Just bought a bare set of ported #781 heads cut for 2.19/1.88 valves. After getting home and looking thourgh the box of extras that came with the heads there are 16 spacers approx. a 1/4" thick. I remember reading a post on here about some #781 heads having deeper spring pockets. I dont have another set of bare heads to compare them too at the moment to see if they are indeed deeper. Is there a problem running the spacers for performance application if they are indeed needed on the heads????? Just thinking maybe thats why the guy got rid of them, he said he went to SQ ports and didnt need them anymore...............

I bought a set of bare 781 heads a few months back. Valves, springs, etc in a box. There were 16 valve rotators 1/4" thick.

Slip a valve in there, put a retainer and keepers on, see what your installed spring height would be.


The other two sets of 781s I have have no rotators...one set under the valve covers on my 1968 RatVette, the other set buried under my bench.

Most 781s used an exhaust rotator under the exhaust valve spring. When using dual springs it is required to remove the rotators and put in the spacers. They (the spacers) are fine for performance use.

ONLY the exhaust get the spacer and they are .300 thick, which is the thickness of the rotator they are replacing. The spring seat "bore" in the head is 1.750 on the exhaust side and the spacers are machined with a 1.750 OD to fit. They will not fit the intake side, if they do, beware, something has been "modified"

If someone has made some spacers for your heads then this all goes out the window, and different than stock length valves will change things even further.

The only way to know for sure how to set up your springs is to put the valves in the head and intall the retainers and measure the distance from the spring seat on the head to the spring seat on the retainer.

Most 781s with stock length valves come in around 1.800 installed height, but I,ve seen them with as much as 1.950. Do not assume anything on your spring heights, and dont just stick in some spacers because they came with the heads. It has to match YOUR cam and spring requrements.

Scott

my 781's also have the rotators on the exhaust side.
Are you saying not to use them with double springs?
Ps. whats their purpose?

Stock is like 1.88" and the later heads at 1.80" installed height!!

I ran into this w/ CRANE after buying their kit and nothing fit right and they said that I needed different retainers and I said, funny,your package say's they will fit so I think I'm getting hosed!! The guy on the phone sent me back my money and said to return the parts!!

Went w/ Comp Products stuff..

Like I needed an extra set of retainers sitting around!!!!!!!!

Come to find out they mixed and matched so to be able to hit both 1.88" AND 1.80" using different height keepers AND installed height springs!!!

It's all in their charts if you want to dig it out...........

But I figure their business practice was, "Buyer beware" so that they sold more stuff b/c they could blame it on the customer!!

Kinda like spec'ing a too big a cam, then a too smalla cam and finally the right one!! They've sold THREE f-- cams, right!!!!!!!!!!!

pdq67

my 781's also have the rotators on the exhaust side.
Are you saying not to use them with double springs?
Ps. whats their purpose?

The rotators have a lip on the top side. They work fine with a single spring, but with dual springs the inner springs dont have a good flat surface to set on because of the lip.

The rotators purpose is to simply help the valve rotate as it opens and closes. The theory is that the valve and the seat will last longer if they seat in a different position each time the valve closes. They are common on many engines.

The spacers are Comp part number 4779-8 (from memery, so I hope that is right)