Leaky exhaust valves

[Klimek]

Gentlemen,
At 37 hours I replaced the exhaust valves on my AeroVee. Being an old VW tech, I have rebuilt too many VW engines due to a burned or broken #3 exhaust valve.
I had an excessive amount of leakage from two cylinders. Now at 80+ hours and at least 6 valve adjustments, it seems something needs to be done again. The exhaust valves were always tight. I set the exhaust at .008 and intake at .006. The exhaust valve clearance closed 3-4 thousandths after 10-12 hours of operation. I kept the temps below 400f on climb out and they run 310-325 in cruise. The face of the first set of exhaust valves were dished and seats seemed way too wide and evidenced leakage. I run 100ll and am considering using MOGAS from now on, as I set the compression ratio at 7.5:1 so I could run either fuel.
I have called about the "Panchito" heads but CIP no longer gives out info on the machine shop that can drill and tap for a second set of plugs, for liability reasons.
IF I could find someone who can and will do the machine work, I would consider installing a set of these heads. According to CIP they run cooler and have air flow on both sides
of the exhaust port. Looking at there website (California Import Parts) they are available in the same valve size and bored for the cylinders as used in the 2180 cc
AeroVee. Check them out, on the surface they look great.
If anyone has any ideas or suggestions or any reason I should not try them please chime in.
Other than being skittish about the valves, I love my AeroVee and AeroInjector.

Frank
ONEX 090
N1970T
At home polishing, painting, new windscreen, adding Aero Conversion hyd. disc brakes.

[Area 51%]

Not 100% sure, but I think Great Plains offers that service.

[airscribe]

Gotta chime in on the recommendation against flying if you believe the engine has issues; a ground-run, taxiing around, should warm the engine sufficiently to recheck for valve leaks and compression levels... Don''t fly. There's nothing to be gained in terms of warming the engine...

And feel compelled to comment on the prospect of the engine swallowing a valve....it's not an automatic disaster...it is a challenge.

While there's never, ever, a good place to suffer an in-flight engine problem, most pilots who suffer such a failure do survive....in fact, total engine failure for a swallowed valve isn't an automatic outcome....many times the engine continues to run, albeit -- and obviously -- at far below normal power.

Three good friends of mine suffered such a failure...one in a Lyc-powered Cherokee, one in a Continental-powered Champ, one in a big-bore Continental powered Debonair....the latter two were at cruise altitude when their failures occured -- luckily for them -- and both found an airport close enough to nurse the plane to a safe, no-damage landing. The third fellow was doing pattern work; the engine made barely enough power for him to declare an emergency and cut from downwind directly to final...he ground-looped and damaged on gear and the wingtip on the same side as the gear.

In all three cases, cool heads and prior practice/training kept their incidents from unfolding into something worse.

And personally, suffered a seized exhaust valve in an O-200 in a Cessna 150 -- a considerable distance from an airport....the engine continued to let me stay level; my decision: slip over to above a four-lane road that lead back to my departure airport, a decision requiring me to fly a longer return leg while keeping a landing option right below me until the last mile...going direct would have put me over urban and industrial landscapes with few-to-no open-space options....

It was a tense 12, 13 minutes, worrying that the engine might fail completely...the observer pilot flying with me told me later he would've gone direct -- but when making the airport -- I stayed at 2,500 agl all the way back -- was a given he saw the point of the longer route...my fault for not verbally sharing my logic, but my attention was on flying the airplane and communicating our situation to the approach controller handling me...

All's well that ends well...and to end well, we gotta fly the airplane.

Dave

[NWade]

Gotta chime in on the recommendation against flying if you believe the engine has issues; a ground-run, taxiing around, should warm the engine sufficiently to recheck for valve leaks and compression levels... Don''t fly. There's nothing to be gained in terms of warming the engine...

While I know everyone on this forum is well-meaning, I really do wish people would post their qualifications or experience when they make a recommendation for or against a procedure.

Lots of well-meaning people repeat old-wives-tales or information that they believe to be correct; but is actually incorrect, or at least misunderstood. As Kerry said in an episode of the Sonex Flight podcast: Newer builders & pilots tend to believe that anyone handing out advice automatically knows more than they do. This can lead people down the proverbial garden path, regardless of your intentions...

When it comes to warming the engine: Heat causes metal to expand, and therefore it can change the way the engine behaves and the result of tests (like compression and leak-down tests). So yes, it makes a difference in the strictest sense of the word. The question is: should you use the "cold" or "hot" readings as the "true" answer? And what does a difference between a cold & hot reading mean? Something may be gained; or it may not indicate a safe condition for flight at all. Without knowing more, none of us can say for sure. A blanket admonishment (or endorsement) is not helpful or wise.

Personally I defer to Mike Busch, an award-winning A&P who has lots of experience with air-cooled engines. Here's one of his articles on compression, leakage, hot vs. cold tests, and a couple of other items.

Blanket statements on the internet without a careful explanation of why should always be considered suspect. Even if a line of reasoning is explained, the qualifications of the person doing the explanation should also be factored into how much value you place on the information.

Let's use facts, not fear, to guide our decision-making and our safety.

--Noel
P.S. For my own experience: I've helped build and operate race cars - from 2.0l 4-cylinder Fords, to Miatas, to a 750hp V8 GT-1/Trans-America Series car. And a lot of the same theory and basic information carries over to any Otto-cycle gasoline engine. However, I'll freely admit that I am at the beginning of my experience with AeroVees in particular and cannot offer specific advice about how they wear and change over time; or best practices with VW aircooled engines.

[N190YX]

Guys, if your airplane is not 100%, please don't fly it! The notion of flying an engine that is not 100% to see if the issue will correct itself is a recipe for a disaster! ... TCM Continental allows no leakage past an exhaust valve, if leakage is detected in a compression test, the engine is not airworthy, the cause must be corrected. I repeat, please do not fly if your entire airplane is not 100% operational. We have got to keep our safety record as good as we can!

TCM Continental no longer has the strict "no leakage" rule for valves--they replaced it almost 15 years ago with SB03-3. They have a calibrated orifice that seems to correspond to around 45/80 on most testers. They recommend you do a borescope inspection, fly, and retest if you fail it. I think they got smart and realized the previous rule was unrealistic.

https://www.aircraftspruce.com/catalog/ ... lletin.pdf

Note you can only fly a TCM engine (and this should be considered for any aircraft engine) with leakage past an exhaust valve is after a boroscope inspection shows a normal exhaust valve. Leakage past an exhaust valve is really bad, think about it, the hot gasses going through a closed valve that should be in total contact with the head for cooling between exhaust strokes of the engine.

[NWade]

Note you can only fly a TCM engine (and this should be considered for any aircraft engine) with leakage past an exhaust valve is after a boroscope inspection shows a normal exhaust valve.

Excuse me, can you please provide a citation for this? Saying you can "only" fly the engine implies that the procedure is mandatory.

If your source is the "Service Bulletin" that was referenced in the previous post, its worth noting that Service Bulletins are not mandatory (with a few narrow exceptions - including when they are incorporated into an AD and incorporated into a Users/Owners/Maintenance manual).

Thanks,

--Noel
P.S. I'm not trying to be a jerk; but the claim goes perfectly to my earlier point about well-meaning facts and careful explanations.

[rizzz]

For those who have had to replace the valves and service the heads on your VW conversion,
Did you need to replace/recut the pushrods as well after this or would the old ones still fit?

[Brett]

Old pushrods were fine. I've had different heads done 3 separate times. My local machine shop usually cuts the seats for me on the exhaust valves and my bill often is around $40-$100 depending on time taken to do all 4 valves and test for leaks. So far I haven't actually needed to change any valves yet. This would no doubt bump the cost up.

[rizzz]

I have called about the "Panchito" heads but CIP no longer gives out info on the machine shop that can drill and tap for a second set of plugs, for liability reasons.
IF I could find someone who can and will do the machine work, I would consider installing a set of these heads. According to CIP they run cooler and have air flow on both sides
of the exhaust port. Looking at there website (California Import Parts) they are available in the same valve size and bored for the cylinders as used in the 2180 cc
AeroVee. Check them out, on the surface they look great.
If anyone has any ideas or suggestions or any reason I should not try them please chime in.

Scott Casler at Hummel engines will do that, his website states $150 for a pair:
https://www.hummelengines.com/price-list

[Corby202]

Here's one of his articles on compression.
That is an interesting link that Noel posted. For us Jabiru owners (in Aus anyway) regular leak down tests are required. I also believe there are so many variables doing that test. I think the best practice is to have your own leak down tester with a known orifice size and keep that tester along with a compression tester for all tests.It is the best way to know the condition of YOUR engine as you can compare test to test correctly.