Sorry....a misfire on my part. Let me try that again. If you had carbon "everywhere", then more than likely the engine was detonating badly due to reduced compression chamber volume, and perhaps pre-ignition from glowing carbon deposits. Your low compression on that cylinder could very well be broken rings and that sort of thing, so that bears examination as well. If you have the heads off....might as well replace the pistons and cylinders and remove all doubt. They're cheap, by comparison to a deadstick landing later.
As you know, the crack between valves is quite common, and usually not a big problem, although my personal experience that perfection in the VW valve train should definitely be a primary goal, as that is THE weak point of these engines. Steven Bennett once told me "they all do that within a few hours", and indeed N891JF's were cracked when I bought it from him. As you've seen at http://www.n56ml.com/n891jf/vw , I've been down that road, and I ended up with the Revmaster heads. I was also reluctant to spend a $1000 for a pair of heads, but I kept hearing that Revmaster heads are the benchmark, so I bought some. The engine in N891JF only has a single ignition system, a 009 distributor running a Compufire ignition (simple little blue CDI triggering distributor cap, firing a four coil pack), so i only needed single plugs. I called and asked Joe if there was any difference in the materials between the car heads and aircraft heads, and he said they were the same, mainly just the plug hole delta. I asked about his heads cracking, and he said they almost never do that. He also said that their valve seat material was the best in the business, which had been a real concern for me, given the DRD and other heads I went through. So I bought a pair of the car heads, for roughly $500. I have not needed to pull the Revmaster heads yet, but can tell you that the valve adjustments rarely change, and then only slightly, which is an indication that the valves and seats are not receding into the heads like all of the other heads I've used subjected to these temperatures and duty cycle. Surely you are planning on replacing both heads, as the other side probably looks just like this one, and you want the same compression ratio, which you can specify through chamber volume when you order them. You need to know the "deck height" of the piston in the cylinder to specify this. Stick with the low end. I think mine are 8.4:1 or so (see my engine rebuild thing on this). I personally dislike the method of running the bottom sparkplugs through the oil bath in the valve cover....it just sounds like an oil leak or a shortwaiting to happen, so if I were determined to run dual plugs, I'd machine another set of holes in the cylinder heads like Great Plains does. I'm OK with single plugs in the VW, because as Jeff Lang says, "I'd rather have one very reliable ignition system than two flaky ones". Sorry, but my responses to this thread may be minimal, as I'm on a business trip with a bare-bones "burner" laptop and very marginal internet. I hope to be back in time to fly to SNF, but it's in serious doubt at the moment.... Mark Langford, Huntsville, AL ML "at" N56ML.com www.N56ML.com _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
