John in RI

iTrader: (167)

I'm currently rebuilding a 305 SBC and while digging thru my heads I took a peek at a set of centerbolt heads that I've had in storage. Everything I've ever read or noticed in the past has told me that centerbolt (87 + or Roller Lifter ) engine require Self Aligning Rocker Arms & that Non Self Aligning Rocker Arms were used on all non-roller lifter, perimeter valve cover bolt engines.

I understand that guide plates can be added to centerbolt heads and NSA can then be used..... I'm thinking in terms of a stock engine.

Here's a couple stock rocker arms:


Everyone will notice the non-self aligning rocker at the top and a Self Aligning Rocker at the bottom.

I've got 2 pairs of 081 heads,... I KNOW they were both removed from 87 TPI cars. Why is it that BOTH of these sets of heads have NON Self Aligning Rockers ??






Both sets of 081 heads I've got have been in storage a LONG time. I find it very hard to believe that these rockers were ever swapped in the past. COUld have been swapped - sure,.... but I HIGLY doubt it. Can anyone tell me if they have even seen this before ??

novaderrik

they did kind of build them both ways in 87...

i'd use the self aligning rockers- but only if you aren't using guideplates and only if the pushrod holes in the heads aren't slots that act as guides.. you don't want more than one method of lining things up..

sofakingdom

iTrader: (1)

Yup; I've seen the same thing; apparently the transition wasn't all at once...

John in RI

iTrader: (167)

You can Kinda' see the 081 head with a "hole" rather than the slot found on the earlier heads in the pic above. Here is a pic of the "slotted" 416s



What gets me is that EVERYONE says that guide plates MUST be used when NSA rockers are installed on a centerbolt ( roller ) head because at least 1 form of guide is needed. ( I can understnad why 2 guides working together is a BAD thing )

If GM was building roller motors in 87 with NO way to guide the pushrod then why arn't there more complaints about pushrod problems on 87's ?? How bad can it really be to install NSA rockers on a roller head if GM was making them that way ?? Is it possible that they learned there was a problem that year and that's what caused a change in the rocker design ? ( but again - why isn't the NSA rockers in 87 more widely known about - I've NEVER seen it mentioned anywhere before !? )

TreeFiddy

Dunno, the pushrods holes in the 081's are hard to see in that pic, but look like guide slots to me. Shorter than the 416 slots yes, but slots nevertheless. I though SA pushrod holes were quite large to avoid any possible contact.

sofakingdom

iTrader: (1)

Depends on how wide the slot between the "rails" on the rocker is... if there's enough slop in there, they might never even touch.

The "better" the rockers, the more likely they'd be to cause problems, IOW.

John in RI

iTrader: (167)

You might be onto something there.....


Here is the FIRST set of 081's I started messing with. ( These had NSA rockers) Clearly these appear to be "slotted" heads.




This is the second pair of 081's I had (pictured above.) They also had NSA Rockers & the pushrod "area" appears to be rounded when looking from the top - but slotted when viewed from the bottom.



At first glance it almost appears like pushrod wear made them 'rounded' - but the marks are just to prefect and I think it was machined. You can just about make out the counter-sink on each hole in this pic:




I had ALWAYS taken it for granted that the 87+ centerbolt heads required Self Aligning Rockers, But It seems as if the type of pushrod area is the determining factor ( Slots Vs. Holes ? )

paulo57509

Very interesting discussion.

I know the engine in my car is the factory installed original. It's a roller cam engine.

The heads are 14101081 centerbolt castings with date codes of J166 and J206. These heads do not have self-aligning rockers. I don't recall what the pushrod holes/slots look like.

I've never actually held a self-aligning rocker arm in my hands, but from the posted photos it appears that the valve stem would need to be a bit longer above the retainer to fit a self-aligning rocker.

What if you have an assembled head without the rocker arms. How would you tell if self-aligning rockers are needed? The pushrod slots? Valve stem lengths?

That one photo looks like the pushrod slots were drilled out using a Louis Tool.

TreeFiddy

A quick search here turned up this:

https://www.thirdgen.org/forums/tech...ide-holes.html

First pic is narrow slot to guide the pr for non sa rockers, second pic has round holes to clear the pr for sa rockers (or guide plates).