Took a 25 minute flight from KJNX to KTTA to show a good friend that I had a well running airplane.   Everything was running perfect, and I was really feeling good about it all. Then two miles out, she started back firing. A few seconds later, it was a rhythmic pop in the exhaust, about once per second. I radioed that I was having engine problems and would be landing against the traffic.   Pointed the nose at 21 in a descending turn, and she quit as I was lining up. A short glide to a normal engine out landing, and I was able to coast most of the way to a parking space.
Got a taxi back to KJNX so that I could drive back with tools.  The plugs all looked good, if not indicative of running extra rich.  But when I pulled the valve cover, number two's exhaust rocker arm was cocked sideways, and the push rod was bent about 30 degrees where it exits the guide.  How does this even happen after 20 flight hours? Can I expect this to ever happen again?  Is there a way to prevent the rocker arms from rocking side to side?

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It would be nice to think it was simply a defective pushrod, however I wouldn't come to that conclusion too quickly.  3100cc "Bigboy" corvairs requred a lot of skill and hand fitting of parts to build properly.  Not all 3100cc conversions were built to high degree of quality and fit. For example, 3100's require custom length pushrods to ensure proper valve train geometry. This is due to the different deck height from the 94mm VW cylinders.  Replacing the pushrod is not as simple as ordering a stock pushrod from Clark's. Being that you didn't build the engine I suggest you confirm the entire valve train geometry and ensure that the rocker arms are adjusted properly.  Its difficult to tell from your picture but it seems like your head gasket area on the head might of been cut a tad too deep as evidenced by the tops of the pushrod tubes protruding above the head casting.  Again, its hard to tell by looking at your picture.  Of course, this also affects deck height.

Additionally, you should be running exhaust valve rotators along with Decalin runup in your fuel assuming you're running 100LL (hopefully you are running 100LL because most 3100cc conversions have higher compression ratios.) The rotators and Decalin Runup greatly extend valve life and decreases deposits.  

Lastly, I agree with Dave's sentiment that you should consult with someone who knows what they're doing and has experience with 3100cc conversions.  You just had an inflight engine failure with a precautionary landing.  You got lucky this time. Stack the odds in your favor and seek solid advice. You obviously have some issue with William Wynne and his 30+ years of Corvair experience so I suggest you call and speak with Dan Weseman at SPA 904.626.7777.  

Good luck,

Ken

Hi Ernest,  I would agree that you don’t seem to have the approximate 1/3 sphere rotators on your rocker studs and it seems that the lifter tubes may be installed backwards since the lifter tubes are not the same on both ends.  The longer tanged end should be mounted in the hydraulic valve assembly (into the engine block) so you might want to check that too.  There are very limited ways to break a valve lifter rod.  1.  The exhaust valve got stuck in the closed position because the valve guide was not lubricated or the wrong size guide installed.  2.  That cylinder detonated in flight due to an excessive advance on your timing at the same time the cam was lifting the exhaust valve open. 3.  That exhaust valve rocker arm was over tightened from the get go and the rod was already bent before you took that last flight, but during the flight it finally failed via the usual stress crack.  Of these 3 the most likely is item 3.  You can check to see if the exhaust valve is stuck in the closed position by getting a piece of hard wood and tapping the valve stem with the wood via a rubber hammer.  If it moves down while doing that then it was stuck in the valve guide.  Always check your wide open throttle timing to be sure it does not exceed 28-32 degrees BTDC.  I stick to 28 on my 3100cc conversion.  To be sure this does not happen on any other cylinder you should find TDC on each cylinder (both valves closed) and while cold there should be .001” lash between the valve stem and the rocker arm after you push the oil out of the lifter by depressing the valve rod rocker arm end.  If not they are likely to be tightened down too much.  You can chat with WW or SPA and then send your engine to them for evaluation and fixing these issues especially if you did not build the engine yourself.  You can also talk to Bill Clapp at Azalea Aviation who sells these engines too.  He too is quite knowledgeable in Corvair conversions he sells and including both WW and SPA offerings.  Because your butt is sitting behind that engine it is best to leave these issues to the experts to ensure your future safety.  John

I used a bar with a hole in it to test the valve.  Slit it over the rocker stud, and used it to compress the valve.  The travel was perfectly smooth and unimpeded.  I don't think it is a stuck valve.

I'm starting to come to the conclusion that this was just a bad rod from day one.

I'll definitely check the lifter tubes, and I'm just now hearing about exhaust rotators.  They seem like a good idea, but considering I've never heard them called out by anyone until now, I don't think lack of them could be considered a builder "asking" for anything.  Clark's doesn't sell them, so I'm searching at this point.

Bill Clapp has them for sure.  His number is 1-229-834-8996 and you need those rotators on ALL valves not just the exhaust valves!  Tell Bill I sent you to him and tell him exactly what happened.  He is located in Adel, Ga so if you live near there you can take your engine over to him for a professional look.  This is where I built my 3100cc engine.  By the way unless you know exactly what you are looking for the Clark catalog is a nightmare to navigate!  John

Ha!  I disagree.  If it were best to leave these issues to the experts, I wouldn't have built an airplane.  :-)

The longer tanged end should be mounted in the hydraulic valve assembly (into the engine block) so you might want to check that too.

I had to research the information about the pushrod tubes after I found that I had the long tang on the head side in o n every one.  Referencing Figure 33, on page 6-22 of the 1965 Corvair Shop manual, the long tang belongs on the head side.  This is further confirmed by Figure 19, on page 6-12.  The tube is just above "View B", and shows the long tang in the head.

Yep Clark has them, see page 18 of the online catalog.  Search was done from online catalog, choose “R” for rocker arm assemblies and choose pg 18.  John

I see them on page 17.  Part number is CU1299.  Both it and CX3885 are out of stock.

I did find a set that claims to support Corvairs on eBay.  But, I know nothing about them or their reliability.

https://www.ebay.com/itm/Sealed-Power-Exhaust-6PCS-Engine-Valve-Rot...

Ermest: See:  http://www.corvair.com/user-cgi/catalog.cgi?show_page=18 buy the grooved ball set of 12 with matching rockers if you can, otherwise, just buy the grooved ball set:  (Part C2303 set of 12), along with C1157A locking nuts set of 12 (a must have) and C236X lifter rod which is exactly 10.26" long (std.)  (page 19 has non standard lifter rod lengths but it is unlikely you will need them)  Check the length of your lifter rod by pulling out the intake valve rod (same size as exhaust lifter rod).  When you put it back in be sure its centered in the hydraulic lifter resting on the camshaft, you will know this when the rod is shortest coming out of the lifter tube.  Be sure that the oil hole is up in the rocker arm.

John

Thanks, John.  But, it wasn't the rocker arms that I was having trouble finding.  I've ordered the roller rockers as replacement.  I was having trouble with the valve rotators.  It doesn't look like ANYONE carries them as a standard part.

Ernest, by the way if you go to this website you can download the assembly manual for free.  see:  

http://azaleaaviation.com/Spyder%20Engine%20Assembly.pdf or you can go to this page http://azaleaaviation.com

and click the red Spyder sign to get several critical documents all free.  John

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