The valves, springs and guides were all from the 302 heads. Only thing i took off the other heads was the rocker arms and shafts
Help! Swapped 302 heads on my 318.
- Thread starter victa15
- Start date
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The valves, springs and guides were all from the 302 heads. Only thing i took off the other heads was the rocker arms and shafts
xLURKxDOGx
"An angel fat, at satan's feast"
If you dont get it sorted out before the weekend and If you cant find someone local to help out, i can come down and lend a hand. Let me know.
Jake
Thanks!!!
Wyrmrider
Well-Known Member
way to go LURK
my kind of guy
my guess is lifter is bottoming out
at least it's not going to hurt anything
my kind of guy
my guess is lifter is bottoming out
at least it's not going to hurt anything
Slantsix64
Well-Known Member
How long those heads been sitting? The guy at my machine shop always taps the tops of all the valves before he gives me the heads back.
Good chance your fighting some rusty valves and guides there. Heads may need to be gone back through and cleaned up unless they have been coated in oil and sealed in plastic with some form of desiccant.
Slantsix64
Well-Known Member
Try loosening the rocker arms not completely loose but a tad bit un plug the coil crank the motor and see if you get any cylinder PSI with your comp tester that would let you know if your push rods are too long
He heads were sitting for a few years. But i just got them rebuilt about a week before i swapped them
Okay, that's good to know! Pardon my ignorance, I think you had mentioned they were recently rebuilt in some of your first postings.
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THis is the second time someone has asked this.
How could the valve spring height have any effect? The height of the tip of the valve does not change no matter what spring is in it. Once the valve is seated in the head, the height only changes if the valve seat comes loose or gets recessed due to damage.
Do you know if the heads were just lightly surface for a cleanup or had they been heavily milled. Also, how deep are the pistons below deck at TDC?
True, but there were other questions I asked as well? LOTS more knowledgable on here than me. How bout you? Suggestions/ideas?
The height of the valves can absolutely change.
If the head is rebuilt with new valves they may not be the same height as stock, that’s easy.
Now the OP says all stock parts were used, but if the machine shop sinks the seats in the chambers when they’re installed the height changes.
Or the new seats that are installed are thicker and put the valves further out into the chambers.
Or both of those things happen. I picked up a “rebuilt” set of heads for cheap as part of another deal. Got them home and something didn’t look right. Laid a straight edge across the valve tips and they’ll all over the place, nothing lined up. Between the seats and valve job there weren’t two valves that came out at the same height. Not all machine shops are created equal.
I agree with most of that but hydraulic lifters are pretty forgiving.
I have never had the problem that the OP has had. I'd have to have it in front of me to have a better shot at fixing it.
Maybe something like this:
Remove the valve covers and have someone slowly rotate the engine until # 1 cylinder intake valve closes. Then back off the bolts to the rocker shaft. IF the valve tip rises, the pushrods are too long. Try the same with other cylinders THis would indicate that the resurfacing of the heads may have exceeded .030 which is far outside the tolerances of hydraulic lifters.
Of course, a head milled that far should also have intake fitment problems but...
I have never had the problem that the OP has had. I'd have to have it in front of me to have a better shot at fixing it.
Maybe something like this:
Remove the valve covers and have someone slowly rotate the engine until # 1 cylinder intake valve closes. Then back off the bolts to the rocker shaft. IF the valve tip rises, the pushrods are too long. Try the same with other cylinders THis would indicate that the resurfacing of the heads may have exceeded .030 which is far outside the tolerances of hydraulic lifters.
Of course, a head milled that far should also have intake fitment problems but...
I had the '452 heads for a 440 milled .050 to raise compression on the first 440 I rebuilt...way back in 2001. I used the stock pushrods and it ran great!
So you got lucky.
I had .010” cut on my 308’s and had to have the intake milled to line up the intake, that shouldn’t have been necessary. They were stock with no indications of previous milling. Same with my 340, no signs of previous decking and my piston heights were right on. Of course I don’t know for sure what was done to the block or the heads before I got them, which is part of my point too. With a set of 302’s from the junkyard like the OP has there’s no guarantee that they haven’t been cut before.
According to stock specs my 340 with hydraulic lifters and factory style adjustable rockers should have 7.25” long push rods. I measured and I use 7.1” pushrods. A .010” cut didn’t make that difference, my cam and lifters did.
The OP does not have a stock cam or lifters, he has a set of heads that he doesn’t know the history on, and quite frankly who knows if his valve height and geometry is stock. Maybe it is, maybe it isn’t. But he could very well be well out of spec using stock pushrods, even with hydraulic lifters.
At this point he has an issue, so he needs to check and measure all of this stuff.
I agree. It could be that with a collection of non stock things going on, a "tolerance stack up" could have led to this.
Any chance the rocker assembly got some rockers mixed up?
Only ran for 10 seconds, what procedure was implemented to assure the hydraulic lifters would not be "pumped", there is no guarantee that the oil will come back out of a "used" lifter just by reassembling the components, especially now that different pieces are being used the preload on that lifter will want to be different. That lifter likely isn't letting the valve close.
Only ran for 10 seconds, what procedure was implemented to assure the hydraulic lifters would not be "pumped", there is no guarantee that the oil will come back out of a "used" lifter just by reassembling the components, especially now that different pieces are being used the preload on that lifter will want to be different. That lifter likely isn't letting the valve close.
67Dart273
Well-Known Member
I did not read quite all of this but here are are examples of causes of this problem:
First, you may not know the history of the engine block. It could have been surfaced at some point, and that makes the pushrods effectively longer
You likely don't know the history of these heads and THEY might have been surfaced. Same as above.
Last, when some folks do valve jobs, when you grind the head seats this "sinks" the valves further into the heads. Likewise, when you grind the valve, that removes material and causes the valves to be "too long." You are supposed to adjust for that, by taking some off the end of the valve stem.
So, with just simple changes, the pushrods "got too long."
First, you may not know the history of the engine block. It could have been surfaced at some point, and that makes the pushrods effectively longer
You likely don't know the history of these heads and THEY might have been surfaced. Same as above.
Last, when some folks do valve jobs, when you grind the head seats this "sinks" the valves further into the heads. Likewise, when you grind the valve, that removes material and causes the valves to be "too long." You are supposed to adjust for that, by taking some off the end of the valve stem.
So, with just simple changes, the pushrods "got too long."
383Scampman
Well-Known Member
I'm thinkin' the heads have been milled too much by a PO
PRH
Well-Known Member
Aftermarket crane cam and stock 318 springs.
Not likely a good match.
A stock 318 cam, which is what the stock springs are designed for, is under .400 lift
Also, depending on the lift, there’s also a possibility of retainer to seal interference.
Fundamentally....... it pretty much has to be one of these things.......
-pushrods too long
-springs coil binding
-retainer to seal interference
Since it fired, and clattered, and shut off...... and now has no compression...... based solely on that, my guess is pushrods too long.
Valves hit pistons after start up(the clatter), now the valves are bent(no compression).
I’d turn the motor over until both lifters on number one cyl were as low as they can go(tdc , #1 firing).
Then slowly remove the rocker shaft bolts and see if the valves move(close).
That will at least tell you if the valves are being held open.
If they don’t move, it’s time for a leak down test to verify the valves aren’t bent.
Even if they do move...... well, still best to do a leak down test.
You should also measure for the correct pushrod length and see how much different that is than the pushrods you’re using.
Not likely a good match.
A stock 318 cam, which is what the stock springs are designed for, is under .400 lift
Also, depending on the lift, there’s also a possibility of retainer to seal interference.
Fundamentally....... it pretty much has to be one of these things.......
-pushrods too long
-springs coil binding
-retainer to seal interference
Since it fired, and clattered, and shut off...... and now has no compression...... based solely on that, my guess is pushrods too long.
Valves hit pistons after start up(the clatter), now the valves are bent(no compression).
I’d turn the motor over until both lifters on number one cyl were as low as they can go(tdc , #1 firing).
Then slowly remove the rocker shaft bolts and see if the valves move(close).
That will at least tell you if the valves are being held open.
If they don’t move, it’s time for a leak down test to verify the valves aren’t bent.
Even if they do move...... well, still best to do a leak down test.
You should also measure for the correct pushrod length and see how much different that is than the pushrods you’re using.
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