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Discussion Starter · #1 ·
I have what I presume to be a 302 motor. The heads and lifter valley both say 302, and supposedly it's a 1969 engine. It was rebuilt somewhere around the early 90s and put in this T-bucket my dad had when I was kid. 20 years ago, we sold the car, and I bought it back last month.

It had tapping coming from the valvetrain when I picked it up. No misfires. I checked the lash, everything was tight. I have replaced the lifters and planned on replacing the pushrods for good measure and putting it back together. Well, I've been trying to measure pushrod length, but using a dry erase marker on the valve stem isn't giving me a good reading. Based on the markings, it seems my pushrods should be between 6.900" and 7.000". The ones that came out of the engine are somewhere around 6.875 or so. The problem is, there isn't a clear wear pattern in the marker ink after setting the lash and cranking the engine by hand. It's kind of smudged from the top of the valve stem to about halfway or past, depnding on the rod length. The only time the top of the valve stem has ink, is when I set the adjustable rod to 7.000" and then the bottom of the wear is just past the middle, with ink still on the top and bottom. I think the problem is that where the rocker contacts the valve stem is worn as shown in the pics below.

The lifters that came out and the new ones that went in are hydraulic flat tappets (new ones from Comp). I'm not sure about the specs on the cam because the engine was (re)built 30 years ago. I'd be willing to put money on it not being the stock cam because of the choppy sound. Any advice on getting an accurate measurement for my pushrods or should I replace these rockers? I really don't want to spend to replace them if I don't have to.
 

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I use a black Sharpie Pen and get great patterns.
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If your heads are from 1969 they have positive stop rocker arm studs. You do not adjust the lash- you screw the nut down until it bottoms out on the shoulder on the stud. If you are trying to adjust the rockers like you would do on a pre-69 engine you will never get a consistent reading.
Of course this is a moot point if the studs in the heads have been replaced with screw-in studs.
 

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Discussion Starter · #4 ·
So sharpie was my first try. Cranked it over 3 or 4 times and didn't get any marks in the sharpie.

The studs do not have a shoulder that I can see. Threads all/most of the way down to something hex shaped. I assume these are aftermarket screw-ins.
 

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With hydraulic lifters and screw in studs, I adjust to a 0 lash, then turn the nut down 3/4 of a turn. Check with your lifter specs to see what they say to turn the nut.
 

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Discussion Starter · #6 ·
With hydraulic lifters and screw in studs, I adjust to a 0 lash, then turn the nut down 3/4 of a turn. Check with your lifter specs to see what they say to turn the nut.
Thanks for the information, but the lash is not my problem. My problem is correctly measuring pushrod length.
 

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I'm thinking, you first, need to verify your rocker stud setup. Since your heads are already in-place, order a set of "checking springs" and an adjustable PR. Use these to check your PR geo. If your witness mark is biased towards the intake, too short towards the exhaust, too long. II've followed the idea, a witness mark of approximately .070 is about right and should be more centered.
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I’m no expert, but AFAIK, hydraulic lifters don’t have a lash spec,they should be adjusted to zero lash+some amount of preload. It doesn’t make sense that a sharpie wouldn’t leave marks on the stem while a dry erase marker would. I used a black sharpie on a 289 rebuild with an Edelbrock top end kit, but had no problem getting clear marks with a sharpie and a checking spring.




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To me, the rockers look good.

Are you using a solid lifter with your adjustable pushrod?
 

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The rockers are not the problem. If you have the correct valves for those rail-type rockers, then the only real question is whether your pushrods are the correct length. Show us your valves.
 

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Discussion Starter · #11 ·
I'm thinking, you first, need to verify your rocker stud setup. Since your heads are already in-place, order a set of "checking springs" and an adjustable PR. Use these to check your PR geo. If your witness mark is biased towards the intake, too short towards the exhaust, too long. II've followed the idea, a witness mark of approximately .070 is about right and should be more centered.
View attachment 813541
Thanks, I have the springs and adjustable PR already. The problem I have is the rockers don't leave a clear witness mark. It's always very smudged and difficult to read.

I’m no expert, but AFAIK, hydraulic lifters don’t have a lash spec,they should be adjusted to zero lash+some amount of preload. It doesn’t make sense that a sharpie wouldn’t leave marks on the stem while a dry erase marker would. I used a black sharpie on a 289 rebuild with an Edelbrock top end kit, but had no problem getting clear marks with a sharpie and a checking spring.






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Thanks. The lash is not the problem I have. I can set that. Measuring the PR length and getting a clear witness marks is my issue. I wasn't clear above about the sharpie. The sharpie WILL mark on the valve, but the rocker will not rub off the sharpie to create a witness.

To me, the rockers look good.

Are you using a solid lifter with your adjustable pushrod?
Thanks! That's good to know. Hydraulic lifters. I can set the lash fine, and know the appropriate preload for these lifters. My problem is measuring the pushrods for proper valvetrain geometry.

The rockers are not the problem. If you have the correct valves for those rail-type rockers, then the only real question is whether your pushrods are the correct length. Show us your valves.
Right. That's why I'm trying to measure the pushrod length. I just can't get a clear witness mark to show through.

Here are the valves and stud.

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I'm editing my last comment, since it appears you have the tools, "super clean" the tips and use engineer's blue. I, for one, have not your problem. Perhaps the rocker tip is "sliding" across the tip due to the PR being too short already? I'm not sure this will work, but, maybe if you used a roller rocker just for testing?
 

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Discussion Starter · #13 ·
Really? I mean, if that's what I need to do, I can buy a solid lifter to use for measuring. The cam is not a solid flat tappet cam (assuming, based on hydraulic lifters coming out).

I haven't seen anything in my research about using a solid lifter when measuring valvetrain geometry, but it makes sense why I would want to use it.

As stated, I already have check springs on the head and am using an adjustable pushrod length checker.
 

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Really? I mean, if that's what I need to do, I can buy a solid lifter to use for measuring. The cam is not a solid flat tappet cam (assuming, based on hydraulic lifters coming out).

I haven't seen anything in my research about using a solid lifter when measuring valvetrain geometry, but it makes sense why I would want to use it.

As stated, I already have check springs on the head and am using an adjustable pushrod length checker.
Yes, you can use a solid lifter. It won't hurt the cam for this test. There are methods to make a solid lifter, if you can't purchase or borrow a couple for this check. If you already have the checking springs then, no need for a solid lifter.
 

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Discussion Starter · #15 ·
Yeah, just for checking length and cranking by hand, I would imagine it to be okay. Especially with check springs. My first time diving into an engine so I'm trying to make sure I do everything right the first time. I don't want to have to come back. I want to DRIVE! 😁
 

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Since you have light duty check springs, then the solid lifter isn't necessary as long as the hydraulic lifters aren't being compressed.

You do have screw in studs so the rocker is adjustable (not positive stop).
 

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Thanks, I have the springs and adjustable PR already. The problem I have is the rockers don't leave a clear witness mark. It's always very smudged and difficult to read.



Thanks. The lash is not the problem I have. I can set that. Measuring the PR length and getting a clear witness marks is my issue. I wasn't clear above about the sharpie. The sharpie WILL mark on the valve, but the rocker will not rub off the sharpie to create a witness.



Thanks! That's good to know. Hydraulic lifters. I can set the lash fine, and know the appropriate preload for these lifters. My problem is measuring the pushrods for proper valvetrain geometry.



Right. That's why I'm trying to measure the pushrod length. I just can't get a clear witness mark to show through.

Here are the valves and stud.

View attachment 813573
Those appear to be early style rail rockers. I notice as well that your pushrods come through a round hole instead of slotted. The early heads had slotted holes combined with the rail rockers to keep the rockers aligned on the valve. You will need to install some type of guide for your pushrods. Also if your valves weren't designed for the rail rockers the tips may not be long enough to clear the rail, and may not be touching the rocker and that could be why you aren't getting a mark.
 

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PA, I think it comes one way or the other, you get the rails on the rocker to keep it centered or you have slots in the heads instead of holes to keep it aligned, I have never seen both together. As for the OP, it’s much easier to get a wear pattern with a roller rocker than it is for a stock one, since the roller will slide as much as it rolls across the tip of the valve. See if you can fine some layout fluid like this, it might work better, I think I’d even try some white grease if you have some handy before doing anything else, that might get pushed out where it rides and allow you to see a pattern.
 

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I hope this does not come off as a dumb question, but you are installing the pivot balls in the rockers before checking for pushrod length right? I don't see them in your pictures anywhere.
 

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So from the photo you have screw in studs, rail rockers and the correct valve stem for rail rockers. With rail rockers you will not need guide plates. If you switch the rocker arms to a roller or roller tip, you will need guide plates and hardened pushrods, unless you get self aligning roller tips. They have the same design as a stock rail rocker but with a roller tip. They will leave witness marks on the valves. You will not be able to get a witness mark with those rockers because the tip/pad has already conformed/worn themselves to match the attack angles at the valves. The pads are constantly sliding across the top of the valves, that is why you get indistinct smudges. Those were never meant to be performance rocker arms. As stated above, there is no lash. Set to zero and lock it down at 1/4 - 3/4. Without the factory positive stop studs, those nuts may loosen over time. You may want to consider a better set of locking nuts at least.
 
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