64 Dart 273 Engine Vacuum

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Vcode

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What should the vacuum be on a 1964 Dart 273 - 4bbl with 4-speed have for stock engine.
 
Vcode said:
What should the vacuum be on a 1964 Dart 273 - 4bbl with 4-speed have for stock engine.
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That will depend on:
Ignition timing,
Idle-Rpm,
Engine load during testing,
Cam timing,
Cranking cylinder pressure/compression ratio,
elevation, and
the exhaust system.
Especially the first two or three.
 
17 is good. Valve adjustment will improve vacuum. especially if they are tight from seat wear due to today's fuel with no lead. Without hardened seats and no lead in the fuel to prevent seat wear the valves tighten up. Hydraulic lifters will compensate for that wear . Solids lifters will not and they will tighten up. When you adjust them set them on the loose side. .002 more especially on the exhaust. sometimes a little noisy is better.
 
I am helping my friend and mopping up from a pass mechanic. We don't know what was done to the engine but working at it in the blind. I am sure they have the cam timing off and will need to pull the engine, maybe in the winter.
Thanks guys
Bob
 
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Vcode said:
I am sure they have the cam timing off and will need to pull the engine,
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I wouldn't jump to that yet.
I would;
1) reset the valve lash as already described
2) do a proper compression test with a fully charged battery and all plugs out, with the throttle more or less at WOT. If the engine runs, then warm it up first.
3) prove the balancer TDC mark is true TDC of the #1piston using a piston-stop, and re-index it as may be required, then
4) make sure the vacuum advance is NOT plumbed to full-time manifold vacuum
5) install a NEW PCV valve on a proven to be good hose
6) reset the idle-timing to in the range of 8 to 10 degrees
7) set the idlespeed to 650/700 in Neutral
8) reset the mixture screws for best idle
9) Prove that the only air the engine is getting, is passing thru/past the throttle valves.
10) now, you have eliminated about 90% of the cause of a low idle-vacuum, in your case only the cam is left, and maybe the CCP.
As for me, I would not care what the idle vacuum might be at this point.
But if you think it is still low, and the engine does not have a pronounced idle-lope, then you might like to check the cam timing. BUT, you do not have to take the engine out to do this.
and there is a shortcut, which on a solid-lifter engine is pretty easy. You just go find Split overlap on #1 cylinder and if it is within the range of 4*advanced to 2* retarded; forget about it. Save yourself a lotta work.

Notes;
TDC is Top Dead Center
WOT is Wide Open Throttle
CCP is Cranking Cylinder Pressure.
Split overlap should always occur within a few degrees of TDC, on the switchover from the exhaust stroke to the intake stroke; no matter what size the cam is. Almost 100% of the time the cam will be in slightly advanced. You can read the amount, right off the proven balancer. Easy peasy. The best time to do this when you are adjusting the valves. The cam-chain should be reasonably tight. You are only looking for a gross error. Theoretically, the valve-lash on the cylinder to be tested, (usually #1 but could be #6) should be reduced to zero, prior to checking, then restored afterwards. But you can do a quick-test without doing that, and be close enough to tell if the cam is out a tooth. This will not be accurate with a sloppy chain.
IMO, Your CCP at your elevation in NY should be close to or over 140psi on an original 2bbl engine, more on an original 4bbl engine.
 
you can make a piston stop with a spark plug anti fouler and a piece of all thread. put all thread in bottom hole and run two nuts. You can even adjust it. Or just buy a cheap piston stop online. Super down and dirty is an old plug with the porcelain knocked out and a bolt welded in.
 
Hi Guys, I am starting back for the winter to find out the problems with my friends 1964 273 Dart Convertible with a 4-speed.
How do I tell from any engine #s what engine we have? Not sure and it has been worked on many years ago. Is there any way to tell if it's originally a 64 or 65 273 w/ 2bbl or a 65 273 Commando 4-bbl.
Bob
 
IIRC, pre 67 cars did not have VIN-branded engines, so the date code on the engine is as good as it gets.
There should be a number stamped onto the front of the block, just below the driver's side head. This number is a code, and from it you might be able to tell a bit about the engine.
 
If I remember correctly the exhaust valve on the 273 sordid cams lash were set at .022. Made them a little noisy. Might check the valve lash.
 
I saw some Cam Specs and has 0.13 intake and 0.21 Exhaust. Just going by that. I am assuming that would by HOT.
Is that correct adjust HOT and do those gaps seem correct.
Bob
 
Vcode said:
do those gaps seem correct.
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yes; just be sure you are actually measuring between the stem and the rocker proper, and NOT bridging across a grove worn into the rocker-pad, which occasionally happens.To ensure success I use a feeler that I have cut narrow to fit in there from the end.
 
Vcode said:
Ok, Thanks I have some great info here and will report back late next week on what I have found.
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After going over the timing and checking everything, I think I got it. Seems that the guy that worked on it before I took over had a few exhaust rockets too tight. It did run better at idle. I did not take it out on the road yet. The vacuum came up to 17-18
 
17-18 is good. You want to set the idle at 700 (eg) then turn the mixture screw until you get the best idel and highest vacuum then reset the idle set screw to 700 and do the mix screws again. Keep doing this until there is no change.
 
Vcode said:
After going over the timing and checking everything, I think I got it. Seems that the guy that worked on it before I took over had a few exhaust rockets too tight. It did run better at idle. I did not take it out on the road yet. The vacuum came up to 17-18
Click to expand...
UPDATE:
The Dart was running Great for 3 months. I fixed the misadjusted Rockers from the past bad mechanic. My friend said it never ran so good, he was so happy. Disaster struck when he was driving it on the highway about 60 mph and it started to stumble, running rough and one backfire and pulled over. it stopped running and now hard to start and if it does start it will not run for more than 20 seconds. I had carb bench checked, points, coil, ballast, fuel pump pressure 6 and gas is clean and no water. I think the only thing left is check compression, valve timing or adjustment screws moved. I had 18 inches of Vacuum and a smooth idle, 12 degrees initial timing. Am I missing something.
Bob
 
CAVEAT!!!! Don't rely on parts store vacuum gauges, the typical fuel pressure/ vacuum gauge

Not long ago, I put an AC system into my neighbor's son's house, this is R410A, and I read that they are way more finicky on vacuum, so I ended up with a new pump, some additional test equipment, a nice big 3" gauge, and 4 old automotive gauges I've had for years

NOT ONE of those old automotive ones (along with some of my other stuff) was anywhere near correct. I believe they were off 2-3" Hg in some cases
 
If the vacuum has changed AND, the timing has changed, AND it takes a lot of throttle to achieve rpm, then in all liklyhood, the Timing chain has jumped.

There is an easy way to check chain stretch; just crank the engine over by hand until she meets resistance, Then crank it the other way. First it will move easy, but then, suddenly, as the slack is taken up, it will get hard again. If you cannot feel it, then pop the Distributor cap off and watch the rotor. If the crank moves more than 4 degrees with no reverse motion of the rotor, go to plan-B
Plan-B
With Solid lifters there is an easy way to check this.
1) First prove that the timing marks on the damper are correct to within a degree or two.
2) remove whichever valve cover is easiest. If the Driver's side, go to the front cylinder, if the passenger side, go to #6.
Crank the engine over until the chosen cylinder is making compression, bring it to TDC, then manually crank it over exactly one revolution.
3) this puts her on the overlap cycle where one valve is just opening and the other is just closing. Shuttle the crank back and forth a few degrees looking for a position where both valves are approximately the same amount open, When you find it STOP. read your timing. It should be in the window of TDC>6 or 8 degrees BTDC.
4) if it is then the cam is in pretty close.
5) but if it is not, then the cam is out of phase

AFAIK the original factory 273 top sprocket was all steel and those are hard to jump a chain on.
But the nylon-capped 318 sprocket only lasts reliably to maybe 90,000 miles, and then it tears all those nylon caps off, or sometimes just 25% of them cuz the engine quits running.
 
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AJ/FormS said:
If the vacuum has changed AND, the timing has changed, AND it takes a lot of throttle to achieve rpm, then in all liklyhood, the Timing chain has jumped.

There is an easy way to check chain stretch; just crank the engine over by hand until she meets resistance, Then crank it the other way. First it will move easy, but then, suddenly, as the slack is taken up, it will get hard again. If you cannot feel it, then pop the Distributor cap off and watch the rotor. If the crank moves more than 4 degrees with no reverse motion of the rotor, go to plan-B
Plan-B
With Solid lifters there is an easy way to check this.
1) First prove that the timing marks on the damper are correct to within a degree or two.
2) remove whichever valve cover is easiest. If the Driver's side, go to the front cylinder, if the passenger side, go to #6.
Crank the engine over until the chosen cylinder is making compression, bring it to TDC, then manually crank it over exactly one revolution.
3) this puts her on the overlap cycle where one valve is just opening and the other is just closing. Shuttle the crank back and forth a few degrees looking for a position where both valves are approximately the same amount open, When you find it STOP. read your timing. It should be in the window of TDC>6 or 8 degrees BTDC.
4) if it is then the cam is in pretty close.
5) but if it is not, then the cam is out of phase

AFAIK the original factory 273 top sprocket was all steel and those are hard to jump a chain on.
But the nylon-capped 318 sprocket only lasts reliably to maybe 90,000 miles, and then it tears all those nylon caps off, or sometimes just 25% of them cuz the engine quits running.
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Thanks for the info, I had checked the timing chain 4 months ago. Past mechanic changed it to a Summit one and it was correct. Has a new dual exhaust system. Was thinking to check mufflers, maybe clogged. Just something else to clear up. Can't get this thing to run long, maybe 10 - 20 seconds to check vacuum now. Will check chain again.
 
Vcode said:
UPDATE:
The Dart was running Great for 3 months. I fixed the misadjusted Rockers from the past bad mechanic. My friend said it never ran so good, he was so happy. Disaster struck when he was driving it on the highway about 60 mph and it started to stumble, running rough and one backfire and pulled over. it stopped running and now hard to start and if it does start it will not run for more than 20 seconds. I had carb bench checked, points, coil, ballast, fuel pump pressure 6 and gas is clean and no water. I think the only thing left is check compression, valve timing or adjustment screws moved. I had 18 inches of Vacuum and a smooth idle, 12 degrees initial timing. Am I missing something.
Bob
Click to expand...
First thing to check is do you have spark and does it have fuel in the carb. A bad condenser can cause your issues.
 
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