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Loose pushrod

1880 Views 28 Replies 9 Participants Last post by  chuzz
I'm in the process getting a '66 Coronet 500 with a 318 poly running again after sitting in a garage since 1993. I'm extremely new at this and took this on as a learning project with the goal of keeping it stock and as original as possible. As I turn the engine over with no valve covers on and no plugs in all of the valves are moving as they should except for 1 intake valve. It seems the rocker arm is going through its full motion but isn't pressing the valve down, when the pushrod is in its lowest postion it has about a quarter inch of play, at its highest it just pushes the rocker until it touches the valve stem but doesn't push it. Everything I look at says these are solid lifters. Not sure where to go from here?
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These are mechanical lifters, and the clearance between the tip of the valve and the tip of the rocker arm is critical. It's measured with a feeler gauge, and typically, is on the order of something like 0.010 inches for intake valves, 0.020 inches for exhaust (this is not necessarily the exact value for your engine, this is for a slant-6, but representative of the scale).
So if you see a quarter inch with the pushrod fully down, someone has seriously backed off that adjustment. On the slant-6, the adjustment is made with engine hot and idling, which is difficult, but necessary to get the clearance right, with thermal expansion. On the 318, the gap and the procedure may be different. But you turn the hex nut at the rocker arm clockwise to decrease the gap, and counterclockwise to increase.
With that kind of a gap, the valve isn't opening.
 

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1966 Coronet 500 Hard Top 318 poly Former: 2011 Grand Caravan 3.6 1988 Lebaron Convertable 2.5
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Discussion Starter · #3 ·
It's definitely not opening. There only seems to about an 1/8" of adjustment left on the adjuster, not enough to close the gap. Also when i compare it to all the other valves it seems to have the same adjustment as them.
 

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If it were parked and shut off with the #1 intake fully opened, it could have stuck down from sitting. The valve stem might be rusted to the guide and the valve spring can't overcome the seizure?
Sometimes with penetrant and some 'mechanical shock' persuasion, these can be freed up without disassembly.
 
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1966 Coronet 500 Hard Top 318 poly Former: 2011 Grand Caravan 3.6 1988 Lebaron Convertable 2.5
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Discussion Starter · #5 ·
If it were parked and shut off with the #1 intake fully opened, it could have stuck down from sitting. The valve stem might be rusted to the guide and the valve spring can't overcome the seizure?
Sometimes with penetrant and some 'mechanical shock' persuasion, these can be freed up without disassembly.
That was my first thought, stuck valve, but it lines up with the other valves and if I crank the engine by hand and put a 1/4" allen key between the rocker and valve stem it will open as I crank.
 

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If you can't adjust the rocker any more, you may have a camshaft lobe that has been wiped out by the lifter. Remove the rocker arm and pushrod, and sometimes you can get a wire and hook the lifter and pull it out of its bore with the head on. From there, rotate the engine by hand and see if the lobe is worn down.
 

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1966 Coronet 500 Hard Top 318 poly Former: 2011 Grand Caravan 3.6 1988 Lebaron Convertable 2.5
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Discussion Starter · #7 ·
Like i said above, I'm new to this, but from what I understand about the poly I have to unbolt the head to remove the rockers and thus the pushrod. Am i missing something?
 

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Like i said above, I'm new to this, but from what I understand about the poly I have to unbolt the head to remove the rockers and thus the pushrod. Am i missing something?
Really? On most V-8s, you just take the valve covers off, unbolt the rocker arms from the head, and from there you can remove the pushrods. To get at the lifters, usually you remove the carb and intake manifold, and any accessories necessary to get them off.
 
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Bob, the late Poly head engines had the pedestals cast with the head and the rocker shaft was essentially pressed in from one end with the rockers installed. He can pull the intake and see the lifters, but I do not remember if the lifter can be removed without pulling the head (it was a long time ago when dad had a 1962 Plymouth with a 318 Poly head.

According to the 1960 Dodge shop manual I have the lifters can be removed from the engine after compressing the respective valve spring with the lifter on the low side of the cam lobe. Intake manifold still has to come off though. I would try to get two intake pushrods out and compare them for length. That can possibly be done without pulling the intake, but you will need a good strong light to see when reinstalling them. If you give me your email I can send you a copy of the 1960 manual.

Bob, you were real close on clearances, 0.010 intake and 0.018 exhaust hot clearance in 1960.
 

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Discussion Starter · #10 ·
Bob, the late Poly head engines had the pedestals cast with the head and the rocker shaft was essentially pressed in from one end with the rockers installed. He can pull the intake and see the lifters, but I do not remember if the lifter can be removed without pulling the head (it was a long time ago when dad had a 1962 Plymouth with a 318 Poly head.

According to the 1960 Dodge shop manual I have the lifters can be removed from the engine after compressing the respective valve spring with the lifter on the low side of the cam lobe. Intake manifold still has to come off though. I would try to get two intake pushrods out and compare them for length. That can possibly be done without pulling the intake, but you will need a good strong light to see when reinstalling them. If you give me your email I can send you a copy of the 1960 manual.

Bob, you were real close on clearances, 0.010 intake and 0.018 exhaust hot clearance in 1960.
Thank you for the advice and the offer of the shop manual, i do have access to the 66 service manual so I'll have to look to see how it shows to pull a lifter.
 

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Discussion Starter · #13 ·
Poly's a bit nuts but it was a stopgap solution.
Was it? My impression was they switched to the LA motors because the Poly didn't fit into the A bodies (too wide) which didn't exist when the poly was developed.
 

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I always understood that the Poly was a cheaper to build option than the Hemi and I know there were some Poly head and Hemi head engines that were the same displacement down to the bore and stroke.

I second the thought of a bad or wrong pushrod. The service manual does not list the pushrod length. The 1965 parts list I have shows only 1 pushrod PN 1637721.

Dave, you will enjoy this one. I had to put a remanufactured short block in a 1975 Dodge Van. It was a 318 and after I got it in and reassembled the top end I found it wouldn't start, acted like the cam was installed wrong. I started watching the valve action, cylinders 1,4,5 & 8 were correct, 2,3,6 & 7 were backwards, the exhaust was open on the down stroke and intake on the upstroke. The engine warehouse it had come from was a friend's business and he set up a conference call with the rebuilder. He admitted a mistake on their end, the "wide block" as he called it, 318 was the same block as the Poly and someone had put a Poly cam in it. I was given the option of pulling everything out or swapping the cam and lifters. I opted to swap the cam and lifters.
 

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Was it? My impression was they switched to the LA motors because the Poly didn't fit into the A bodies (too wide) which didn't exist when the poly was developed.
1) Hemi V8
2) "We need to make these cheaper and faster to build" - Poly V8 based on Hemi
3) "We need to make these even cheaper and faster so we can get them into Plymouths" - A-series V8 based on Poly
2a) "We need bigger, cheaper engines" - completely new B/RB series (my timing may be off, it might be 2a)
4) "We need to make these lighter and smaller" - LA series V8 based on A series
5) "We need about 1.5 times as much power" - Magnum series V8 (really, continuation of LA series)
 

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Dave, you will enjoy this one. I had to put a remanufactured short block in a 1975 Dodge Van. It was a 318 and after I got it in and reassembled the top end I found it wouldn't start, acted like the cam was installed wrong. I started watching the valve action, cylinders 1,4,5 & 8 were correct, 2,3,6 & 7 were backwards, the exhaust was open on the down stroke and intake on the upstroke. The engine warehouse it had come from was a friend's business and he set up a conference call with the rebuilder. He admitted a mistake on their end, the "wide block" as he called it, 318 was the same block as the Poly and someone had put a Poly cam in it. I was given the option of pulling everything out or swapping the cam and lifters. I opted to swap the cam and lifters.
Ha!!! Yes, the two 318s! From the company that brought you two 383s! I never got why they didn't make the second one a 319 or 322 or some such...!
 

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Ha!!! Yes, the two 318s! From the company that brought you two 383s! I never got why they didn't make the second one a 319 or 322 or some such...!
You mean like Ford. 389, 390, 391 all the same displacement, just for different applications, or the 361 Edsel and 360 truck engines and the 359 HD truck engine.
 
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With that much play you have a severly bent pushrod or a completely wiped cam and lifter.
- a bended pushrod can be checked by just rotating it if its this much play.
Get a look at the lifter and cam..
 
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You mean like Ford. 389, 390, 391 all the same displacement, just for different applications, or the 361 Edsel and 360 truck engines and the 359 HD truck engine.
Pretty much. Yet they had the 313 ... they did separate the 360 from the older (though based on a newer design, depending on how you count) 361.
 
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