0 compression cylinder 4
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Laughing Gas
Joined: Oct 2013
Posts: 947
Likes: 6
From: Manitoba, Canada
0 compression cylinder 4
So I finally got my truck on the road once it came back from paint earlier this summer. It has a 79 351W that I was fortunate to get from a low mileage LTD. It's stock except for an Edelbrock Performer cam, intake, springs, lifters and timing chain and gears. I had a used Edelbrock 600cfm carb but all summer I tinkered with it and finally gave up and bought a new one a few weeks ago after I f^*ed the jets trying to get them out. Last week I was out for a spin pleased as a pooch with a bone. It was finally running GREAT. 3 blocks from home accelerating up a block long hill in 2nd... clink,clank, rattle, rattle and a total loss of power. I shut it down and got help to push it home. (Oh the shame!) Did a compression test and got 0 on #4. Pulled the valve cover and it looked fine. Blew some air down #4 and it came out the exhaust. ?valve? I pulled the head today. The valve snapped off 1/2" from the top. The valve head is bent over but not broken or chipped. Cylinder is fine. The piston has a couple of dents the deepest dent maybe 1/16" deep. I'm thinking I can get away with replacing the valve?
Logistics Pro
Joined: Aug 2015
Posts: 4,093
Likes: 14
From: Lind, WA- Eastern WA
I would strongly consider doing a valve job, or at least have a shop check them all out. If you didn't replace the old valves when you upgraded the lifters & springs, then the valves are the weak link(s). Also for the cost of a stock piston(with standard sized rings), I'd replace that one. It will be the weak link and may go next. It's not too hard to fix it now.
Posting Guru
Joined: Mar 2016
Posts: 1,412
Likes: 1
From: Barre Mass
Man I hate when that happens. I feel for you man. I have to agree with Gary. Be a real good idea to pull the piston and inspect the connecting rod and replace the piston. When that valve hit the piston something's got to give. I hope it all works out. You have a great truck.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Hmm, I've seen worse that did no damage to the lower end or the piston.
But replacing the piston do you need to replace the rings since any movement will cause them to loose their seated position.
So if you just hone the cylinder and call it good with old rings.?
Or replace with new rings an hone the cylinder?
Things to think about!
Cheap insurance is any engine with 75k is replace all exhaust valves with new ones since they get the hottest.
I will say you were very lucky not to suck a valve and destroy the head and piston.
Which is not a pretty sight, it gives ya a sick feeling deep in your gut & wallet.
If anything, I'd at least have all exh valves replace and do a 3 angle valve job
Hope your using a tach in your truck to know your limits.
Orich
But replacing the piston do you need to replace the rings since any movement will cause them to loose their seated position.
So if you just hone the cylinder and call it good with old rings.?
Or replace with new rings an hone the cylinder?
Things to think about!
Cheap insurance is any engine with 75k is replace all exhaust valves with new ones since they get the hottest.
I will say you were very lucky not to suck a valve and destroy the head and piston.
Which is not a pretty sight, it gives ya a sick feeling deep in your gut & wallet.
If anything, I'd at least have all exh valves replace and do a 3 angle valve job
Hope your using a tach in your truck to know your limits.
Orich
Logistics Pro
Joined: Jan 2011
Posts: 4,762
Likes: 54
From: Antelope Valley ,CA
THAT SUCKS
like others said do a valve job while you have it apart .damage to piston is not bad .
like others said do a valve job while you have it apart .damage to piston is not bad .
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Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
I'm more cautious than most but once I fix something I never have to do it over. That divot in the piston may not look to bad but I'm also worried about the material under the divot. That metal has been stressed IMHO. You may get away with leaving the piston alone but I wouldn't. I'd buy a piston and some new rings for it. There wouldn't be any question marks in the bubble above my head.
While you have that piston out check the rod. Make sure it isn't bent.
At a bare minimum I would take that head to a machine shop and have that valve guide replaced.
From here you have to figure out why this happened to that valve. If the reason is mechanical then handle that situation also before you start the engine back up. If you ran old gas that "can" tie up an intake valve in it's valve guide.
While you have that piston out check the rod. Make sure it isn't bent. At a bare minimum I would take that head to a machine shop and have that valve guide replaced.
From here you have to figure out why this happened to that valve. If the reason is mechanical then handle that situation also before you start the engine back up. If you ran old gas that "can" tie up an intake valve in it's valve guide.
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Posting Guru
Joined: Mar 2016
Posts: 1,412
Likes: 1
From: Barre Mass
Had a similar problem with a carb screw falling down the carb when idling. Messed up the piston. Just a dent in the top under side and skirt broken. Should at least remove the piston to check it. Could have also damage the crank. I hope this is not the case here though.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
I'd say you better check your cam & lifter and all your push rods by rolling on your kitchen table when your wife or mom is not looking an replace as needed.
You may have floated the valves and had started eating up the back side of the cam lobes. While you had it wound up going up that hill.
Orich
You may have floated the valves and had started eating up the back side of the cam lobes. While you had it wound up going up that hill.
Orich
Posting Guru
Joined: Aug 2012
Posts: 1,241
Likes: 2
From: Rockville, Ct.
I feel ya...
How hard is it to pull or drop the pan to get to the #4 rod? If it's easy, I'd get a new piston and rings.
Not sure if a hone job is doable w/o dropping the pan totally. Maybe you can rig up a plastic bag under the cylinder when you hone? Just an idea, might be totally undoable.
I agree with the head job though. New guides, valves and a grind job minimum.
Not sure if a hone job is doable w/o dropping the pan totally. Maybe you can rig up a plastic bag under the cylinder when you hone? Just an idea, might be totally undoable.
I agree with the head job though. New guides, valves and a grind job minimum.
Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
Orich is right. Roll the pushrods on wifey's coffee table when she is at bridge.
If you are going to drop the pan you will have to go all the way. If you pull #4 you will find the usual sloppy wrist pin. If one piston is out, pull them all. Hone, re-ring, oil pump, new shells on the rods. Maybe a total rebuilt.
Or, just a valve job.
That valve hung and snapped for a reason. The head shop will tell you why.
The OP said he has a 1/16 dimple in the piston. Do any of you old salts have a junk piston lying around to cut into to see how thick a piston top is?
Semper Fi
If you are going to drop the pan you will have to go all the way. If you pull #4 you will find the usual sloppy wrist pin. If one piston is out, pull them all. Hone, re-ring, oil pump, new shells on the rods. Maybe a total rebuilt.
Or, just a valve job.
That valve hung and snapped for a reason. The head shop will tell you why.
The OP said he has a 1/16 dimple in the piston. Do any of you old salts have a junk piston lying around to cut into to see how thick a piston top is?
Semper Fi
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Orich is right. Roll the pushrods on wifey's coffee table when she is at bridge.
If you are going to drop the pan you will have to go all the way. If you pull #4 you will find the usual sloppy wrist pin. If one piston is out, pull them all. Hone, re-ring, oil pump, new shells on the rods. Maybe a total rebuilt.
Or, just a valve job.
That valve hung and snapped for a reason. The head shop will tell you why.
The OP said he has a 1/16 dimple in the piston. Do any of you old salts have a junk piston lying around to cut into to see how thick a piston top is?
Semper Fi
If you are going to drop the pan you will have to go all the way. If you pull #4 you will find the usual sloppy wrist pin. If one piston is out, pull them all. Hone, re-ring, oil pump, new shells on the rods. Maybe a total rebuilt.
Or, just a valve job.
That valve hung and snapped for a reason. The head shop will tell you why.
The OP said he has a 1/16 dimple in the piston. Do any of you old salts have a junk piston lying around to cut into to see how thick a piston top is?
Semper Fi
Orich
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
How hard is it to pull or drop the pan to get to the #4 rod? If it's easy, I'd get a new piston and rings.
Not sure if a hone job is doable w/o dropping the pan totally. Maybe you can rig up a plastic bag under the cylinder when you hone? Just an idea, might be totally undoable.
I agree with the head job though. New guides, valves and a grind job minimum.
Not sure if a hone job is doable w/o dropping the pan totally. Maybe you can rig up a plastic bag under the cylinder when you hone? Just an idea, might be totally undoable.
I agree with the head job though. New guides, valves and a grind job minimum.
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