VW 2180 cc Aircraft Engine

VW 2180 cc Aircraft Engine

created April 2016,

I have 1130 hours flying behind a Corvair engine over a five-year period. Other than breaking crankshafts, which is no longer an issue with the advent of the "fifth bearing" and the 4340 crankshaft, they are pretty reliable engines. These same two advancements were what ended crankshaft breakages in VW engines as well. But by most accounts, the VW seems to have recurring valve and case problems, with valve jobs and head replacements commonplace in the VW world. At least valve problems are usually gradual and are more annoying than dangerous, which can't be said for a crankshaft failure.

When I bought it, N891JF's 2180cc engine logbook chronicled:

  • @ 69 hours - valve job
  • @ 105 hours - valve job
  • @ 195 hours - replaced heads
  • @ 250 hours - valve job
  • @ 307 hours - I bought it
  • @ 321 hours - it spun a bearing and was rebuilt with new case, crank, pistons/cylinders, cam, lifters, etc. The valve seats were pitted and rusted, but I cleaned them up, reground the seats with a three-angle job, put new stainless steel valves in them, and optimized the valve train geometry for minimal wear. The guides were still in great shape, as these heads only had 120 hours on them.

    After the engine spun a bearing just a few flying hours after I bought it, I rebuilt the 2180 on N891JF, and found a crack between all four pairs of valves. I'd seen this before as a VW mechanic, and always junked them in response. But Steve Bennett at GPASC told me "they all do that after a few hours...they've probably been that way for years". This is especially true of the big-valve heads, where the distance between the two valve seats is just a few mm. But valve seats rarely seem to fall out of the head on aircooled VWs, certainly not as often as valve heads breaking off and wreaking havoc. I have since replaced my pair of heads, but the quality of the replacements is pretty poor these days.

    Valve jobs on Type 1 VWs are a recurring theme. I was shocked at how much higher the head temps were on N891JF's VW as compared to my Corvair...about 100 degrees F! The big problem I see with these heads (044 heads from CB Performance) is that there are few fins and very little in the way of air passageways around what few fins there are, even after an extensive session of deflashing (removing the casting flash with drills and files). You can see below that a Corvair head easily has 3x the air passage area as a VW head does, with much more passage area and thinner fins.

    This temperature difference was measured under the spark plug in both VW and Corvair engines, on all plugs, using the same thermocouples. I suspect this scary high temperature is the basis for the recommendation that VW CHT be taken from under the head stud rather than surrounding the plug, which makes the temps appear to be about 75F lower than when taken under the plug. If nothing else, it makes the pilot feel a lot better! Really...where do you think it's hotter...right at the heart of the combustion chamber or two inches away? The 2012 Great Plains Engine Assembly Manual calls out the following temperatures as operational limitations:

  • CHT at cruise (under spark plug) - 350F to 375
  • CHT at cruise (under head stud) - 275F to 300F
  • CHT during climb (under plug) - 420F
  • CHT do not exceed (under plug) - 450F

    Also mentioned is "The use of AVGAS will shorten the exhaust valves' life, and cause increased valve related wear due to lead in the fuel".

    Above is one of the 044 heads (presumably from CBF) that came with N891JF. It has the normal "stock" fins on it, but not much in the way of air passages. If the air can't get through a passage, it has no incentive to go between the fins...no way out, really, so the pressure builds in the intake plenum and cooling air that was intended for the heads spills right back out the inlet and around the sides of the cowling. Anybody that's developed an oil leak around the prop hub seal or near the front of the engine will have seen how oil streaks come OUT of the inlet and stream down the sides. Lack of air passages is why. Not aluminum cooling shrouds on the lower left and right of the fins. There are fins around the combustion chamber, but they are hidden by these shrouds. They are almost identical to the passages around the fins in the photo below.

    Above is a MOFOCO 040 head. It's touted as having significantly more fin area than a stock VW head, and it does (on the "bottom" side), but again, it's lacking air passages to take advantage of those fins, worse than the 044. Amost all of the holes that you see here were drilled by me with a 1/16", an 1/8", and 3/16" long drill bits. The only reason I couldn't take more out is that the aluminum is so thick it appears to be structural, not just casting flash, and the holes are so small it's difficult to get anything else in there to expand them further. Using this head was purely wishful thinking on my part. This may work in some other applications, but not so good in an airplane with down-draft cooling.

    This is an Auto Linea G01 head as sold by GPASC (a few years ago, at least). I bought them because they were drilled for dual plugs, and I paid way too much for them. Not much in the way of passages here...almost NONE! Other than between the two chambers, the only other two holes were drilled by me with a 3/16" and 1/8" drill. I could tell from this drilling exercise that there was no real hope for saving these poor castings. Cooling was simply not a matter of concern to this manufacturer. And the casting quality looked pretty flaky as well, almost incomplete in places where fins should have been.

    Above is an 041 Brazilian VW "factory" head, which I put on my 2110cc Karmann Ghia back in 1980 (I don't throw anything away). This head clearly has better air passages than anything else I've seen in the aftermarket world these days. After some research that included the December 2010 issue of Hot VWs Magazine, I found a comparison of 18 VW heads, and a few of them looked very much like the 041 above. The best looking head in 2010 article was a Chinese clone of the 043 head, and the passages are quite generous (even larger than the head above) and casting quality appears to be pretty decent. These Chinese heads are marketed by several VW parts houses in the US now, and reports on the Samba (VW Bus) list indicate that they do indeed cool better.

    This is what I settled on, a Chinese manufactured "043 OEM clone" that DRD Racing sells. These heads do indeed have large cooling passages. Given the overall quality of these castings, I'm going to ASSume that they wouldn't install crappy seats in an otherwise decent looking head, so I ordered a pair, especially after seeing a photo that DRD provided. On the other hand, these DRD heads will require some deflashing between the outer cylinder fins, but that's the easy part. Deflashing in the center part of the head will not be extensive, and I could have bolted them on with zero deflashing and have a much cooler running head than any of the other choices above, except the Brazillian VW 041, which it's almost a clone of, and are no longer obtainable (that I know of).

    This "cooling plate" came on all heads from the VW factory, but you rarely see them on aftermarket heads, unless somebody installed used ones like I did. These prevent the cooling air from simply venting below, and ensures that instead passes over some fins first. I pried them out with a screwdriver and had them reinstalled in under a minute each. The slot is for the factory installed bellows control rod that opens the Beetle's fan shroud flaps. I taped over it with aluminum tape on both sides to close up this leak (and yes, I had to pry it back out to do that).

    Here's the finished DRD 043 head, deflashed and cooling plate installed (hence the darkness in between the fins at the bottom of the photo). I believe these heads will cool nicely.

    Just for comparison, this is a Corvair head. Now those are some fins AND air passages! And this is a "junk" head that had laying around, which has never been "deflashed" (had the flashing cleaned up around the fins). Although there are no "new" aftermarket Covair heads, there are plenty of serviceable used heads around.

    By the way, be careful when putting CHT probes under the head nuts. The corresponding stud broke a matter of a few flying hours after I moved the 14mm CHT thermocouple ring there, likely because the stud was side loaded due to the washer being off center on the stud. If you do this, find a similar thickness washer to completely fill the 14mm opening. The stud broke off flush with the case, and given that it was buried down in the cylinder fins, engine disassembly was required to fix it! I've never broken a stud on a Corvair, nor pulled one out.

    summit During this research, I also called Revmaster, hoping to find some heads with nice air passages as well as "advanced" valve seats. The photo on Revmaster Aviation's website only shows the chamber side, and their website in general had lots of issues, such as an inoperable price list. He told me to go look at the photos on the automotive website, since they were the same RM-049 heads for either application. After seeing that photo, I was not impressed that the passages are much better than what has become normal for VW head castings, although the castings are clearly not stock VW derived. He also said their seat material was something like "latest technology that others are also using, not just cast iron", for what that's worth.

    Above is the photo of the Revmaster RM-049 that's on their website. The cooling passages are not stellar, but it's not a very good picture (it's difficult to see what's aluminum, and what's the background passage), and doesn't cover the entire head. Based on what I see though, these passages are no better than the two at the top of the page. Someone is welcome to send me a photo that clarifies the RM-049 air passages.

    I figure I can drop the CHTs by about 50F with a purpose-built plenum on the VW, but, the VW is difficult to plenum (because spark plug wires and intake manifold are in the middle of the cooling fins), far more than the Corvair, which has a conveniently flat flange with bolt holes where the car engine has a fan plenum mounted overhead. See http://www.n56ml.com/corvair/plenum/ for more on the plenums. These are on the Corvair. The 2180cc engine will be getting this treatment soon, if the DRD heads don't get the temps low enough.

    2017 Update...50 hours on DRD heads

    So I flew with the DRD heads for 49.5 hours, adjusting the valves three times during those 50 hours...once at installation, again after flying for a half hour after installation, again 4 hours later, 28 hours later (Great Plains recommends every 25 hours), and then 14 hours later. CHTs were looking fine at this point, but I had a break in my exhaust system that required a rebuild of the headers, and while spinning the prop with no exhaust installed, I could hear that the exhaust valves were not sealing well on three of the cylinders. So I flew it for an hour to warm things up (which is the proper way to check compression) and found 72/80, 80/80, 63/80, and 73/80 on the four cylinders. I flew it another hour and ran two quarts of water through the engine to see if that might clean away any deposits that could be interfering with valve sealing. After the flight, the 63/80 cylinder dropped to 60/80...so off came the head.

    My first clue that something was awry was how much filing I had to do on these stainless valves to get them to slide out the guide. As you can see, they were quite deformed, and there were even chunks of stainless sprinkled around the keeper area (captured by the keepers until now). It's as if the valves had been running very hot, lost their temper, and had deformed. I'm pretty sure these valves should be up to the task, as they are 21-4N stainless steel with chromed stems and hardened tips (made by HPC in Las Vegas). I don't skimp on exhaust valves, but the next step up is titanium! I removed the TRW valves that came in the DRD heads and replaced them with these, given that I have had a TRW valve "lose it's head" and destroy an engine in flight, so I'm kind of funny that way.

    After removing the first exhaust valve, I immediately noticed that the valve guide had two very extensive cracks in it, which is something I'd never seen in a valve guide before...and I've seen and replaced a lot of valve guides in my life! I started wondering if the guides had been running super hot for some reason.

    Here you can see how far those cracks extended, which is a bit sobering when you consider what could happen if a chunk of this broke off and got in the chamber. Theoretically, it'd go out the exhaust port first, but it's just as likely to punch a hole in the piston crown and start a major calamity. And...this is an airplane, and I don't gamble with this kind of stuff! So why would they crack like this, overheating, perhaps? What else could it be? So I removed the other head and pulled the valves out of it.

    First off, check out these seats...not exactly stellar. No wonder why the compression was so bad! And then I noticed there was a large gap between the valve guides and the head material. I'd never seen this before either, and immediately wondered how the guide was supposed to get support from the head, and more importantly, how was it supposed to dissipate heat with nothing but an air gap between the guide and the aluminum?? It took about a nanosecond to tie this with the cracked guide issue...they are directly related. Clearly this was an accident, and either was not noticed, or it was assumed that the end user wouldn't notice either. Sure enough...I didn't notice either, even though I had disassembled the heads after I received them and lapped and checked the valves for proper sealing.

    I inserted an .030" piece of safety wire down the gap and marked its depth with a Sharpie...at 1.5 inches. The small-diameter part of the guide is only 2.125" long, so there's only 5/8" of surface area remaining for the guide to dissipate it's heat to the finned head. That's only 28% of the contact area the guide should have. Thermal conduction across an air gap is about a thousandth of the conduction rate of a solid material contact area, and this particular gap is HOT!

    Here you can clearly see three cracks on another exhaust guide, which are even more extensive than the first! This picture was lightened to show the cracks better, not because it was running super lean. Needless to say, the valve wobble in the guides was very excessive also, so no wonder the seats and valves were worn enough to yield low compressions...these valves were free to roam around as they pleased! All of this in a mere 50 hours of flying.

    The gaps around the guides are so large you can see the reflection of the flange where the seat is bottomed out against the valve cover side of the head. So what's even holding this thing in place? After I removed the guides, I could see that they were deliberately counterbored by a special stepped cutter, apparently in an effort to minimize the effect of the angled port. That's all I can think of...they must have had issues with the guides skewing since the port is angled and one side is supported and the other side is not, leading to uneven cooling and potential warping of the guide. That's just a guess...I can't imagine any other reason. And if you look at a stock head, the exhaust valve guide boss protrudes out into the port (which is probably seen by "racers" as in impediment to flow) so it supports the guide fully to the end. Not so on the DRD "Racing" heads. "Racing" is not always a good thing...sometimes it means compromise to longevity. I emailed DRD explaining what I'd found, along with photos, requesting (nicely) an explanation, but never heard back from them.

    The condition of the valves was not stellar either...after only 50 hours in the engine in brand new heads!

    OK, so it's time for new heads...AGAIN! I immediately went to the source everybody swears by, Revmaster, and ordered a pair of their RM-049 heads from the automotive side, rather than from the aircraft side, because I'm skeptical of the second set of plug wires coming through the valve covers. I like the GPASC method better, as the plug wires stay out of the oil bath by exiting between the pushrod tubes to the bottom of the engine. And for the time being, my engine is single ignition anyway, and as long as I have a robust ignition system with dual power sources and independent switching, I think I have that covered. Besides that, the automotive Revmaster heads are very well made and about the same cost as the "other" brands, but the aircraft heads (with their special sparkplug machining) are about double the price of the automotive heads.

    I'd originally shied away from large valve heads, because they have a bad habit of cracking quickly between the seats, and even Steve Bennett said they'd crack in a matter of hours. But Revmaster only sells large valve heads, so I'd bought the DRD heads with stock valve sizes. So I called Joe Horvath at Revmaster and asked how his heads hold up with the large valves, and he said "they don't crack, not a problem...these are our own castings, and they are plenty thick enough to keep that from happening". He also said his valves have chrome plated stems and Stellite tips. While I had him on the phone, I asked if he'd ever seen a cracked valve guide. "Nope". How about a gap around the valve guides between the boss material. "Nope...that's not kosher!"

    I also asked the guy at HPC (the valve manufacturer) what he thought about the valve guides splitting, and he said he'd never heard of a valve guide splitting on the chamber end. He also agreed the the N21-4 valve keeper areas had almost certainly deformed due to overheating.

    So...beware of DRD heads! I called Darren at DRD and left a message explaining the cracked guides and gaps around the guides, and to please call me back, as I was interested in hearing his story behind how and why this could happen, and if he had anything to say about this, and all I got back was "CRICKETS"!!!!

    One more comment I have on this, and I'll write lots more later...I put 1130 hours on my two Corvair engines in N56ML. I NEVER had valve issues with either one of them. The last 3100cc engine went 456 hours on a set of stainless valves, and the last compression check showed all six cylinders at 78/80 or above. I'm not a huge GM fan, but even in the 60's they knew how to make valve guides and seats! These heads are over FIFTY YEARS OLD and can be bought for a hundred bucks each off ebay. I'm rebuilding the Corvair engine now, with a 4340 crank with generous journal fillets, and expect to start renovating N56ML later this summer, after I get the Swift back in the air again. For more on my CorvAircraft engines, see http://www.n56ml.com/corvair. I'm a believer...

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