345 engine vacuum

S

scout279

New member
We did a compleat engine rebuild on a 1979 345 out of a Scout II. My question is there is vacuum in the valve covers, that if you take the oil filler cap off the engine will die. Also the pcv sucks air in so there is vacuum under the valley pan. I am sure all this vacuum should not be there. Did we forget or missed something during assembly? Other than that engine starts and runs fine.
 
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You have a bad pcv valve. At idle the valve should be mostley shut off. Also there is a air return host that connects to the valve cover and the other end to the air filter housing. This allows the air drawn out of the engine to be replaced so there is no effective net vacuum in the crank case.
 
We changed the pcv, that did not make a deference. I should have said that we have all hoses in the righful spots. That includes the hose from the spark arrester to the air filter.
 
Ok
if you stick the pcv valve in the hose and hook it up to the engine it will idle normally whether it is stuck into the valley pay or not. The fact that it is sucking the engine down is either a blocked arrestor or a defective pvc valve. Is the pvc valve backwards? The fact that the engine dies when you pull the valve from the grommet or open the oil filler cap indicates an excessive flow through the valve.

Under situations of high vacuum the rattling element draws up and blocks the high flow rate.

Test. Remove the pcv valve and block the hose. Does it idle ok then?
 
Hi Robert, I really appreciate the help you are giving me. From the first time we started the engine and made the normal adjustments. This engine has ran fine. It even idles with no problem. Taking the pcv out of the rubber grummet with the hose still attached. Pcv is working, but if you put your finger in the whole there is enough vacuum ther to suck your fingre right in.
 
With the valve out of the grommet and not blocked by your finger, hows it idle? You feeling the suction is normal.

After you block the valve with your finger the pcv will open because the suction is no longer working to such in the poppet with-in the valve.

Remove and block the valve port at the carb/manifold and block the pcv valve it self. Is there still suction at the oil fill cap?
 
With the valve out of the grommet and not blocked by finger, engine does not idle. With pcv grommet hole blocked engine will idle. Putting finger on bottom end of pcv I can feel and here pcv working. This by putting finger on and off of bottom of valve. The suction at oil fill cap always remains. The suction is always strong there so when you remove it, you got to put a good grip on it. I can here the air sucking in as I remove it, engine instantly dies. I am really at a lose on this. The machine shop that did most all the work. I had the crank turned bearings to match. New pistons, rings and rods recondition. Machine shop also did the heads. The machine shop assemble the block including new cam and bearing. My youngest son and I put the rest together, heads, intake and everything else. The man from machine shop said he would come out around August 16, to check it out. If its something he has done wrong he will fix it.
 
Could you post a few pictures of your engine making sure to capture all hoses and vacuum hose connections?


Just a note, you say that with the pcv valve out of the grommet you still have vacuum in the engine? Unless something is hooked up wrong that is just about impossible. On these sv'c the only connection the engine internal area and the vacuum created by the intake is the hose routing and the rocker arm bolts that you May have that penetrate into the intake runners. If the bolts were missing it would look like an oil fire when running.

I know the vacuum routing on the 79 345 intimately and is it possible the arrestor and pcv valve are both hooked to vacuum?
 
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I like permatex thread sealant. Arp also makes a good version. If you have a favorite sealer that is recommended for threads it will also work.
 
After taking valve covers off. It was obvious what was causing the vacuum problem. There are 4 bolt holes on each head. Each hole going in to the intake valve port. After installing bolt with sealer in all 8 holes. Problem solved. But can you tell me why are they there, and what there used for.
 
They are a carry over from a 9 stand rocker assembly setup. Later on IH eliminated the extra holes and built the engines only with the 5 stand setup with the boat rockers.
 
Yeah, the engine was built with several different rocker assemblies over the years. It started out with a 9 stand, welded rocker with umbrella type pushrods. Later, supposedly for costs, they switched to a stamped steel rocker with ball style pushrods, then later to only 5 stands with springs in between to center the rockers. People will say that they didn't make stamped assemblies with 9 stands, but I have one. Some of the best advice I've read on this site is to clean out the rocker shafts and stands. They clog and fail to oil the valvetrain. Boat rockers = stamped rockers, because they are shaped like a boat, not because they are marine.
 
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