Cooling your heads

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karmarepair

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I got a little push-back on the Sonex forum for this. "my AeroVee cools just fine after 500 hours, and I did nothing special".

While I respect experience, my aim is to eliminate as much risk as possible. I have heard enough horror stories over the last 35 years to confirm what my Sensei, Veeduber, told me: the heads must cool. And he gave me the tools to ensure they do. I miss the SoB...
 

fly2kads

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Personally, I would prefer to stack the deck in my favor where possible. It only takes a little elbow grease and time to open up the air passages around the exhaust ports, so why not?
 

103

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Personally, I would prefer to stack the deck in my favor where possible. It only takes a little elbow grease and time to open up the air passages around the exhaust ports, so why not?
It is the best 1 hour you can invest you your engine. On persistent climb I rarly breach 300f in cruise it settle around 240F +/- 15F I have climbed from 850fee to 6500 feet on a 95f OAT day and only my oil was reaching the limits.
 

Daleandee

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I got a little push-back on the Sonex forum for this. "my AeroVee cools just fine after 500 hours, and I did nothing special".

While I respect experience, my aim is to eliminate as much risk as possible. I have heard enough horror stories over the last 35 years to confirm what my Sensei, Veeduber, told me: the heads must cool. And he gave me the tools to ensure they do. I miss the SoB...
I replied over on that thread and I should know better. There's a bunch of great folks over there and a few that live in a river in Egypt.

VW engines can be a great choice but when asked to produce high power in a heavy airplane they get hot quickly. The right VW build on the right airframe is the key to success. You can run a VW conversion hot and the lower half seems to tolerate it but the heads suffer when they are consistently ran at temps in the 375-400ºF range. Some of the smarter guys move the probes around to get numbers they like and wonder how come the heads are cracked and the valves are leaking after 60-80 hours when the CHTs were in the green (according to their probe placement).

At one time it was recommend (by Great Plains IIRC) to use the head stud near the exhaust valve and add 75ºF to the reading so most were seeing 325ºF and happy. Various people testing probe locations have found that fin probe placements generally read 30ºF lower than a plug probe. Some don't care about the difference. Yet this has been gone through many times over many years. People just now coming to the party don't know what they don't know.

Pops is an excellent resource on here and has proven how to be a successful builder and flyer of VW powered aircraft. There are a number of threads on here about how to keep these things cool. Bottom line is that there is a limit to what one can expect from these engines. You can ask more than that but valve & head problems come with that.
 

103

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Pops is an excellent resource on here and has proven how to be a successful builder and flyer of VW powered aircraft. There are a number of threads on here about how to keep these things cool. Bottom line is that there is a limit to what one can expect from these engines. You can ask more than that but valve & head problems come with that.
I concur I learned much from Bob Hoover over 20 years and Pops is the closest thing we have to Bob on how to build out and care for a Aviation VW. I read everything he writes! Matching the airframe and the load to live within limits of a VW is the key many great single seater fly well on a 1834cc my higher stress 2276 does well on the Cygnet because it has allot of wing and fairly clean I get a solid 500-700ft/minute at 1230lbs. My cruise setting- is about 45hp and the heads are super cool I am blessed by a finely made baffle the original builder Zig Berzins made and use cool tins under the cylinders as the best weight trade off to be had. Many other 2 seaters put too much persistent stress on the VW requiring a much more rigerouse inspection and maintenance schedule and may be responsible for clouding perception of the VW aero engine. Used within it's limits, properly assembled from quality parts following established prop hub practices it is a known quantity that will reliable commit aviation.

I have everything well sealed up and enjoy a bone dry engine compartment after the flight. This should be everyone goal as it makes for better preflight inspections. Peter Limbach would not let a vw engine leave that seeped one drop. It can be done!
 

Hot Wings

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"my AeroVee cools just fine after 500 hours, and I did nothing special".
And how is it running after 600 hours? 500 hours seems to be about the mean time valve problems start to crop up.

At one time it was recommend (by Great Plains IIRC) to use the head stud near the exhaust valve
Probably a reasonable thing to do. VW had plenty of resources to test this. They put the head temp sender for their FI engines here:
FI head.jpg
 

103

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"And how is it running after 600 hours? 500 hours seems to be about the mean time valve problems start to crop up. " Hotwings.

My plan is between around 450 + or - 50 hours to rebuild or replace and rebuild a set for the shelf. Depending on when it approaches the 450 hour mark. I like the idea of sourcing new and putting new seats and guides, valves and springs in the original set and putting them on the shelf.

In the big picture ~$700-800 after 450 hours is still a bargain. A good rebuild is likely $250 if farmed out this could probably be put off a year or two if flying 100 hours a year more if the typical 50-60 hours.

Matt
 
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D Hillberg

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Could adding an oil jet over each exhaust valve stem help with removing heat on the hot side of the heads?
The Brantley B2 had oil jets on it's VO-360...
Might help in extracting more power...
 

karmarepair

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Could adding an oil jet over each exhaust valve stem help with removing heat on the hot side of the heads?
The Veeduber we've been talking about had a set of (HVX) modifications that sought to put more oil near the exhaust valves. Only some of them can be done on a built engine though, and I'm not cracking my case just to do them.

The racers scoff, because they are running super big oil pumps at high RPMs, and they're putting more oil in the heads than can easily drain away. Running high loads are lower RPM, opening up the oil path for more flow is a better plan, without costing the HP of a bigger pump.
 

Bill-Higdon

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And how is it running after 600 hours? 500 hours seems to be about the mean time valve problems start to crop up.


Probably a reasonable thing to do. VW had plenty of resources to test this. They put the head temp sender for their FI engines here:
View attachment 116362
Some of the newer VW "Industrial engines" also have a CHT probe located in this position.
 

Marc Bourget

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NACA conducted a series of test on temperature using a Wright cylinder with a battery of electric heaters in the bore and "mapped" the temperature at 34 or 36 places. The temperature variance, IIRC, was about 300 deg from one area to the next. I believe they picked the most constant spot after checking different "Delta Ps".

Absent repeating this exercise, it's fair to comment, it's all just guessing.

I've asked one of the engine manufacturer's engineers for this information and it's not available for distribution.

FWIW
 
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