Valve Rotation

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
7,683
Location
USA.
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.
I wouldn't use a VW head without the baffles that Bob Hoover is talking about in the link. About Revmaster heads-- Think I read somewhere that there is more fin area. Revmaster is the oldest VW aircraft conversion company in the business, I believe they started in 1968. To many people put VW engines in airframes that require the engine to be run to hard for the design.
 

Daleandee

Well-Known Member
Joined
Sep 11, 2015
Messages
942
Location
SC
I wouldn't use a VW head without the baffles that Bob Hoover is talking about in the link. About Revmaster heads-- Think I read somewhere that there is more fin area. Revmaster is the oldest VW aircraft conversion company in the business, I believe they started in 1968. To many people put VW engines in airframes that require the engine to be run to hard for the design.
The Remaster heads may be better but IMHO a great head for a VW aircraft conversion needs a single port and more room between the valves. Smaller valves could help prevent head cracking between the valves. The big valve, dual port heads, are designed for the race engine guys but the airplane conversions don't need heads that will breathe at 7000 RPMs. I'd even entertain the thought of single plug heads with a hot enough ignition source so a wider plug gap could be used with better plug technology (iridium?).

I should clarify that it's not my intent to be negative at all about the Sonex. As originally designed it was to be an airplane of about 600 lbs empty weight (Jabiru 2200) and would be a fun flyer for around the patch and the occasional hamburger run or fly-in. Things have changed and the design now has a nose wheel (more drag) and a lot more weight being added by builders that want to fill it with creature comforts and fly it cross country. The VW was/is an entry level engine to allow a builder to fly a fun airplane for little money (relatively speaking). But now they seem to be closer to 700 lbs empty with builders bumping up the gross weight so as to have a a reasonable useful load capability. Now the little engine that could, still can, but it just has to have more care to help it keep up. As I noted earlier, if a builder doesn't mind chasing the head/valve issues when working the engine that hard, the VW in a Sonex will work for them. I had a VW Sonex and I absolutely loved the way the air frame handled and it was that airplane that brought me to the one I have now. I wanted a Jabiru 3300 engine on a tail wheel after I flew one because that much horsepower made the airplane come alive! I ended up with the Corvair for various reasons and I'm glad I did after seeing some of the heartburn that others have had with the Jabiru engines.

A pilot flying in the 35 hours a year range (latest average?) could likely get three years on a good set of VW heads. All things considered that's not bad at all when you look at the cost of some of the other options. The money my friend spent on three annuals on a Cherokee 140 would have nearly replaced my engine.

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
 

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
7,683
Location
USA.
Very good post. The VW dual port head starts to breath better at 3000-3200 rpm and above. In a straight drive VW engine the single port head will turn the prop better below that RPM than the dual port engine and there is no problem with cracks between the spark plug hole and the valve seat. With single port heads I use 1 1/4" dia intakes instead of the 1 1/2 dia used on dual ports heads. Gives a higher intake velocity that packs more air in the cylinders. The difference is amazing.
New single port heads ---- http://www.jbugs.com/product/311101353AC.html
http://carcraftstore.com/brandnewsingleportcylinderheads.aspx
http://www.mamotorworks.com/VW/subcategory/engine-cylinder-heads-single-port
 

Marc W

Well-Known Member
Joined
Mar 31, 2017
Messages
367
Location
Colorado
Would single port heads breathe well enough for a 2180 cc VW up to about 3000 RPM? If so I might try a set. I am not really interested in spinning the engine over 3000 RPM.
 

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
7,683
Location
USA.
Would single port heads breathe well enough for a 2180 cc VW up to about 3000 RPM? If so I might try a set. I am not really interested in spinning the engine over 3000 RPM.
I need to finish my flywheel drive , single port heads drilled for dual ignition, 2180 cc engine with a Zenith carb. I want a mag on the pulley end and no one sells one, so making my own.
 

samyguy

Well-Known Member
Joined
Sep 19, 2011
Messages
111
Location
Lincoln Nebr
Hi guys; Take look at both a single port and duel port heads exhaust cooling fins.
You will see that the single port has passages or holes for cooling air to flow though.
Now look at the Duel port head, those same passages are closed off with casting flashing
or when the head was cast, the mold was worn and the holes were not left open.

Gammaxy quoted BOB HOOVER go read all of what he has written, good stuff.

Now those passages or holes need to be drilled and filed open to get proper cooling.
Add a oil filler and a big oil cooler to up the oil capacity, this will help cool also.

http://bobhooversblog.blogspot.com/2009/01/head-drawings.html

http://www.eaa691.net/images/pdf/VW aircraft engine building.pdf

Check out the head drawings closely, you will see what I'm talking about.
Most of that can be done in the airframe.
Then just as importantly get the high baffle kit from Sonic,and seal it well to your cowling.
Get good air pressure though the motor cooling fins/passages to cool it.

All credit goes to BOB HOOVER
 

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
7,683
Location
USA.
Very good post. If you are interested in using a VW engine, you should read all of Bob Hoover's blogs. Its an education in VW engines.

Local friend of mine did the fat fin mod on his VW engine that he was using in a Zenith 701 with a redrive belt. It did help the CHT a certain amount. He was running the engine very hard cruising at 3800-3900 rpm and on the way to OSH the case cracked at 78 hrs if I remember correctly. Just trying to get to much HP from the engine for the design. He replaced it with a R-912 engine.
 

Marc Bourget

Well-Known Member
Joined
Feb 28, 2011
Messages
354
Location
Stockton, California
In an earlier post in this thread, Pops said: "Most VW engine problems is a result running the engine with high CHT's for different reasons."

I learned engine cooling from John Thorp. I have a 3" ring binder full of NACA reports and my "book reviews" of those reports. Most everything I learned validates Pops' point.

I've attended many cooling seminars at OSH and avidly follow the RV forum threads (ref Dan Horton and RV6guy). Until I do some of my own testing, I'm not sure if anybody today has a full grasp of what the guys in the 40's and 50's understood about cooling piston engines.

I have a question for TFF - on his post where he said: " . . but it will also wear the valve and seat out as it grinds it self down. "

What with valve lash, I think the valve rotates between the keeper and retainer, not valve and keeper. Additionally, I also think the mechanism of rotation is while the rocker is in contact with the valve head, not while it's on the seat. But that's just "my think" if I'm wrong, please let me know.
 
Last edited:

Brasov

New Member
Joined
Feb 5, 2020
Messages
2
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.
Hi, I operate a motorgider with 2165cc vw engine (not limbach), Ive had it since 1992. Same story as you, I had to remove heads every 100 hours because of exhaust valve leakage. I got very tired of doing that. The exhaust valves and the seats had some kind of hard brown deposits on them that prevented sealing, they did not have metal loss. I noticed lots of lead build up on top of pistons and on the head chamber. I also looked at trying to get valve rotator to possibly abrade the deposits away but never found a way to do that. 5 years ago I switched to unleaded non alcohol 91 octane gas. I have flown 5 years now without removing a head to fix valve leaks. I was amazed that fixed it. VW cars do not need head removal every 5,000 miles to fix exhaust leaks. I have read that the lead scavenging bromides are corrosive and that they can build up on valve seats. Anyway switching to unleaded gas made my engine go the last 5 years without any valve leaks.
 

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
7,683
Location
USA.
I use local 91 octane non ethanol fuel about 90+ % of the time and a little 100 LL if I have to. CR-- 7.55 to 1. No problems with valves leaking. I also use Marvel Mystery oil in the fuel for the valve guides and STP (zinc) in the oil now that a large percentage of zinc has been taken out of most oils.
Been as reliable as a Cont A-65
 

Brasov

New Member
Joined
Feb 5, 2020
Messages
2
wish I had discovered what was causing my vw valve leakage 30 years ago! Would have made for more pleasant/less expensive flying experience . I just started using MM oil in my fuel at 4 oz/10 gal couple months ago. I did reset my timing to 25 BTDC and at 6000' MSL my corrected compression is 7.2 to 1.
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
12,823
Location
Port Townsend WA
Unleaded fuel can cause seat wear in an old engine made for leaded fuel with soft seats. I put some leaded fuel in to lubricant the seats.
 
Group Builder
Top