Collapsed lifter or wiped cam lobe?

[Weathersbytaylor]

Finally got the engine together and ran it for the first time. It ran rough but as the engine warmed it will smooth out. Went to adjust the rockers (I like to do a final adjustment check while running) and found one of my intake valves barely moving. I pulled the rocker back off and can move the valve by hand. Compared it to the working valve next to it and they have the same resistance so I know it's not sticking. Is there any way to differentiate between a worn cam lobe and a collapsed lifter? The person before me diagnosed this as head gasket and tore it apart then sold it to me. I never heard it run before this. Thanks for any input guys!

 

[Weathersbytaylor]

Definitely a wiped cam. Pulled the lifter out and you can see unmachined lobe. Guess the engine is coming out

 

[gm280]

Have you checked for a backed out rocker stud first? Just wondering. I don't know your setup, but that does happen at times. Something to check before removing the engine. JMHO

 

[Bt Doctur]

pulled the rocker back off and can move the valve by hand.
If you mean push it downward you have bigger problems

Compared it to the working valve next to it and they have the same resistance so I know it's not sticking. Is there any way to differentiate between a worn cam lobe and a collapsed lifte

Another problem, you cannot simply push an intake valve by hand.

 

[Weathersbytaylor]

When I say by hand I mean with some weight behind it. The engine actually runs surprisingly well with one valve barely moving. I didn't notice anything was wrong until I went to make final adjustments. Although the engine never left idle. I imagine under load I would have noticed.

 

[Bt Doctur]

In my best Superman day I could never "push" a valve inward. If your pushing it down and it`s moving you have badbroken valve springs or you are
SUPERMAN
How do you determine the right spring then? First, you need to decide what type of lifter you will be using. For flat tappet cams a seat pressure of 105-125lbs for small blocks and 115-135lbs for big blocks is appropriate. Open pressures should be in the 220-250lb range for low rpm street use and 250-350lbs for hi-performance or racing use

 

[Bt Doctur]

Hydraulic roller (HR) cams require higher pressures to control the inertia of the heavier roller lifters and the faster acceleration of valve train components allowed by the use of the roller follower. Pure street small blocks should have 260-300lbs open pressure. For performance use, aim for 300-350lbs open. Racing small blocks that regularly see 6,000+rpm need over 400lbs open pressure.


https://www.summitracing.com/search/part-type/valve-springs/open-pressure-lbs/350-lbs

 

[Weathersbytaylor]

Fair point. Lucky enough the engine is getting a rebuild and will be installing new springs when I do the rebuild. Thanks for the imput!

 

[boatman37]

agreed with btdoctor. i weigh over 250lbs and can guarantee i could never open a valve by hand with a good spring. can't say for sure on a stock motor as i rarely ever built a motor with stock cam and spring pressures though but i still doubt i could even open a stock one

 

[Scott Danforth]

what are you working on?

everyone is correct, not even standing on the valve retainer would i be able to move a good spring/valve

dont use the motor as it is, something is broken