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Joe's explanation makes perfect sense to me. Thank you for breaking down the details. Glad to know I can use this setup in my other engine without issue!
Originally Posted by joe_padavano
Totally different issue. The problem here is not reading the instructions that came with the timing set.
And by the way, there is zero confusion here. Once again, if the marks are aligned at 12 - 12, turn the crank one full turn and they will also be aligned at 12 - 6. The piston is at TDC both times. The issue is compression vs exhaust, and that only matters once the distributor is installed.
I've seen debate on this subject too and that also makes perfect sense. Learned a lot here today.
Last edited by ck__joel; April 16th, 2023 at 09:21 AM.
Good catch you guys, I couldn't even see the other marks until I zoomed in a lot. Yes, always follow the manufacturers instructions. It doesn't really matter if you degree the cam, which you should. Then you know if something is off.
So with the valve contact issue solved, I realized I still have a question about the valvetrain geometry since fixing the timing issue won't change that.. But I am new to the small block Olds, and maybe this is the way they are and my former experience doesn't apply here.. From my experience in working with OTHER engine platforms, the angles that the rockers are operating at would indicate to me that the 8.250" pushrods in this build were too long. (why i thought a possible reason for the valve contact). What I'm referring to is the rocker being perpendicular to the stud at base circle.. In my experience that should happen around mid-lift, and starting perpendicular like it is will lead to a wide sweep pattern on the valve. I would think that's true regardless of manufacturer, but I'm also not sure how to correct this given the stud height... shorter pushrods alone would not fix it.. So is there a fix? Is there nothing that needs fixing? Is this the issue with running roller rockers and roller lifters together?
Base circle 8.250 pushrods
Max lift as built with 8.250 pushrods.
What i think would be a more ideal base circle angle, but the stud height doesn't allow contact to accommodate a shorter pushrod:
Please clean the tip of the valve, mark it with some dycom or a sharpy.
Mount the rocker and pushrod, adjust to spec.
Then after rolling the engine over a few times, remove the rocker.
Now check where the roller of the rocker left the marking/wear patern on the valve tip, this should be, as close as posible, in the middle of the tip.
Last edited by Altered 1978 350 Olds; June 16th, 2023 at 02:41 AM.
Please clean the tip of the valve, mark it with some dycom or a sharpy.
Mount the rocker and pushrod, adjust to spec.
Then after rolling the engine over a few times, remove the rocker.
Now check where the roller of the rocker left the marking/wear patern on the valve tip, this should be, as close as posible, in the middle of the tip.
Thanks…I am familiar with the concept of centering the rocker tip on the stem and also choosing a pushrod length that minimizes the sweep across the top of the valve stem as it related to valve guid life expectancy etc. problem i was seeing is that clearance to the stud wasnt going to allow adjustability if there was an issue.
that being said, this engine is just a bunch of parts at the moment and I can’t really test anything. But i will be putting it back together eventually so i am still interested in knowing if the geometry i pictured above is normal on an Olds? On an sbc (what im accustomed to), this geometry would be an obvious indicator of too much pushrod length.
My engine needs a complete rebuild, which i want to give it. But given that, i decided it wasnt the best candidate for the current project car. But i think this will be a solid runner when put together so im going to build it over time and find it a home somewhere
April 16th, 2023, 08:39 AM
