Hello:
Engine is a 305 with stock stamped steel rocker arms.
I had a problem with bent rocker studs -- I finessed (bent) them back to my best conservative approximation with a lot of careful measurement, so they're all nearly the same, and the engine runs a lot better, but still stumbles (not ready to pass smog), and pretty much all other possible causes have been eliminated other than the current position of the rocker studs.
The engine is a bit stiff to turn over by hand (plugs out, of course), and some valve noises are audible in running the car. It seems to me that I did not go quite far enough in bending the studs back towards the valves.
The wear patterns on the rocker arms (on the polished curve where the arms contact the valves) are all displaced towards the tip of the rockers from what would seem to me to be the position where the lowest forces would occur -- I'm guessing this would be with the wear pattern equally distributed on both sides of the highest prominence of the curved area on the rocker-arm-to-valve-stem contact area. It makes sense to me that this would reduce the friction in the valvetrain because instead of forcing the valvestems to spend a lot of time sliding up an inclined plane with things set as they are now, more time would be spent moving more or less sideways across that highest prominence.
Is my supposition true that distributing the motion equally on either side of that highest prominence is how it was designed to work? Is this equally-distributed wear pattern what is normally observed in a well-functioning valvetrain?
Engine is a 305 with stock stamped steel rocker arms.
I had a problem with bent rocker studs -- I finessed (bent) them back to my best conservative approximation with a lot of careful measurement, so they're all nearly the same, and the engine runs a lot better, but still stumbles (not ready to pass smog), and pretty much all other possible causes have been eliminated other than the current position of the rocker studs.
The engine is a bit stiff to turn over by hand (plugs out, of course), and some valve noises are audible in running the car. It seems to me that I did not go quite far enough in bending the studs back towards the valves.
The wear patterns on the rocker arms (on the polished curve where the arms contact the valves) are all displaced towards the tip of the rockers from what would seem to me to be the position where the lowest forces would occur -- I'm guessing this would be with the wear pattern equally distributed on both sides of the highest prominence of the curved area on the rocker-arm-to-valve-stem contact area. It makes sense to me that this would reduce the friction in the valvetrain because instead of forcing the valvestems to spend a lot of time sliding up an inclined plane with things set as they are now, more time would be spent moving more or less sideways across that highest prominence.
Is my supposition true that distributing the motion equally on either side of that highest prominence is how it was designed to work? Is this equally-distributed wear pattern what is normally observed in a well-functioning valvetrain?
Are your studs bent from a .600" lift cam using stock rocker arms? If not you may be looking at normal tolerances from stud to stud as they will very up to 1 degree. If a straight edge is placed across all studs you could see up to .040" maybe more. If you have or are using a stock valve train your problem is eligible for... give more information. I think your trying to fine tune something that is a acceptable tolerance. With out input I'm done thinking
The cause of the bending is incidental but probably the spring compressor was a factor. Also I'm not the only one who worked on them so it's possible they were bent another way. The cam is stock, pretty much everything is stock. My question is about where the wear pattern on the tips of the rockers should be.
Thanks!
Thanks!
Here are two pic of a 1990 305 rocker arm with 190,000 miles. At 100,000 (more or less ) miles I installed a crane compucam (#104211 compucam 2020 camshaft ) . The new cam with the same base circle as the gm stock cam has the rock arm in the same location when closed. The added lift extends further to the tip. The wear that I have noted is from were the valve is closed.
Many factors are in play. On a stock engine if you can measurer a step of more than .003" your rocker's could be worn to much.
Why? stock rocker arm are case harden. Look up case harding.
I do not know how deep your rocker arms are harden to. I do not know GM's spec's are on this
Many factors are in play. On a stock engine if you can measurer a step of more than .003" your rocker's could be worn to much.
Why? stock rocker arm are case harden. Look up case harding.
I do not know how deep your rocker arms are harden to. I do not know GM's spec's are on this
Thanks for the pictures and going out of your way!
I ended up trying two things in succession:
1) I bent studs to where the round area of the rocker arm tips was about centered on the valve stems -- but this bound the pushrods in their holes
2) I then set the studs to a measurement that put the pushrods near to center of their holes -- this seems like a good idea but I can't fully endorse it yet because, while the car seemed to idle nicely after i did this (despite some rocker arm chatter, see below), after leaving it overnight, the engine would mostly die when trying to idle, would certainly die when put into gear, and would fluctuate in rpm when held at higher rpm with stable throttle.
Here are some known problems that I will look at today:
1) Battery was low, has been on charger now overnight
2) Rocker arm chatter. It seems a few of the wear patterns in the mating surface of the rocker arms (where they meet the rocker *****) are wrong enough with the new stud positions that they are causing some chatter. I don't think this is likely to have settled differently overnight to be causing my running problem but I do plan to get to rocker arms and may do some grinding/polishing today to see if I can take out the worst of the chatter.
3) The water pump is going south and the resistance to rotation might have increased overnight or at startup. Doesn't seem to me that this would the whole problem but it seems to be the best candidate for the largest effect. I'll try turning it by hand today to get some sense of it. Of course I'll be replacing the pump and am looking for a decent deal on an aluminum one if anyone has a good clue there.
Thanks again!
I ended up trying two things in succession:
1) I bent studs to where the round area of the rocker arm tips was about centered on the valve stems -- but this bound the pushrods in their holes
2) I then set the studs to a measurement that put the pushrods near to center of their holes -- this seems like a good idea but I can't fully endorse it yet because, while the car seemed to idle nicely after i did this (despite some rocker arm chatter, see below), after leaving it overnight, the engine would mostly die when trying to idle, would certainly die when put into gear, and would fluctuate in rpm when held at higher rpm with stable throttle.
Here are some known problems that I will look at today:
1) Battery was low, has been on charger now overnight
2) Rocker arm chatter. It seems a few of the wear patterns in the mating surface of the rocker arms (where they meet the rocker *****) are wrong enough with the new stud positions that they are causing some chatter. I don't think this is likely to have settled differently overnight to be causing my running problem but I do plan to get to rocker arms and may do some grinding/polishing today to see if I can take out the worst of the chatter.
3) The water pump is going south and the resistance to rotation might have increased overnight or at startup. Doesn't seem to me that this would the whole problem but it seems to be the best candidate for the largest effect. I'll try turning it by hand today to get some sense of it. Of course I'll be replacing the pump and am looking for a decent deal on an aluminum one if anyone has a good clue there.
Thanks again!