Dropped valve??
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Dropped valve??
First off Happy Thanksgiving yall
1979 f100 with 400
I was driving my truck down the highway at about 60, BOOOM!! Backfired so hard it blew off the muffler and tailpipe, no smoke or anything, i pulled over to look at it and everything looked fine, i tried to start it and its getting fire but it seemed like it was out of time, just kept spitting out of the carb, towed it to the house and put #1 at tdc and it was piointing to the #1 plug wire. so it isnt out of time, pulled the intake and valve covers and timing cover off. with everything off it still spits out of the back left intake port. havent had time to pull off the heads yet but could i have bent a valve or something? sorry if it seems obvious but im 17 and still inexperienced on the whole troubleshooting deal.
thanks in advance to anyone that can help me out.
71 f100 347 stroker.
87 bronco 545
79 f100 400
1979 f100 with 400
I was driving my truck down the highway at about 60, BOOOM!! Backfired so hard it blew off the muffler and tailpipe, no smoke or anything, i pulled over to look at it and everything looked fine, i tried to start it and its getting fire but it seemed like it was out of time, just kept spitting out of the carb, towed it to the house and put #1 at tdc and it was piointing to the #1 plug wire. so it isnt out of time, pulled the intake and valve covers and timing cover off. with everything off it still spits out of the back left intake port. havent had time to pull off the heads yet but could i have bent a valve or something? sorry if it seems obvious but im 17 and still inexperienced on the whole troubleshooting deal.
thanks in advance to anyone that can help me out.
71 f100 347 stroker.
87 bronco 545
79 f100 400
Hotshot
Joined: Apr 2009
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From: Stanley, VA
Run a compression test, that will pinpoint any bad cylinders.
From your description, it's possible that you have dropped a valve or at least broke a valve spring.
In 1977 I bought a new F250 XLT with a 400. In the three years I had it, it broke three valve springs. Like you I was going down the road about 60 and all of a sudden it started popping and missing. I made it to where I was going (fortunately I was headed to the shop). I pulled in diagnosed the problem, the truck was out of warranty by 4500 miles. I ended up replacing a broken valve spring. I was able to do this without pulling the head. A few months later the same thing happened, only this time the valve hit the piston and bent. I ended up pulling the head, replaced the valve and all the valve springs on that head (it was the same head). All was good untill a few months, again, same thing. Only this time it was the other head. Replaced all the springs on that head and it lasted untill I got rid of it.
From your description, it's possible that you have dropped a valve or at least broke a valve spring.
In 1977 I bought a new F250 XLT with a 400. In the three years I had it, it broke three valve springs. Like you I was going down the road about 60 and all of a sudden it started popping and missing. I made it to where I was going (fortunately I was headed to the shop). I pulled in diagnosed the problem, the truck was out of warranty by 4500 miles. I ended up replacing a broken valve spring. I was able to do this without pulling the head. A few months later the same thing happened, only this time the valve hit the piston and bent. I ended up pulling the head, replaced the valve and all the valve springs on that head (it was the same head). All was good untill a few months, again, same thing. Only this time it was the other head. Replaced all the springs on that head and it lasted untill I got rid of it.
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wow, bad luck haha
also i forgot to mention the valve stem seals were in pieces scattered on the head, so im pulling both heads to do that anyways, while there off might as well gring the valves too... are the 400 heads worth goign through and rebuilding or is there another set that would be better that is a direct bolt on?
also i forgot to mention the valve stem seals were in pieces scattered on the head, so im pulling both heads to do that anyways, while there off might as well gring the valves too... are the 400 heads worth goign through and rebuilding or is there another set that would be better that is a direct bolt on?
Hotshot
Joined: Apr 2009
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From: Stanley, VA
Unless you're building up the engine, I'd just go with a good valve job.
On the stem seals, that's pretty much normal, when they get old, they harden and break into little pieces. Sometimes the pieces collect in the oil returns from the head and clog them up making the oil puddle around the valve stems cause oil burning and smoking.
On the stem seals, that's pretty much normal, when they get old, they harden and break into little pieces. Sometimes the pieces collect in the oil returns from the head and clog them up making the oil puddle around the valve stems cause oil burning and smoking.
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Yea man I pulled it out and checked it, even with all the intake and everything off it still spits out of the intake port on the head?
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i still have no idea what happened, i pulled the whole motor out put it on a stand, pulled the head, head hasket was good, valve isnt stuck open. what else do i check?
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Hotshot
Joined: Apr 2009
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From: Stanley, VA
In post #6 you said that it still "spits out the intake port". Take that head and lay it on the bench, combustion chamber side up, and fill that combustion chamber with a very thin liquid (gas, diesel, kerosene, mineral spirits) BE CAREFUL!!! No open lights or sparks!. Watch the intake port. I'll bet you'll see the liquid leaking out through the intake port.
A compression check before teardown would have shown the same thing, probably a burned valve.
A compression check before teardown would have shown the same thing, probably a burned valve.
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Hotshot
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From: Stanley, VA
Nope, different engine family.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Yeah, get a valve job done and you should be good to go.
Lead Driver
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Only heads that are decent that can be used are are 351C 4v heads... good luck finding a set of those. Other than that youre stuck with aftermarket.
This is what i had done on my 400. GOOD valve job, mild port work, milled .040" (iirc) , energizer cam, headers, edeljunk intake and carb. After that it was "bearable", however someone dosed it with some sand would be my guess and spun a main. Dropped in the diesel and havent looked back.
This is what i had done on my 400. GOOD valve job, mild port work, milled .040" (iirc) , energizer cam, headers, edeljunk intake and carb. After that it was "bearable", however someone dosed it with some sand would be my guess and spun a main. Dropped in the diesel and havent looked back.