<VV> Failure of Chinese made "New" rocker arms

[BobHelt at aol.com]

     (http://flycorvair.net/author/williamwynne1989/)   
_Safety  Alert: Chinese Rocker Arm Failures_ 
(http://flycorvair.net/2014/08/10/safety-alert-chinese-rocker-arm-failures/) 
by _William  Wynne_ (http://flycorvair.net/author/williamwynne1989/)   
 
DATE and  REVISION: 10 August, 2014. Original Safety Alert.
. 
........
. 
SUBJECT:  Failure of Chinese made "New" rocker arms for Corvairs, marketed 
by several  firms in the US, most commonly sold by Clark's Corvairs as "new 
replacement  rocker arms," sold as set #C-8641.
. 
.........
. 
APPLICABILITY:  Recommendation for all Corvair flight engines that have 
these installed.
. 
............ 
. 
EXCLUSION:  This does NOT apply to any Corvair flight engine using original 
GM US made  rocker arms, just engines using the Chinese replacements. NOTE: 
We have  never built any production FlyCorvair.com engine using these  
rocker arms. If you own an engine actually built by myself, this Safety Alert  
does not apply to it. This Safety Alert is issued for the  benefit of 
builders who may have independently elected to purchase the  Chinese rockers for 
their personal engines.
. 
...........
. 
COMMENTARY: Yesterday  (9 August, 2014) in California, a Corvair powered 
aircraft experienced a severe  loss of power following a failure of an exhaust 
rocker arm. The power loss was  progressive over a few minutes. Excellent 
pilot judgment, to turn to  the nearest airport at the first sign of an 
issue, paid off. The airplane landed  on the runway back at the airport without 
damage.
. 
( When a four stroke  engine has an intake rocker arm fail, the engine only 
looses power from  that cylinder. Conversely, an exhaust rocker failure 
does not allow  burning air/fuel to exit the combustion chamber, and when the 
intake valve opens  it tends to "flash back" up the intake tract and rob 
power from the neighboring  cylinders.  Intake rocker failure on a Corvair would 
be less than a 20%  power loss, but an exhaust rocker failure could be up 
to a 50% power loss.)
.
32 days earlier we had  received a detailed report on the failure of a 
Chinese made Corvair rocker arm  in Arizona, in the intake position on a 3,000cc 
Corvair.  That aircraft  also flew back to the airport and landed without 
damage nor incident. Although  there had been a report of 1 other failure in 
the previous 5 years, that engine  had many extenuating conditions such as a 
previous piston/valve collision. The 6  July 2014 failure was the first one 
that was on a "pure" engine. The parts were  carefully inspected by a 
professional engineer, and the probable conclusion was  that they were 
incorrectly made. The rockers had been purchased from Clark's  Corvairs, and they were 
contacted for a failure history in cars. They stated  that they had seen a 
very low rate of returns in cars. (As a reminder, Clark's  does not sell 
these as "aircraft" parts, that is a builder choice.) I supplied a  set of GM 
rockers to the flyer in Arizona and his aircraft was returned to  flight with 
about 2 hours of work and less than $100 in parts.
. 
At Oshkosh I spoke with a  number of builders of flying Corvair powered 
planes to asses how widespread the  use of these Chinese rockers are. I had 
previously thought it was a small  number, as I used none of them in our 
production engines, I have never sold nor  promoted the Chinese part, and I have 
been long recognized as a tireless critic  of Chinese manufactured parts. My 
estimate is now that 20% of flying planes may  have these rockers, it was 
our intention to make a comment on them upon our  return to Florida.
.
We have not yet returned  to our shop, we are still on the road, but in 
light of yesterday's failure, we  are issuing this Safety Alert immediately. 
The fleet of Corvair powered planes  is less than 500 aircraft, and the number 
of engines built to our exact  recommendations is a still smaller number. A 
single failure gets my attention  and is worthy of comment, however, a 
second failure of the same part, even if it  is one we do not recommend, 
warrants a Safety Alert.
. 
......................
. 
SUGGESTED  ACTION: I highly recommend that all flying Corvair engines with  
the Chinese rockers remove them before further flight and replace them with 
 cleaned and inspected original GM rockers. The failed rockers had 80 and 
160  hours on them. These are roughly the equivalent of 2,000-4,000 miles of  
operation in a car. It is important to understand that this is not an 
"infant  mortality issue," and having 100, 200, or even 400 hours of operation on 
Chinese  rockers without issue does not justify their further use.
.
The rocker arm is a  deceptively simple looking part, but it's correct 
manufacture is a  complex process involving careful quality control and very 
high levels  of manufacturing expertise. By comparison, a small, but highly 
skilled shop  of precision machinists can make a billet crankshaft, but it is 
highly unlikely  that any small shop could make a Corvair rocker arm. The 
design is a deep  stamping done under very controlled conditions. The GM 
rockers were done in  several hits on a blank that was thicker in areas that would 
be stretched. The  Chinese units appear to be made from uniform thickness 
blanks, which leads to  very thin sections in the ball area. That is the 
location of both failures. GM  units are twice as thick in the ball area. There 
will always be some fool to say  that GM's design was not good but this is 
pure BS; it is the most prolific  rocker arm in history, also on almost every 
small block Chevy 1955-2003. We are  speaking of nearly 1 billion rocker 
arms. Since 1978 I have owned about 40 cars  and trucks. Other than 2 Buicks, 
every one of them has been a Chevy, a Chevy  truck, or a GMC. They all had 
these rockers, I have never broken one. I have  seen the inside of more than 
500 Corvair core engines, and I am pretty sure I  have never seen a broken 
GM rocker arm. If your local 'expert' tells you he has  seen dozens of broken 
rockers of this design, nod politely, but understand he is  dishonest and a 
liar.
. 
This is a "Safety Alert"  and I am issuing a "Suggested Action" because 
Corvairs are experimental engines,  and as such do not have Airworthiness 
Directives and Service Bulletins in the  same form as certified engines do. I 
cannot require any builder to take any  action, I can only appeal to his better 
judgment by making a serious  recommendation. Airworthiness Directives are 
only issued by the federal  government, and Service Bulletins are issued by 
certified part manufacturers,  thus the difference in the Safety Alert.
.
This said, I appeal to  builders to follow this recommendation. The most 
frequent form of push back on  suggestions of this kind is a builder who is 
myopically looking at his one plane  and making a conclusion based on his 
impression of his own plane. Conversely I  get to see all the data, understand 
the extenuating or aggravating conditions, I  had world class training in 
statistical decision making at Embry-Riddle, and I  always further consider 
what still works, not just looking at what  broke.  I am not a genius, but for 
the above reasons, my  recommendations on Corvair flight engines carry more 
weight than those  of one guy with a flying plane, even a well intentioned 
one. We don't have  to speak of opinions of internet personalities that have 
no direct  personal involvement nor experience with flying Corvairs.
. 
..............
. 
DISTRIBUTION:  I ask that this information be shared with others who 
personally involved in  building a Corvair flight engine. This should be done just 
by people who have  read and understood the information themselves, who 
also are Corvair  builders.  If someone named "Flyboy26" shares this with an 
airframe  builders group or a general pilot discussion board, and includes a 
comment like  "no one should fly car engines" or "Corvairs break", neatly 
deleting the Chinese  source of this issue, you can be assured that their 
motivation  for commenting has nothing to do with promoting safety or assisting 
others  in managing risk.
. 
............................................
.
FURTHER  READING:
.
_Chinese  Crankshafts for Corvairs, update 2/17/13._ 
(http://flycorvair.net/2013/02/22/chinese-crankshafts-for-corvairs-update-21713/) 
_Cessna’s  Chinese adventure a failure._ 
(http://flycorvair.net/2013/10/23/cessnas-chinese-adventure-a-failure/) 
_Communist  Chinese government at Oshkosh_ 
(http://flycorvair.net/2013/07/23/communist-chinese-government-at-oshkosh/) 
_Mooney  sold to Chinese, Fake endorsements._ 
(http://flycorvair.net/2014/04/22/mooney-sold-to-chinese-fake-endorsements/) 


_William Wynne_ (http://flycorvair.net/author/williamwynne1989/)   | August 
10, 2014 at 4:14 pm | Categories: _Engine_ 
(http://flycorvair.net/?cat=40472)  | URL: http://wp.me/p22sJL-2hj 
_Comment_ 
(http://flycorvair.net/2014/08/10/safety-alert-chinese-rocker-arm-failures/#respond)  _See  all comments_ 
(http://flycorvair.net/2014/08/10/safety-alert-chinese-rocker-arm-failures/#comments)