Rocker tips off-center of intake valves-Why?

Leif · #1 (**permalink**) 08-02-2010, 01:44 PM

Hi, we just installed a set of the Comp Camps Long Slot 1.72 Roller Tip rockers on a new build of a BBC with all new L88 Replacement heads, and stock guides. The tips of the rocker arms of most of the intake valves are off-center by as much as 30 degrees. Can anyone give me a reason for this? We used stock guides-Should we use some other guides? I was under the assumption that these roller tipped rockers could be used as a direct replacement instead of the stamped steel factory units.

Any help would be appreciated!

amick · #2 (**permalink**) 08-03-2010, 07:06 PM

From what I can see in the pictures the rocker arms are definitely not curved so I don't think they are your issue. If the slot was binding against the rocker, that could cause the issue also. I would try to play with guide plate to move it to the side more if you have not already done this. If the pushrod was not a chromemoly pushrod I could see it possibly flexing to allow the rocker to twist under that much spring pressure from a 26120 spring. Can you tell me what the cam size in the motor is?

ken · #3 (**permalink**) 08-05-2010, 04:39 PM

Aaron,

I have a set of CC red aluminum rockers on 351C heads. The tips are not perfectly aligned side to side, but how good do they need to be? A pic is attached, the far right rocker is about the worst.

This isn't a race motor, I have your 292H hydraulic cam, maybe 6,500 red line.

Thanks,

Ken

iwannagofaster · #4 (**permalink**) 08-06-2010, 09:34 AM

Hi Leif,
Aaron has gone out of town to work at an event. If the far right rocker in that pic is the worst, then you are in good shape. All that we really look for is that none of the actual body of the rocker contacts the valve stem. If you have at least 90% of the roller on all of the valves, and the body doesnt hit, that would be good in my book.

iwannagofaster · #5 (**permalink**) 08-06-2010, 09:35 AM

Sorry, Ken, I was responding to a Leif before you and I guess it just stuck (or it is really early on a Friday and my brain hasn't clocked in yet).

ken · #6 (**permalink**) 08-06-2010, 04:18 PM

Hi William,

Thanks for the answer. By 90%, do you mean that the roller is in contact with at least 90% of the top surface of the valve stem (so the contact C is at least 0.9 the diameter D)?

Leif · #7 (**permalink**) 08-07-2010, 02:54 AM

Hi William, if you take a look at the left picture, Center rocer (intake), you will notice how far off the rocker is on the head. I would say that some of them are off by as much as 30%. Some have said that I should simply move the guide plates around to see if that fixes my problem but I doubt GM did that when they were building the engines! Do you have any suggestions?

These heads were all GM with the exception of your rockers.

Thanks,
Leif

iwannagofaster · #8 (**permalink**) 08-09-2010, 11:01 AM

Ken,
That is absolutely correct!

iwannagofaster · #9 (**permalink**) 08-09-2010, 11:06 AM

Leif,
I have personally even had to go as far as to drill out the stud hole to get the rockers a little more close to center on big block applications. You do need to adjust the guide plates and you may need to take the steps that I had to take as well, but you need to get them closer to even thanthey are now, if nothing else.

Leif · #10 (**permalink**) 08-09-2010, 11:19 AM

Hi William, My first guess was that the heads were not machined correctly when built. Those heads are a brand new set of the GM L88 replacement heads. Your rockers just illustrate that the studs were not positioned correctly-at least in my opinion. I think my next step is to contact someone at GMPP or Edelbrock (who makes the heads now for GM) to get their opinion.

Thanks again for your help!

-Leif