Aerovee Turbo Woes...again x 3

[jjbardell]

I flew the prior Sunday with the best performance to date. I had been studying the effects of the factory air filter. I tested flying with the factory air filter, no filter and a high flow K&N filter. The test involved tuning the engine mixture and then doing 2 passes up the runway at 1,000 ft agl @ 34" followed by a max climb rate to 4,000 ft. I tracked IAS, CHT, EGT, VS on climb.

Results: The factory filter is a choke on the engine, it's the bottleneck into the turbo. It resulted in 200+ rpm loss, higher temps and much lower speeds. The K&N tuned slightly rich achieved 168mph IAS (yes, IAS) on the level upwind, 1,500 ft/min climb with a max CHT of 395 degrees. At 4k cruise and 31.5" I was able to cruise at 6.1gph and achieve 156mph TAS average over 45 min of flight. And that cruise flight was with a 706lb nose dragger, 13g fuel and my wife with me...

I cannot climb over 950fpm on the stock filter without CHT spiking.

So, after 120 hours, I am once again working on my engine. This will be the third time. During my annual the next day, I found the following compression readings:

1- 10/80
2- 30/80
3- 20/80
4- 78/80

It is very apparent the leak is not in the rings this time (that was tear down #2), but the exhaust valves. We put in a borescope and the valves look clean and there are no burn marks, apparent carbon, etc. We tried a few mechanic tricks to achieve better seals, but were unsuccessful. Below is the pic of exhaust valve on cyl #1. Nice and clean.

Frustrated and reaching out to a few other Aerovee owners, I was not surprised to hear several people have gone though 2-3 pairs of heads over 200-300 hours due to the same issue. That got me thinking, something just isn't right. I tried to reach out to Sonex, but tech is shut down for the week and didn't care to send another email. Plus, I'm sure it's my fault again... :roll:

I called a few of the top bug tuners in the country and received their insights. I wanted to share with the larger group to get your thoughts on what they say is clearly the problem:

1) We are running too hot of a plug (AL-4163) and recommends a cooler plug (Denso 24)
2) The valves need to be 3-angle ground to get a better seal and need to be hardened stainless steel
3) We should be using dual springs, not the stock spring. At minimum, a heavier racing spring
4) They recommend a valve size of 42/37 or 40/35 for a high torque / low rpm application
5) They all said our 92mm bore is wrong for our application

The last bullet was the most shocking for me. A 92mm bore is the hottest running bore out there (according to 2 bug tuners). He strongly recommended moving to a matched / forged 90.5mm bore as it doesn't require new heads or block. It increases wall thickness, helps with torque, and significantly improved cooling, which should result is much longer head life. The 375-400 degree + temps on climbs are putting too much stress on the heads between 1 and 3.

Although we lose some cc's, we shouldn't notice much difference in speed because we are running such low RPMs. He said we need the engine built for torque, not increased HP. And with a turbo, we can just increase throttle to make up for the cc loss. He said a big prop and such low RPM is putting too much torque on the engine for a 92 bore. A 90.5 bore paired with 42x37 or better yet a 40x35 valve setup will give us more torque to move the prop efficiently.

He makes ported, matched heads for about $800 with 3 angle valves, dual springs, with dual plugs.
He also has split heads (so we can pretend we are a real airplane engine) which are also dual plugs and awesome looking on the roller rocker, but the cooling fins are smaller and may cause heat issues with the turbo engine. He believes the ported heads will be better for us. But, they would solve the valve issue flexing as the stress across cylinders becomes non-existent. (I'm tempted to try a set, but they are $1,400...ouch, and risky if they overheat on climb).

Questions:
1) What are the valve sizes?
2) Are the valves sodium filled or solid stainless?

With that info, I'd love some opinions...GO!

[robbwerks]

Great info, thanks.

[NWade]

Question: Are you actually down on power, or is the compression test the only indicator that something is wrong?

I ask because compression tests have been shown to be unreliable in many engines (not AeroVee specifically; but other aircraft and automotive engines). Doing the check on a warm vs cold engine will give lots of different readings, as will the random alignment of the piston ring gaps.

Here are a couple of Mike Busch's articles on the subject (he's penned several, and gone into this issue in some EAA Webinars):
http://www.avweb.com/news/savvyaviator/savvy_aviator_56_before_you_yank_that_jug-197497-1.html
https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2013-07_compression-in-context.pdf
(and here's an EAA Webinar where he talks about compression tests)

...Can you get the borsecope pointed at the valves and visually check for hot spots or a burned valve? You might do that before finalizing your diagnosis and yanking the engine apart.

Good luck,

--Noel

[gammaxy]

The Aerovee uses 35.5 and 40mm valves.

http://www.sonexaircraft.com/eshop/cart ... 7&pageID=5

I would expect you should be able to examine the spark plugs to tell if they are really too hot. The electrode should appear worn and the ceramic might be damaged or bubbling. Too cold tends to become carbon fouled. Not sure how plug temperature affects the valves unless they are causing detonation.

I lapped my valves early on and haven't noticed compression problems since. If I were building another engine, I'd probably lap the valves from the start. Wish I knew the cause. I wonder if the lead in the fuel fouls the seats.

[WaiexN143NM]

Hi all,
Just a couple comments, we have a jab3300 so not going to claim any knowledge about vw's aerovees etc, but may apply to them. A few posts years ago about the stock aerovee filter for the jab 3300 was too small and choking the engine. Either double up the filters with longer bolts, or, buy something bigger k&n etc. this filter may be ok for a stock aerovee but not the turbo version. Fuel , we use tcp , which is a lead dispersant , when we fuel up. Can be bought from aircraft spruce. Hopefully keeps lead buildup from plugs valves etc.
Josh let us know where your research takes you. Good luck. Its interesting reading. Im sure all the aerovee guys/gals will be interested.

WaiexN143NM
Michael

[jjbardell]

Question: Are you actually down on power, or is the compression test the only indicator that something is wrong?

...Can you get the borsecope pointed at the valves and visually check for hot spots or a burned valve? You might do that before finalizing your diagnosis and yanking the engine apart.

Good luck,

--Noel

Thanks for the input all. Noel - Compression is the only indication I am down on power. I make 40" at about 70% throttle. I talked to an AI who is on the field and he looked at my plane with me. He says he sees Lycomings come in with 5 of the 6 cyl in the 20's and the pilot never felt a power loss.

We did get the borescope (digital HD) and recorded all sides. No hot spots, plugs are colored well, no noticeable carbon built up. We did talk about doing a warm test this weekend, just not too hot so I don't risk stripping a plug. I will try that Sunday and post my results before I yank the heads.

But I think it is safe for anyone building or rebuilding to lap the valves and get the 3-angle cut done prior to finishing the engine.

[Brett]

I thought the single faced valves were used due to the ability to transfer more heat to the heads and keep the valve cooler?

Down side is they dont have as much contact pressure as the 3 angle valve style.

I just did a leakage teat on my aerovee turbo the other day at the 42 hour mark and 1 x year.

74/80
73/80
76/80
76/80

Ive done heaps of mods to the cooling and fuel system though. I was hoping for 78/80 all round but I'm happy enough.

From my experience every time the exhaust valves don't seal it's not usually the valve but the seats that need cutting. I have found that the valve sits on two high spot on the seat and bypasses. I'm sure in my case it's from excessive heat in the heads. I have been through this about 5 x times in my other plane with an Aerovee. The Aerovee just isn't suited to the airframe and will be removed soon for a rotax 912.
My Aerovee Turbo Sonex though I made a real rookie mistake with the Aerocarb after tuning and put the needle in upside down and roasted the engine. Had to do the heads on this plane due to both back cylinders having valve sealing issues and melting a piston. Since that little distraction though I have fitted a Rotec Tbi and made heaps of mods for the cooling and been super anal with temps. I have never seen a CHT over 385 ever, even in climb, and it gets bloody hot here over summer. Hense I have gone to major lengths to get it going well and was hoping for A+ cylinder leakage figures. Maybe I was expecting too much and maybe I didn't warm it up enough before doing the test. I basically ran it for about 5 mins at 1200-1400 rpm then did the leakdown test.

Will see how it goes next time I do the leak downs or next annual.

I have always wondered how a real hard material type valve and seat combo would go with the 3 angled valves but I have been unwilling to gamble with those sorts of dollars involved when other ppl have been having success. I bet ya though that new UL power engine that seems to be getting attention has that exact system in the valve and head machining. I could be wrong but I have never seen a modern engine these days without It done that way.

Good luck and keep on going.

-Brett

[intoaircooled]

Could you send me the contact information for the 90.5 advise. I have a newer GP engine that I would like to build with high torque advise.

Thanks.

[rizzz]

My VW guy told me the same thing about the 92's, they are made with thinner walls so they fit in the same 90.5mm hole to avoid machining the case.
There are "thick wall" 92's available but they require machining the case. You might as well go 94mm then. and take your engine up to 2276cc.

[jjbardell]

Could you send me the contact information for the 90.5 advise. I have a newer GP engine that I would like to build with high torque advise.

Thanks.

You want to talk to Tommy at SCAT. His number is 310-370-5501 x141.

I'll be ordering new heads from him tomorrow.