Stock 3400 Lifter preload

[3400-95-Modified]

Just do what i did.. measure the new cam VS the old one, take the difference in radius and add it to the new pushrods. Simple, effective and way faster.

Logic says that the lifter is .035 (or whatever) further down in the lifter bore.. you need to make up that difference to keep the stock lifter preload.

THANK YOU!!!!! Someone who understands what the hell I'm talking about. And thinks the same way! But I think you’re right, the cam is .035 smaller radius wise... SO the lifter drops .035 in the bore... SO it shouldn’t matter what angle the valve/pushrod is at, I'm still missing .035 at the source...

I don’t think the splayed valve train matters when it comes to what I'm trying to do... for the exact reasons I described above.

BUT if someone has already done the method I was thinking of then I guess I'm just going with that.

Just do what i did.. measure the new cam VS the old one, take the difference in radius and add it to the new pushrods. Simple, effective and way faster.

Also this is what I tried doing but when I explained that to the guys at Smith Brothers they told me to do the adjustable and add .030 method... I guess I'll just be adding .035 to my stock length then... It makes the most sense in my head.

[sprucegagt]

Just do what i did.. measure the new cam VS the old one, take the difference in radius and add it to the new pushrods. Simple, effective and way faster.

Logic says that the lifter is .035 (or whatever) further down in the lifter bore.. you need to make up that difference to keep the stock lifter preload.

Your missing what I'm saying. The pushrod is not inline with the lifter, instead it's at an angle. So just measuring the difference between cam base circles will not directly relate to the amount needed to extend the pushrods. If it was a traditional layout like in the 3800, where all the pushrods are like this "|", then you could do that. Basically the amount needed to extend this "|" does not equal what's needed to extend this "\" the same amount. When measured from top to bottom on a 90* angle.

That's why I'm asking how do you do it with a BBC that has splayed valves.

[bszopi]

I'll see if I can't find out the location of the rockers in their splayed configuration and draw something up in CAD to show that there is in fact a difference. But as a quick mathematical method, look at the pythagorean theorem (yeah, I have no clue how to spell that word!).

A^2 + B^2 = C^2

A = the distance that the rocker is splayed from the centerline of the lifter.
B = the distance to the rocker exactly vertical from the centerline of the lifter (or, the length of the pushrod for non-splayed heads)
C = length of pushrod

B will increase by the change in the base circle/2 (so, 0.35 in this example). Therefore, C will not increase by the same amount.


Example
1.0^2 + 5.400^2 = 5.490^2 Stock

1.0^2 + 5.435^2 = 5.526^2 0.035" change in base circle means 0.036" change in pushrod length

Not much, but depending on how much the pushrod is splayed, it can make a difference.

[3400-95-Modified]

I think you hit the nail on the head, that definately sounds right now...

Now I just need to figure out the splayed amount.

I'll attempt to measure it but I dont know how accurate it will be.

Then again you showing a 1" splayed valve distance is only a .001 difference in length leads me to believe if I did get .035 longer they would probably be perfectly fine.

[3400-95-Modified]

well just looking at it I cant see the valves being splayed out any further than a inch... so I'm just going to go with the .035" longer rods, and if they are slightly under sized it wont kill me because GM puts a ton of preload on there to prevent ever having to service it...

The .035 should get me close enough to where I want to be, and I know they wont be too long.

[SappySE107]

Stock is setup for 1 to 1 1/4 turn from setting the pushrod in the lifter and rocker seat so it spins by not side to side, to being torqued down. The 1280 grind I sell gives you 1/4 turn. Im trying to find the base lobe measurement difference but I can't find the folder its in. Ill measure it myself monday if I dont find it today.

[3400-95-Modified]

So your saying with stock pushrods you can still get 1/4 turn preload on your 1280 grind?

And do you put longer ones in or suggest longer pushrods with this 1280 grind?

In measuring the rockers, I cant see either one being more than 1" off of 90* angle, so I should be ok with the .035 longer.... correct?

I could probably go with just stock pushrods and see what happens and if it floats then I get longer ones... but I really don't want to tear into this thing again once its done...

[ForcedFirebird]

Stock is setup for 1 to 1 1/4 turn from setting the pushrod in the lifter and rocker seat so it spins by not side to side, to being torqued down. The 1280 grind I sell gives you 1/4 turn. Im trying to find the base lobe measurement difference but I can't find the folder its in. Ill measure it myself monday if I dont find it today.

Did you come to a conclusion on this?

My concern is that the lifters were new when I checked mine, but they were full of oil.

7/8's to 1 turn is bout what I got from spinning to the pedistals being snug (about .037" of lifter travel), then of course the lifters started to sink again after a moment as they emptied.

[SappySE107]

Heh, great. well i was wrong on the number of turns because the thread is different on the roller rockers vs the gen2 stud/nut deal. you want 1/2-3/4 but 1 turn is fine. Spec is .020 to .040 but you can go .050 without problems.

So glad you bumped this old thread.

[ForcedFirebird]

Heh, great. well i was wrong on the number of turns because the thread is different on the roller rockers vs the gen2 stud/nut deal. you want 1/2-3/4 but 1 turn is fine. Spec is .020 to .040 but you can go .050 without problems.

So glad you bumped this old thread.

No-one answered me in my thread, then the site was down. Had a chance to search today, lol...

http://60degreev6.com/forum/showthread.php?t=39642

I'm using stock 3500 rockers, Gen2 pushrods.

I got about 7/8's to 1 turn or so from resistance while spinning to the pedistal seating.

Can I put a feeler guage between the rocker pedistal and head to check at zero lash?

EDIT: I'm fimiliar with the stud/nut adjustment, that's what I had on the iron heads, lol.

[SappySE107]

I use an adjustable pushrod to figure out the 0 lash. I don't know about a feeler gauge but I don't see why not other than maybe needing 2 to hit both sides of the notch. As long as you are on the base lobe with that much preload, you should be good.

Site going down sucks for everyone

[ForcedFirebird]

I use an adjustable pushrod to figure out the 0 lash. I don't know about a feeler gauge but I don't see why not other than maybe needing 2 to hit both sides of the notch. As long as you are on the base lobe with that much preload, you should be good.

Site going down sucks for everyone

Yes, base circle. I used the adjustable valve lash method of rotating the engine to TDC at #1 and #4 cyls and adjusting the corisponding valve.

I have a bunch of scrap pushrods, and just haven't gotten around to making an adjustable one, I was hoping that these will work OK. If anything, I feel they could be a little longer, but as mentined in the other thread, I will be using the full rollers soon (adjustable).