ZERO VACUUM AT INTAKE, 1951 CHEVY 216

[crazycars]

1951 Chevy, inline 6, 216 cu in. Almost no vacuum at the intake manifold, barely enough to pull fuel down.  I checked my manifolds over carefully, belt sanded them and they looked perfect using a straight edge. Cleaned everything and installed with new gaskets and gland rings.  Zerol  The engine is pretty tired with cylinder compression around 65 lbs, 90 with oil added. It's possible to get the engine to run with a completely closed choke but that pretty much stinks. Soots up the plugs in no time, too.  No water in the oil, no oil in the water, no steam.  What do you guys think?  Sure appreciate all answers. 

[Bloo]

2 minutes ago, crazycars said:

The engine is pretty tired with cylinder compression around 65 lbs, 90 with oil added

is that on all cylinders? 65lbs and fairly even? A low compression engine like a 216 should run fine I think even if a bit tired. What's the history? Did it happen suddenly? 

 

 

[roysboystoys]

Valve timing or adjustment is where I'd start. Are you checking the vacuum while the choke is closed?

Certainly will lower vacuum.

[crazycars]

I checked vacuum with the choke open, full open throttle. Checked compression with chole open. 65-70 lbs. Do not know history just that it sat for a long time. I haven't had it very long.

[rocketraider]

Where are you checking vacuum? Might try running a piece of stiff wire through the vacuum port to make sure it's not plugged with carbon, mud dauber nest etc.

[Oldtech]

How are you checking? hand over the carb? or with a gage. If using a gage you must have the throttle closed.   It should run ok with those comp numbers. It sounds like the carb or fuel supply has problems if it only runs at full choke. Clean the carb, if not done already, and check the fuel delivery from the pump. remove the line and have it pump into a can, should have a health squirt every 2 revolutions. 

[Bloo]

There's gonna be no vacuum with the throttle full open. That's normal.

 

You would normally check compression with the throttle open, but everybody has their own method it seems. I wouldn't worry at all about 65psi for now. You had it running, right? Just badly? If it wasn't knocking you probably have a runner. We can help you figure this out.

 

 

[Rusty_OToole]

Try checking vacuum with the engine idling. Use the port for the vacuum wipers not the one for the vacuum advance.

[roysboystoys]

Plugged exhaust can cause zero vacuum, but I think you are testing it wrong. Rusty had the best tip yet, check at wiper port.

[crazycars]

I did disconnect the exhaust pipe to make sure. Same. Not giving up!

[TTracing]

I agree recheck the carb it should run sounds like fuel issue

[Rusty_OToole]

An engine can't run at idle without pulling vacuum. In other words what you say is impossible. I don't know how you are checking vacuum but if the engine is idling normally and you have a good gauge connected to the manifold you should have about 21 inches of vacuum if the engine is healthy, maybe 15 or 16 if it isn't. The needle should be steady, if it wavers that is a sign of burn valves. You can tell quite a bit from a vacuum gauge if you know how to read it. I don't have time to write a million words explaining it but you can probably find something on the net.

[DFeeney]

I have read the above comments and agree  with the "Real World" mechanics.  I am surprised in your description you have not said how you are checking   the vacuum.    Put a vacuum gauge on it and post the reading.  This how you know where to start.  It's not "Rocket Science"

[Rusty_OToole]

Could be the idle jets are plugged and it will only run if you rev it high enough for the main jet to kick in. Could be a massive vacuum leak. Could be a lot of things an old time mechanic would recognize at once. Not enough information to tell much.

[c49er]

When, if, you get it running ok and running for a while re-check the compression on the engine hot. Numbers should be higher.

Throttle wide open for this compresson check.

Edited June 24, 2023 by c49er
Spell check (see edit history)

[crazycars]

I can barely keep it running by closing the choke completely. Have to keep pumping the gas. Cannot find any vacuum leak. Had the manifolds milled and I installed with new gaskets.   Tried other carbs but the issue is that the intake doesn't draw. I am going to scrap this 216 and go with a later 235.  Maybe there is some kind of internal crack. The oil and water are all ok.

 

[Bloo]

I wonder if the intake has an internal hole in the heat riser letting exhaust in? As I understand it, a Chevrolet manifold is all cast iron around the intake passage through the heat, so it shouldn't rust out.

Pontiacs on the other hand used steel tubing inside there. They do rust out and the symptoms are very much like what you describe. It's hard to develop much vacuum when the intake is open to the exhaust. Maybe it is time for a close critical second look at the manifolds on this 216.

 

[Rusty Heaps]

Don’t scrap it. Have you checked the Bakelite carburetor insulator? I had one that was cracked and wouldn’t let the engine run right, had to choke it out. Just a small part can make a big difference.

[DFeeney]

Engine problems are like a marriage,  Sometimes you have a choice,  "Give Up" or work through the problem.   You say you have good vacuum but you have not posted the reading taken at idle.  If you have 17" at idle I would suspect a fuel problem.  You say it will not run with the choke open.  I would leave the choke open and start it with  spray either.  If it won't run without more either looked into your carb/fuel pump.  216's ran forever "Back in the Day"

[Rusty_OToole]

This is the kind of problem an experienced mechanic could diagnose in 10 seconds if he saw the car. Not so easy from 1000 miles away depending on a half assed description. My guess is a bunged up carburetor that I could fix in 2 minutes but it could be a lot of things, most of them easy and cheap to fix. Easier than replacing the whole engine anyway.

[crazycars]

Rusty, I have tried three carburetors, one I rebuilt.  There is nothing sucking the air/gas mixture down the venturi.  Had the manifolds off and trued. It's got to be some sort of internal crack.  Wish an average compression of 60-65 lbs, this engine is not a great candidate.  I am in the process of buying a lo mileage, rebuilt 235 from a 56 BelAir. Not crazy about doing an engine swap but I do like this car.

 

[c49er]

Did you leave rags in the intake/exhaust ports while the maniflolds were e engined used abeing surfaced then not remove said rags?

Those engines used a fiber camshaft timing gear...maybe damaged teeth...

 

[Rusty_OToole]

4 hours ago, crazycars said:

Rusty, I have tried three carburetors, one I rebuilt.  There is nothing sucking the air/gas mixture down the venturi.  Had the manifolds off and trued. It's got to be some sort of internal crack.  Wish an average compression of 60-65 lbs, this engine is not a great candidate.  I am in the process of buying a lo mileage, rebuilt 235 from a 56 BelAir. Not crazy about doing an engine swap but I do like this car.

 

Sorry, I guess you are right. The old engine is pretty tired, if you can get a good 235 reasonable it is a good swap.

[crazycars]

I appreciate your input, Rusty.  This car won't win any trophies but it's a nice driver.  

 

[Rusty Heaps]

On 6/25/2023 at 6:26 PM, c49er said:

Did you leave rags in the intake/exhaust ports while the maniflolds were e engined used abeing surfaced then not remove said rags?

 

 

I forgot to pull the paper towels out of the intake and exhaust ports on the 216 in my ‘50 Fleetline when I pulled the manifolds. They were sucked through and blown out as sooty confetti! 🤣 No harm done.

Edited June 29, 2023 by Rusty Heaps (see edit history)

[john hess]

3 hours ago, Rusty Heaps said:

I forgot to pull the paper towels out of the intake and exhaust ports on the 216 in my ‘50 Fleetline when I pulled the manifolds. They were sucked through and blown out as sooty confetti! 🤣 No harm done.

you are not the only one who has ever done that.!!!. guilty myself..

[Frank DuVal]

One of my body men, back in the shop days, 90s, bought a 429 that was said to be rebuilt and stored, but would not turn over 360 degrees. Not stuck, but not able to do a full rotation. So he didn't pay much for it.

 

Pulled heads, red shop rag in one cylinder.🤣

[Rusty Heaps]

On 6/26/2023 at 10:58 AM, crazycars said:

I appreciate your input, Rusty.  This car won't win any trophies but it's a nice driver.  

 

Won’t win trophies? Hmm, that has a familiar ring to it. 

But it’s fun!

Edited June 30, 2023 by Rusty Heaps (see edit history)

[Rusty_OToole]

Those fastback or torpedo body Chevies are rare around here. I have only seen 2 or 3 of them. The pre 49 ones were never sold in Canada at all.

[WPVT]

On 6/25/2023 at 1:48 PM, Rusty_OToole said:

This is the kind of problem an experienced mechanic could diagnose in 10 seconds if he saw the car. Not so easy from 1000 miles away depending on a half assed description. My guess is a bunged up carburetor that I could fix in 2 minutes but it could be a lot of things, most of them easy and cheap to fix. Easier than replacing the whole engine anyway.

I agree. The 216 is about as simple as an engine can get. There just aren't any mysteries. 

Pulling an engine because you don't understand what's wrong with it is questionable.

 

 

[Rusty_OToole]

On the other hand, compression is down to 65PSI and he knows where he can get a good 235.

[chistech]

I just put a new head on a 30 that the owner overheated badly. With the cooling system full, it was pushing compression into the water and 4 of the 6 cylinders were down to 50-60 and the other two at 65. That motor actually ran well in that condition and it is an updraft carbureted engine. Something seems off with you not being able to get enough vacuum for fuel draw at those compression readings with a downdraft carb. This 30 was in pretty bad shape but still ran well enough but pushed water.
     It now has a new head on it as the other was badly warped and cracked in three places into the valve seats. I was lucky to find a good, crack free head as they’re getting hard to find.