Why advance timing?

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FrozenCaveman

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I posted something about the longtime overheating issues with my stock 225 automatic (20k miles on the rebuild) in another thread, but I think I just resolved things by advancing my timing to 5* and idle to 800.

I'd previously had it at TDC, idle somewhere between 700 and 750 (750 is spec according to the sticker). Dwell is at 39, which is slightly below the 41 to 46 spec, but it's always a crap shoot for me to get it close, so 39 makes me happy. :p

I'd tried a new radiator and cap, new water pump, new thermostat, and only gotten incremental improvements.

So why do I care if I've "fixed" my problem? I want to make sure I'm not just masking an underlying issue by advancing the timing. I've seen a bunch of posts about advancing timing until it pings. Shouldn't a stock motor be able to run at the original spec of TDC timing?

Thanks, all.
 
Well of course it "quote" should "unquote" but you are sort of shooting yourself in the foot by doing so in the first place, regardless of heat issues

You must understand that NOTHING concerning engine controls the automakers did from about 68 --?? the advent of EFI was "for" the consumer, and "all" was for govt smog regulations.

Retarded timing and too--lean carburetion worsened everything from cold starts to poor warmup, to poor general driveability, hot starts, run on on shutdown, poor mileage AND performance, and on and on and ON. Of course not all of that was called by such retarded timing, but some of it WAS.

Also, unless your engine (which is how old, again?) radiator and all other components are in "like new" condition, one would expect some deterioration in systems.
 
Believe me, you'll like the way it runs a lot better if you ignore the specs and give it what it wants.
Dwell you can't change much without changing ignition systems, but base timing, curve and total timing changes can make a huge difference in performance.
 
Thanks for the reponses!

Just got back from another parts run and it's still running hot enough to steam a bit. Dieseled very briefly when I got home.

Maybe advance the timing even a little bit more? Hot start issue I was having with timing at TDC also got a lot better at 5* advance.

Saw a '68 cuda coupe while I was at NAPA... Made me smile. :)
 
I'm thinking you have overheating issues beyond timing, but check that the distributor advance mechanism is working
 
Putting on my newb hat and cringing...

Physically, I can't advance the distributor more than 6 degrees. It won't turn farther. Is my distributor off by 180 degrees?
 
There is another bolt in the adjustment plate that screws into the distributor that allows for more travel. Mine loved anything from 10-15ish BTDC
 
The slot in the bracket near the wire is what you see on the engine block. Notice the second slot and bolt up under the housing, left side of photo

But here's the thing----DID it run previously at TDC without overheating, or have you just got it together?

You seem to be concentrating on "advance" and there are many more possible issues.

dist-wrench.jpg
 
Sorry, you mean there are 2 bolts on the metal bracket holding the distributor in place? I've loosened the one into the block and now I'm reached the extent of travel at 6*. I can't see a 2nd bolt unless it's underneath the body of the distributor somewhere.
 
Oh, thanks for the pic. Do I need to access that 2nd bolt from underneath?

I drove it about a hundred miles from my mom's house in fairly high outdoor temps a few years ago. No problem. I let it sit for a year and now it seems to overheat and I've just been trying different things for the past couple years. With the advance, it's as close to normal as I've been able to get it.

Judging by the condition of the old radiator, it _may_ have had issues prior to me picking up the car. None of the fins were attached to the tubes, according to my radiator guy. I put the rebuilt engine into it for my mom and she drove it around for about 20k miles, and she had the transmission rebuilt, so the drive train is hopefully in pretty good shape. I've hardly put anything on it in the time I've had it because of the overheating.
 
I was running a vacuum advanced distributor and it (vacuum advance) went bad, I noticed my temp was going higher and I unplugged my vacuum advance and set the timing myself and it went back down to normal, know I have a recurved distributor that does not require a vacuum advance, I had it set a bit to high and my temp went up, I brought it down to 33 degrees full in, set it with a digital timing light at 2.200 rpms and it has ram perfect, yes your vacuum advance could be leaking and not doing it's job..
 
I replaced the guts of the radiator with completely new, only the frame was kept. That (or maybe just the cap) made a big improvement, but it was still boiling. Then I replaced the thermostat for a 2nd time (had tried a 180, went back to a 195) and the water pump (which may have been fine). Just came back from an evening drive and no heat issues, but the temps were down to maybe 70 instead of the 90 degree middle of the day temps I was testing it out earlier. Didn't diesel at all from driving maybe 10 miles at 45-60 mph.

I don't know. I'm frustrated with it. My gauges aren't working either, figured it was the voltage limiter based on the temp gauge not functioning even when grounded. Ended up disconnecting the speedo cable when I put it all back together. But that's a completely separate problem, other than the fact I can't tell for sure how hot it's running. I guess the gauges are fried and I need to replace them (gas and temp).

I'll look at it again in the morning...

Thanks!
 
Didn't end up doing much yesterday, but I got the speedo cable plugged in again. Seems the plastic connector is broken around the cable, so eventually I think I'll try putting a hose clamp around it.

Anyway, I drove it to work this morning (almost 25 miles @ 65mph) and I just had one tiny drop from the overflow hose. Seems to be better, but it's still fairly cool outside.

Regarding the suggestion that it could be the advance, I did check that a couple months ago. I had my timing light, pulled on the throttle, and saw that the timing jumped quite a bit - I don't recall where it ended up. Is that good enough? Should it be advancing to about 32* with the vacuum advance? Maybe it's intermittently having a problem, and so me manually advancing the timing to 6* w/o vacuum is compensating for it?
 
FrozenCaveman said:
I posted something about the longtime overheating issues with my stock 225 automatic (20k miles on the rebuild) in another thread, but I think I just resolved things by advancing my timing to 5* and idle to 800.

I'd previously had it at TDC, idle somewhere between 700 and 750 (750 is spec according to the sticker). Dwell is at 39, which is slightly below the 41 to 46 spec, but it's always a crap shoot for me to get it close, so 39 makes me happy. :p

I'd tried a new radiator and cap, new water pump, new thermostat, and only gotten incremental improvements.

So why do I care if I've "fixed" my problem? I want to make sure I'm not just masking an underlying issue by advancing the timing. I've seen a bunch of posts about advancing timing until it pings. Shouldn't a stock motor be able to run at the original spec of TDC timing?

Thanks, all.
Click to expand...

I'm glad that helped you out. I'm going to have to check mine now to see if it'll help me out some on my slant.
 
I've been looking around for ways to test the vacuum advance and saw some videos on using a Mighty Vac. I happen to have one! So when I go home I'll check to see if the advance cannister is holding vacuum and if I can see the internals moving at all when vacuum is applied...
 
Mine was not moving after my up dates, must be a low vacuum draw on the 390 4 barrel , because it works pulling a vacuum manually myself, I just don't think I had enough vacuum for it to operate correctly, I believe I am running a ford Carb now, and the vacuum system are not matched anymore . A recurved Distributor does not use vacuum, it reads and advances on it's own, If I had the fists picture set up I had (first picture) the vacuum may have worked but I never checked
 

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Pretty sure I replaced my plugs less than 1000 miles ago, but I'll take a look at them to see if anything's going on with them. I didn't have a chance to work on it at all last night. By the time I got home from work, I had to spend time with the wife and kid.

I drove between 65 and 70 to work today, had it up to 75. No heating issues. Maybe the distributor springs are shaking off the rust. :p

Nice setup, memike!
 
A new (larger) carb will have a different vacuum level on accel/cruise so it will cause the vac. canister to behave differently. You can change it for a canister that is more sensitive. It doesn't matter where the carb came from (Ford, Chev, Mopar) as long as it has a ported vacuum nipple.

A recurved distributor still uses a vacuum advance - all 'recurving' means is modifying the advance curve to optimize spark advance for your engine. You CAN have a distributor recurved to eliminate the vacuum advance but it's not recommended for a street car since vacuum advance is important for fuel economy.

memike said:
Mine was not moving after my up dates, must be a low vacuum draw on the 390 4 barrel , because it works pulling a vacuum manually myself, I just don't think I had enough vacuum for it to operate correctly, I believe I am running a ford Carb now, and the vacuum system are not matched anymore . A recurved Distributor does not use vacuum, it reads and advances on it's own, If I had the fists picture set up I had (first picture) the vacuum may have worked but I never checked
Click to expand...
 
have you flushed the block yet? overheating can be; and often is more then timing issues, I've seen a block so plugged up its just a small passage for water to flow! thats why when engine is out its very important to replace core plugs and clean behind them
 
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