88TPI406GTA

I have Pro Topline 220cc heads, 7.8" pushrods, stock length valves...and 1418 Competition Cams Magnum SA 1.6 ratio rockers along with ARP rocker arm studs (3/8" inch)

The problem now is that when I tighten down the rocker arm nut to set the valve lash, the spring starts to compress, thus opening the valve, all while the pushrod isn't even lashed yet...so when I actually set the lash according to the procedure, the valve is open a bit...

The procedure I use is to make sure the lifter is fully seated in the valley (indicating valve is closed) and then I tighten down the rocker arm nut until I start to feel tension on the pushrod, then go 1/2 to 3/4 turn...which means the valve isn't seating properly...

I don't know what to do here...it is almost like I need either different rocker arms or need to add a spacer under the rocker arm, so it can't go down so far on the stud...

Any ideas here? TIA...

Momar

I only have limited experience here, but could you need a longer pushrod?

88TPI406GTA

I checked the pushrod length using the Comp Cams procedure...

http://www.compcams.com/Technical/Products/Pushrods/

and I found that with stock pushrods, the rocker arm tip was in the middle throughout the whole range of motion...

ede

with flat cams there's a very good chance the lifter is spinning in it's bore making you think there is no preasure on the push rod. besides spinning the push rod it's a good idea to move it up and down to tell when you're getting close to zero lash.

RB83L69

If you're compressing the valve spring as you tighten then you're already way beyond zero lash, and adjusted all the way through the "correct" range of lifter plunger travel, and beyond. You've got them about 1½ turns too tight.

Rockers, push rod length, etc. have nothing to do with it. You're just simply doing it wrong.

Try backing them off and jiggling the push rod up and down between the rocker and lifter, and tighten it until it just quits being able to jiggle up and down in there, and then go ½ turn more.

Since you're using self-aligning rockers, make sure you're not also using guide plates. One or the other, but not both.

88TPI406GTA

OK...just so I understand this correctly...the way that I have been doing it is to spin the pushrod between my fingers and tighten the rocker arm nut until I feel resistance with the pushrod. That is zero lash...then tighten down 1/2 to 5/8 turn (correction from above).

So another way to look at this is to simply eliminate the vertical space between the bottom of the pushrod and the lifter and the top of the pushrod and the rocker arm...right? When I reach that point, then I am at zero lash?

When the valve lash is set, am I supposed to be able to spin the pushrod at all?

88TPI406GTA

Also, i am using the SA rockers and no guideplates...

Momar

Yes, you should still be able to turn it some. It shouldnt be as loose as with no tension obviously though.

Ben

88TPI406GTA

Update:

There is another issue here...when I go to put the socket on the rocker arm nut, I can't get it on unless I turn the engine over so that the cam is moving the lifter up and actuating the valve. I didn't mention this because Comp Cams already told me last week that it wasn't a problem...

Well, it is a problem...when I go to tighten down the rocker arm nut, the valve is starting to open before I get to zero lash...and after talking to a local race shop, I think my solution will be to get poly-locks...or to switch to a different rocker arm...I think the poly locks will work though because then the nut part will be higher up on the stud and it shouldn't be causing any bind issues because I won't need to put a socket in there to tighten....

This isn't the 1st time I have ever built a SBC, but it is the 1st time I have run into this wierd issue...I will post results after I try the poly locks and see if that solves the problem...

RB83L69

Get stock rocker nuts from GM. Jam them with some regular 3/8"-24 (fine) nuts.

If you get Poly-locks, you open up a whole other can of worms; namely, they may not fit under whatever valve covers you're using.

I dislike the nuts Comp supplies with those rockers. I do as I described above. But, the longest I've ever had a set of those on an engine set up that way has only been about 140,000 miles, so I don't know yet if it's a good long-term fix or not; but so far, so good. When I get some real miles on them I'll let you know how they hold up.