Valve Rotation

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gammaxy

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I now have ~250 hours on an Aerovee in my Sonex. I've found leaky exhaust valves three times during that time. I re-lapped the offending seats a couple times, but I'm starting to think the correct remedy is to use something like a Neway cutter to re-cut the valve seat and replace the valve.

I've read the Sonex forum for several years and recently read just about everything on the Sonerai forum. This seems to be a common maintenance item on all VW conversions. I didn't see anyone claiming to have hundreds of hours with no exhaust valve issues.

I'm pretty sure these heads are from CB Performance and are also used by many of the other VW conversion companies. My first thought is that perhaps the valves don't come lapped into the seats well. When I buy my next set of heads, I'll definitely check this.

I've also considered that the deposits left in the head from 100LL are abrasive to the valves faces and have begun using Decalin Runup to prevent the deposits from forming. I've found others who have done the same, but nothing conclusive. I'm doubtful it will fix this problem.

I'm also curious about valve rotation. The Aerovee instructions have us assemble the rockers slightly off-center on the valve stems to impart a small torque to help spin them around. I monitor the wear on my valve stems and am almost certain no valve in my engine has rotated a noticeable amount in those 250 hours. I'm starting to believe that a lot of what I believe to be premature valve wear would be solved if the valves were actually able to rotate. I've talked to other builders and read other aircooled VW forums and I get the impression that the lack of rotation is extremely common.

I'm aware that some engines use rotator caps to rotate the valves. I haven't found anyone who has tried them on aircooled VWs. I did find some people who claimed the original stock valve keepers (at the valve stem) didn't have a gap between them when installed fully so didn't grip the valve stem as tightly and allowed the valve to rotate, but others say that running with loose valve keepers pounds on the valve stem and creates its own problems.

Is anyone flying a VW with valves that rotate? Any thoughts on a rotator cap that would fit the VW?

I'm leaning towards buying a second set of heads and just swapping them out whenever I notice low compression, but part of me things something simple like valve rotation might be the answer.
 

rv6ejguy

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I haven't found many people who have a ton of hours without valve issues on any auto engine burning 100LL. Mogas, yes, leaded fuel, not so much.

I doubt if the Decalin will do much for you. Didn't do anything for me.
 

BBerson

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How many years since new? My VW based Limbach needs valve service about every 4-5 years from lack of use, I think.
If not run every day the seats corrode. I doubt I get more than 150 hours valve service before compression is bad because of infrequent use. A bit of lubricating lead at break in is recommended. I run half unleaded car gas and half 100LL mix to get 94 octane.

Lapping doesn't do much. The valve service job "narrows" the seat contact back to new book specs. A wide contact area doesn't seal properly. Three Neway cutters or grind wheels are needed to narrow the seat (15°, 75° and the 30° or 45° seat cutter). The factory seat contact should be about .063", I think. Then do the lapping.

I haven't tried Neway cutters yet, but might.
Of course the guides must be correct also.
 

gammaxy

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I've been flying the engine for about 3 years, but the engine was first run closer to 4 years ago. The first time I noticed low compression was around 100 hours within the first year of flight, but I also wasn't looking for it as closely as I am now. BBerson, can you tell by examining the valve stems whether the valves in your Limbach engine rotate? I've never seen one of those heads and am curious how different it is from what I'm using.

Speaking of corrosion due to infrequent use, I've also considered adding plugs to my exhaust pipes to possibly reduce that sort of corrosion.
 
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BBerson

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The original heads are long gone. Probably CB now.
I never thought about valve rotation on the VW. Have no idea if it rotates or not or if it helps to rotate on an aircooled engine.
 

pictsidhe

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I don't know what material VW uses for exhaust valves, but many engines come with better valves than speedshop valves. I knew someone who 'upgraded' from stock Nimonic80A valves to 'race spec' 214N, then had to revert a few thousand miles later...

Just try setting your rockers so the valves don't rotate, you'll stop worrying about that then!
 

TFF

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I think what you have is an economy of size problem. Rotating the valve can cause it to seat well, but it will also wear the valve and seat out as it grinds it self down. Your not driving a dump truck. In relative terms, a VW is small and delicate. The plus is parts are available and its easy to work on. If a 200 hr valve lap works, thats probably a good thing. Still an auto engine; not a bad idea to have a look in there.
 

Pops

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Using Stock VW parts, the valve is designed to rotate. The surface contact is .063 between the valve and seat for proper sealing and cooling. I use stock valve train components with SS exhaust valves and use non ethanol auto fuel as much as possible with MM oil added to the fuel for the valve guides. No problems, I do change the oil every 25 hrs and check and record the valve lash to spot a trend. Most VW engine problems is a result running the engine with high CHT's for different reasons. To many people relate VW engine hotrod knowledge into VW engines used in aircraft with poor results.
 

BBerson

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I haven't tried stainless exhaust valves. But the valve seat isn't stainless so it could still corrode.
How long does stainless valves last?
Does Aerovee use stainless valves?
 

gammaxy

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The heads in my Aerovee use these Stainless Steel valves: http://www.cbperformance.com/product-p/supergripvalve.htm

Pops,
I'm assuming your valves rotate. Any speculation as to why mine (and others') don't? Here's a post I made a couple years ago that shows the wear pattern on the valve stem that convinces me mine don't rotate: http://www.sonexbuilders.net/viewtopic.php?f=7&t=2533. Is the wear on your valve stems different? I suspect it might have to do with the design of the valve keepers. Mine squeeze the valve so tightly I think the whole spring would have to spin and it doesn't seem like that's the case. Where do you source your heads and valves?

In level flight on a warm/hot day at WOT I get about 350F on the hottest cylinder measured at a tapped hole on the fin near the spark plug. I've occasionally measured 400F on the hottest, when intentionally climbing steep for several minutes, especially during Phase 1 performance testing, but that's the hottest I allow. Winter time like now I am usually < 300F. I don't really think high CHTs are my issue. I have recently become aware of this small baffle that is missing from mine and probably most other VW engines that has got me thinking I could possibly improve things a little: http://bobhooversblog.blogspot.com/2006/12/vw-head-baffles.html
 

TFF

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Valves will rotate until they go "square ". Then they ride in the same spot mostly. Rings will do the same thing. A rotator cap is something else to fail.
 

pictsidhe

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"Stainless" valves are usually 214n. There are better materials out there, often in stock engines such as my friends 60's Mini. I am not a VW expert, so don't know what they have.
 

Pops

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I have never had any valve problems in aircraft VW engines. Believe I have built 6 aircraft VW engines. Always use SS exhaust valves and MM oil. I use single port heads for more torque with a straight drive engine under 3K rpm. I still have VW parts from where I used to have a business rebuilding VW engines back in the 1970's. On the SSSC with a 1835 cc , 60 hp engine my CHT runs 270 degrees at cruise of 2650-2700 rpm and on a 100 deg OAT day I can climb as long as I want and it will not go over 290 degs. Oil temps are almost to cold. Never seen it past 190 degs and if the OAT is 70 degs or colder I have to unhook the air to the oil cooler. I take long small round files and clean all the flashing up down in the air passages in the heads. Common to find the passages plugged up with flashing. Have to have a good airflow DOWN through the heads with the baffling.
 

Daleandee

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In level flight on a warm/hot day at WOT I get about 350F on the hottest cylinder measured at a tapped hole on the fin near the spark plug. I've occasionally measured 400F on the hottest, when intentionally climbing steep for several minutes, especially during Phase 1 performance testing, but that's the hottest I allow.
I've seen many that say that 400ºF on VW heads will destroy them pretty quick. Back when Sonex gave the numbers for the Aerovee they had us all using the "under the plug" CHT senders. They have since gone to the fin mounted senders but never changed the numbers for the limits on the heads. I bring this up because, at one time many years ago when i was flying a VW Sonex, Charlie Radford & I were part of an club of Sonex flyers known as the "Hot Headed Club." Seems many could get some tremendous CHTs but mine always wanted to show 400ºF on climb and 385ºF in cruise on a warm day (CHT senders under the plugs).

Charlie did some flight testing and learned that the fin mounted senders and the under the plug senders read differently i.e. the fin mounted senders read at least 20ºF cooler than under the plug. If you want a real good reading you can use a head bolt near the exhaust and lower temps about 75ºF. The fact that head work is required on a VW engine in a Sonex on the average of every 60-80 hours proves that the engine is just being worked too hard in that environment. The core of the engine will last a long time so if you don't mind chasing the valve problems the VW conversion can be used on the airplane. If you really want to hammer the valves on a VW ... put a turbo on it.

BTDT,

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
166.7 hours / Status - Flying
Member # 109 - Florida Sonex Association
 

Marc W

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Revmaster claims that they use a harder valve seat that solves the VW valve problems. They also make their own heads which they claim to be more durable and cool better. I have never seen them but if i need a set of heads I will look closely at the Revmaster heads. They may be worthwhile on the larger VW conversions.
 

Pops

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On the SSSC the engine is developing about 33/34 HP at cruise of 2650/2700 rpm by the fuel burn. The 1835 cc engine is rated at 60 hp. That is one of the reasons the engine is running cool. I have it in an airframe that does not need a lot of HP to fly. It has 120 sq feet of wing area and the EW is 485 lbs, light with lots of wing area. At WOT it will climb 1200+ ROC. Its a draggy airframe but it cruises at 80 mph with the 33/34 hp. Also the engine is swinging a 60"x 26" prop, not a 54" dia prop. The engine is built for higher torque below 3000 rpm.
 

BBerson

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That beats VP-1 performance, especially climb. Need a low wing version, a SSPP. (Single Seat Piper Pawnee)
 

gammaxy

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Pops,
I was going to make a similar comment about your cool running engine. If I throttle back to similar power levels I also get similarly low temperatures. 2400 rpm results in 70-80mph burning a couple GPH with temperatures in the mid 200Fs. You've definitely got me beat in a climb, though, but I don't think I've made any measurements at a similar power level. Most of my cruise hours are flown at WOT at around 140mph with measured temperatures between 300-350F. I'm sure I could learn a thing or two from your baffles, but I don't think mine are bad. What do you know about those head baffles I linked to earlier and have an opinion on them? http://bobhooversblog.blogspot.com/2006/12/vw-head-baffles.html

Marc,
Thanks for reminding me about the Revmaster heads. I've read the same thing about their valve seats, but would like to find reports from people flying it in a similar application to know if I believe whether the valve seats are actually better. For all I know they're using the same material as my CB Performance heads and just marketing it better.

I don't necessarily disagree with those who would say I'm running my heads too hot/hard especially compared to Corvair heads and Pop's heads. I also understand that exhaust valve issues are a common maintenance item on many aircooled engines, except on a longer timeframe (300-500+ hours?). In searching for a difference between my engine and other aircooled engines that seem to go longer, I can't help but notice my valves don't rotate despite Lycoming engines using valve rotators, WW Corvair engines using valve rotators, documentation claims original VW valves rotate, etc. I'm not sure about Jabiru engines, but I imagine they tend to go a little longer than VWs. It makes me curious if something simple like figuring out how to allow the valves to rotate might get another hundred or more hours from them.

I also admit that I haven't performed leakdown tests on these valves, so it's possible I've removed my heads earlier than others would on other engines--I just turn the propeller over by hand and notice when one cylinder is lower than the rest. I also inspect the valves if the heads are off for another reason. The valves never have the classic burned look that you see from Lycoming valves on the Van's RV forum. The valves that I've worked twice were ones that I lapped the first time and didn't replace the valve or re-cut the seat. I suspect if I made a high quality cut in the valve seat and replaced the valves the first time, they would have lasted longer.
 

TFF

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Not saying some Lycomings have valve rotators, but the ones I have messed with don't.
 
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