So i have a 72 318 in my 68 valiant. Its .030 over with a mild cam that i got from a guy about 8 years ago. Ran good but i wanted to give it a little more hp. So i had a set of 302 casting heads that i had redone at a local machine shop. Stock everything. I put them on with a ld4b intake and eddie 650 carb. When i tried to start it it wont idle. It started for like 10 seconds but sounded like marbles bouncing around in the valve covers. I took the valve covers off and inspected everything on both heads. The pushrods dont seem loose and the rockers or torqued to spec. I checked compression on cylinder 1 and nothing. I put my finger over the hole and i can just feel sucking. But when i had turn the motor you can hear compression. The local shop says i have too long pushrods. But my motor isnt a roller and i thought the pushrods were all the same sizes for LA 318 non rollers. Nothing looks bent or messed up from looking at the top. I did tap and seal the smog ports cause i have headers on it. Is there anything i did wrong? Still has the same sold cam, lifters and pushrods. I used the rockers and rails from the first set of heads cause the 302s didnt come this them
Help! Swapped 302 heads on my 318.
- Thread starter victa15
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MOPAROFFICIAL
Oogliboogli
Pull the rocker shafts, check and see if all the valve stems are the same height.
If the push rods were the same as before i dont see any issue with them.
Fwiw there is about a 4 cc difference between open chamber "typical #675 heads" and closed chamber #302@64cc
If the push rods were the same as before i dont see any issue with them.
Fwiw there is about a 4 cc difference between open chamber "typical #675 heads" and closed chamber #302@64cc
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MOPAROFFICIAL
Oogliboogli
Same springs, rockers and push rods?lt should work fine. Only thing maybe different is the factory valve stem height, taller.
Adjusted properly, it should be fine.
You either have valves hitting pistons or , well for sure have them hanging open because it never pushes air and only sucks
So how do i measure them with the springs on? Do i just measure the spring hight the old heads and see if they are the same as the 302s? I dont have any adjustments on the rockers. What would i do then if they are taller?
Ok, lets back up a little........what heads did you take off? What is the lift of the cam? You stated it is a solid, tell us more. Do you have the adjusters set correctly? Are the push rods seated into the lifters correctly? Were/are the retainers running into the valve guides? Are you coil binding the springs? There are lots of things it could be, observation will tell you what is wrong.
MOPAROFFICIAL
Oogliboogli
Rockers off, ruler across valve tips/retainers
Well now lets think here for a sec, i gotta ask you stuff i always assume is done and therefore miss the diagnosis.
I base the 1st response on you saying it only sucked air at the plug and didnt push your finger off..that would mean the valves are open .
Btw Did you needlessly pull the distributor out when changing the heads?
So i dont know the cam specs. It was in the motor when i got it years ago. I know its a mild cane cam. When i put the pushrods in i had the intake off and made sure they were seated in the lifters. They were the same ones that were already in it. The cam looked really good still. When i hand turned the motor with the valve covers off i didnt notice anything out of the ordinary. There isnt any adjustment on the rockers. They are just the stamped steel ones. I didnt see anything popping. When you try to crank it you dont hear anything radling around only when i fires up
I did. I also got it back to top dead center and checked the timing. Everything is good there.
If you changed heads there absolutely no guarantee the pushrods are the right length. None. Just because they all used the same pushrods from the factory doesn’t mean anything now you have an aftermarket cam and rebuilt heads. The spring height may have been changed during the rebuild. They may have machined the head surface to true it up, which would shorten the required push rod length.
The other thing is, 302’s are closed chamber heads. You have a cam in there, we don’t know what the piston height is, whether or not there are valve reliefs, etc. With the change to closed chamber heads you may be having piston to valve or even piston to head interference.
Some of that is kinda unlikely, but there’s a lot of stuff you need to rule out.
The other thing is, 302’s are closed chamber heads. You have a cam in there, we don’t know what the piston height is, whether or not there are valve reliefs, etc. With the change to closed chamber heads you may be having piston to valve or even piston to head interference.
Some of that is kinda unlikely, but there’s a lot of stuff you need to rule out.
I checked the compression on the 1st cylinder. And my gauge didnt move. Im it was getting late so i didnt check the others. When i hand crank it. You can hear the air from the compression. Im going to check the valve hights. The heads were completely redone at the machine shop. So if i had a bad seat or valve he would of told me.
Remove valve covers. With the piston at TDC, see if the pushrod spins, or does the rocker feel like it's pushing on a valve... Shouldn't be slop, but should have movement. A lot of good suggestions posted above, just take your time and check one thing at a time. I'd start with the easiest, what I just posted.
nm9stheham
Well-Known Member
Uuuuh.... You can't stamped, non-adjustable rockers with a solid lifter cam unless you are incredibly lucky on all 16 valves! Are you sure it is a solid lifter cam? That needs to be known 100 percent up front.... No guessing or speculation. Do you have any pix of the lifters? Any paperwork at all? If you don't know please find out 100 percent so we don't all send you to buy the wrong new parts!
nm9stheham
Well-Known Member
And were there some curved metal shims under the rocker shafts on each of the rocker stands (bosses) where they bolt down on each original head?
Valve spring issues? Height change?
Along the same lines as everyone else, did you measure lifter pre-load when you where putting it back together? It should be between .020-.060 typically, but good to measure before disassembly so you know what to shoot for upon reassembly. More than likely that when oil pressure comes up it's hanging the valves off the seats.
What do you mean height change? Sorry im still learning. I got the 302 casting heads from a junk yard years ago. Just had them rebuilt at a machine shop that i e been using for years. When i called they said they checked the springs and the were good. But. Im going to check for coil binding on friday. I will measure the springs on the ild heads to see if they are a little taller. How do you measure lifter preload? Sorry Like i said im still learning
We are all learning, that's what fabo is here for. I'm trying to throw questions out there that may lead to a solution.
IF a valve is hanging open....wrong pushrods?? Valve guides too small(grabbing the valve?? Coil bind as mentioned?? Valve height too tall?
You say heads rebuilt....pretty broad statement....new valves/guides/springs? Or were they transferred over from previous heads?
I'm hoping to learn from this as well.
IF a valve is hanging open....wrong pushrods?? Valve guides too small(grabbing the valve?? Coil bind as mentioned?? Valve height too tall?
You say heads rebuilt....pretty broad statement....new valves/guides/springs? Or were they transferred over from previous heads?
I'm hoping to learn from this as well.
Lifter preload is the amount the lifter plunger goes down in the body at TDC on the base circle of the cam. It's somewhat difficult because the lifter body is usually below the lifter bore at this position but it's the depth the plunger is inside of the lifter body. The most accurate way to do it is put the cylinder your checking to TDC. If the push rod is tight back off the rockers until the plunger returns to top of the lifter body (the pushrod will be loose enough to spin) and install a dial indicator parallel to the lifter body with the contact point on top of the plunger. Set the indicator to zero, and tighten the rocker arms back down and read how much the the plunger goes back in the body.
Unfortunately, this is a lot harder than it sounds thanks to our small blocks 59 degree layout. It makes finding parallel to the lifter body a headache.
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