merc 350 heads

[thundercat 9]

Re: merc 350 heads

I got this info from the Crane cams site, but that doesn't mean the info is correct:

Chevy Rockers: ?To Align, Or Not To!? - In 1988, Chevrolet changed their small block V-8 and V-6 rocker arm design to what is called a self-aligning type. The nose of the self-aligning stock rocker arm has a dimple on each side of the nose that contacts the valve stem area to hold the rocker arm over the valve stem. There is no guide plate or machined slot in the head to guide the pushrod. The pushrod only contacts the push rod seat of the rocker arm and the lifter. The pushrod should not touch any part of the cylinder head. Crane makes self-aligning rocker arms for both the 305/350 V-8 and the 4.3L V-6 engines, either 1.5 ratio 10751-1 or ?16 or the 1.6 ratio 10758-1 or ?16. These rocker arms cannot be used on engines that have pushrod guide plates or with heads that have pushrod aligning slots machined in the cylinder head. The rocker arms can only be guided by one method, not both.

 

[Mkos1980]

Re: merc 350 heads

Yea, I've seen that before but accually any centerbolt head is SA "87-95". All Hydraulic roller motors with cast heads were SA.

 

[Mkos1980]

Re: merc 350 heads

It doesnt matter about the hole on the centerbolt heads. You still have self aligning rockers on your 217 heads.

 

[thundercat 9]

Re: merc 350 heads

Hey

The rockers on my original 217 head are not self aligning, the casting has a rectangular machined hole to guide the pushrods and the head I used to replace
it with has larger oval holes for the pushrods which is why I have to use self-aligning rockers. When I get home, I'll take some picks and post them. The new(used) head came out of a 1990 305 cid.

 

[Mkos1980]

Re: merc 350 heads

Yesp please. I'd like to see these. Can you also post o pic of the rocker arm? Speciafically where it hits the valve stem. Usually a convex tip where it touches is NSA and a concave tip is SA

 

[thundercat 9]

Re: merc 350 heads

Here are a couple of pics, the pic of the head is the #217(original), as you can see,it has rectangular machined holes.I couldn't get a pic of the replacement head I put on because of the valve cover installed, but it had round holes for the pushrods which reguired the self aligning rockers.The self aligning rocker is obviously on the left

 

[flabum]

Re: merc 350 heads

The valve stems do not protrude high enough on the older heads to allow use of the self aligning rocker arms. The self aligning rocker arms will hit the spring washer before it will make contact with the stem. This is why the tell you not to mix them.

 

[Mkos1980]

Re: merc 350 heads

Hmmmm. Thats a first. I am wondering if the 217 used to be a perimeter style valve cover head and non self aligning and then GM just changed the intake bolt pattern and added center bolt covers. hmm.. I learn something new everyday. I have a set of 083 350 Tune Port heads in the basement from a 87 IROC with the round holes. hmm.

 

[Mkos1980]

Re: merc 350 heads

The valve stems do not protrude high enough on the older heads to allow use of the self aligning rocker arms. The self aligning rocker arms will hit the spring washer before it will make contact with the stem. This is why the tell you not to mix them.

What if you were able to use the correct lock and retainer set which gave more stem exposure? Would you be able to run SA or would the 2 combinations of alignment totally mess it up?