Ford Muscle Cars Tech Forum banner
1 - 13 of 13 Posts

·
Premium Member
Joined
·
509 Posts
Discussion Starter · #1 ·
Got a question for the experts out there.

I've not done a lot of timing and tuning, but I've always felt the 390 in my LTD wasn't set where it needed to be. Put a timing light on it and it was set @ 12 BTDC, manifold vacuum was low (around 12 and slightly moving back and forth, vac advance disconnected and plugged). Turned dist CW got up to 16 (steady) on the vac gauge, but the timing is now off the scale and somewhere around 40 or greater BTDC. No pinging or anything else negative, car idles smoother, trans is shifting better as well (vac modulator I assume).

Using a dowel and with the pass side valve cover off it would appear that the timing marker is correct, but I can't make sense of why it would want to be so far advanced. From what I was told when I bought the car in 2009 the engine has about 25k on it, 30 over, I didn't ask about the compression (was originally 10.5:1), stock heads and 4v intake, has a 750 Holley Vac secondary carb and a Crane 343901 cam.

Where I have the distributor now the vac advance is hitting the thermostat housing, so I couldn't turn it CW any more. #1 plug is off two positions CCW, but verified when @ TDC on the marker the rotor in the ballpark of where the #1 plug wire is attached. Replaced cap, rotor and wires last summer, order is correct just off two places. I don't think that is causing the issues though.

Any ideas or suggestions? Even though there is no pinging should I lower the timing back to where it was or below 20 at least? Planning on driving it around 25miles this weekend to have the transmission serviced. Took a 5min drive today after advancing and it ran better then it ever has since I've had it.
 

·
Registered
Joined
·
10,461 Posts
Careful - you may become a real "tuner". :D Set it all back where it was until you're ready to make the changes that your engine obviously wants. You found it likes more idle timing, but changing one thing (base timing, vacuum advance off, mechanical unchanged, etc.) will improperly affect other areas. You have to change them too as a whole package. So, I suggest you get a piston stop (parts store $5-7) and a timing tape for your diameter harmonic damper. I'll find where someone already did all the blabbing on how to do the whole timing process or a collection of mine and post it up for you.

David
 

·
Premium Member
Joined
·
509 Posts
Discussion Starter · #4 ·
Well when I drove it the advance was hooked back up, not saying you are not correct though.

I did read earlier (can't remember where, I've been doing a few searches today :rolleyes:) about finding true TDC using a piston stop. Doesn't appear like the local parts stores sell them so I'll have to order one. Basically what I read was install the stop, rotate around until it hits, make a mark and then go the other way make a mark when it hits and then half the distance between them.

Are there varying degrees of scale to the tape? I would assume the spacing on the damper is still valid (in reference to the distance between 10 BTDC and 20 BTDC even if the damper has shifted).

I'd like to become a tuner, I'd rather save myself the $350 (as a start) that a local carb shop opens with to do a full carb and timing tuning, I am thinking about looking into having them do a recurve of the dist if I can get this ironed out.
 

·
Premium Member
Joined
·
6,162 Posts
Hey, that happened to me, too. Engine kept getting better as I turned Dizzy CW - hit the housing and could improve no further. But I was suspicious, too.

It's fixed now but I'm not sure what the cure was, maybe one of these steps: 1.) measured the points carefully, mine looked like they were closing but actually I don't think they were, 2.) When the engine is nice and warm, free up/open the choke, could be getting jammed up in the lnkage, 3.) Replace the timing chain, 4.) pull up the distributor and turn it maybe 20-30 degrees CCW and set it back in. Because of the gear the dizzy will turn CW as you push down, hopefully it will end up right on #1.

Just some ideas, good luck.
 

·
Registered
Joined
·
203 Posts
I would definitely index the damper to make sure TDC is really TDC. The damper is a 2-piece unit and it is possible for the outer ring to slip when they get old and the rubber starts to get hard.

I would also make sure that the timing pointer is correct for the engine and installed correctly. That shouldn't account for that much of a difference, but it's an easy enough check.

Good luck!
 

·
Registered
Joined
·
10,461 Posts
Well when I drove it the advance was hooked back up, not saying you are not correct though.
Right, but that's the point - you changed your idle timing to something high, which affect all your timing after that. So when your vac advance came in, instead of giving you perhaps 48° at cruise, you got something far greater and functioning but far from correct. One thing affects all. This is why most 'tune by ear' instructions are useless, as you need to make the ignition fire at the right time at all speeds and all loads - not just idle or WOT. Without that, you are killing some segment of operation, such as your highway mileage. You can also do quiet long-term damage, like valve seat erosion.
Basically what I read was install the stop, rotate around until it hits, make a mark and then go the other way make a mark when it hits and then half the distance between them.
You got it. And it's "gently bumps". ;)
I would assume the spacing on the damper is still valid (in reference to the distance between 10 BTDC and 20 BTDC even if the damper has shifted).
Yep. And you don't need 360 little marks. Every 5 or 10 is good enough to accurately eyeball, if they are accurately placed. So, most use a timing tape. When you get tired of doing that, you'll invest in a 'dial-back' timing light, where you only need one mark - TDC.
I'd like to become a tuner, I'd rather save myself the $350 (as a start) that a local carb shop opens with to do a full carb and timing tuning, I am thinking about looking into having them do a recurve of the dist if I can get this ironed out.
Do the re-curve yourself. It really isn't that hard, and you're doing all the legwork to let someone else finish. Try it. You'll find it rewarding to finish it for yourself, and get more understanding from it, which you can build on when you move to other tuning areas. Anyone can read a book and know, but far fewer have done it and understand. The understanding is what takes you from "monkey see - monkey do" to knowing how to tune. It will take an afternoon. I say go for it. The only exception is if the shop will explain and let you watch everything they do so you can see exactly how it's done; whereupon you will say "Really? I could have done that."

David
 

·
Premium Member
Joined
·
509 Posts
Discussion Starter · #9 ·
Thanks all, I figured out the deal with the tape soon after I posted when I checked on Summit for the tool and the tape. Will be ordering tonight.

Not sure that it plays into things at all, but this car has a Pertronix unit in the dist. so there are no points. I'm guessing the dist is the original one, PO didn't mention anything about replacing it or having it recurved that I recall when I purchased the car. If it is on it's last legs (worn springs and internal parts) would that be causing any issues with timing?

I think the timing chain is ok, when I turn the crank the rotor turns pretty much right away, if I reverse directions there doesn't seem to be much slop. Based off what I've seen on the net the pointer looks correct, and it has a 3 groove pulley which would have been correct since it had AC and PS. I don't think any of that was changed but the engine was rebuilt before I owned the car.

Picture of the front of the block stripped from a few years back:


Even if the dist. is in a tooth or two off, that shouldn't cause the need for excessive timing for it to run better as far as I understand, correct?

I'm thinking it may be a combination or distributor wear and incorrect timing marks, but assuming that and that it may be in the 5-15 BTDC range now, that would mean it was running 20 degrees or more retarded before, is that even possible?

Going to get the piston stop, find TDC and go from there.
 

·
Registered
Joined
·
10,461 Posts
Greg, engines love idle timing. The factory reduced idle timing to both ease cranking starter load, and to reduce the stink of NOx in the exhaust, along with emission requirements. For your engine to like a lot more idle timing is normal. Now that computers control ignition, they retard for cranking, then apply a lot of idle timing up to the emissions limit. For example, the 5.0L Mustang has a base timing of 10°BTC, but only uses that for cranking. Once running, it has an idle timing of 28°BTC. Without emissions requirements, it can be much higher as you have found, and many engines like 30s and even 40s to be happiest.

Yes, distributor condition can certainly affect your tuning. Using your timing light, you can see how much 'wobble' there is in the timing. That is what the engine actually sees. A degree or two is normal for a mid-mileage working engine. More than that can noticeably affect your power and efficiency, as sometimes it lights at say 36° and the next firing may be at 32°. Also, wear in the parts can prevent proper or complete mechanical advance, and vacuum systems are commonly weak or inoperative. You can imagine what 8-12° of running retard would do to mileage and engine longevity. So, yes, as part of tuning, you will check how your parts are working, and how accurate and consistent they are.

BTW - that's why modern cars don't even have distributors, as the cumulative slop in parts affects timing quality. Distributorless systems determine timing directly from the crankshaft's position, and are accurate to within fractions of a degree with no slop. That level of accuracy is nice for emissions control and mileage, and mandatory for bleeding-edge racing, but fortunately not required for hobby-level fun.

David
 

·
Registered
Joined
·
240 Posts
Another suggestion, as I went down this road on my old 390: Run a leakdown and compression test. If the motor is worn out to hell, it will take a TON of timing to get it to even idle because it is making no compression. I had leakdown rates of 80% on some cylinders and it was taking initial base timing close to 30 to get it to even idle. Still ran halfway decent despite it's 1qt per 100 mile oil habit. :D
 

·
Premium Member
Joined
·
509 Posts
Discussion Starter · #12 ·
It idles fine @ 10-14, just seemed better when I advanced it and took care of a flat spot on acceleration. Could be I just convinced myself it was better, I'll be the first to admit I still got a lot to learn. I doubt there are any compression issues, but I still may run a test Sunday if I have a chance.

Piston stop arrived today, spent a few hours out in the garage after work and based on spinning things around with the stop in the TDC mark on the damper is correct.

As I mentioned I dialed it back to 14 BTDC, played with the carb and I have a steady 13" of vacuum @ 650rpm idle in park. Plugs don't show it's running way rich (light brown ceramic), timing mark wasn't wandering so the dist doesn't appear worn. Seems from something I read, vacuum readings drop with altitude, from what I remember 3 down for where I am 5100' up.

So think I'm going to run with things as they are, tune the carb this summer and when I have the engine out before the car gets painted I think I'll look into the timing set and cam degree at that point.
 

·
Premium Member
Joined
·
509 Posts
Discussion Starter · #13 ·
Booster is leaking, disconnected and I'm now @ 15" and was able to lean out the carb and get a steady idle. Going to swap the booster and MC as a unit (MC has always leaked out the top even after replacing the gasket), just need to do some pricing. Suspect vacuum gauge in runner by coil (was on car when I purchased), going to remove and cap. I haven't even been using it since it's angled back and hard to read, lens is cracked but sprayed with carb cleaner and didn't notice any change in idle.

Guess I missed a few things before I jumped on timing, going to get all this sorted out and I may check the timing again. Feeling a bit better that there isn't anything major wrong.

Learned a few lessons for sure.... :D
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top