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Corvair Rocker Arm Question
Posted by: jimc ()
Date: October 13, 2018 02:28PM

Not a new topic, but an interesting difference of the OEM and GM replacement rocker arms.

I bought a corvair rocker arm part #5723559 recently to compare to my used rocker arm. Before purchasing I checked my Parts book and it listed the 5723559 rocker part for all corvairs 1960-69.

There is another corvair rocker arms part #6255648 which appears to be an older number and replaced by the 5723559 based on internet info.

Below are comparative photos of an oem vair rocker from a known vair motor from 1969 which I still have and a newer rocker arm is the 5723559 which I recently acquired.

My question is not on the part number history, but the shape of the rocker arm as it pertains to function.

I laid both rockers on a flat surface and assuming that the tops are similar contour and measurements from the pivot points I measured a realistic 1/16" difference between the contact surfaces.

Again I am assuming the rocker body contours are similar to the pivot points and I have not cut one in half to confirm, but if all is same these later replacement rockers may be off by 1/16" and would not this affect overall lift?

OEM Vair rocker


Newer GM replacement rocker


Tell me I missed something simple?

Jimc
1965 Corsa Coupe, two owner history


HACOA Member
CORSA 2017 Concours Senior Gold Award
AACA 2015 Award

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Re: Corvair Rocker Arm Question
Posted by: toms73novass ()
Date: October 13, 2018 02:43PM

The top is not a reference surface and its shape can be way off and still function properly.

The ball seat and tip are references surfaces.

-Tom


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Re: Corvair Rocker Arm Question
Posted by: Seth Emerson ()
Date: October 13, 2018 03:55PM

I believe Chevy sold two different rockers for the Corvair. (First one, then replaced by another). The newer rocker has a narrower, but longer contact surface for the tip.This later style is the style that Clark's modeled for their replacement. I actually prefer the earlier ones with the wider face. There may be other differences in their design.

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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Re: Corvair Rocker Arm Question
Posted by: dryenko ()
Date: October 13, 2018 07:39PM

The shape of the valve tip contact face can affect the lift , and possibly vary the ratio.

Bob C aka Dryenko
Dobson, NC 27017

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Re: Corvair Rocker Arm Question
Posted by: flat_six ()
Date: October 18, 2020 03:53PM

Apologies in advance for the old post, but the question never really got answered.

6255648 is the correct PN for Corvair with the correct geometry. PN is for the arm only.

5723559 is listed for Corvair and includes a pivot ball and nut. I can not confirm if this PN has the correct geometry or is simply the small block Chevy rocker.

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Re: Corvair Rocker Arm Question
Posted by: RobertC ()
Date: October 18, 2020 04:32PM

Looked on gmpartswiki:

Found a 67 parts catalog where:

6255648 is the rocker arm alone 60 - 67

5723559 is the rocker arm, ball and nut 60 - 67

Have to assume the rocker arms are the same / same ratio (correct term?).

There might have been slight cosmetic differences between runs, but I assume the ratio was always the same.

One catalog mentions a diamond shaped ID mark on the rocker arm - which I very vaguely remember from decades ago.

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Re: Corvair Rocker Arm Question
Posted by: Seth Emerson ()
Date: October 18, 2020 04:32PM

If there is a hole in the side of the well, above the pivot ball seat, it is not a CHevy V8 rocker and is, most definitely, a Corvair rocker. A small block Chevy rocker will not have that hole. Was that the question? Unless you are building a race car, that difference in lift won't matter much, if at all. The V8 rocker had a slightly different geometry than either Corvair rocker.

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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Re: Corvair Rocker Arm Question
Posted by: RobertC ()
Date: October 18, 2020 05:27PM

In looking up Corvair rocker arms, I stumbled across this thread from 2015 - with commentary rom Bob Helt:

[corvaircenter.com]

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Re: Corvair Rocker Arm Question
Posted by: wittsend ()
Date: October 18, 2020 07:18PM

That link ends with a discussion about using the Chevy 348/409 CID rockers that are listed as a 1.76 ratio. Maybe a lot for most cams but when I run the numbers on the very low lift 332/609 cam (80HP) the numbers on lift become:

Intake .314 to .368, a .054 lift increase

Exhaust .344 to .403, a .059 lift increase

These lift numbers come close to other higher HP early cams (.380-.403) and as such would seem not to tax the valve springs or generate excessive pressure. It seems a way of getting more cam without having to open the case. The availability of those 1.76 rockers and the cost may negate the concept but at least for the low lift 332/609 cam something to consider.

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