a consistent spark with inline spark checker between coil and distributor even when idling badly, installed new spark plugs, and checked for carburetion problems but did not find anything carb-related yet. Get a lot of smoke and fumes out the exhaust, probably just a lot of unburned gas coming out.
 
Did you use plastic zip ties to lock out the timing and have one of them break on you at the track? I did that lol
 
It sounds to me that there is no proof that you have a timing issue.

You said that the engine is pretty fresh which makes me think that a jumped timing chain is unlikely.

You have checked for proper firing order, changed plugs, etc. Great. - Often it's the simple things that bite you. - Good to rule them out.

You also stated that the problem may have started after revving the engine to check out new exhaust system. I think I'd pull your valve covers and make sure that the valvetrain is in good order. I've seen guys send a pushrod through a rocker arm when taking an engine to high RPM and the motor hiccups on them. Even if it doesn't damage a rocker I've heard of it bending a pushrod. I'm not saying that it's likely but it has been known to happen.

At any point did you disconnect the wires to your distributor? Even though the MSD will run with the wires reversed, - it will run like crap.
 
Need to get a timing light. Buying that cool MSD distributor and box won't help one bit if you can't properly tune the motor. Timing light, vacuum gauge & even a compression gauge should all be in your tool box before you spend another dime on the motor.
 
I doubt the engine would run with all cylinders timed 30* retarded.( are you sure your light was in fact on #1 wire?) As you begin to retard the timing the rpm drops. By 10* retarded the curb idle screw would need to be adjusted a lot to keep the engine running. By 20* you would likely be having to open the throttle manually. Now if the chain had jumped thus retarding the cam timing as well, no way it would still run, w/o a lot of help.
-Now if it was cross-firing just on #1, (assuming you were checking timing using #1 wire) or the #1 wire was inadvertantly swapped to another tower, well there are still 6 correctly timed and normally functioning cylinders. It would idle at a much lower rpm, but, depending on the original idle rpm, might continue to run. So prove your firing order and rotor phasing.
-And finally, if during the muffler test, a valve kissed a piston,(or you bent a pushrod or punctured a rocker arm) it would run rough, leading you on a troubleshooting trail that just discovered the previously slipped ring.
-I suggest; proving the TDC mark again, a compression test, and as a previous poster mentioned; a timing chain stretch test. These are simple basic tests and will give you a tremendous amount of information.
-You could also begin by determining if the problem is just in one cylinder by performing an ignition isolation test. Just remove one wire at a time until you find a no difference cylinder(s).
-Of course all this pre-supposes that your carb is functioning correctly.
-Gee, I hope this helps
-One more thing, if you had a backfire during the muffler rapping, and you have a Holly/Holly type carb, then the PV may have ruptured and is causing the rough running, and again the previously slipped ring was just discovered. You might want to have a peek at the main nozzles for dribbling during idling.That would be not good.
 
... I cannot rotate the distributor any farther advanced because the distributor cap mounting ear contacts the riser of the intake manifold. I think something may have slipped a cog?.. Sorry I don't know if the LA camshaft is driven by a chain or a gear. Is it possible my camshaft (chain) has slipped a cog? Or is there a way to remove some screws to advance the distributor rotor by about 30 degrees so I have some room to then adjust timing properly by rotating the distributor? I am stuck.

Not sure about your other problems but you can always move all the plug wires either CW or CCW one position on the distributor cap. Then No. 1 will be in a new position, and you can start over.
 
To digest this all down:

YOU NEED to resolve the timing

1.........CHECK TDC and there is only one practical way......a piston stop



You can make one easily. This one is mine, I still have it now, it was made in the 1970's



2....MSD is known for having issues with timing lights. A cheap old "all manual" light generally works.

3....As suggested above, I'd check the valve train, maybe a compression check. I waste no time when I have a problem. Compression check, leak down test, NEVER hurts.

4...The "wild cards." There is always that possibility you have a plug electrode pounded shut, dropped, cracked. A plug wire went bad. Or your -- "friends" -- thought it would be funny to swap a couple of wires..........
 
YEs, knock electrode ceramic out of a plug and screw in a bolt like shown. Use it to hit piston on the way up when you turn motor by HAND (pull all other plugs out) look at damper and make a little mark, rotate the other way until you hit and then back it off slightly to remove chain slack (youll feel it) then make second mark. Bisect the marks and you have TDC. take stop out, turn to new TDC mark (ignore old one as it may have slipped) and then look at rotor and see if its pointing at #1 tower, if not center distributor so pot is facing passenger side and then make wires correct by reinstalling them onto towers using rotor pointing at closest tower as new #1. CW 18436572
jturcotte_117.gif


you may have jumped a tooth or 2. I doubt you broke a pushrod, that wouldnt change timing but timing chain runs dizzy.
 
Pishta, while your method is correct,for an uninitiated it could be a little vague as to where to start from and where to make the index marks. Also on the sbm, #1 tower is usually where your drawing has #2
 
I will begin checking further. First a couple questions.
-- If the timing chain did jump, then would that mean my camshaft and valve train is out of phase with the piston strokes? And this could only be fixed by removing timing chain, realigning cam, and reinstalling a new timing chain? Just shifting the wires on the distributor cap to a new #1 location seems like my camshaft would still be out of time with the pistons.

-- AJ/FormS said: -One more thing, if you had a backfire during the muffler rapping, and you have a Holly/Holly type carb, then the PV may have ruptured and is causing the rough running, and again the previously slipped ring was just discovered. You might want to have a peek at the main nozzles for dribbling during idling. I do have two Edlebrock 1404 4-bbl carbs and I did have a backfire while trying to start the engine recently. What is the "PV" and main nozzles you are talking about, probably carb parts?"
 
Why should anyone find true TDC? That's too much like work.
 
Or time it by ear for that matter.
-In response to post #19; yes: new chain, and usually gears,and retime the cam.
-edelbrocks dont have a PV ( Power Valve) like Holleys.
-It sounds to me like yes, youre stuck. #1 thing is this; reread this thread from the beginning.Maybe a couple of times until you understand whats being said. If it doesnt sink in, dont be discouraged. We all started out knowing nothing. If you build a house on shifting sand eventually it will crumble and collapse. A house needs a firm foundation.
-We are out here in the wild blue yonder. We need to know that the foundation is solid or we are just chasing our tails. We need to know that the TDC mark is exactly where its supposed to be. We need to know that the cam is near to where its supposed to be. And that the rotor is correctly phased and that the firing order is exactly correct and that the cylinders are all contributing nearly equally. Our contribution is diagnostics. Your contribution is to perform the tests and report back. Until you report that the foundation is built and secure we cant begin to build the rest of the house. Now read, do, and report.
 
... Just shifting the wires on the distributor cap to a new #1 location seems like my camshaft would still be out of time with the pistons...

Correct. I was trying to help you with your problem where the distributor could not be turned enough to get the ignition timing where you wanted it.
 
Man this is frustrating to diagnose over the net.
 
Thanks for the efforts guys. I made progress tonight and found an error in my earlier timing analysis. Tonight I removed valve covers, removed distributor cap, removed spark plugs. Turned engine over slowly by hand and confirmed that harmonic balancer 0° mark perfectly aligns with TDC of compression stroke on cyl 1 (i.e, both cyl1 valves closed, thumb on spark plug hole to feel compression building, a wooden dowel on top of piston until crankshaft is just barely past the point where piston stops moving). At this point the distributor rotor points about 30° past the cyl 1 post on the distributor cap, with the distributor set where I previously had it. This means my previous ear tuning (fast smooth idle) must have been 30° advance timing, but the engine did seemingly run well and I never detected any knock or ping. Aha, but I then found that the harmonic damper has at least 3 other strike marks around the perimeter. So when I reported 30° retarded timing (using a 12V inductive pickup timing light on cyl 1 wire) at the start of this thread, the real 0° mark is not yet visible and I was instead seeing one of those other strike marks that comes around about 1/3 rev before the real timing mark.

So other than the fact that I have been using about 30° advanced timing at idle which is probably not good, I no longer think I have a timing problem causing the bad missing. I can turn the distributor in the retard direction to properly set timing, and I did try this a couple days ago but it was making the miss even worse (daughter in car feathering the throttle and keeping the rpm's up to keep the engine limping along). But I still have not found the real problem, so maybe I had a backfire that did something to one of my Edelbrock 1404 carbs. The name of this thread is now wrong, but before I started thinking I had a timing problem I did remove all 4 fuel/air idle screws and shoot a blast of compressed air in each hole to remove any debris from the idle circuit, this tip came from an Edelbrock youtube video I saw earlier from an Edelbrock guy. I also pulled out all 4 metering rods and wiped them off but they were clean.
 
Waitaminut. Are you saying that your engine is a dual 4bbl?
-The dowel in the hole aint good enough. If you watch closely you will see the piston sit(dwell) at TDC for several degrees. This method isnt even good enough for your lawnmower. If you time a snomobile this way it will very likely burn up. While your mark may be correct, you havent proven it.Until you prove it we cant help you, cause the next step is even more critical of it being correct.
-The way you tell your story is very confusing.
-A circle has 360*. If you divide the circle into 8 equal parts, each part would be 45*. So if the rotor was 30* past the no 1 tower, then the ignition system might be firing into the next tower past the true #1 at full advance or it wouldnt run at all. I conclude therefore, that you are referring to the tower labeled on some caps as #1, and not to the actual wire that goes to the no 1 sparkplug. Depending on how you have dropped the dist. in, any tower could actually be no 1. But the only real no 1 is the tower with the wire that goes to no 1 sparkplug. Do you follow? Am I getting close?
-Some balancers have 4 strike marks, equally spaced around the perimeter (ie at 90*).These will help you set your valves, among other things. They are at 1/4 intervals.
- the clearing of the idle circuits is a delicate operation
-This next paragraph is for after you have proven TDC.
-Heres what I do.Starting with the engine at TDC #1 compression stroke.Take the cap off. Clock the distributor rotor so that it is pointing to, or very near to,the #1 cylinder(driverside front).The rotor doesnt absolutely have to be installed this way,it just makes it more likely that the true #1tower will be the one marked #1, and it makes the wires lay out nicer. Make sure the advance springs have properly parked the cam. If the rotor is not pointing there, the way to get it there is by removing the dist. and reclocking the oilpump driveshaft. This can be tricky. Take your time. Be absolutely certain when clocking the shaft to get it to drop down home, before you drop the dist. back in and all the way down. It may take several tries and the crankshaft may have to be rocked. A helper may be needed. Ok so thats done. Next we would clock the vacuum can to where it clears every thing, by pushing it all the way back to the fire wall. Since your dist. doesnt have a can,we will use the previously interfering mounting ear instead. Next rotate the crankshaft in reverse rotation to about 20* advanced.(If you cant see the mark that far up, heres what I do: with the crank at TDC mark the balancer adjacent to the 10* retarded line, then rotate the crank to align this mark to the 10* advance mark). Next advance the dist. to the point of firing the coil. I do this by popping the coil wire out of the cap and near-grounding it, and with the ignition sw on,rotate the dist.CCW, until it fires the coil. So, you heard or saw the spark ,right? Do it several times so you are sure. Now we just have to steer the spark towards #1 cylinder. Make a mark on the side of the dist.where the rotor is relative to the body.This is where the true no 1 tower must line up.Next drop the cap on, index it properly and secure it. Is there a tower that lines up with that mark? If yes, thats the tower to connect to #1 plug. If no, we may be in trouble. It needs to be within a few degrees. Its very rare that it doesnt line up. So next be sure to install all the other wires in the correct order. You are now ready to start it up and finalize the timings. As mentioned earlier some timing lights dont like the MSDs.If your balancer has no timing tape installed, you will need a dial-back type.So now the engine is running.Stabilize the idle rpm and check your idle timing. It should be very close to whatever you set it to during the set-up procedure( the 20*). Adjust as required. Now rev it up a little, if ok rev more until advance is all in. If no missfires then you are good to set the power timing. If it does missfire, we may have to re-phase the rotor. In the past I have taken a spare cap and drilled a 1/2 inch hole in the top, between the coil tower and the true #1 tower, such that when you shine the timing light in there on a running engine I could observe where the rotor was. If it gets too far off, it will crossfire.We will talk about re-phasing later if needed.
 
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