breaking rocker arms

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Bill MC
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breaking rocker arms

Post by Bill MC »

I am on my 2nd rocker arm failure in a couple of months.
Motor is 110hp with Isky 260 cam.
I considered this cam to be pretty mild to change rocker arm geometry.
Is that true? Is the cam why I am breaking rocker arms?
I had original rocker arms and switching to a complete set of Clark's Corvair aftermarket rockers.
notched
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Re: breaking rocker arms

Post by notched »

Do you have original GM rockers or have you switched to the Clark's aftermarket rockers already?
1966 Corsa turbo
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Bill MC
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Re: breaking rocker arms

Post by Bill MC »

the failed ones were both original...i have two of the clarks aftermarket on the motor since rebuild. I have them all off the motor now. I'll take them to work tomorrow and do a wet fluorescent magnafux inspection to see if any more are cracked. I am replacing them all, just curious.
66vairguy
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Re: breaking rocker arms

Post by 66vairguy »

260 is mild, but still a little more lift than stock. Should not be an issue.

Are you running the original valve springs? If not, then was was installed?

Were the heads machined?
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bbodie52
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Re: breaking rocker arms

Post by bbodie52 »

:think: You did not actually describe the nature of the rocker arm failure in each case. Did both rocker arms fail at the same location, and in the same way? Did they look anything like this?

Image

I've seen push rods inserted backward that resulted in a broken rocker arm. There is a small hole in the side of each push rod (one end only) that is there to spray oil on the rocker arm to lubricate it. If the push rod is inserted upside down, the side hole will be near the hydraulic lifter instead of the rocker, and the rocker arm may not be getting adequate lubrication!

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In this picture of the rocker arm, you can see the hole in the rocker, next to the pushrod cup, that permits oil from the side of the pushrod to squirt through the rocker to lubricate the pivot ball inside...

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:link: http://www.corvair.com/user-cgi/catalog ... IN&page=18
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There might be other causes of the valve train damage to multiple rocker arms, but the above described random improper assembly is a likely cause that you should consider.
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terribleted
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Re: breaking rocker arms

Post by terribleted »

Push rod geometry may have influence. You should check it. The rockers arms should ride on the top of the valve stem in an area from around 1/3 of the way down from the top of the stem down thru the middle and to about 1/3 of the way up from the bottom of the stem as the rocker moves thru its cycle. So when the rocker is not active it should rest on the valve stem a bit below center and should be a bit above center when fully open. You can look closely from the side and pretty much see if the geometry is far off (rocker riding from middle to top or middle to bottom of valve stem for example). Cam lift, machining of the head gasket seats and amount of head gasket/cylinder base gasket stack all influence geometry. Excessive valve spring pressure could also cause breakage issues perhaps. (of course old overheated worn rockers can break just because)
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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Bill MC
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Re: breaking rocker arms

Post by Bill MC »

yes, the picture is typical of my failures.
No deck machining on the heads...(not to say someone in the past has machined them) but they looked original
These are the original springs (as far as i can tell) I did not replace them
I bought the stock head / base gasket when I re-assembled

You got me thinking about the valve springs....I bought new valve springs and lifters
from NAPA Auto- listed as a a stock replacement
the springs are from Applied Power
2.109" free height and 284 lbs / in.
The spring seems just a bit long....but the 284 lbs pressure seems high now.
66vairguy
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Re: breaking rocker arms

Post by 66vairguy »

Spring tension comparisons are tricky as you have to see the spec. for a given height.

The NAPA spring is a sealed power unit. See specs at https://autoplicity.com/851673-sealed-p ... lve-spring

The specs. don't match up with the Corvair for height and LBS. but the compressed numbers look close and the "solid" height seems safe for the Corvair with a 260 cam, but I don't have my math handy.

With a high lift cam like a 270 or 280 special valve springs with higher tension (and thinner so they compress more) are the norm.

If the broken rockers, or ball seats, don't indicate a lack of lubrication, it could just be the newer springs (that will have greater tension vs. old) are taking a toll on the old rockers.
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caraholic4life
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Re: breaking rocker arms

Post by caraholic4life »

I was only about eight or nine at the time but seem to recall our Monza Wagon having a rocker arm replaced while on a trip.
We were traveling from Maryland to Nebraska for Thanksgiving when this occurred, which is why I remember it.
We stopped in a small town and were fortunate to get the dealer to replace the rocker arm on a Holiday weekend.
Years later I had a conversation with my Dad where this was discussed. He told me that he had a rocker arm replaced under warranty.
Dad mentioned that after having one break twice, he started carrying a spare rocker arm with ball and push rod tube in the glove box. Apparently it didn't happen a third time. :my02:
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Bill MC
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Re: breaking rocker arms

Post by Bill MC »

I checked my warranty...I am $%^$# lol.

I am not seeing any "blue'ing" from heat at the fracture initiation point, or on the ball, and when removing the valve cover I need a drain pan handy since there is a lot of oil falling out, so I don't think lack of lube is the bad actor here.
MY old book says the spring should have 170-180 lbs @ 1.260". The sealed power says, they have 284 lbs. That seems like a big difference?
I REALLY don't want to pull the heads to replace the springs, but I have a dependability concern now driving it.
I would think though that if spring tension really is the root cause, we would be seeing a lot broken rocker arms. I mean, there must be a bunch of people driving around with these same springs. Does Clarks springs post a spring compression value?
66vairguy
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Re: breaking rocker arms

Post by 66vairguy »

284 is the spring RATE, not the tension at a specified height. In a linear spring that means it takes 284LBS to compress the spring 1".

The sealed power spring is a 82.6LBS at 1.696" for example and increases to 193LBS at 1.306". Applying that to the sealed power values suggest the spring is close to linear after the initial compression . So -- 1.306 - 1.260 = 0.046 x 284LBS =13LBS + 193LBS = 206LBS at the Corvair spec. of 1.260"

I suspect this is a SBC V8 spring that a lot of folks use in Corvairs. So yes a higher tension spring versus the stock Corvair spring, but folks do use them in Corvairs.

My machinist has a valve spring rating machine and showed me the difference between a NEW and correct Corvair spring and the SBC. Due to all the camshaft hysteria with the new oils, and the fact I built an engine for cruising, not racing, I went with the lower tension valve springs that match the Corvair spec.

Bottom line - if the Clark's rockers work fine then it just may be old rockers breaking from age with the new springs. Time will tell.
Bill MC
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Re: breaking rocker arms

Post by Bill MC »

The new set should arrive soon and will see what happens!
Thank you for the in depth replies and the education in spring rate vs. tension.
So you mentioned you "went with the lower tension valve springs". What springs did you use?
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terribleted
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Re: breaking rocker arms

Post by terribleted »

FYI you can change valve springs without removing the heads. There is a valve spring compressor made to work from the rocker arm side and compressed air can be used to hold the valve closed if needed (most times you can remove and re-install a spring without needing to manipulate the valve at all).
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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66vairguy
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Re: breaking rocker arms

Post by 66vairguy »

Bill MC wrote: Sat Jun 17, 2017 6:43 am The new set should arrive soon and will see what happens!
Thank you for the in depth replies and the education in spring rate vs. tension.
So you mentioned you "went with the lower tension valve springs". What springs did you use?
My machinist used Elgin valve springs, but that was several years ago and he had a HUGE box of them he bought when they were available. Now Elgin does not list a Corvair valve spring, but they cross reference to a RV-685X that is listed for all the GM sixes and small block V8's (one size fits all). Sadly this is what happens with obsolete engines as the demand isn't there so the OEM suppliers make a "one size fits all" product. Same with lifters, but to be fair several types were used in the Corvair when new with no explanation as to why, but I suspect no one supplier could meet demand (or price) so there were variations even when new.

As I said before, the SBC V8 springs are used in the Corvair to increase the RPM before valve bounce/float (the Corvair books state that with a 140HP cam valve bounce/float would happen between 4,500 and 5,000RPM - the Isky 260 is very close to the 140HP cam, but a little more lift). So those who want to rev to the redline use the higher tension springs. With a more aggressive cam like a 270 or 280 you need the higher tension competition springs sold by cam makers.

I'd just try the new rockers and see what happens. Oh - You probably know this, but do make sure the pushrod side oiling hole is at the end that fits into the rocker. I've seen experienced Corvair folks forget to check it. Easy thing to miss.
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bbodie52
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Re: breaking rocker arms

Post by bbodie52 »

66vairguy wrote:...Oh - You probably know this, but do make sure the pushrod side oiling hole is at the end that fits into the rocker. I've seen experienced Corvair folks forget to check it. Easy thing to miss.
:goodpost: :dontknow:

I covered this extensively in an earlier post in this thread on June 14.

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Bill MC wrote:Fri Jun 16, 2017 9:14 pm

...I am not seeing any "blue'ing" from heat at the fracture initiation point, or on the ball, and when removing the valve cover I need a drain pan handy since there is a lot of oil falling out, so I don't think lack of lube is the bad actor here...
The only answer I saw was talking about the large volume of oil in the valve cover area. But you can have five push rods installed correctly and one reversed and still set the stage for a lot of oil in the valve cover area and one rocker arm still failing due to lack of lubrication around the pivot ball. Exhaust valve rocker arms might be even more prone to breakage if a lack of lubricating oil is coupled with a hotter rocker arm (due to physical contact with the hotter exhaust valve stem). I'm not sure the frictional heat generated due to a lack of lubricating oil would be sufficient to cause blue discoloration of the rocker or ball.

When reassembling the valve train the repetitive nature of the task makes it easy to make a mistake, like accidentally inserting a push rod with the side oil hole down — next to the hydraulic lifter — instead of up — next to the rocker arm. That simple, overlooked error could surface much later in the form of a seemingly random, failed rocker arm. :doh: I always give the valve train a second look when I think I'm done, just to verify that I didn't make such an error.

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Rocker Arm Failure
:link: http://corvaircenter.com/phorum/read.ph ... 235,599245

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Safety Alert: Chinese Rocker Arm Failures
DATE and REVISION: 10 August, 2014. Original Safety Alert.
:link: https://flycorvair.net/2014/08/10/safet ... -failures/

Corvair Valve Train Geometry
:link: http://n56ml.com/corvair/valve_geometry.html
My first clue that my rocker geometry wasn't right was when I ran out of adjustment on the first valve that I tried to adjust after adding .020" of cylinder shim to decrease my compression ratio to 8.4:1. It's something I've always been a stickler for when setting up high performance solid-lifter VW engines, but as soon as I started thinking about the hydraulic lifters on the Vair, I wondered how in the world to set it up correctly, since the lifter would simply compress. Ray Sedman gave me a pretty good description over the web, and Tom Cummins clued me in to what was included in Clarks' "Valve Train Geometry Kit"...

...The bottom line is that if you throw your engine together with non-stock valves, different cam, different rockers, and different thickness cylinder shims and head gaskets, your pushrods are probably not going to be the right length. Mine, with stock-length pushrods, were barely on the edge of the valve stem face. Side loads would have been high, valve guide wear would also have been high, and some small fraction of power would have been lost to friction. Even if you're just changing cam and valves, and buying new rockers and balls, your geometry is going to change. The procedure above works just the same with the stock rockers. The least you can do is take a look at it while you're assembling your engine. And even if your engine is assembled and running, you can check it...


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:link: http://www.corvair.com/user-cgi/catalog ... IN&page=20
Push Rod Geometry Kit.jpg
Part number C8640: PUSH ROD GEOMETRY KIT

Weight: 2 lbs 0 oz
Catalog Pages(s): 20,OT,8,T,3
Price: $ 56.50
Brad Bodie
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Rdhog99
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Re: breaking rocker arms

Post by Rdhog99 »

A long time ago I had a similar rocker failure at the ball pivot area. During my recent rebuild I thought new rocker arms would be wise until I saw the information from the Covair aircraft conversion group about the Chinese rockers failing prematurely. These aircraft engines do not run much over 3K RPM and do not use high spring pressures or radical cams. New rockers I had purchased for the rebuild were then compared to original GM rockers. The ball pivot area was found to be much thinner on the new Chinese rockers. I decided not to use the Chinese aftermarket rockers.

Another thing to watch for no matter what valve spring is used is the spring pressure at the installed height. Stock springs should run around 80-85 lbs at the installed height dimension. Aftermarket springs may need a different installed height to get the seat pressure in the ballpark. A little more seat pressure can really add to the ability to rev higher but be careful to not go way up in pressure. It depends on the cam and what you want for maximum rpm. Excessive spring pressure can over stress even good GM stamped rocker arms.

Measuring the spring pressure can be done with a few common tools even with the engine assembled. Using a chevy on the engine valve spring compressor tool the springs can be removed while compressed air is keeping the valves closed. If you don't have a spring pressure gauge I have used a known accurate bathroom scale on a press and recording lbs of force at the installed height dimension. If you need more or less seat pressure, adjust shims or use different retainers for a different installed height.
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