340 build

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jays 72 duster

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OK A BODY PEEPS...building a 1971 340, swap meet find carb to pan in a crate, ran the #'s on the parts, everything is correct so far...bolting down the rocker shafts and have rocker screws backed all the way off and im still opening the valves before i ever get the rocker shaft tight??? different length pushrods??? 1st mopar dont know what interchanges with what? any help please thx
 
yes...as you tighten the shaft the valves will open
pushrods all the same length...some valves will open because where the lifter is on the cam...
 
Could be a few things out of spec that add up and make pr too long. Head or block decked + valves ground/faced that make stems stick up higher,+ cam bigger base circle all add up. You will have to get an adjustable pushrod checking tool to determine correct length then order cut to length.
 
70aarcuda said:
yes...as you tighten the shaft the valves will open
pushrods all the same length...some valves will open because where the lifter is on the cam...
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This is what's going on. ^^^^

All push rods are the same length. On the valves where the cam lobe is up, you will be opening the valve when you tighten the shafts down. It's normal and nothing to worry about with stock stamped steel rocker arms.


The 340 used to be called a SB Chevy with funny rocker arms.... :twisted:
 
Make sure the rockers and shafts are on right. There's only one correct way.
 
RustyRatRod said:
Make sure the rockers and shafts are on right. There's only one correct way.
Click to expand...

As far as rocker shaft and arm installation goes. The correct way is with the notch on the shaft facing down and on the left side, yeah? The rockers themselves are stamped left and right so I figure that's pretty self explanatory. Just trying to clarify for OP.
 
He did say first MoPar so that is a good thing to write down!
It is an easy mistake even for someone who has done a engine or two. 1 quick slip is all it takes!
 
BlueDream said:
As far as rocker shaft and arm installation goes. The correct way is with the notch on the shaft facing down and on the left side, yeah? The rockers themselves are stamped left and right so I figure that's pretty self explanatory. Just trying to clarify for OP.
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I remember it by orienting the push rod ball sockets away from each other for each set...
 
The 340 used to be called a SB Chevy with funny rocker arms.... :twisted:
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Have owned/built several 340's don't ever remember it being called that...don't insult my 340's...
 
Double check the torque spec for the rocker shaft bolts. It is wrong in several aftermarket books. I think 18 ft lbs is correct, not 45
 
Thank you all for tips, as of now I havnt done much to it, but the guys saying that the valve is going to open with the lobe up I understand that but I have the rocker adjuster screw backed all the way out and its the actual rocker pushing the valve open, didnt look for left or right rockers (maybe thats my issue) or maybe too many heiny's that evening during build lol...will keep updated thx guys
 
jays 72 duster said:
Thank you all for tips, as of now I havnt done much to it, but the guys saying that the valve is going to open with the lobe up I understand that but I have the rocker adjuster screw backed all the way out and its the actual rocker pushing the valve open, didnt look for left or right rockers (maybe thats my issue) or maybe too many heiny's that evening during build lol...will keep updated thx guys
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What pushrods do you have?
 
'71 340 came with non-adjustable hydraulics on a central shaft.
You might have to start from scratch here with adjustable rockers.
 
The correct rocker shaft placement is the passenger side shaft notch goes down and to the rear. The driver side notch goes down and to the front.

I actually thought I remembered the rocker pushrod indents went toward each other, but it's been a little bit since I have assembled one. It's very apparent which way when you assemble.
 
dont know sleepyhead what rockers? guessing 340 stuff there adjustable, but seen on here didnt know there is a left and a right (1st problem) and yes it is a solid cam (never had one before) im getting there lol thx
 
how about a pic of what you have? would help out with giving advice.

do they look like these?
 

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Dont forget to tighten those bolts down in steps, evenly from end to end. They say it prevents the shaft from bending. Theres usually only one or two valves per side that are going to move significantly more than, or move earlier than, the others, and some almost not/not, at all. Tighten the bolts on either side of those first, to finger tight, then work the pattern.
 
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