73 360 Ignition timing after Chain replacement

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AJ/FormS said:
No, on the first and
yes on the second.
But
First put all-new fresh gas in the tank, and drive it, If it still has problems getting down to a TRUE 2.5*; AND if you installed the original Holley 2-bbl; get rid of that trouble maker. The low speed circuit in that carb is nearly impossible to get right, it will take you hours and days. The simplest is to just get rid of it.

Here's the deal;
I ran the Mopar 292/292/108 cam, in from 4* retarded to 8* advanced and it idled just fine at from 5* advanced to 18* advance in any of those cam-timed positions. And with a Holley 4-bbl , after the tune was in, it took throttle like a champion.
So what you say.
So I don't care where your cam-timing is. IMO, for your application, if it starts and runs at 15*, the cam-timing is close enough.
Why it won't idle at 5* is a whole nuther problem. And I agree with everyone who says to go out and get a piston stop and PROVE your TDC mark! A dowel in the whole means absolutely nothing no matter how careful you think you are being. At TDC your 360 has a window of crank rotation, of at least 5*, where the piston just about dwells, with almost no piston movement. That's problem #1. And saying it looks the same as another one laying on the bench, is just as vague and means nothing.That's problem #2.
Problem #3, is that you haven't said a word about your Power-Timing so I assume you don't know it. And this is almost critical to know, far more critical than your Idle Timing. Lets say your mechanical advance system is set up for 2.5* advance at idle. That means the factoryD for that engine would have been designed for it and would probably bring the PowerTiming to at least 32* at some unknown by me higher rpm, guessing 3600. That means the centrifugal would be about 30 Degrees. Now, if you set the Idle Timing to 15, and the D brings in another 30, that totals 45, which is enough to rattle all your piston skirts straight into the oilpan. That's problem #3.
Problem #4 is we don't know your elevation, nor at what temperature your engine was running when it stalled, These are key things to know.
So you gotta fix these problems before you do anything.

However this does not prevent you from doing some other diagnostics as to why it won't idle with short timing. And my guess is,either;
1) the carb is not fueling correctly, or
2) the engine is getting too much air from an unregulated source, or
3) the valves are not sealing.

I suggest you start by making sure all the vacuum accessories are properly hooked up and functioning correctly, including especially the PCV system,and the brake booster; and if everything is; then
do a LeakDown test
Why?
If the valves are not sealing, the vacuum will be low. To compensate for this; You will either increase the throttle opening, or increase the timing, or perhaps both. But in either case the throttle blades will not be in the right place as regards the transfer slots.
So if you try to run at say 5*, you will have to increase the throttle opening, but the engine will not get enough fuel, so you will likely max out the mixture screws in an attempt to keep her running, or you will end up with a high idle.
But, at 15* you can reduce the throttle opening, and the Idle-vacuum will be higher, so now the carb is working "better". But the fact is still, that the manifold vacuum is too low in the first place due to the valves not sealing.
Without doing a LD test, you can chase yurazz around for hours because you don't know that the vacuum is or what it should be.
A compression test could be done, but has to be interpreted by the numbers and the environment. Saying "good" means exactly nothing to me. Your "good" is gonna be different from my "good" which is gonna be different than somebody else's "good" . Furthermore, this test gas to be done properly, which means;
disable the coil, wire the throttle at WOT, ALL plugs out, and with a fully charged battery, crank it as many compression cycles as it takes to get two consecutive same/near-same readings. Whether it be 5 or 12 cycles, just crank it.
But these numbers do not, by themselves, prove your valves are sealing.
They just give a general view of the condition of your engine. See, you said you put in new bearings, but you never mentioned rings nor boring nor honing, or what the ring gaps were, so the compression numbers would be somewhat meaningless, especially not knowing your elevation; Oregon is not Kansas.
Click to expand...

Tank full of fresh gas.

2 barrel carb is all i'm gonna run. I am not putting a 4 barrel on it for many reasons.

Heads where just done with all new valves, hardended seats and new guides. spent over $1000 bucks on those alone. the damn valves better be seating, lol. i'm sure they are, vacuum is steady on the gauge when checked.

Timing set with vac to dusty plugged, and brake booster isn't leaking. Checked weights for free movement and vac can for operation before it was installed. All Ok.

I did not have to raise idle on the carb at all.....It's functioning well.

I live and drive between 200-1500 ft elevation. not really in the mountains.

Drove it today pulling a 5000 lb trailer. perfect throttle response, no ping, no hesitation.

I'll have to calculate fuel mileage to see if it's abnormal, but all seems okay.

If I get time I'll make a piston stop and check the TDC mark, but again, it matches the other pulley I have exactly, so it's unlikely that both are slipped the same amount. I think the mark is as good as it ever was from the factory.
AJ/FormS said:
No, on the first and
yes on the second.
But
First put all-new fresh gas in the tank, and drive it, If it still has problems getting down to a TRUE 2.5*; AND if you installed the original Holley 2-bbl; get rid of that trouble maker. The low speed circuit in that carb is nearly impossible to get right, it will take you hours and days. The simplest is to just get rid of it.

Here's the deal;
I ran the Mopar 292/292/108 cam, in from 4* retarded to 8* advanced and it idled just fine at from 5* advanced to 18* advance in any of those cam-timed positions. And with a Holley 4-bbl , after the tune was in, it took throttle like a champion.
So what you say.
So I don't care where your cam-timing is. IMO, for your application, if it starts and runs at 15*, the cam-timing is close enough.
Why it won't idle at 5* is a whole nuther problem. And I agree with everyone who says to go out and get a piston stop and PROVE your TDC mark! A dowel in the whole means absolutely nothing no matter how careful you think you are being. At TDC your 360 has a window of crank rotation, of at least 5*, where the piston just about dwells, with almost no piston movement. That's problem #1. And saying it looks the same as another one laying on the bench, is just as vague and means nothing.That's problem #2.
Problem #3, is that you haven't said a word about your Power-Timing so I assume you don't know it. And this is almost critical to know, far more critical than your Idle Timing. Lets say your mechanical advance system is set up for 2.5* advance at idle. That means the factoryD for that engine would have been designed for it and would probably bring the PowerTiming to at least 32* at some unknown by me higher rpm, guessing 3600. That means the centrifugal would be about 30 Degrees. Now, if you set the Idle Timing to 15, and the D brings in another 30, that totals 45, which is enough to rattle all your piston skirts straight into the oilpan. That's problem #3.
Problem #4 is we don't know your elevation, nor at what temperature your engine was running when it stalled, These are key things to know.
So you gotta fix these problems before you do anything.

However this does not prevent you from doing some other diagnostics as to why it won't idle with short timing. And my guess is,either;
1) the carb is not fueling correctly, or
2) the engine is getting too much air from an unregulated source, or
3) the valves are not sealing.

I suggest you start by making sure all the vacuum accessories are properly hooked up and functioning correctly, including especially the PCV system,and the brake booster; and if everything is; then
do a LeakDown test
Why?
If the valves are not sealing, the vacuum will be low. To compensate for this; You will either increase the throttle opening, or increase the timing, or perhaps both. But in either case the throttle blades will not be in the right place as regards the transfer slots.
So if you try to run at say 5*, you will have to increase the throttle opening, but the engine will not get enough fuel, so you will likely max out the mixture screws in an attempt to keep her running, or you will end up with a high idle.
But, at 15* you can reduce the throttle opening, and the Idle-vacuum will be higher, so now the carb is working "better". But the fact is still, that the manifold vacuum is too low in the first place due to the valves not sealing.
Without doing a LD test, you can chase yurazz around for hours because you don't know that the vacuum is or what it should be.
A compression test could be done, but has to be interpreted by the numbers and the environment. Saying "good" means exactly nothing to me. Your "good" is gonna be different from my "good" which is gonna be different than somebody else's "good" . Furthermore, this test gas to be done properly, which means;
disable the coil, wire the throttle at WOT, ALL plugs out, and with a fully charged battery, crank it as many compression cycles as it takes to get two consecutive same/near-same readings. Whether it be 5 or 12 cycles, just crank it.
But these numbers do not, by themselves, prove your valves are sealing.
They just give a general view of the condition of your engine. See, you said you put in new bearings, but you never mentioned rings nor boring nor honing, or what the ring gaps were, so the compression numbers would be somewhat meaningless, especially not knowing your elevation; Oregon is not Kansas.
Click to expand...

200-1500 Ft. elevation. I live at 400. truck doesn't really ever see any long drives into the mountains, lol.

Heads were just machined with new valves, hardened seats, guides and seals. They damn well better be sealing since I spent $1300 on them.

I'm keeping the 2 barrel. I have no need for a 4 barrel and I've already spent too much on this truck.....Besides, I like it being original. Didn't have to mess with carb idle. Mixture screws are 1-1/4 turns out.....adjusted per the Holley instructions and again, seem "good"

Vacuum is steady at idle at 21 inches....... no bounce on a gauge. Timing was set with vac advance plugged, and brake booster holds vacuum no leaks. I could try disconnecting and plugging PCV, but it's new and hooked up proper.

Harmonic balancers match up exactly. I'm sure that the one that's on is not slipped.....however, If I get time I'll make a piston stop and check it's exactness. But I'm sure it's right where it was in 1973 when it was installed.

Checked disty weights for free movement, and vac can holds. It's good. Again, If I get some free time I'll check the advance at higher RPMs under load, but again, it seems ok.

Drove it today pulling a 5k lb trailer.....no ping under load up steep hills. Perfect throttle response. Thanks for all the help......If I decide to dig in more I'll update this thread but like I said this is work truck...not a hotrod or a show car....i just need it to work a few times a month reliably. I wouldn't have even installed this engine except the original tossed rods. (it was worked to death, truck used to be owned by the local electric utility, and had an insanely heavy tool box bed on it for most of it's life, probably has 300k miles or more on it.)

This engine from a low mileage RV with fresh heads runs so much happier. Hope to keep the truck on the road til I'm too old to work or drive it anymore.
 
I think the real answer to the Original Question is that changing ONLY idle timing without also adjusting the idle mixture as you go will cause what you experienced: failure to maintain idle speed.

Sounds like the current tune up doesn't suck, so unless the plugs indicate it needs tweaking then AJ is right - just run it.
 
Gloyale said:
Yes I am assuming that the Mopar Performance Gear set is accurate. Why wouldn't it be? You think factory mopor parts would not be accurate?

At any rate.....i drove the truck today, and it was excellent. I don't think it would have run as well as it does, if the Cam was a full tooth off, which is the only possible mistake I thought I might have made. I didn't just throw the chain on any old place....lol.....I know that I used the correct marks, and like I said in my initial post I'm nearly certain that the marks where lined up correct. The excellent drive-ability pretty much confirms that. As to the ignition timing, best guess is that the Cam is an RV cam, not the stock.....and setting initial timing at 15 is gonna be fine.

This is a work truck. I'm not trying to build a hotrod or drag engine. So long as it runs well with good power and throttle response, I don't see a need to tear the waterpump and cover off again.

Thanks to all for letting me bounce my thoughts off your knowledgable group, even though this isn't actually an "a body"
Click to expand...


I never assume anything. I don’t care what name is on the box, ALL a parts have a manufacturing tolerance.

Every time this comes up, I ride hard on it. No one should put an engine together without degreeing the cam. Ever.

Those dots are there so some dude on an assembly line can stand there and throw the timing set on and send it.

If you don’t degree the cam you have no clue where the cam is installed and it’s just a wild assed guess. And yet and still, guys will continue to do it just because.
 
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