Guest btate Posted May 9, 2013 Share Posted May 9, 2013 The word idle is used a lot and I know the service manual states idle at 450 rpm at least on an 264 ci nailhead. What would it be with a/c added. I found a chart that gave proper vacuum pressures requirements and RPM was listed 800 to 1200. That is a big spread. The chart listed 17 to 21 as proper vacuum. At about 450 rpm my vacuum runs about 14 to 15 but speed up the idle to 800 and rpm goes to 18 and 1200 rpm goes to 20. It seems many times things are too vague. Help me clear this one up. Thanks Bill Link to comment Share on other sites More sharing options...
Aaron65 Posted May 9, 2013 Share Posted May 9, 2013 I think that as long as the needle's steady, you're fine. Link to comment Share on other sites More sharing options...
TexasJohn55 Posted May 9, 2013 Share Posted May 9, 2013 Aaron, my needle is steady when it is diconnected, is it ok? TexasJohn Link to comment Share on other sites More sharing options...
buick5563 Posted May 10, 2013 Share Posted May 10, 2013 Aaron, my needle is steady when it is diconnected, is it ok? TexasJohnThen it is probably broken... Link to comment Share on other sites More sharing options...
JohnD1956 Posted May 10, 2013 Share Posted May 10, 2013 Ken found a bulletin for the 56 that states a fluctuating needle is not unexpected due to the design of the cam. I do not know if that applies to the 55 also. Meanwhile on the V8 forum there is a thread about how to read and interpret the vacuum guage reading. It's very eductional and I will try to find it an post a link in a day or so, unless someone else beats me to it. Link to comment Share on other sites More sharing options...
TexasJohn55 Posted May 10, 2013 Share Posted May 10, 2013 Vacuum guage interpretation already posted under thread "264 breakin" thread but it deserves a revisit. John Link to comment Share on other sites More sharing options...
Guest btate Posted May 10, 2013 Share Posted May 10, 2013 Thanks JohnD, my needle swings about two places or so but as I increase the rpm to 800 it becomes more steady. Link to comment Share on other sites More sharing options...
TexasJohn55 Posted May 10, 2013 Share Posted May 10, 2013 As for the fluctuating needle on stock engines, it indicates an interrupted and irregular air flow. That would be expected if he had a "lumpy" or high performance cam because of valve overlap and they are known to have low vacuum at idle, some won't even operate heater and accessory controls.. TexasJohn Link to comment Share on other sites More sharing options...
Aaron65 Posted May 10, 2013 Share Posted May 10, 2013 Aaron, my needle is steady when it is diconnected, is it ok? TexasJohnSounds like it's time to call in a professional... Link to comment Share on other sites More sharing options...
TexasJohn55 Posted May 10, 2013 Share Posted May 10, 2013 I think clarification of my post is in order. I should have said that my vacuum guage needle is steady when not connected to a vacuum source, is that normal? As for being broken and needing help, that's true but I am a little sensitive about that. TexasJohn Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 11, 2013 Share Posted May 11, 2013 Have you disconnected and plugged all vacuum sources? I like to connect the vacuum-gauge to the port at the base of the carburetor, the one for the vacuum-advance. I try to get 18-21-inches of vacuum, anything lower and something's wrong. A slight jitter is okay, but a radical "beat" is bad. Make sure your timing is set correct too; a vacuum-gauge will help you set it, and make sure it's right. Again, you want to have all your vacuum-sources disconnected while checking the timing.Hope this was some help?Jaybird Link to comment Share on other sites More sharing options...
old-tank Posted May 11, 2013 Share Posted May 11, 2013 As for the fluctuating needle on stock engines, it indicates an interrupted and irregular air flow. That would be expected if he had a "lumpy" or high performance cam because of valve overlap and they are known to have low vacuum at idle, some won't even operate heater and accessory controls.. TexasJohnThis may be part of the problem. The stock nailhead cams had a long duration and overlap to the point there were a lot of customer complaints (lumpy idle) in 1956. On my first 'rebuild' I reused the original cam and when I took it to the machine shop to check if it was still serviceable, they asked what race engine it was from. (There is a definite visual difference from a stock chevy and nailhead cam --- I would guess that if the nailhead profile was used in other engines it would be considered a race cam)The original 264 engines had a different cam than the 322's (I don't know what the differences are), but the available cams from Egge list the same part number no matter what engine.The 264 in my 51 F-1 truck was rebuilt before I got it and an unknown cam was installed (it does not have the identifiers that the stock cam had) and it is lumpy, with lower vacuum than my 322's and runs better that it should (scary fast!).My point is, we have no idea what effect the cam may have on your engine. When you get the brakes sorted out drive it!Willie Link to comment Share on other sites More sharing options...
Guest btate Posted May 11, 2013 Share Posted May 11, 2013 Jaybird, you didn't say at what rpm you were able to get 18-21 vacuum. If I run mine up to say 800 rpm I get a much better reading Link to comment Share on other sites More sharing options...
Guest btate Posted May 11, 2013 Share Posted May 11, 2013 Willie, this is exactly the reason why older engines should never be re built. The supplier are un reliable. When I tried to buy shafts for my rocker arms, the manufacture makes them for all the stocking distributors and he made them wrong and all suppliers had the defective one in stock. So, you never know what you got. I think the rotors I purchased were wrong Link to comment Share on other sites More sharing options...
TexasJohn55 Posted May 11, 2013 Share Posted May 11, 2013 This may be part of the problem. The stock nailhead cams had a long duration and overlap to the point there were a lot of customer complaints (lumpy idle) in 1956. On my first 'rebuild' I reused the original cam and when I took it to the machine shop to check if it was still serviceable, they asked what race engine it was from. (There is a definite visual difference from a stock chevy and nailhead cam --- I would guess that if the nailhead profile was used in other engines it would be considered a race cam)The original 264 engines had a different cam than the 322's (I don't know what the differences are), but the available cams from Egge list the same part number no matter what engine.The 264 in my 51 F-1 truck was rebuilt before I got it and an unknown cam was installed (it does not have the identifiers that the stock cam had) and it is lumpy, with lower vacuum than my 322's and runs better that it should (scary fast!).My point is, we have no idea what effect the cam may have on your engine. When you get the brakes sorted out drive it!WillieWillie, I should explain. I won't speak to how "jittery" or how large the fluctuations might be on a performance cam engine, maybe you can enlighten us on that from your 264 and what the vacuum is at 500 rpm. The point I was trying to make is not the jitter, but whether it is high frequency,which would indicate all cylinders contributing equally or whether it is a slow singular pulse spanning 2" hg on guage. If you hook up an inductive pick up timing light to any plug wire you can judge the frequency of the pulse on vacuum guage and determine if it is occurring once every 2 rpm or once every single rpm,etc. It really doesn't matter which plug wire you use, it will fire the light once every 2 rpm, so, if any ONE cylinder is abnormal, it would pulse at the same frequency as the timing light, if TWO cylinders are contributing abnormal dips or pulses, the frequency would be twice for every flash of the timing light. The slower you can idle engine, the more pronounced the fluctuation and the easier to pinpoint how many cylinders are contributing fluctuations. If you can get it to idle low enough, the faulty cylinders will go cold with a very pronounced miss and shake. I am fond of using my infrared temp gun to look at exhaust manifold temperatures but you have to learn on each engine just where to aim, usually within 1/2" of the mounting flange but that varies. If you start with a cold engine and can keep the rpm down it is really very easy to spot. Yanking plug wires also works but I hate getting bit! My point being even if lumpy cams are "jittery", again, I can't say, the frequency is key,assuming all cylinders are contributing, rather than 1 or 2, that's why I recommend using the timing light. CLEAR AS MUD NOW ? I may have confused myself. TexasJohn Link to comment Share on other sites More sharing options...
buick5563 Posted May 11, 2013 Share Posted May 11, 2013 When you get the brakes sorted out drive it!WillieThis^^^ Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 11, 2013 Share Posted May 11, 2013 Sorry: 450-RPM. Are you using a timing-light to check your timing: correct timing is vital when you're setting your RPM's, as well as having all the vacuum sources unplugged, otherwise your readings will be way off. To me anyway, 800-R's sounds exceptionally high, but I have a 322, but still... If they're too high, it's going to sound like you've knocked the brains outta yer car when you put into drive..."WHUMMMMMMMMMMMMP!"Jaybird Link to comment Share on other sites More sharing options...
Guest btate Posted May 11, 2013 Share Posted May 11, 2013 This coming Thursday I will be going to the Goodguys show in Nashville and that is about 130 miles or 260 round trip. Brakes come first but I still want to know compression ------and will not take long to check it. Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 11, 2013 Share Posted May 11, 2013 I should also point out that if your carb's air-fuel mixture screws aren't set right, you'll get some pretty wonky readings too; things like stumbling at low-RPM's...Jaybird Link to comment Share on other sites More sharing options...
Guest btate Posted May 11, 2013 Share Posted May 11, 2013 Jaybird, how many vacuum lines would I have? I know of the vacuum advance connecting from carb to distributor, line to wipers. I guess that is all. Did I miss one? Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 11, 2013 Share Posted May 11, 2013 Brake-booster if'n ya got power-brakes! Pull off the air-cleaner, and do a quick scan of the intake-manifold, see if you have any weird ports... I drilled one myself so that I wouldn't have to be reachin' around a really hot motor, but most people don't do that, but it's my car, and the next person who gets it will be when I'm D-E-D, and they won't be able to (expletive-deleted) at me! (Dead men tell no tales, yarrrrrr matey!)Jaybird Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 11, 2013 Share Posted May 11, 2013 If you feel comfortable enough, you may want to pull the air/fuel-mixture screws and polish them: with some wet 600-grit paper, take a wee-bit and fold it over with the screw in it, turn the screw a few times with ONLY the tip in the paper. You may also want to see if they're bent or someone with gorilla-knuckles has tried to turn them in to far. To put them back, screw them in until they stop, DO NOT OVER TIGHTEN! Turn them out again 1 1/4 turns, this is a rough setting, then play with them watching your vacuum-gauge until the motor smooths out...Jaybird Link to comment Share on other sites More sharing options...
Guest btate Posted May 11, 2013 Share Posted May 11, 2013 Jaybird, I did run the bleed screws out 1 1/2 turns and watched the vacuum go up and then did the other side to get max vacuum. Of course I would have to turn the rpm down as I adjusted the bleed screws. After that I would turn the distributor to gain more vacuum and again lower the rpm to like 500 rpm Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 11, 2013 Share Posted May 11, 2013 SCREEECH! No, the distributor is ONLY for timing!!!!!! Once that is set, don't touch it: you set all of the rest with air/fuel mixture and RPM-screw-does this help? I can see you're a bit confused as to the process, that's okay, we all have to learn somewhere.I will check back in tomorrow, good luck my friend...Jaybird Link to comment Share on other sites More sharing options...
old-tank Posted May 11, 2013 Share Posted May 11, 2013 SCREEECH! No, the distributor is ONLY for timing!!!!!! Once that is set, don't touch it: you set all of the rest with air/fuel mixture and RPM-screw-does this help? I can see you're a bit confused as to the process, that's okay, we all have to learn somewhere.I will check back in tomorrow, good luck my friend...JaybirdYou can use the vacuum gauge to set timing and move the distributor to get the highest vacuum. I advance the timing until I get the highest vacuum reading (maybe back off a little) and then check with a timing light. The completely original 322 in one of my 55's likes 5* btdc just like the factory specs. The other 2 322's with repro cams likes 7-1/2*. The 264 in my truck likes 10*. Once you get the readings, write them down so you can duplicate later or if big changes in the reading, you know you have to investigate.Willie Link to comment Share on other sites More sharing options...
old-tank Posted May 11, 2013 Share Posted May 11, 2013 For your reading pleasure:How to Use and Interpret a Vacuum GaugeVacuum Engine Timing | MILEPOSTS Garage (Tech Tips) Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 12, 2013 Share Posted May 12, 2013 Willie, yes, I was well aware, but I was trying to keep this simple, and that's more advanced timing... that's a joke 'cause, timing... and you...um...oh-boy...never mind... I had a friend who could set the timing just by listening to the tail-pipe, and it was always very accurate: ya gotta be really good to pull that one off! But, gosh, if you have something that explains the procedure...super cool!Jaybird Link to comment Share on other sites More sharing options...
Guest btate Posted May 14, 2013 Share Posted May 14, 2013 Willie, didn't know the needles actually moved under "How to use and interpret vacuum gauges" my Ipad did not bring up the scenarios. My desktop did. Best thing I have seen yet. Link to comment Share on other sites More sharing options...
TexasJohn55 Posted May 14, 2013 Share Posted May 14, 2013 NikeAjax, TIMING? Yeah, just advance it till it pings on hard acceleration, then back it up till it don't, that's all. TexasJohn Link to comment Share on other sites More sharing options...
Guest NikeAjax Posted May 14, 2013 Share Posted May 14, 2013 "my Ipad did not bring up the scenarios. My desktop did"Exactly why I'm a work-station kinda guy... Have y'all seen this one: Sorry, I just couldn't resist, yeah, I know I'm-a trouble maker!Jaybird Link to comment Share on other sites More sharing options...
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