1970 GTO Lifter Issues - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 05-27-2018, 05:31 PM Thread Starter
 
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1970 GTO Lifter Issues

Hi there,

I was hoping someone could assist with advice on my issue. My 400 motor started knocking from the lifter some weeks ago, i thought i would pull the cover to investigate, i took out the push rod and inspected and also adjusted the tension on the rocker which seemed to quieten it down, all else looked ok. I took the car for a short drive and it seemed to lack power and knocking appeared again. I tried adjusting again but rocker is as tight as allows, i noticed that I dont seem to getting the same length of stroke compared to the other rockers. I have taken out the push rod again and it all looks in good order, latest is that the rocker isnt working at all now. When i push on the rod now i think i can feel the lifter compressing which i couldnt do previously.

Does this sound like a collapsed lifter? Would i have damaged the cam? Is it possible to inspect and replace lifters and cam without removing the heads?

Motor was rebuilt approx. 6 years ago by previous owner, car is only driven from time to time and not driven hard, it had been sitting idle for a few months when the issue first appeared.

Any advice would be appreciated, im keen to replace myself if i can.

Regards,
Phil
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post #2 of 3 (permalink) Old 05-27-2018, 07:10 PM
 
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It could be a bad lifter. If the cam went bad, you would get some lift at the rocker. You could even have some debris blocking the oil passage that pumps oil into the lifter, but that would be a long shot - so I would go with a bad lifter. Assume you have screw-in rocker arm studs? If not and they are press-in studs, they can pull up and this would not allow the rocker arm to work correctly.

You will have to remove the intake and valley cover to expose the lifter galley. You don't have to pull heads. Just make sure you clean real good all the grime or dirt on the valley cover before removing so you don't drop a lot of junk down into the engine.
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post #3 of 3 (permalink) Old 05-27-2018, 09:46 PM
 
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Originally Posted by Phil Hoyle View Post
Hi there,

I was hoping someone could assist with advice on my issue. My 400 motor started knocking from the lifter some weeks ago, i thought i would pull the cover to investigate, i took out the push rod and inspected and also adjusted the tension on the rocker which seemed to quieten it down, all else looked ok. I took the car for a short drive and it seemed to lack power and knocking appeared again. I tried adjusting again but rocker is as tight as allows, i noticed that I dont seem to getting the same length of stroke compared to the other rockers. I have taken out the push rod again and it all looks in good order, latest is that the rocker isnt working at all now. When i push on the rod now i think i can feel the lifter compressing which i couldnt do previously.

Does this sound like a collapsed lifter? Would i have damaged the cam? Is it possible to inspect and replace lifters and cam without removing the heads?

Motor was rebuilt approx. 6 years ago by previous owner, car is only driven from time to time and not driven hard, it had been sitting idle for a few months when the issue first appeared.

Any advice would be appreciated, im keen to replace myself if i can.

Regards,
Phil
This is how I checked mine in 1974. I took off valve cover on side noise came from. Then have someone start motor and watch your rockers . If bad lifter you will know in 30 seconds. Put a towel down as I remember my bad lifter shot oil out fast but you will know just by looking . I was 18 years old and it did the trick . Doug
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