Valve Problem

[Vigilant1]

I don't know what's going on. Next time I land in Hesperia I'll stop over and see what's going on with their shop.

I don't want to come across as overly critical. Joe and his guys know more about VW engines than I could ever learn. I just want Revmaster to be around for a long time.
And while you are shooting the breeze in beautiful Hesperia, ask 'em if they would ever considered selling a Type 1 head made just for airplanes. The head they use now has very good cooling, but at our RPMs we don't need valves as big as the street racers use. At our RPMs, smaller valves would give better VE and (more important) more metal/less cracking between the valves. Oh, and just put the second plug where everyone else does, eliminate the access port Revmaster puts in the valve cover.
There, >that< should start a conversation with the good guys at Revmaster!

 

[Mike Stewart]

I don't want to come across as overly critical. Joe and his guys know more about VW engines than I could ever learn. I just want Revmaster to be around for a long time.
And while you are shooting the breeze in beautiful Hesperia, ask 'em if they would ever considered selling a Type 1 head made just for airplanes. The head they use now has very good cooling, but at our RPMs we don't need valves as big as the street racers use. At our RPMs, smaller valves would give better VE and (more important) more metal/less cracking between the valves. Oh, and just put the second plug where everyone else does, eliminate the access port Revmaster puts in the valve cover.
There, >that< should start a conversation with the good guys at Revmaster!

Yeah . . . that plug access through the valve cover has never been a good solution. Great Plains does a much nicer job of that.

Re valves, I'll certainly bring it up when I have an opportunity but my thoughts on that issue are a bit different from yours. Since heat is the major bugaboo with the VW, large diameter valves allow better cooling - I forget the percentage but a very large percentage of cylinder heat is transferred out of the cylinder through the contact between the valve and the seats.

Regarding those notorious and often illusionary cracks between the two valves, again, such things are caused by running the engine hot. I'm coming up on a thousand hours with my GP 2180 and there's nary a crack between my valve seats or from valve seat to spark plug holes. I've read and discussed those supposed cracks and some people even feel they are an inevitable part of owning a VW but I disagree wholeheartely. I've been fortunate I guess in starting out with good heads, EMPIs from Brazil but with enough consistent hot running anything will eventually crack. Running lean means running cool (something that's opposite to what many engine operators seem to think). Mike Busch writes a lot about that . . . or John Deakin. I get them confused frequently. Rich mixtures are only of use when excess fuel is needed for cooling when operating at high percentages of power. The fuel does not reduce cylinder combustion temperatures. The excess fuel is used to flood the valves, rings, etc. to "wash away" the heat. As soon as one is at the magic 75% power level, Mike recommends the "BIG PULL", that is, you haul back on that mixture lever with all your might. An engine monitor certainly helps with this and if I had an engine worth $40K I'm sure I'd have one along with GAMI's, but since I've got simply the lowly and lovely Type 1 VW, I lean to the edge of smoothness. . . or better said perhaps, the edge of roughness. Once one gets to know ones engine, it's not a hard spot to find. I have a dynamic prop balancer called a DynaVibe which of course helps a lot with smoothness but I swear, up high with the VW turning around 3100 the engine (the rotating mass to be more precise) is literally as smooth as a turbine. It's a real pleasure to experience, especially when it's using so little fuel and going at quite a clip. I'd rather have a Lear 23 of course .

 

[Vigilant1]

Yeah . . . that plug access through the valve cover has never been a good solution. Great Plains does a much nicer job of that.

Re valves, I'll certainly bring it up when I have an opportunity but my thoughts on that issue are a bit different from yours. Since heat is the major bugaboo with the VW, large diameter valves allow better cooling - I forget the percentage but a very large percentage of cylinder heat is transferred out of the cylinder through the contact between the valve and the seats.

My understanding is that the exhaust valve is hotter than the head, so heat flows from the exhaust valve to the head. Also, a smaller valve has a higher ratio of seat area (a function of the valve radius) to valve face area (a function of radius squared). A smaller exhaust valve should be cooler.
As you pointed out, the thing that limits Type 1 continuous HP is CHT. Folks do run them too hot, and cracks are common. The cracks reportedly do occur in heads that aren't abused. Having more meat between the valves (and between the plug holes and the valves) would be a plus. Moreover, smaller valves would improve performance at our RPMs. As far as I can tell, we use big valves with seats that nearly touch each other only because that's the way the auto racing heads are made (for 5000 rpm use).

 

[Pops]

My understanding is that the exhaust valve is hotter than the head, so heat flows from the exhaust valve to the head. Also, a smaller valve has a higher ratio of seat area (a function of the valve radius) to valve face area (a function of radius squared). A smaller exhaust valve should be cooler.
As you pointed out, the thing that limits Type 1 continuous HP is CHT. Folks do run them too hot, and cracks are common. The cracks reportedly do occur in heads that aren't abused. Having more meat between the valves (and between the plug holes and the valves) would be a plus. Moreover, smaller valves would improve performance at our RPMs. As far as I can tell, we use big valves with seats that nearly touch each other only because that's the way the auto racing heads are made (for 5000 rpm use).

We need a special built VW head for aircraft VW engines. The auto heads are poor for our use in several ways. For 1915 cc engines and smaller the single port heads are not bad if you pay attention to the complete cooling package. In the larger VW aero engines, a new designed head is very much needed.

 

[Hot Wings]

Designed with no regard to it also having to be able to fit under a stock VW cooling tin.

large diameter valves allow better cooling

No, they don't. In fact, exactly the opposite.

You have to remember that the diameter of a circle, the shape that contains the most area per perimeter of any shape, is Pi x D. The area is Pi x R^2 (Hey, what happened to out superscript!?!) so the ratio of area to valve face has a square in it. Contact area can be brought up by widening the seat, but that introduces another variable that can actually reduce the rate of heat transfer through the face.

The same math applies to the valve stem, but there the heat dissipation there is limited by the diameter of the valve stem, not it's contact area.

 

[Vigilant1]

We've had a few very good threads on some of the needed features of a VW head for aircraft use. Appropriate valve sizes, really effective fins that flow freely (no flash blocking them), etc.
If Revmaster made these, they'd probably sell a lot. Folks flying VWs take the heads off every few hundred hours, and this would be a meaningful upgrade that is a lot cheaper than a new engine. They might even be popular (single plug version) with some car engine builders who are willing to pay more for the most bulletproof daily driver possible. There are folks who like their Beetle, don't race them, and want to spend less time on maintenance. A cooler head with modest size valves and good fins (esp around the exhaust valves) accomplishes that.

 

[Pops]

VW made a mistake in 1970, they should have stayed with the 53 Hp, 1500 engine with the single port heads. They should have stayed with the displacement and used the "Dog House"fan housing, oil cooler and not used the distributor that retarded the timing of #3 cylinder 3 degrees. Also going to the case with the two oil pressure regulators was a good move. Also they should have done the BoB Hoover oil mods like they did on the Type 4 engine.

They went with the increase of HP in the 1600cc engine by turning the engine at a higher RPM and that required the increase air flow of the dual port heads with bigger valves, larger intake manifold, larger poorer carb, and with the higher rpm to get the 60HP, the problem of the wear on the center main bearing just got worse.
I understand the reasons why, but it didn't make a better engine.

VW engine codes. TheSamba.com :: VW Engine Letter Codes

 

[Chris Matheny]

Can you buy a bare casting from the better head manufacturers and have it H.I.P. processed before machining it for use? HIP is hot isostatic preessing, they basically put a head casting under pressure and heat it right to the melting point. It makes for a very strong and crack resistant casting. A lot of big turbo and nitrous guys use this. Or should we design a billet head for them that I could CNC here? We could use any size valves we want have any fin area and shape we want and keep the port size small for high VE at the 3200 rpm area. Maybe after I finish this LE2 engine I'm working on now I'll look into this.

 

[Vigilant1]

Maybe after I finish this LE2 engine I'm working on now I'll look into this.

You'd be a hero to many. The VW is a great, inexpensive airplane engine, but the existing heads are the weakest point (for aircraft use, in the stroked engines >1915cc) and improved ones could be a big deal.

If you go down this road, you'll probably want to start a new thread to solicit ideas. Here are previous threads with food for thought:

1) Hot Wings started this one to discuss his idea for VW heads, His idea is to make 'em for single cylinders (so, use 4 of them for a regular Type 1, or use 2 for a 1/2 VW): Market Survey--VW heads

2) There are lots of ideas sprinkled throughout this thread started by Pops: Just talking about VWs

3) These two posts covers the same ground. What engine would YOU build and What engine would YOU build

4) I think there's another thread just on "from scratch" heads for aviation VWs, but I can't find it.

As Hot Wings mentioned earlier, if designing just for airplanes (and the stock automotive baffling/tin isn't a factor), going a little bigger on the fins would be a real plus. Judging only from how Lycoming does it, maybe finer fins are in order.

On the marketing side--VW flyers are notoriously cheap, er, frugal. That means making a buck in this market can be tough.

 

[TFF]

Power and cooling is always a compromise. Cooling valves can be handled by better materials that don’t need to be babied. Lycoming with the first “big” engine O-290 had all sorts of valve problems in the begging. O-235 valves cooked in them so they kept increasing the stem size. Until they stoped breaking.

Cooling the head is the only real reason a VW can’t run the extra 100F CHT a Lycoming can stand. Lycoming with the screw on heads transfer more heat to the cylinders to help. VW with separates will always have a thermal break between the head and cylinder.

 

[Pops]

I might have said this before, but Bob Hoover had drawing on his blog of a VW head that he designed. When I get time, I'll dig through the posting and find it. I have copies of the drawing from his blog. In his design the exhaust is coming out the bottom like the Type 4 engines.
In desiging the fins for the new heads, if you enlarged the fins and also stamped out larger cooling tins over the cylinders and heads to fit the fan housing on the auto engines that would open up a huge market.

 

[Chris Matheny]

I am fortunate to have a great cylinder head casting company (and know the guys) about 15 minutes from my house if this does take shape. I am committed at the moment to the LE2 engine conversion i'm currently working on and its taking up a lot of my spare time so until its running this would be back burnered. I would guess I should be running by early summer and working the kinks out over the summer/fall and putting hours on my PSRU design to test reliability. Maybe if we can figure out what everyone deems important in a head, draw up some cad files I could see what they would charge to make the castings in small volume. I am not familiar with the air cooled VW stuff but have always been intrigued by it. What about adding some sodium filled exhaust valves from the factory GM heads of the mid/late 90's to help with cooling? This is what Rotax did in the turbo 140hp 915is engines to help with heat. I tend to try and use existing components to keep cost down instead of reinventing the wheel on every component of a project. Would a head with liquid cooling like Rotax uses be of interest? Heads can handle a lot of heat but tend to crack when its concentrated in one area, that's where water cooling has an advantage to normalize temps better.

 

[Vigilant1]

In desiging the fins for the new heads, if you enlarged the fins and also stamped out larger cooling tins over the cylinders and heads to fit the fan housing on the auto engines that would open up a huge market.

I also think the idea proposed by bberson here (VW Heads Designed for Aircraft- Poll ) has merit. The head would be simple with flat surfaces, then attach the widely available extruded aluminum heat sink fins to that. This makes fabrication of the head much simper (no fins) and allows users to customize the fin size, shape, spacing, etc. As Bill points out, this wouldn't be a great approach for mass produced auto engne (speed of making parts and of assembly is key), but would probably be fine for homebuilders and allow customization based on required BTUs to shed, available space, etc.
Small fins under the rockers (to do a good job of moving heat to the oil and out of the head) would also help.
Key would be attaching the extrusions and allowing good heat transfer across the parts. Braze them on? Bolts with heat transfer paste? Tension clamps?

 

[Chris Matheny]

Attaching fins rather than them being part of the casting reduces their thermal transfer efficiency a lot. When they are part of the casting with the same grain, density and material they work much better.

 

[Vigilant1]

Would a head with liquid cooling like Rotax uses be of interest? Heads can handle a lot of heat but tend to crack when its concentrated in one area, that's where water cooling has an advantage to normalize temps better.

I don't think introduction of a separate cooling system (pump, radiator, coolant, hoses, etc) would be very popular. It has been done before in Type 1s, and the results weren't good.
If the head casting was beefy enough so that it could accommodate an optional closed oil passage, that might be more popular. Oil doesn't have the heat capacity of water or water/glycol, but it can still move a lot of heat compared to an aluminum block. Using oil allows use of the existing (or modified) oil pump and oil cooler. Moving oil around the head could help make the temps more consistent from the intake to exhaust side. The oil cooled BMW heads work well.
If the oil passages could be drilled externally (meeting at the corners, then the entry holes plugged), folks could choose whether they want 'em or not.

Still, I think most people would choose to stay with just air cooling if the heads had better "finnage." This is a simple engine, and I think the goal should be better reliability within the currently accepted HP/CC range. If we try to get more specific power (e.g. a 100 HP 2180cc engine), we'll just find the other limits of this engine that are waiting right around the corner (bearing saddle pounding/wearout, case cracks, re-emergence of the finally solved problems with prop bearings/cranks, etc).

 

[Hot Wings]

If Revmaster made these, they'd probably sell a lot

1) Hot Wings started this one to discuss his idea for VW heads, His idea is to make 'em for single cylinders (so, use 4 of them for a regular Type 1, or use 2 for a 1/2 VW): Market Survey--VW heads
<< >>
On the marketing side--VW flyers are notoriously cheap, er, frugal. That means making a buck in this market can be tough.
[/QUOTE]

I got a lot of push back over the split head design. - old pic below. I've gone on to a hybrid, more like the 911 head and cam carrier. They are still modular, thus easily adaptable to a 1/2 VW, which is where I will be going after I get the AV-36 plans back on the market.

The rocker assembly has also been changed to eliminate the potential shaft leak and use modern OTS parts.

The 'frugal' part may be the tough nut of the whole project. Getting over the "A few more $s up front saves you in the long run" has always been a marketing problem - even in aviation.

 

[Mike Stewart]

I think I can get my head around a smaller valve having a higher percentage of its radius giving more percentage surface available for heat transfer, but still . . . doesn't the larger valve have more actual seat surface? The more seat surface, the more heat is transferred from the head to the valve. Heat, along with other (less important) paths, then is carried up the stem and dissipated. Excess fuel is used for heat dissipation too when we (wastefully) use it in that way. It's been ten years since I studied this stuff so obviously I could easily be mis-remembering things. I hesitate to question my understanding of valve size/function though since it seems to violate common sense. Or maybe there's just some confusion of ways of thinking about this. Quite apart from any geometry considerations, it seems if there is more seat surface (there's gotta be . . . it's a larger valve!), there will be more heat absorbed, thus a hotter valve. Heat transfer is one of the primary functions of the valves so it only makes sense that if the larger valve absorbs more heat, it's going to run hotter than a smaller valve. It's also going to do a better job of heat extraction due to its larger mass with which to absorb this heat. A smaller valve is of course going to run cooler in this comparison but since a primary function of the valve and seat is to transfer heat, what is the advantage of the smaller, cooler valve?

I've had no trouble at all from combustion chamber cracks between the valve seats. No trouble with over heating (because I prevent it through attention to oil temp and through extracting power using what I think of as torque as opposed to running it at a high RPM.) Other than the broken springs problem I've had no troubles at all with this GP 2180. My only problem was due to RIMCO re-using old valve springs when they did the TOH for Steve. Since I've no doubt they re-used the valves as well, given enough time I could have eventually had a valve failure. Putting things back together using the best components I could buy and operating the engine within its heat limitations has prevented any of the issues mentioned on this thread. I think if everyone carefully built their own engines from kits and, if not, re-built their engines to make sure everything is correctly lined up (replacing parts with better ones if necessary), there wouldn't be much discussion about problems with aviation use of the VW.

The idea of sodium-filled exhaust valves is a good one but when I went looking I didn't find any that would fit my engine. Maybe I just didn't look hard enough but don't think so . . . they just weren't made for the VW at that time. Since the D-3000 uses Chevy pistons and cylinders (I think), it's not unlikely there might be sodium-filled valves available for this engine.

 

[Vigilant1]

The exhaust valve is hotter than valve seat. Heat doesn't flow from the seat to the valve, it goes the other way.

The valve gains heat through the valve face, and some through the back side. It loses heat through the valve stem and the valve seat. Lets look at 2 valves, a 40mm and a 48mm. Assume both valve seats have a contact area width of 3mm.
40mm valve face area: 1257 sq mm
40mm valve seat area: 377 sq mm.
Ratio of heat gaining area to heat losing area: 3.33

48mm valve face: 1810 sq mm
48mm valve seat area: 454 sq mm.
Ratio: 3.99

The bigger valve has proportionally more heat gaining area than heat losing area compared to the small valve. We can disregard the valve stems, they will be the same. If we added the heat gain on the back side of the valve, the bigger valve does even worse.
Mark

 

[Mike Stewart]

> "The exhaust valve is hotter than valve seat. Heat doesn't flow from the seat to the valve, it goes the other way."

Of course. Not awake yet.

 

[Pops]

JP sent me an email on where to find the drawing of Bob Hoover's heads that he designed. January 23, 2009. Thank you JP.
Here is also a picture of Steve Bennett of Great Plains visiting Bob Hoover.