Pushrod length after milling heads

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Standardissue

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I was hoping someone might be able to point me in the right direction on pushrod length for a new build I’m doing. My 318 in my Dart seized and I’m “building” a 360 to replace it. I have a freshly rebuilt ‘85 short block 360 that has the pistons about 0.045 in the hole. I got a set of J heads off another member and CC’d them at 72 CC. A local machine shop that does good mopar work is milling the heads 0.050 and taking some off the intake side for fit. He believes I may need slightly shorter pushrods but the stock may do fine with the non-adjustable rockers. I have had trouble finding a set in my price range. I’m planning on running the stock style stamped rockers. Is it necessary to change pushrods? If so does anyone have any recommendations?
 
Standardissue said:
I was hoping someone might be able to point me in the right direction on pushrod length for a new build I’m doing. My 318 in my Dart seized and I’m “building” a 360 to replace it. I have a freshly rebuilt ‘85 short block 360 that has the pistons about 0.045 in the hole. I got a set of J heads off another member and CC’d them at 72 CC. A local machine shop that does good mopar work is milling the heads 0.050 and taking some off the intake side for fit. He believes I may need slightly shorter pushrods but the stock may do fine with the non-adjustable rockers. I have had trouble finding a set in my price range. I’m planning on running the stock style stamped rockers. Is it necessary to change pushrods? If so does anyone have any recommendations?
Click to expand...


Yes, you need the correct pushrod length. You start milling stuff down .050ish, and then the guy doing the valve job fudges his work a bit and sets the stem hights on the high side (or maybe a touch more because what's .010 between friends) and we have a block that we don't know how much if any has been removed.

Then we have the cam, which may be a regrind which could have a slightly smaller base circle, or it could be a core with a with a bigger than usual (yet still in spec) base circle and you start adding it all up and you are burying the plunger in the lifter.

Or, it could be all whack and everything is on the opposite end of tolerance and the pushrods are too short, which will be highly unlikely in your case because of the milling.


The point is don't guess. Preassemble and measure everything and order the correct length pushrods.
 
What YR said
what compression ratio is your target since you cc's the heads show the math
and what gasket?
Thick Fel Pro gasket you offset some of the mill job so you might get lucky- might not
trying to get a little more CR with a .028 or shim gasket "might not" is more likely
new springs?
 
yellow rose said:
Yes, you need the correct pushrod length. You start milling stuff down .050ish, and then the guy doing the valve job fudges his work a bit and sets the stem hights on the high side (or maybe a touch more because what's .010 between friends) and we have a block that we don't know how much if any has been removed.

Then we have the cam, which may be a regrind which could have a slightly smaller base circle, or it could be a core with a with a bigger than usual (yet still in spec) base circle and you start adding it all up and you are burying the plunger in the lifter.

Or, it could be all whack and everything is on the opposite end of tolerance and the pushrods are too short, which will be highly unlikely in your case because of the milling.


The point is don't guess. Preassemble and measure everything and order the correct length pushrods.
Click to expand...

I was worried that would be the case, but pretty well knew it would be. I just wanted a second opinion before doing anything. I’ll defiantly go ahead and measure it before just assembling. I am not sure how long that will be, I am off for school so my engine is almost 2 hours from me. I do appreciate the shared knowledge.
 
Wyrmrider said:
What YR said
what compression ratio is your target since you cc's the heads show the math
and what gasket?
Thick Fel Pro gasket you offset some of the mill job so you might get lucky- might not
trying to get a little more CR with a .028 or shim gasket "might not" is more likely
new springs?
Click to expand...

My target is just above 9:1 or at 9:1. I am running a .474 lift Mopar Purple Shaft from my 318 if it wasn’t hurt. Using Summit’s CR calculator(I understand this is not completely accurate) I came up with about 9.58:1. The engine is bored 0.030 over, Pistons I measured to 0.045 in the hole, stroke is stock 3.58”, and pistons are valve relieved to 10CC. I plan on running a set of Mr. Gasket 0.028 head gaskets. The 0.050 off the heads I expected to bring it from 72CC to 62CC. I am unsure of the springs as the guy I bought them off didn’t know much about them. It looks like they have a valve job done recently, but the shop is going to check coil bind on them
 
How much are you going to have in your entire engine project? You are worried about pushrods "in your price range"? You can get any custom pushrod length you want for probably right around 100 bucks. If you're worried about an extra 100 bucks, you may as well just sit around and watch Beavis and Butthead reruns all day.
 
If you liked the 280 purple shaft in a 318 you will love it in a 360
while dated it is still better than any chevy grind out there
For info: a 280 mopar has more seat duration than a 285 Comp or other cam rated at .006 and more than a 290 Crane or any White Box cam rated at .004 or by the SAE method the mid 9 compression should be fine with that big cam
hope you kept the lifters in order, if not get them refaced (budget build) new timing chain if needed and new springs that lift - well I'll ask the group if stock 340HP springs would work they can be had about as inexpensive as anything- and good viton stem seals the center two exhausts do get hot
if you have the 280-280 version you should have headers
check your rockers for wear- channels where the stem was riding I would not use worn rockers on new valves
thin lash caps will prevent grooving the rockers but should not be a problem with moderate valve spring pressure
If you need new lifters get Magnum/AMC and oil through the pushrods to help with pushrod push through the lifter cup problem
 
play the straub utube vid on "rocker geometry", highly recommended by Mike at B3 racing, a top of the line guru on this stuff. in a nutshell once you get the geometry right you hold the rocker "up" with your finger & at that point measure the pushrod length you need, adding .020" or so for preload if hyd or subtracting your lash if solid. EDIT & if you ain't changing geometry (raising/lower the shaft or screwing the rockers down the # of turns in the vid), just mock it all up & same thing, lightly raise the rocker with your finger & lengthen the checker pushrod as noted to take up the slack, & + or - a bit more depending if hyd or solid.
 
Last edited:
Wyrmrider said:
If you liked the 280 purple shaft in a 318 you will love it in a 360
while dated it is still better than any chevy grind out there
For info: a 280 mopar has more seat duration than a 285 Comp or other cam rated at .006 and more than a 290 Crane or any White Box cam rated at .004 or by the SAE method the mid 9 compression should be fine with that big cam
hope you kept the lifters in order, if not get them refaced (budget build) new timing chain if needed and new springs that lift - well I'll ask the group if stock 340HP springs would work they can be had about as inexpensive as anything- and good viton stem seals the center two exhausts do get hot
if you have the 280-280 version you should have headers
check your rockers for wear- channels where the stem was riding I would not use worn rockers on new valves
thin lash caps will prevent grooving the rockers but should not be a problem with moderate valve spring pressure
If you need new lifters get Magnum/AMC and oil through the pushrods to help with pushrod push through the lifter cup problem
Click to expand...

I am hoping the cam is still good, I have not had free time to pull the 318 yet as school has taken all my time, so the lifters are still in order. Otherwise the short block has a new Melling .458 lift. That’s all I know about that cam, so I would like to use the Purple Shaft for sure. The heads’ rockers are a little worn but I have a set and shafts that look like new the guy threw in with the short block. I am mostly just trying to plan things right now, I have four years left of school so I currently have no income and all parts to get my car back up will be paid with loans meaning I’ll be paying interest on any parts I buy.
 
Rapid Robert said:
play the straub utube vid on "rocker geometry", highly recommended by Mike at B3 racing, a top of the line guru on this stuff. in a nutshell once you get the geometry right you hold the rocker "up" with your finger & at that point measure the pushrod length you need, adding .020" or so for preload if hyd or subtracting your lash if solid. EDIT & if you ain't changing geometry (raising/lower the shaft or screwing the rockers down the # of turns in the vid), just mock it all up & same thing, lightly raise the rocker with your finger & lengthen the checker pushrod as noted to take up the slack, & + or - a bit more depending if hyd or solid.
Click to expand...

I will definitely have to look up the video. I have very little experience working on cars, and my Dart is my first car purchase. I am trying to do as much of the work restoring it myself as possible, so I really appreciate the shared knowledge
 
melling has a great catalog
should not be too tough to determine what cam it is given the lift
when you do post all the details
nothing wrong with melling's quality
 
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