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Discussion Starter #1
Installed the intake manifold back to the block (with new gaskets) after have it cleaned and painted. Some minutes after fired it up, the engine was bad idling (erratic) and shaking/vibrating a little. I need to keep high RPM (about 800/900) to improve idle. After a while, it started to make a rhythmic and loud noise like something (metallic) loose inside. It seemed came from the top end passenger side and intermittent. I've made the valve lash adjustment as much I know and learned online but the noise remained. After sometime when idling, it disappeared but the erratic/poor idle is still there as for the low power. Took the car out today for a road test and it really lacks power specially if you drive it in a small ascent street. It has a small leak where the exhaust manifold joins the head near to the #5 cylinder but I don't believe it's the cause for this low power and bad idle. Everything was fine just before restoring the intake. Engine is from an '67 Impala stock sbc 283 2bbl with power pack heads on it. Video post here: https://www.youtube.com/watch?v=w1g0jn07Ljw. Can it be some vacuum leak from intake/heads or something else? Any suggestions are welcome!
 

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That's interesting. I think i would start by pulling the valve covers back off. Maybe a loose or broken rocker arm? Very strange that it is intermittent. Doesn't sound like a noise that should be intermittent. If it was anything serious it would do i all the time i would think. Something get left in the intake port? I am stumped.

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Sounds like you may have let something fall in an intake port that has banged around the valves and perhaps got through one and is now on top of the piston, or bent a valve while banging around in there, or jammed a valve open and the piston is hitting it....I think you are going to have to pulll a head to find out.
JW
 

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As far as the poor idle, it's probably a vacuum leak. However that loud metallic noise could spell disaster. I would pull the intake, which you have to anyway to seal the vacuum leak, check for bent pushrods, pull the valve covers and turn the engine by hand and see if the valves are opening and closing. If you dropped something inside, it will bend the valve before it destroys the piston. JMO
 

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Go back to the last thing you did before the issue, pull the intake. Either way majority says dig back into the top end. Let us know.
 

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Discussion Starter #6
A fallen bolt or washer was the first thing I thought. But what I can't understand is how sounded the cadence of the noise like it was perfectly synchronized with something mechanic inside the motor. As the engine was idling about 600 RPM at that time, I doubt it was hitting pistons or valves. Very unlike of something loose and hitting somewhere and gone suddenly after some seconds. Anyway I have to fix the poor idling and need to start doing checks. Maybe I will pull the intake and check for bent pushrods and the lifters. BTW, any suggestion how to check for vacuum leaks? I'm going to do next weekend since I'm at work untill there. I will keep you fellas update anyway. Thanks a lot for all your inputs!
-Luís
 

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If you dropped a washer it will bang around couple of time and exit through the exhaust.
Get some carb cleaner and spray it around your manifold. If the rpm's go up and idle smooths out. You got a leak.
Use short directed puffs to localize the leak. Stay away from exh. Manifold and keep a old shirt and fire extinguisher handy in case it flares up. It usually never does but just to be safe as it is flammable.
 

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I would tear it down to the short block. If it is an original 1967 short block it is going to have 10.25:1 static compression and the stock two barrel cam isn't going to bleed off any of your static compression by holding the intake off the seat.

That means unless you retard the initial ignition timing to the four degrees before top dead center that it needs to run on todays gas it risks getting into detonation if the octane rating is below 93.

You don't want a 0.015 inch stamped steel head gasket on one side and a 0.042 thick composite head gasket on the other bank (what happens when you pull just one head). To drop compression you are going to want a set of two 0.042 inch thick gasket on both sides. The problem is a 283 isn't worth the $90 bucks you are going to fork out for two FelPro composite fire ring head gaskets.

A 283 beats a 305 hands down but you really want a four inch bore block to build a 327 a 350 or a 383. That is where you need to put your money, if you can find one on the cheap on your side of the pond. Otherwise you are stuck with the short stroke 283 (if you can find a 327 crankshaft you can build a 307).

Big Dave
 

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Discussion Starter #9
I would tear it down to the short block. If it is an original 1967 short block it is going to have 10.25:1 static compression and the stock two barrel cam isn't going to bleed off any of your static compression by holding the intake off the seat.

That means unless you retard the initial ignition timing to the four degrees before top dead center that it needs to run on todays gas it risks getting into detonation if the octane rating is below 93.

You don't want a 0.015 inch stamped steel head gasket on one side and a 0.042 thick composite head gasket on the other bank (what happens when you pull just one head). To drop compression you are going to want a set of two 0.042 inch thick gasket on both sides. The problem is a 283 isn't worth the $90 bucks you are going to fork out for two FelPro composite fire ring head gaskets.

A 283 beats a 305 hands down but you really want a four inch bore block to build a 327 a 350 or a 383. That is where you need to put your money, if you can find one on the cheap on your side of the pond. Otherwise you are stuck with the short stroke 283 (if you can find a 327 crankshaft you can build a 307).

Big Dave
I'm running 98 RON gas and the manual says the (original) compression ratio is 9.5:1. As I'm intending to keep this motor all original as possible and since I'm on this side of the Atlantic (Portugal) where isn't easy to find block parts like heads, crankshafts or whatsoever big iron for the block, have no other way. I know this setup lacks power (67 Impala 4-door sedan with 283 2bbl w/ powerpack heads) but for cruising during the weekends it's ok. I guess keeping an all original number matching car+engine & components as long as you can will be interesting in the years to come and with the today's gas price increasing all the time, even better.
As for the head gaskets, how you figured out Dave? 3 years ago, I had to replace the driver bank head gasket not due some issue but for inspection the heads, valves and cylinder chambers/pistons top (it's was all acceptable w/o any major concerns given its age/+100k milled motor). A Mr Gasket black composite gasket was used in place of the thin (factory?) stamped steel gasket. I believe the right bank still have the original steel style gasket.
I'm going to do is go back in what I did before the issue and checking what could be cause of it but keeping in mind it would be a simple minor cause like a small top end leak and going up as the simptons shows another direction, counting on you for help of course:thumbsup:

Greetings from Portugal to all!
-Luís
 

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The 283 with flat four valve relief cast pistons and 64 cc PowerPack Heads (introduced with the 283 in 1957 as an improvement over the original 265 heads) had a 10.25:1 static compression ratio with the 0.015 inch compressed thickness stamped steel head gaskets. There are variations in production from motor to motor but that is what the factory was striving for at the time. In the US we have 87 octane gas at the pump with 92 being the highest octane in many states, which is two octane points below the octane rating of the leaded gas that was sold as regular when the car was new. Your octane meets the minimum octane rating required for safe engine operation when the motor was built.

Chevrolet had no idea that the car would still be on the road this long after being produced (GM designed the car to offer seven years of trouble free operation with the consumer expected to trade the car in on a new one every five years). The second issue is that pump gas has fallen so low in octane in the states that newer version of this engine had a 74 to 78 cc combustion chamber to drop the octane requirements by dropping the static compression ratio. A lot of people on this side of the pond are not aware that their engines are on the edge of detonation thinking that because it says regular gas in the owners manual that Chevrolet is talking about todays regular, when they are not.

Everything I address on this board I use as an opportunity to address everyone who owns a car or motor that you might ask about in any post. For every person who asks there are a lot more that don't but could learn by reading my response. So sometimes what I am responding to may not make a lot of sense especially if you are translating it into a foreign language. For this I apologize.

I also suffer from a bias that is typical of Americans of my generation where we have lots of real estate with fourteen foot wide traffic lanes on multi-lane roads that were not built by Roman legionaries to accommodate their fixed by decree width carts and chariots. Additionally we have fixed speed limits (that are ignored by many) as opposed to unlimited speed limit super highways. So we Americans like to be able to accelerate quickly to pass someone going slower . This is why Americans have big V8 engines in our cars as opposed to a small efficient four cylinder with a six speed manual gear box. It takes horsepower to run at high speed (to overcome air resistance and rolling friction) but to accelerate requires torque. The heavier the car the more torque that motor has to produce. Torque is achieved in an Otto engine (a spark fired gasoline burning engine) by increasing the displacement. Hence the ever increasing size of the small block as the car grew heavier every year it was produced.

Big Dave
 

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Discussion Starter #11
I understand Dave, no apologizes need. So, in your opinion better I replace also the right head gasket, right?
BTW, what specs would be the closer camshaft replacement for it in case I would find it necessary (worn lobes)?
Thanks!
-Luís
 

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Cam wear is a problem with modern engine oil designed for engines with roller lifters and roller rockers from the factory. A flat tappet cam like yours has to have Zinc that is no longer put into modern engine oil because it could possibly pollute the catalytic converter you don't have.

You have to either buy special oil formulated for your car such as Joe Gibb motor oil or Brad-Pitt motor oil (the former Kendal GT motor oil before the name if not the formula was sold); or add a zinc rich oil supplement to your favorite motor oil.

I learned twenty years ago that oil was changing and since I was already running roller rockers the switch over to roller lifters was prompted more by performance gains than engine oil failures.

If you can not switch add GM-EOS or any name brand zinc (ZDDP) additive to your oil today. Your engine will thank you.

Big Dave
 

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Discussion Starter #13
Yes I'm already adding ZDDP in the Castrol 15W40 mineral motor oil.
My concerning is what cam specs as close as the original one (assuming the one in the motor is still genuine GM) I should use in order to replace it if need.
 

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Yes I'm already adding ZDDP in the Castrol 15W40 mineral motor oil.
My concerning is what cam specs as close as the original one (assuming the one in the motor is still genuine GM) I should use in order to replace it if need.
That is going to be tough. The cam is the same as used in almost all SBC V8 base motors. I can give you the part number and the specs and the identifying casting marks to identify what you have as being original, but finding a replacement will not be easy.

If you find a donor motor with a base cam in it and wish to use it in your motor you will have to keep all of the lifters on the exact same lobe that they came off of.

I use an old lifter box to segregate the lifters and know where they go by writing front on the one end of box so I know how the box is oriented and then rite E1,I1,I3,E3,E5,I5,I7,E7 down the right side of the box with a black permanent ink Sharpie felt pen to tell me it is a SBC cam. That tells me what the lifter's orientation in the engine so they can go back on the cam in the correct location. On the other side of the box I write down the grind number or casting number of the cam so that it can be used again if it doesn't get too rusty sitting in the storage room awaiting it's day to run again.

Back in the old days before simulation software and computer aided cam design I used to buy five or six cams to try out in an engine that were only a few degrees apart to see which one of my guestimates came closest to my expectations.

If I found what I was looking for it went into my data logs of engine builds and the others went back on the shelf as having been broken in and ready to try in a different engine at some future point in time. I used to have thirty to forty SBC cams lying in a drawer under my work bench until I pulled out the drawer one day to find a pile of rust.

Big Dave
 

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Discussion Starter #15
I just checked for leaks around the intake, carb, etc. using a carb cleaner and it seems everything sealed all around as the poor idling haven't changed. And the strange noise didn't appeared anymore, which is curious in my opinion :confused:
I'm wondering if the rough idle and lack of power would be one faulty cylinder (or two). I've made a spark check for each one and all worked, which means it has current but what I don't know is if the all plugs are sparking. I'll have to check the plugs one by one. In case they will, then I'll make a compression test and/or valve adjustment (again). And so on, until find out what is wrong with this motor. What you guys think about this logic? Is there anything else I'm forgetting?
I'll do all these checks in the next week and this time I'm going to a mechanic shop as it's a mess every time I do it in my shared car parking...
As soon I have some (positive I hope) news I'll post here.
 

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To test to see if we bent valves between rounds we would do a leak down test. I requires a leak down tester that costs about $35 to $50 bucks on this side of the pond and access to compressed air.

The test tells you if your cylinders are sealing (tests rings and valves) and if not how bad are they.

A dead cylinder (especially one that moves around) is usually an electrical problem (burnt wires or carbon tracks inside the distributor cap). I know you said all of your electrical parts are new, but when it gets dark tonight crank it up and then turn off the shop lights to see if you have a visible electrical leak (arcing).

Big Dave
 

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Discussion Starter #17
Solved😄

After some weeks at the shop, I got the car running fine again. During the compression test, they found the plugs of the cylinders #6 and #8 smashed by a (possibly) piece of metal which should be going around these cylinders. That noise I heard and after a while is gone and the motor died would come from this metal (maybe a washer) pressed between the top of piston and the chamber eventually tapping to the plug as both 6 and 8 were destroyed. Also the top of these piston were dented. Luck for me, the compression test was ok around 128 average. The plugs were replaced (all), hydraulic valves cleaned, both heads decarbornized, new head and manifold gaskets, some adjust and tuning and that little 283 is live again and even stronger than before! Also the lack of power made sense as both faulty cylinders were ftom the same side. Now you know, never let some foreign material fall inside you engine while working on it. I learned the lesson and was "lucky" this time😃. Thanks all for all your inputs👍
 

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After some weeks at the shop, I got the car running fine again. During the compression test, they found the plugs of the cylinders #6 and #8 smashed by a (possibly) piece of metal which should be going around these cylinders. That noise I heard and after a while is gone and the motor died would come from this metal (maybe a washer) pressed between the top of piston and the chamber eventually tapping to the plug as both 6 and 8 were destroyed. Also the top of these piston were dented. Luck for me, the compression test was ok around 128 average. The plugs were replaced (all), hydraulic valves cleaned, both heads decarbornized, new head and manifold gaskets, some adjust and tuning and that little 283 is live again and even stronger than before! Also the lack of power made sense as both faulty cylinders were ftom the same side. Now you know, never let some foreign material fall inside you engine while working on it. I learned the lesson and was "lucky" this time��. Thanks all for all your inputs��

You are going to laugh: but I run a screen beneath my Holley Dominator because all of the throttle linage that is supposed to be on the outside of the carb is located in the cavity in the center of the carb. These parts fall off all the time and go into an engine that has intake ports large enough for a six year old to reach out to touch the valve from out side the engine.
Why do I do that? Because said parts have fallen off into one of my engines in the past and the motor didn't like it one bit.

Big Dave
 
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