Safety Alert: Chinese Rocker Arm Failures

DATE and REVISION: 10 August, 2014. Original Safety Alert.

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– 18 Aug.2014 – amended with ‘further reading’ with link to Roller rocker story.

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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.

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APPLICABILITY: Recommendation for all Corvair flight engines that have these installed.

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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.

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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.

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( 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.)

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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.  This happened on a ground run up, not in the air.  Obviously as a ground issue, there was no damage to the airframe. It was of concern to the owner, but not the kind of stress as in the 9 August failure.  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.

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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.

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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.

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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 350 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.

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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.

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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.

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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.

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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.

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FURTHER READING:

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Pros and Cons of Roller Rockers

Chinese Crankshafts for Corvairs, update 2/17/13.

Cessna’s Chinese adventure a failure.

Communist Chinese government at Oshkosh

Mooney sold to Chinese, Fake endorsements.