Just got done setting the valve lash with the new 3/8 conversion studs and the roller rockers, I just realized the pitch on the new studs are probably different, so 1 1/2 turns isn't going to be the same. If any body knows what I should turn them too, or if it is a big enough difference to matter it would save me a lot of time. I figure the only way I'll be sure is to measure the travel on the 10mm studs and just duplicate that travel.

3/8's is the usual GM V8 thread isnt it? being the lifters are the same as GM V8's as well - use the GM V8 spec.

or - do some math. look up the travel of the lifter plunger, divide by 2. that is the lash depth. then see how many threads the 3/8 pitch needs to achive that lash depth.

but - pretty sure just using the common GM V8 spec will do the job - being you are basicly using V8 studs & V8 lifters

quote Originally posted by fierofinder: I just realized the pitch on the new studs are probably different, so 1 1/2 turns isn't going to be the same.

You are correct. The original studs are metric thread, your new studs are SAE thread.

quote I figure the only way I'll be sure is to measure the travel on the 10mm studs and just duplicate that travel.

I don't know the answer offhand, but if you know the pitch of the threads on both the old and new studs you should be able to calculate it rather easily. If you don't know the old and new thread specs, a couple of cheap thread pitch gauges will tell you all you need to know.

quote Originally posted by Pyrthian: or - do some math. look up the travel of the lifter plunger, divide by 2. that is the lash depth. then see how many threads the 3/8 pitch needs to achive that lash depth.

No! Doing it your way you would also need to correct for the rocker arm geometry: Lifter plunger travel = (adjusting nut travel) x (rocker arm ratio + 1). It's much simpler to just calculate a correction based on the different thread pitches.

you mentioned rocker arm ratio makes a difference in plunger travel as well. i have 1.6 rockers as well. do i need to do (1.6+1)(x)=1\2plunger travel. figure out the plunger travel is suppose to be and solve for x?

quote Originally posted by fierofinder: you mentioned rocker arm ratio makes a difference in plunger travel as well. i have 1.6 rockers as well. do i need to do (1.6+1)(x)=1\2plunger travel. figure out the plunger travel is suppose to be and solve for x?

Forget that. As an alternative, you could use a dial indicator to measure total plunger travel, and then use the dial indicator to measure the number of turns needed to achieve 50% plunger deflection. But this is still simpler, and just as accurate:

quote Originally posted by Marvin McInnis: ... if you know the pitch of the threads on both the old and new studs you should be able to calculate [the new number of turns] rather easily. If you don't know the old and new thread specs, a couple of cheap thread pitch gauges will tell you all you need to know.

If your rocker arms are a different ratio than stock, then you should correct for that also:

X = 1.5 x (P_oem / P_new) x ((R_oem + 1) / (R_new + 1))

Where:

X = New optimum number of turns of the adjusting nut past zero lash
1.5 = OEM specification (number of turns)
P_oem = OEM thread pitch (inches or mm)
P_new = new thread pitch (inches or mm)
R_oem = OEM rocker ratio
R_new = new rocker ratio


Edit: To correct formula term for rocker arm ratios

[This message has been edited by Marvin McInnis (edited 06-09-2011).]

The setting on a SBC V8 is zero lash plus 3/4 turn. On a TPI V8, it's zero lash plus 1 turn. I'm not sure why the discrepency, since AFAIK they both use SAE 3/8" rocker studs.

But IMO, instead of rummaging around for the proper V8 valve lash spec, just do the math as described above. You can take the rocker studs to a hardware store to find out the thread pitch, if you don't know it already. You already know that the 2.8 V6 spec is zero lash plus 1.5 turns. Find out how much distance the rocker nut travels in 1.5 turns on the stock studs, and then calculate how many turns you need on the new studs to travel that same distance.

Dial indicator sounds like the easiest way. Seems like there is some room for error though if I don't measure the total lifter travel correctly. Will the plunger go in easy enough by pushing down on the rod with my hand. Can I just find what the travel is suppose to be in the manual or somewhere on PFF. I'll try a search for that and see what I find.

If the lifters are new, you can easily push the plungers by hand. Older lifters may be stuck.

quote Originally posted by TopNotch: If the lifters are new, you can easily push the plungers by hand. Older lifters may be stuck.

Correct! I have, in the past, disassembled, cleaned, and restored old hydraulic lifters to like-new condition. It's not difficult if you are careful and well organized, but I still don't generally recommend it.

[This message has been edited by Marvin McInnis (edited 06-08-2011).]

How would you recommend I check the full travel of the lifter. Should I just tighten the rocker down and check it that way.

This is getting frustrating. For the third time, I recommend:

quote Originally posted by Marvin McInnis: ... if you know the pitch of the threads on both the old and new studs you should be able to calculate [the new number of turns] rather easily. If you don't know the old and new thread specs, a couple of cheap thread pitch gauges will tell you all you need to know.

quote Originally posted by Marvin McInnis: X = 1.5 x (Poem / Pnew) x ((Roem + 1) / (Rnew + 1)) Where: X = New optimum number of turns of the adjusting nut past zero lash 1.5 = OEM specification (number of turns) Poem = OEM thread pitch (inches or mm) Pnew = new thread pitch (inches or mm) Roem = OEM rocker ratio Rnew = new rocker ratio Edit: To correct formula term for rocker arm ratios

Of course, you are free to do it however you choose. I compliment you for at least thinking about it ahead of time, but you're making the task a lot more difficult than it actually should be. Good luck.

[This message has been edited by Marvin McInnis (edited 06-09-2011).]

quote Originally posted by fierofinder: Dial indicator sounds like the easiest way. Seems like there is some room for error though if I don't measure the total lifter travel correctly.

There is room for error using this method, too. You can probably do it by tightening the rocker nut on an installed lifter / pushrod / rocker. But you will need to put the dial indicator on the top of the lifter plunger. Getting the needle on the dial indicator pointing exactly straight down onto the lifter is the key. Because if the dial indicator is off by even a few degrees, you will get an inaccurate reading.

The only error you'll get in doing the math method is if you punch the wrong numbers into the calculator.

quote Originally posted by Marvin McInnis: This is getting frustrating. For the third time, I recommend: Of course, you are free to do it however you choose. I compliment you for at least thinking about it ahead of time, but you're making the task a lot more difficult than it actually should be. Good luck.

I do believe it was you that suggested doing it with the dial indicator

[This message has been edited by fierofinder (edited 06-08-2011).]

Both thread pitch values must be in the same units (inches per turn or millimeters per turn are most convenient for our purposes here) for computation:

1 mm pitch = 1 mm per turn = 0.039 inches per turn
1.25 mm pitch = 1.25 mm per turn = 0.049 inches per turn.
16 TPI (SAE 3/8-16 UNC thread) = 1.59 mm per turn = 0.063 inches per turn.
24 TPI (SAE 3/8-24 UNF thread) = 1.06 mm per turn = 0.042 inches per turn.

[This message has been edited by Marvin McInnis (edited 06-09-2011).]

Thank you for all the great help. With the math, I get 2 full turns. [(1.5/1.06)(1.52/1.6)]1.5=2.02 rounded to the nearest hundredth [(Po/Pn)(Ro/Rn)]1.5

quote Originally posted by fierofinder: With the math, I get 2 full turns. [(1.5/1.06)(1.52/1.6)]1.5=2.02 rounded to the nearest hundredth [(Po/Pn)(Ro/Rn)]1.5

I'm not sure that's right. We agree that:

R_oem = OEM rocker ratio = 1.52 (I believe that's correct)
R_new = new rocker ratio = 1.6 (data you provided)

But what are your actual:

P_oem = OEM thread pitch (inches or mm per turn)
P_new = new thread pitch (inches or mm per turn)

N.B. 1.5 mm pitch for the OEM studs seems pretty coarse for the adjustment end. I'll try to check an old V6 I have in the shop. Edit: Mine appear to be 1.0 mm pitch, but the adjusting nuts are still in place so I couldn't get a good measurement.

Note also that I edited the original formula I posted to correctly adjust for rocker arm ratio:

X = 1.5 x (P_oem / P_new) x ((R_oem + 1) / (R_new + 1))

If you'll post your actual known thread pitches, I'll be glad to do the calculation along with you.

[This message has been edited by Marvin McInnis (edited 06-09-2011).]

Thank you for catching that. The base thread pitch is the 1.5mm the adjusting thread pitch is 1 mm. 1.5[(1/1.06)(2.52/2.6)]=1.5(.9434)(.96923)=1.5(.91437)=1.37156 Let me know if this sounds right to you. Po=1mm Pn=1.06mm Ro=1.52 Rn=1.6

I agree. Given:

P_oem = 1.0 mm
P_new = 1.06 mm (24 TPI)

R_oem = 1.52
R_new = 1.6

X = 1.5 x (1.0 / 1.06) x ((1.52 + 1) / (1.6 + 1)) = 1.37 ... or about 1 3/8 turns

After all that work, the answer is still really close to 1 1/2 turns past zero lash, but at least now we know for sure.

[This message has been edited by Marvin McInnis (edited 06-09-2011).]

Yes I agree, definately better than being sorry. Thank you for all the great info.