Compression issue, probably more
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Cross-Country
Joined: Jan 2013
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Compression issue, probably more
1978 F150 4x4 w/ 460
Trying to troubleshoot a no start issue (turning over fine, spark on each plug shows with a test light, fuel is getting to the carb fine), I wanted to check the timing. Trying to find TDC, I had no compression on the first cylinder. I did a dry compression test on each cylinder, and here is what I found, by cylinder order (not firing order - passenger side, front to back then driver's side front to back)
1: 0
2: 60
3: 130
4: 120
5: 90
6: 0
7: 0
8: 90
On the passenger's side, the 2nd of 8 and 3rd of 8 (from front to back) valves aren't moving, and the 3rd valve's pushrod is sunk down.
I didn't check the driver's side but can if it may matter.
The last thing I did on it was replace the starter and check and reinstall the pushrods, and change the oil. Haven't been able to start it since then, and that was two months ago. Gas is only a couple months old.
Before I dig into it further, is there any chance that this could be a timing chain failure or something similarly easy to fix? Much more may be beyond my ability level.
Trying to troubleshoot a no start issue (turning over fine, spark on each plug shows with a test light, fuel is getting to the carb fine), I wanted to check the timing. Trying to find TDC, I had no compression on the first cylinder. I did a dry compression test on each cylinder, and here is what I found, by cylinder order (not firing order - passenger side, front to back then driver's side front to back)
1: 0
2: 60
3: 130
4: 120
5: 90
6: 0
7: 0
8: 90
On the passenger's side, the 2nd of 8 and 3rd of 8 (from front to back) valves aren't moving, and the 3rd valve's pushrod is sunk down.
I didn't check the driver's side but can if it may matter.
The last thing I did on it was replace the starter and check and reinstall the pushrods, and change the oil. Haven't been able to start it since then, and that was two months ago. Gas is only a couple months old.
Before I dig into it further, is there any chance that this could be a timing chain failure or something similarly easy to fix? Much more may be beyond my ability level.
Senior User
Joined: Mar 2004
Posts: 280
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From: Alabama
I doubt it's a timing chain issue because its turning the cam which is open and closing your valves. And you have compression in some of the cylinders so apparently they are opening and closing when you did the compression test while cranking the engine (right?)... Maybe it's related to the lifters or oil pump related?
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
It seems strange that you have zero compression on #1 cylinder when the exhaust valve doesn't move but the intake does. Same brain (on my part) fuzziness on #2 cylinder's intake - doesn't move but you have some compression.
Sounds like the cam is toast. Try pulling a lifter from #1 exhaust and #2 intake - if you can. I think they're the easiest without yanking the intake. If they don't come out, there's proof the cam is gone - mushroomed lifter foot due to cam lobe failure.
Sounds like the cam is toast. Try pulling a lifter from #1 exhaust and #2 intake - if you can. I think they're the easiest without yanking the intake. If they don't come out, there's proof the cam is gone - mushroomed lifter foot due to cam lobe failure.
Senior User
Joined: Feb 2013
Posts: 266
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From: Idaho
Are you having someone turn the engine over when you check the compression? Or are you checking the compression when #1 is a TDC and checking the others at the same time? Are you rotating the engine 360 degrees for each cylinder and checking compression that way? Sounds like either your cam is toast or the rockers are torqued set improperly but with out know what and you did something its hard to say. If you truly don't have compression in those cylinders you have other major problems...
Senior User
Joined: Feb 2013
Posts: 266
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From: Idaho
Also you cant just take off the rockers and install them back on unless the rockers aren't adjustable...you have to put them on in a sequence and torque them correctly. Once it starts and runs at idle you can set them (rocker arms)and not have any problems if your cam isn't toast. And if you have adjustable rockers.
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Elder User
Joined: Mar 2013
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From: In Hastings Delton area
I'd rerun the compression test putting some oil in the cylinders first and see if compression goes up also pull the lifters check for wear on lifters .If lifters are really worn so is your camshaft lobes
Elder User
Joined: Mar 2013
Posts: 559
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From: In Hastings Delton area
Just another tip when checking compression when you oil the cylinders and recheck compression ,If compression goes up its a ring problem if no change a valve problem.But all in all sounds like a cam lifter problem
Senior User
Joined: Feb 2013
Posts: 266
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From: Idaho
Are the rockers adjustable? The sequence for checking the compression should be the same as the firing order and you have to get the piston for each cylinder at TDC on the compression stroke so both valves are closed. If either the intake or exhaust valves/rockers are adjustable and are over torqued you could be losing air out the valves...to have more than one cylinder reading zero there is something not set right.
Having flat lobes on a cam wouldn't give you zero compression on a cylinder. Its either on the top end--heads/valves/valve seals/seats. Which would make this thing smoke like crazy... Rockers not set/torqued properly etc or major ring problems...I would suspect you over tightened the rockers and didn't torque/set them in the proper sequence which is allowing air to bypass the valves at TDC for each piston. Just my keyboard diagnostics...
Having flat lobes on a cam wouldn't give you zero compression on a cylinder. Its either on the top end--heads/valves/valve seals/seats. Which would make this thing smoke like crazy... Rockers not set/torqued properly etc or major ring problems...I would suspect you over tightened the rockers and didn't torque/set them in the proper sequence which is allowing air to bypass the valves at TDC for each piston. Just my keyboard diagnostics...
Thread Starter
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Cross-Country
Joined: Jan 2013
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To check the lifters, just remove the pushrod and use a magnetic tool to fish the lifter out? No luck using that method.
Also, the 2nd and 3rd (from front to back) pushrods on the passenger side and the 4th and 5th (front to back) on the driver's side are significantly bent. The rest are straight. Does scorching on the pushrods have some significance?
Time to remove the intake and have a better look?
Also, the 2nd and 3rd (from front to back) pushrods on the passenger side and the 4th and 5th (front to back) on the driver's side are significantly bent. The rest are straight. Does scorching on the pushrods have some significance?
Time to remove the intake and have a better look?
Senior User
Joined: Feb 2013
Posts: 266
Likes: 0
From: Idaho
To check the lifters, just remove the pushrod and use a magnetic tool to fish the lifter out? No luck using that method.
Also, the 2nd and 3rd (from front to back) pushrods on the passenger side and the 4th and 5th (front to back) on the driver's side are significantly bent. The rest are straight. Does scorching on the pushrods have some significance?
Time to remove the intake and have a better look?
Also, the 2nd and 3rd (from front to back) pushrods on the passenger side and the 4th and 5th (front to back) on the driver's side are significantly bent. The rest are straight. Does scorching on the pushrods have some significance?
Time to remove the intake and have a better look?
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