LOW budget engine not working well....HELP!

[jberenyi]

Another possibility is that there is a vacuum leak someplace.......

As noted earlier we have a lean condition.  Cupping the airhorn raises the rpm.  After changing the mixture screws from 5 turns out to 8 turns out the roughness got better.  Probably 90% there.  I plugged all vacuum sources and sprayed all gasket areas with starter fluid and no change.  We don't have a vacuum leak.

[jberenyi]

"Do I have to wait for the engine to break in due to a lower compression till the rings seat?"
No. Should be no difference

So your saying an engine with 10 miles on it has the same compression as when it has 1000 miles on it?  Really?

"one month ago my friend let the oil get low and spun a bearing "
Why would the engine oil go low on a good engine?

I can't account for someone's lack of checking their oil. 

"While at it we ground the valves and put new seals in"
When you say we I hope you mean a Professional

Yes.

"The cam is the same one when I bought it."
A used cam?

Original used cam as noted in my thread above.
 
"I don't understand why the carb has a rough idle"
Have you ever thought it might not be the carb. Why was the carb fine before the motor was taken apart?

That's the $50,000 question

 
"Vacuum is about 15Hg at 1000 rpm"
Maybe you should be checking your engine repairs / valve job.

I don't question the valve job.  I do question how long it will take the rings to seal though.  BTW when the idle was at about 650 to 700 it was 10Hg if I remember correctly.

[Mudsport96]

Bump your timing to 16 degrees btdc and see gow it reponds.

[jberenyi]

Bump your timing to 16 degrees btdc and see gow it reponds.

At 14 deg she's doing fine.  At 2800 rpm she pulls in at 36 deg with vacuum cannister blocked.  I don't think I want to go any higher than that.  When Clifford did my disty he also made sure the cannister was correct.  Lately I've done a fair amount of study how the idle metering circuit works and IMHO I think I don't have enough manifold vacuum to pull fuel up the idle tube on through to the down restrictor.  With having the cylinder bores professionally honed and new rings maybe we have to wait for full break in to happen so we can get the increased vacuum like it had before.  Looking at all the variables this is the only thing I can come up with other than the valves being jacked up which I know is not the case.

[Cliff Ruggles]

How much manifold vacuum did the engine make before the "rebuild"?

There is not going to be any improvement in engine vacuum based on ring seal.  If it was done correctly the rings were sealed as good as they will ever be a few minutes after you fired up the engine. 

Did you change the timing set?

If so what did you use?

[Kenth]

10 in/hg at 650-700 rpm´s is about half of what´s expected on a std 1974 350.
Check valve settings, adjust with engine running. 1 turn down from just stopped clatter is fine.

[old cars]

"BTW when the idle was at about 650 to 700 it was 10Hg if I remember correctly."
If this is correct then there is the answer. You have a mechanical problem.
Do as Kenth said. Compression test and cylinder leak down test also. You could have an intake leak on the valley side. You need to chase down down the reason for low vacuum.

Last year I had a fellow show up saying he had a carburetor problems on his 383 mopar. I looked at the vacuum gauge, wandering from 8 to 10 inches and and told him it wasn't the carburetor. Never seen the car on the road since.

Four years ago I built a new 454 motor for my Monte Carlo. Bored and finished with a boring plate, new pistons and Total Seal rings. I tour with this car and have never added a drop of oil since firing it up. I change the oil once a year.

A few years ago someone asked me to assemble a 455 Pontiac engine that just came from the machine shop. They bored the cylinders , machined the crank, did a valve job and valve guides, supplied all parts for assembly. This was an original numbers matching 1970 GTO. The new pistons were "rebuilder pistons" with the wrong compression height. Sent them back. I checked the valves for leakage and sent the heads back. The machinist said the valves would seat in when you start the motor. Not good enough for me. We also sent the Camshaft back.
A couple months later I was rebuilding an AMC motor and doing a valve job ( I have my own equipment) . The owner of the 455 pontiac walked in and watched me do a leak test on the valves. He asked , any leaks. No there wasn't.
A few weeks ago a mechanic friend told me he was going to "freshen up" a motor for a numbers matching 1968 Cougar. He asked if I thought it would need boring. My answer was. I've never seen one that didn't need boring.

[Cliff Ruggles]

+2

I've never seen a used block that didn't need bored either.  Even if it was decent, the pistons will ALWAYS have wear in the ring lands.

The blocks will also have tapered wear, less at the bottom and more a the top.  This is why you find a "ridge" in the bores and even if it is very minimal you'll see a dark area about 1/4" below the deck surface when you hone them.

Between taper in the bores and wear in the piston ring lands your freshly "rebuilt" engine is doomed from day one.  The piston rings, traveling up and down the bores many times per second will have the rings moving all over the place.  They will loose their tension quickly and it only gets worse the more time you put on it.

This is why ring seal and ring life is never good on an engine that just gets honed, new rings and put back in service.  The bores absolutely need to be round and the rings need to fit tight in the pistons.

Putting a used cam back in an engine is another recipe for disaster.  I've seen a few folks try that over the years and knock lobes right off of them which puts millions of particles of ground up iron thru the assembly.

Anyhow, with a "stock" cam in one of those engines, even if the builder wasn't smart enough to check piston deck height and use the OEM .020" thick head gaskets to keep quench tight and compression high it still should be making up near 17-20" vacuum with normal timing in it.  I've seen folks try to run manifold vacuum advance on some of those engines (most were ported) and they idled so smooth with so much vacuum they weren't able to get the idle speed slow enough even with the throttle plates completely closed. 

I'm talking about the L-48 or base engine.  The L-82 will not make nearly as much vacuum and pretty much require higher compression and a LOT of timing at idle to make decent vacuum.

The L-82 camshaft is actually too much cam for one of those engines using the 882 castings.  They never did run all that great right off the showroom floor.  I was heavy into the muscle car thing at that time and can't say "turd" loud enough here.  From 1974 on the 350's topped with 882 heads were gas guzzling gutless pigs. 

GM didn't figure out that low compression, poor flowing heads with huge combustion chambers and restrictive exhaust ports isn't the correct approach to reducing emissions.  About all it does is kill fuel efficiency and power for the end user just to reduce emissions a tad to get by EPA mandates at that time........FWIW.......

[jberenyi]

I appreciate everyone's input thus far.  I have learned much from you all during this effort.  I instructed the owner of the Vette to come back in 500 miles when the break-in oil needs changing.  At that time I will perform a compression and vacuum check on the engine and report back my findings.  I'll be curious to see the results and how the engine is running at idle.

BTW, I know that much more could have been done to the engine like boring instead of honing and replacing the camshaft, etc.; but the purpose of this build was to get it back like before and keep cost down for the current owner.  A local performance engine building shop with 40+ years experience did the tear down analysis of the complete engine and said the bores were very nice commenting all it needed was a hone.  They also said the camshaft was fine.  We did have to get another crankshaft off the shelf from them though.  I don't think much mileage was on the engine since its last rebuild when the cylinder bores were bored .030 over.  With respect to the 882 heads; I agree their not the best but it is what it is.  And just to confirm with you all, after the valves came back ground we installed them with new seals and adjusted the preload per these instructions:

How To Set Valve Lash (SBC)
To get started, make sure the engine is cold. You can use timing tape on the balancer or very carefully measure and mark the balancer every 90 degrees to double-check the engine's rotation.
Be sure to apply a generous amount of high-quality assembly lube like Isky Rev Lube or Red Line oil on all of the contact surfaces before starting.
With the valve covers off and spark plugs removed, rotate your engine to the top dead center compression stroke on the number one cylinder. Do this by watching the movement of the lifters or rocker arms – the exhaust will open first, then the intake. As soon as the intake returns to its fully closed position you’ve reached the compression stroke.
Now you can set the valve lash on both the intake and exhaust valve. Most hydraulic lift camshafts will require zero lash for the proper adjustment. The process will be the same whether you have stamped steel rockers or roller tip rockers.
To achieve zero lash, tighten down the rocker as you spin the pushrod in your fingers, do this until you notice slight resistance as you spin the pushrod (this is zero lash). You should also no longer have any lateral movement in the pushrod.
When you know you’ve hit zero lash, tighten the rocker another 1/2 turn to set the optimum preload on the lifter, pushrod, and rocker arm.
Move to the number two cylinder in the firing order and the intake valve should already be open. Then rotate the engine over another 90 degrees or 1/4 turn clockwise while watching the lifters to ensure you're on the base circle of the camshaft lobe and repeat the adjustment procedure.
As you move through the firing order the intake valve should be open on each cylinder. Simply follow the procedure on each cylinder and be consistent as you tighten each rocker.

Again, thank you all for assisting me in this troubleshooting effort.  It has been frustrating to say the least.

[Cliff Ruggles]

Did you change the timing set?

If so what did you use?



There are some flaws in that method of adjusting pre-load on the lifters.

The goal is to make sure that you are making adjustments with the lifter well onto the base-circle of the camshaft. 

Following the firing order will work with a marked balancer, you can also set half of the lifters at TDC on the #1 firing position then again on #6.  Anyone wanting to use that method can Google up which valves to adjust at each position.

Following the firing order it is easy to get confused as you also have to know the firing order of the engine and make sure that you are on the correct cylinder when adjustments are made.  The balancer is also marked in four places at 90 degrees, most will not be so you have to make sure that happens correctly.

One must also take lifter travel into consideration.  Some lifters have more travel than others but typically 1/2 turn down from zero lash will be fine.  Some "high performance" short travel lifters are designed to be ran with less preload.

In any and all cases here I will compute lifter plunger travel first, especially with new lifters and I've seen variations from about .060" of travel to .150".  This is happening these days because there are a lot of manufacturers that have stepped into the lifter business and quite a bit of what we see now is coming from off-shore.  There are also a lot of different types of lifters out there, so very little if any "standards" in that industry these days.

The off-shore lifters are horrible and to be avoided.  Problem is that there is also a good bit of "re-boxing" going on, but that's a story for another thread on another day.  In any and all cases IF you are using a flat tappet camshaft make sure it's getting top quality USA made lifters on it or you will have issues. 

Excessive noise is one of them, and lifter/lobe failure is also very common and not a day goes buy you don't read about someone having an issue on one of the Forums.  The cam lobe failure thing is directly related to using bad lifters, although there are others that are blaming break in procedures, not removing inner springs during break-in, break in lube, lack of trace metal particles in modern oil (zinc), and about half a dozen other things which have nothing to do with the issues we are seeing. 

These cheap imported lifters are NOT made of good quality high nickel iron, nor are they finished and crowned correctly so they spin in operation.

The info above doesn't necessarily relate directly to this thread, but put up there to educate folks as to what's going on with these things.......Cliff

[jberenyi]

Did you change the timing set?

If so what did you use?

The original timing chain and gear was replaced.  There was no slack at all in the original setup.

[tayto]

OP, you need to give more details and answer the questions being asked. I just rebuilt a fresh 350 and had none of the issues you are having (low vacuum,poor running,etc). The carb has needed some minor work as it was a factory calibration minus the primary jets and rods supplied from Cliff. it sounds like not enough attention to detailed was paid to engine build. i hate to say this, but this is not a cheap hobby and when trying to go cheap you get what you pay for. been there done that. I've also found a lot of engine builders (even the "performance" shops) will put there nose up to some of the things you want. i had to be firm what I wanted and had to measured and check the machine shops work. i kept the quench tight even though machine shop warned me I was over 10:1 w/ iron heads. i didn't go crazy on camshaft and degreed it. so far it seems to run just fine on 89 octane, but I still have distributor tuning to do. i also am a firm believer in putting the engine on the dyno before putting it in your car/truck/boat. it is worth the few hundred dollars IMO to not have to worry about things once in vehicle. not trying to rain on your parade here....

[77cruiser]

With that low of vac. on a stock type build, could possibly have retarded cam timing.

[jberenyi]

The original timing chain and gear was put back in.  There was no slack at all in the original setup.

[tayto]

it has been asked twice if timing set was replaced and if so what TYPE. single roller, double roller, link belt (oem), non-adjustable, adjustable, etc. probably would be a good idea to include if the cam was degreed/checked.